To see the other types of publications on this topic, follow the link: String Theory Quantum Field Theories.
Dissertations / Theses on the topic 'String Theory Quantum Field Theories'
Create a spot-on reference in APA, MLA, Chicago, Harvard, and other styles
Consult the top 50 dissertations / theses for your research on the topic 'String Theory Quantum Field Theories.'
Next to every source in the list of references, there is an 'Add to bibliography' button. Press on it, and we will generate automatically the bibliographic reference to the chosen work in the citation style you need: APA, MLA, Harvard, Chicago, Vancouver, etc.
You can also download the full text of the academic publication as pdf and read online its abstract whenever available in the metadata.
Browse dissertations / theses on a wide variety of disciplines and organise your bibliography correctly.
1
Wiegandt, Konstantin. "Superconformal quantum field theories in string." Doctoral thesis, Humboldt-Universität zu Berlin, Mathematisch-Naturwissenschaftliche Fakultät I, 2012. http://dx.doi.org/10.18452/16605.
Full textAbstract:
In dieser Dissertation werden Aspekte von superkonformen Quantenfeldtheorien untersucht, die für die sogenannte AdS/CFT Korrespondenz relevant sind. Die AdS/CFT Korrespondenz beschreibt eine Dualität zwischen Stringtheorien im Anti-de Sitter Raum und superkonformen Quantenfeldtheorien im Minkowskiraum. In diesem Kontext wurde die sog. Wilsonschleifen / Amplituden Dualität entdeckt, die die Übereinstimmung von n-Gluon MHV Amplituden und n-seitigen polygonalen Wilsonschleifen in der N=4 supersymmetrischen Yang-Mills (SYM) Theorie beschreibt. Im ersten Teil dieser Dissertation wird die Wilsonschleifenseite einer solchen möglichen Dualität in der N=6 superkonformen Chern-Simons (ABJM) Theorie untersucht. Das Hauptergebnis dieser Untersuchungen ist, dass der Erwartungswert der n-seitigen polygonalen Wilsonschleifen auf Einschleifenebene verschwindet, während er auf Zweischleifenebene in seiner funktionalen Form identisch zu der analogen Wilsonschleife in N=4 SYM auf Einschleifenniveau ist. Außerdem wird eine anomale konforme Wardidentität für Wilsonschleifen in Chern-Simons Theorie berechnet. Zudem werden die damit im Zusammenhang stehenden Entwicklungen für Amplituden und Korrelatoren in der ABJM Theorie diskutiert. Im zweiten Teil dieser Dissertation werden Dreipunktfunktionen von zwei geschützten Operatoren und einem Twist-Zwei Operator mit beleibigem Spin j in der N=4 SYM Theorie berechnet. Dafür werden die Indizes des Spin j Operators auf den Lichtkegel projiziert und der Korrelator wird in einem Grenzfall untersucht in dem der Impuls der bei dem Spin j Operator einfließt verschwindet. Dieser Grenzfall vereinfacht die perturbative Berechnung erheblich, da alle Dreipunktdiagramme effektiv auf Zweipunktdiagramme reduziert werden und die Abhängigkeit der Mischungsmatrix auf Einschleifenebene herausfällt. Das Ergebnis stimmt mit der Analyse der Operatorproduktentwicklung von Vierpunktfunktionen geschützter Operatoren von Dolan und Osborn aus dem Jahre 2004 überein.<br>In this thesis aspects of superconformal field theories that are of interest in the so-called AdS/CFT correspondence are investivated. The AdS/CFT correspondence states a duality between string theories living on Anti-de Sitter space and superconformal quantum field theories in Minkowski space. In the context of the AdS/CFT correspondence the so-called Wilson loop / amplitude duality was discovered, stating the equality of the finite parts of n-gluon MHV amplitudes and n-sided lightlike polygonal Wilson loops in N=4 supersymmetric Yang-Mills (SYM) theory. It is the subject of the first part of this thesis to investigate the Wilson loop side of a possible similar duality in N=6 superconformal Chern-Simons matter (ABJM) theory. The main result is, that the expectation value of n-sided lightlike polygonal Wilson loops vanishes at one-loop order and at two-loop order is identical in its functional form to the Wilson loop in N=4 SYM theory at one-loop order. Furthermore, an anomalous conformal Ward identity for Wilson loops in Chern-Simons theory is derived. Related developments and symmetries of amplitudes and correlators in ABJM theory are discussed as well. In the second part of this thesis we calculate three-point functions of two protected operators and one twist-two operator with arbitrary even spin j in N =4 SYM theory. In order to carry out the calculations, the indices of the spin j operator are projected to the light-cone and the correlator is evaluated in a soft-limit where the momentum coming in at the spin j operator becomes zero. This limit largely simplifies the perturbative calculation, since all three-point diagrams effectively reduce to two-point diagrams and the dependence on the one-loop mixing matrix drops out completely. The result is in agreement with the analysis of the operator product expansion of four-point functions of half-BPS operators by Dolan and Osborn in 2004.
2
Wang, Yifan Ph D. Massachusetts Institute of Technology. "Lessons on interacting quantum field theories from string theory." Thesis, Massachusetts Institute of Technology, 2016. http://hdl.handle.net/1721.1/106452.
Full textAbstract:
Thesis: Ph. D., Massachusetts Institute of Technology, Department of Physics, 2016.<br>Cataloged from PDF version of thesis.<br>Includes bibliographical references (pages 185-194).<br>In this thesis, we use string theory constructions and dualities to explore various features of interacting quantum field theories. We begin with an overview in Chapter 1, of past and recent developments in quantum field theories, explaining the advantages of string theoretic techniques over traditional approaches in answering a range of questions about interacting dynamics. In Chapter 2 we study the holographic duality between the 6d (1, 1) Ak-1 little string theory (LST) and type II string theory in the double scaled limit. By identifying the low energy states, which are Cartan gluons in the 6d maximal super-Yang-Mills (SYM) that describes the massless sector of the LST, we compute the four-point amplitudes from both sides of the duality and demonstrate matching results. Since the two computations concern different regimes in the parameter space, their amazing agreement implies the presence of certain nonrenormalization theorems in the 6d SYM. In Chapter 3, motivated by the AdS/CFT duality, we develop a systematic procedure to derive an off-shell action for hydrodynamics from classical Einstein gravity. We first identity the boundary fluid degrees of freedom in the hydrodynamic regime, in terms of gapless modes of the metric in the bulk gravity. This allows us to derive an off-shell action, for relativistic fluids that have gravity duals, at leading order in derivative expansion, by explicitly integrating out gapped degrees of freedom in the bulk. We also explain the strategy to incorporate dissipation and higher order effects. In Chapter 4, we discuss 4d N = 2 superconformal field theories (SCFT) of the Argyres-Douglas (AD) type, which can be constructed in string/M theory by either wrapping M5 branes on punctured Riemann surface or probing 3-fold singularity by IIB string. We classify the punctures (irregular defects in Hitchin system) on the Riemann surface in the former construction, that will give rise to N = 2 SCFTs and demonstrate how to extract exact information about the Coulomb branch spectrum and central charges. We further identify these AD theories constructed from M5 branes with a special class of theories from IIB probing compound Du Val (cDV) singularities, thereby establishing a mathematical connection between singular Hitchin systems and cDV singularities through N = 2 SCFTs. We end with a short summary and outlook for future directions in Chapter 5.<br>by Yifan Wang.<br>Ph. D.
3
Corrado, Richard Anthony. "Some aspects of the connection between field theories and gravity /." Digital version accessible at:, 1999. http://wwwlib.umi.com/cr/utexas/main.
Full text
4
Nolland, David John. "Quantum field theories with fermions in the Schrödinger representation." Thesis, Durham University, 2000. http://etheses.dur.ac.uk/4410/.
Full textAbstract:
This thesis is concerned with the Schrödinger representation of quantum field theory. We describe techniques for solving the Schrödinger equation which supplement the standard techniques of field theory. Our aim is to develop these to the point where they can readily be used to address problems of current interest. To this end, we study realistic models such as gauge theories coupled to dynamical fermions. For maximal generality we consider particles of all physical spins, in various dimensions, and eventually, curved spacetimes. We begin by considering Gaussian fields, and proceed to a detailed study of the Schwinger model, which is, amongst other things, a useful model for (3+1) dimensional gauge theory. One of the most important developments of recent years is a conjecture by Mal-dacena which relates supergravity and string/M-theory on anti-de-Sitter spacetimes to conformal field theories on their boundaries. This correspondence has a natural interpretation in the Schrödinger representation, so we solve the Schrödinger equation for fields of arbitrary spin in anti-de-Sitter spacetimes, and use this to investigate the conjectured correspondence. Our main result is to calculate the Weyl anomalies arising from supergravity fields, which, summed over the supermultiplets of type JIB supergravity compactified on AdS(_s) x S(^5) correctly matches the anomaly calculated in the conjecturally dual N = 4 SU{N) super-Yang-Mills theory. This is one of the few existing pieces of evidence for Maldacena's conjecture beyond leading order in TV.
5
Muntean, Ioan Lucian. "Unification and explanation in early Kaluza-Klein theories." Diss., [La Jolla] : University of California, San Diego, 2009. http://wwwlib.umi.com/cr/ucsd/fullcit?p3369373.
Full textAbstract:
Thesis (Ph. D.)--University of California, San Diego, 2009.<br>Title from first page of PDF file (viewed September 17, 2009). Available via ProQuest Digital Dissertations. Vita. Includes bibliographical references (p. 444-468).
6
Wiegandt, Konstantin [Verfasser], Harald [Akademischer Betreuer] Dorn, Prof Dr Gregory [Akademischer Betreuer] Korchemsky, and Jan [Akademischer Betreuer] Plefka. "Superconformal quantum field theories in string : gauge theory dualities / Konstantin Wiegandt. Gutachter: Harald Dorn ; Prof. Dr. Gregory Korchemsky ; Jan Plefka." Berlin : Humboldt Universität zu Berlin, Mathematisch-Naturwissenschaftliche Fakultät I, 2012. http://d-nb.info/1027529372/34.
Full text
7
Wiegandt, Konstantin [Verfasser], Harald Akademischer Betreuer] Dorn, Prof Dr Gregory [Akademischer Betreuer] Korchemsky, and Jan C. [Akademischer Betreuer] [Plefka. "Superconformal quantum field theories in string : gauge theory dualities / Konstantin Wiegandt. Gutachter: Harald Dorn ; Prof. Dr. Gregory Korchemsky ; Jan Plefka." Berlin : Humboldt Universität zu Berlin, Mathematisch-Naturwissenschaftliche Fakultät I, 2012. http://nbn-resolving.de/urn:nbn:de:kobv:11-100205442.
Full text
8
Lavdas, Ioannis. "AdS₄/CFT₃ and quantum gravity." Thesis, Paris Sciences et Lettres (ComUE), 2019. http://www.theses.fr/2019PSLEE041.
Full textAbstract:
Dans le cadre de la dualité holographique entre une vaste famille de vides 1/2-maximalement supersymétriques Anti-de Sitter à quatre dimensions (AdS₄) et des théories des champs superconformes N=4 supersymétriques à trois dimensions (sCFT₃), nous étudions des questions théoriques majeures de gravité quantique et de théories de jauge. Ce travail a deux directions principales : La premiere partie est consacrée aux mécanismes par lesquels le graviton AdS₄ peut acquérir une petite masse, tandis que la seconde partie concerne la cartographie de la variété superconforme des sCFT₃ considérées. En ce qui concerne la question du mecanisme de Higgs pour le graviton d’AdS₄, nous proposons un nouveau mécanisme qui repose sur le couplage ”faible” de deux sCFT₃s, initialement découplées, en jaugent une symmétrie globale commune. Les deux tenseurs de stress initialement conservés se mélangent et le résultat est une combinaison conservée et une combinaison orthogonale, dont la dimension acquiert une petite dimension anormale. Holographiquement, cette configuration correspond à la connexion de deux univers AdS₄ initialement découplés via un AdS₅ × S⁵ fin, autrement appelé une “gorge” de Janus. Le résultat est une théorie AdS₄-bimétrique, avec un graviton sans masse et un graviton massif, dont la petite masse correspond à la dimension anormale de la combinaison duale de tenseurs de stress. Nous calculons la masse du graviton, qui est exprimée en termes de données géométriques de la ”gorge” de Janus et de l’univers AdS₄ vers zéro, résulte en une théorie de gravité massive dans AdS₄. En ce qui concerne la deuxième direction de ce travail, les déformations superconformes des sCFT₃s considérées qui génèrent la variété superconformale sont des déformations préservant N = 2 supersymétrie, générées par des opérateurs exactement marginaux. Nous présentons comment tous ces opérateurs peuvent être systématiquement extraits de l’index superconforme. Les opérateurs de branche de Coulomb et de Higgs sont pris en compte, tandis qu’une attention particuli ère est accordée aux opérateurs mixtes. On montre que les modules de branches mixtes de ces théories sont des opérateurs à double-corde qui se transforment dans la représentation (Adj, Adj) des groupes de saveursélectriques et magnétiques, modulo un surcomptage pour les quivers avec des noeuds de jauge abéliens. Enfin, nous commentons sur l’interprétation holographique des résultats, en affirmant que les supergravités mesurées peuvent capturer l’espace des modules tout entier si, outre les paramètres de la solution d’arri ère-plan, les modules de quantification des conditions aux limites sontégalement pris en compte<br>Based on the holographic duality between a large class of half-maximally supersymmetric four-dimensional Anti-de Sitter (AdS₄) vacua and three-dimensional N = 4 superconformal field theories (sCFT₃), we study quantum gravitational and gauge theoretic questions. This work has two main directions: The first part is devoted to the mechanisms through which the low-lying AdS₄-graviton can acquire a small mass whereas the second part regards the mapping of the superconformal manifold of the considered sCFT₃s. Regarding the question of the graviton Higgsing in AdS₄, we propose a new mechanism which relies on ”weakly” coupling two initially decoupled sCFT₃s, by gauging a common global symmetry. The two initially conserved stress tensors mix and the result of this mixing is a conserved combination and an orthogonal combination, the scaling dimension of which acquires a small anomalous dimension. Holographically, this setup is dual to connecting two initially decoupled AdS₄ universes via a thin AdS₅ × S⁵ or Janus ”throat”. The result is an AdS₄- bimetric theory, with one massless and one massive graviton, the small mass of which corresponds to the anomalous dimension of the dual stress tensor combination. We compute the mass of the graviton, which is expressed in terms of the geometric data of the Janus ”throat” and of the considered AdS₄ universe. A special decoupling limit of this theory, where the effective four-dimensional gravitational coupling of one of the two universes vanishes, results to an AdS₄-Massive gravity theory. Regarding the second direction of this work, superconformal deformations of the considered sCFT3s which generate the superconformal manifold, are N = 2 supersymmetry preserving deformations, generated by exactly marginal operators. We present how all these operators can be consistently extracted from the superconformal index. Coulomb and Higgs branch operators are considered, while particular attention is payed to mixedbranch operators. It is shown that the mixed-branch moduli of these theories are double-string operators transforming in the (Adj,Adj) representation of the electric and magnetic flavour groups, up to overcounting for quivers with abelian gauge nodes. Finally, we comment on the holographic interpretation of the results, arguing that gauged supergravities can capture the entire moduli space if, in addition to the parameters of the background solution, quantization moduli of boundary conditions are also taken into account
9
Nilsson, Daniel. "The Ratio of Reality : A study of the gyromagnetic ratio in theories ranging from classical mechanics to string theory." Thesis, Uppsala universitet, Teoretisk fysik, 2021. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-448767.
Full textAbstract:
In this project a theoretical study of the so called gyromagnetic ratio was done by investigating classical mechanics, Dirac theory and string theory. The gyromagnetic ratio is a constant term appearing in the coupling between angular momentum and magnetic moment for a particle. A universality in quantum field theory claiming g = 2 regardless of spin is known to exist which also agrees with the found values (g = 2) of the Dirac and string theory. The proof of the aforementioned universality in quantum field theory was sketched in the project by showing that the W-boson Lagrangian is well behaved in the massless limit. Furthermore it is shown that the spin equations of motion for a particle is greatly reduced if g = 2 regardless of spin.<br>I det här projektet utfördes en teoretisk studie av den så kallade gyromagnetsika kvoten genom att undersöka klassisk mekanik, Dirac-teori och strängteori. Den gyromagnetiska kvoten är en konstant term som visar sig i kopplingen mellan rörelsemängsmoment och magnetiskt moment för en partikel. I kvantfältsteori existerar en universalitet som hävdar att g = 2 oberoende av spin. Denna universalitet stämmer överens med de funna värden på g från Dirac-teori och strängtoeri. Beviset för denna universalitet testades genom ett exempel där Lagrangianen för W-bosonen i kvantfältsteori visades bete sig som förväntat när massan för partikeln tilläts gå mot noll. Vidare undersöktes rörelseekvationerna för ett system helt bestämt av dess spin. I dessa kan det visas att ett universellt värde på g oavsett spin reducerar dessa ekvationer avsevärt.
10
Davison, Richard A. "Excitations in holographic quantum liquids." Thesis, University of Oxford, 2012. http://ora.ox.ac.uk/objects/uuid:3b1db914-709e-41ec-ba7c-c968cb87b752.
Full textAbstract:
In this thesis we review the gauge/gravity duality and how it can be used to compute the thermodynamic properties and low-energy excitations of holographic quantum liquids - strongly-interacting field theories with a non-zero density of matter. We then study in detail the charge density excitations of two such liquids, the D3/D7 theory and the RN-AdS₄ theory, by computing the poles of their charge density Green's functions, and their charge density spectral functions. Although it is not a Landau Fermi liquid, the charge density excitations of the D3/D7 theory display many of the same properties as one, including a collisionless/hydrodynamic crossover as the temperature is increased. In contrast to this, the charge density (and energy density) excitations of the RN-AdS₄ theory do not share these properties but behave in a way that cannot be explained by Landau's theory of interacting fermionic quasiparticles. This is consistent with other results which indicate that this is not a Landau Fermi liquid.
11
Garolera, Huguet Blai. "Probing gauge theories: Exact results and holographic computations." Doctoral thesis, Universitat de Barcelona, 2015. http://hdl.handle.net/10803/289346.
Full textAbstract:
The holographic duality between gauge theories and string theories has opened a new door to access the strongly coupled regime of quantum field theories and offers, at the same time, a completely new way to understand the elusive nature of quantum gravity and the non-perturbative regime of string theory. After almost two decades of research, the current status of the correspondence is that of a solid conjecture that has passed a great number of nontrivial tests, to the point that it is generally believed to be true.
The present thesis includes a collection of four papers published in peer-reviewed scientific journals, all of them in the context of the AdS/CFT correspondence and with a particular focus on studying gauge theories by inserting heavy external probes, following prescribed trajectories and transforming under various representations of the gauge group.
Each of these works reports a little step forward in the development of new strategies for capturing correc- tions beyond the leading order as well as in using exact results available in quantum field theory in order to derive exact expressions for other relevant observables and new non-trivial string theory predictions.
In chapters 2 and 3 we use the AdS/CFT correspondence in order to compute several observables of N = 4 SU (N ) super Yang-Mills theory related with the presence of an infinitely heavy particle transforming in the k-symmetric or the k-antisymmetric representations of the gauge group and following particular trajectories. This is achieved by means of adding certain D-brane probes with electric fluxes turned on and reaching the boundary of AdS on the very trajectories followed by the dual particles. For the antisymmetric case we consider D5-branes reaching the boundary at arbitrary time-like trajectories, while for the symmetric case, we consider a D3-brane fully embedded in AdS5 that reaches the boundary at either a straight line or a hyperbola. This generalizes previous computations that used fundamental strings, which are claimed to be dual to infinitely heavy point particles transforming in the fundamental. Besides the intrinsic interest of these generalizations, our main motivation in studying them is that, as it happens in the computation of certain Wilson loops, the results obtained with D3-branes give an all- orders series of corrections in 1/N to the leading order result for the fundamental representation obtained by means of fundamental strings.
It is important to remark, one more time, that we can not really extrapolate up to k = 1, since this is beyond the regime of validity of the supergravity approximation. Therefore, it is not justified a priori to set k = 1 in our results. Nevertheless, when compared with the exact results available, we find that the D3-brane computation reproduces the correct result in the large N , λ limit and with k = 1.
This better than expected performance suggests the exciting possibility that certain D3-branes with electric fluxes might capture correctly all the 1/N corrections, but it is fair to say that we still lack of a precise string-theoretic argument to prove this.<br>Durant les darreres dues dècades ha aparegut un nou paradigma que permet reformular completament certes teories quàntiques de camps i ens aporta una nova eina que ens permet realitzar càlculs analítics en règims fins ara inaccessibles. Aquest nou paradigma sorgeix del descobriment d’una correspondència o dualitat exacta entre dues teories aparentment molt diferents. Per una banda de la dualitat tenim certes teories quàntiques de camps, com per exemple les denominades teories de Yang-Mills, similars a les teories del Model Estàndard. Aquestes descriuen partícules interactuant en un espai pla d-dimensional sense gravetat. A l’altra banda de la dualitat trobem teories que inclouen la gravetat, com ara la Teoria de la Relativitat General d’Einstein o les seves generalitzacions en el marc de la Teoria de Cordes. Aquestes teories de gravetat estan definides sobre espais de dimensió més alta que d, i és per això que aquesta correspondència rep sovint l’adjectiu de “hologràfica”. Depenent del context, aquesta rep el nom de dualitat gauge/gravetat, dualitat gauge/corda o AdS/CFT (acrònim anglès per la correspondència particular entre teoria de cordes a espais d’Anti-de Sitter i teories de camps conformes).
Fins ara, una de les correspondències més ben estudiades i que comprenem millor (i sobre la qual es centra la present tesi) és la dualitat entre la teoria quatre-dimensional N = 4 super Yang-Mills amb grup de gauge SU (N ) i teoria de cordes tipus IIB en un espai deu-dimensional AdS5 × S5 .
Aquesta tesi presenta una recopilació de quatre articles publicats en revistes científiques d’alt impacte, tots ells en el camp de la correspondència AdS/CFT i centrats en l’estudi de teories gauge supersimètriques mitjançant la inserció de partícules de prova infinitament massives, seguint trajectòries determinades i transformant sota diverses representacions del grup de gauge. Cadascun d’aquests treballs aporta un pas endavant en el desenvolupament de noves estratègies per calcular correccions més enllà del primer ordre així com en l’ús de resultats exactes accessibles a la Teoria Quàntica de Camps per tal de derivar expressions exactes d’altres observables rellevants de la teoria i realitzar prediccions de Teoria de Cordes.
12
Hartley, David. "Supersymmetric quantum field theories from induced representations." Thesis, University of St Andrews, 1988. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.329888.
Full text
13
Krishnan, Ranganathan. "Spaces of conformal theories and string field theory." Thesis, Massachusetts Institute of Technology, 1994. http://hdl.handle.net/1721.1/28061.
Full text
14
Casali, Eduardo. "Worldsheet methods for perturbative quantum field theory." Thesis, University of Cambridge, 2015. https://www.repository.cam.ac.uk/handle/1810/265833.
Full textAbstract:
This thesis is divided into two parts. The first part concerns the study of the ambitwistor string and the scattering equations, while the second concerns the interplay of the symmetries of the asymptotic null boundary of Minkowski space, called [scri], and scattering amplitudes. The first part begins with a review of the CHY formulas for scattering amplitudes, the scattering equations and the ambitwistor string including its pure spinor version. Next are the results of this thesis concerning these topics, they are: generalizing the ambitwistor model to higher genus surfaces; calculating the one-loop NS-NS scattering amplitudes and studying their modular and factorization properties; deriving the one-loop scattering equations and analyzing their factorization; showing that, in the case of the four graviton amplitude, the ambitwistor amplitude gives the expected kinematical prefactor; matching this amplitude to the field theory expectation in a particular kinematical regime; solving the one loop scattering equations in this kinematical regime; a conjecture for the IR behaviour of the one-loop ambitwistor integrand; computing the four graviton, two-loop amplitude using pure spinors; showing that this two-loop amplitude has the correct kinematical prefactor and factorizes as expected for a field theory amplitude; generalizing the ambitwistor string to curved backgrounds; obtaining the field equations for type II supergravity as anomaly cancellation on the worldsheet; generalizing the scattering equations for curved backgrounds. The second part begins with a review of the definition of the null asymptotic boundary of four dimensional Minkowski space, its symmetry algebra, and their relation to soft particles in the S-matrix. Next are the results of this thesis concerning these topics, they are: constructing two models consisting of maps from a worldsheet to [scri], one containing the spectrum of N=8 supergravity, and the other the spectrum of N=4 super Yang-Mills; showing how certain correlators in these theories calculate the tree-level S-matrix of N=8 sugra and N=4 sYM respectively; defining worldsheet charges which encode the action of the appropriate asymptotic symmetry algebra and showing that their Ward-identities recover the soft graviton, and soft gluon factors; defining worldsheet charges for proposed extensions of these symmetry algebras and showing that their Ward-identities give the subleading soft graviton and subleading soft gluon factors.
15
Rudolph, Felix J. "Duality covariant solutions in extended field theories." Thesis, Queen Mary, University of London, 2016. http://qmro.qmul.ac.uk/xmlui/handle/123456789/23614.
Full textAbstract:
Double field theory and exceptional field theory are formulations of supergravity that make certain dualities manifest symmetries of the action. To achieve this, the geometry is extended by including dual coordinates corresponding to winding modes of the fundamental objects. This geometrically unifies the spacetime metric and the gauge fields (and their local symmetries) in a generalized geometry. Solutions to these extended field theories take the simple form of waves and monopoles in the extended space. From a supergravity point of view they appear as 1/2 BPS objects such as the string, the membrane and the fivebrane in ordinary spacetime. In this thesis double field theory and exceptional field theory are introduced, solutions to their equations of motion are constructed and their properties are analyzed. Further it is established how isometries in the extended space give rise to duality relations between the supergravity solutions. Extensions to these core ideas include studying Goldstone modes, probing singularities at the core of solutions and localizing them in winding space. The relation of exceptional field theory to F-theory is also covered providing an action for the latter and incorporating the duality between M-theory and F-theory.
16
Berman, David Simon. "Chiral gauge theories and their applications." Thesis, Durham University, 1998. http://etheses.dur.ac.uk/5041/.
Full textAbstract:
This thesis is concerned with so called chiral gauge theories, also known as self dual gauge theories. In particular, the aim of this thesis to investigate the role that chiral gauge theories play in duality symmetries in lower dimensions through dimensional reduction. Chapter one serves as an introduction to the notions of duality in field and string theory. The problems of formulating well defined actions for self-dual gauge theories are introduced as well as a brief presentation of the different approaches used to over come these problems. Chapter two introduces dimensional reduction and demonstrates how duality symmetries arise from the dimensional reduction of self-dual theories in a variety of dimensions and on different compact spaces. Examples are presented where the couplings of the resulting theories are calculated explicitly in terms of the geometrical data of the compact space. The duality generators acting on these couplings are also calculated explicitly and related to the geometry/topology of the compact space. Chapter three deals with the idea of duality manifest actions and their relation to the self-dual theories in higher dimensions. Non-linear Born-Infeld type actions are introduced and again dimensional reduction is shown to play a role in the duality of the Born-Infeld action. This leads to a duality manifest version of the Born-Infeld action. Chapter four describes perhaps the main application of this thesis. The effective action of the M-theory five brane wrapped on a torus is identified with the effective action of the IIB D-3 brane dimensionally reduced on a circle (after some appropriate world volume dualizations). The IIB S-duality then arises as a result of the modular symmetry of the torus. The final chapter contains a brief summary and a hint of further directions for research that were outside the scope of this thesis.
17
Zhang, Ou, and Ou Zhang. "Effective Field Theories for Quantum Chromo- and Electrodynamics." Diss., The University of Arizona, 2016. http://hdl.handle.net/10150/621825.
Full textAbstract:
Effective field theories (EFTs) provide frameworks to systematically improve perturbation expansions in quantum field theory. This improvement is essential in quantum chromodynamics (QCD) predictions, both at low energy in the description of low momentum hadron-hadron scattering and at high energy in the description of electron-positron, proton-proton, proton-electron collisions. It is also important in quantum electrodynamics (QED), when electrons interact with a high-intensity, long-wavelength classical field. I introduce the principles and methods of effective field theory and describe my work in three EFTs: First, in the perturbative QCD region, I use soft collinear effective theory (SCET) to prove that strong interaction soft radiation is universal and to increase the QCD accuracy to next-to-next-to-next-to leading logarithm order for new particle searches in hadron colliders. I also compute a new class of non-perturbative, large logarithmic enhancement arising near the elastic limits of deep inelastic scattering and Drell-Yan processes. Second, in the QCD confinement region, I use heavy hadron chiral perturbation theory to study near-threshold enhancements in the scattering of 𝐷 and 𝜋 mesons near the threshold for the excited 𝐷-meson state, 𝐷*, as well as in the scattering of 𝐷 and 𝐷* mesons near the threshold for the exotic hadron X(3872). This work provides a clear picture of the hadronic molecule X(3872) and more profound understanding of the nuclear force between hadrons. Finally, inspired by SCET, I construct a new electron-laser effective field theory to describe highly-relativistic electrons traveling in strong laser fields, extract the universal distribution of electrons in strong electromagnetic backgrounds and its evolution in energy from the separated momentum scales of emitted photons and classical radiation, and predict the rate of wide angle photon emission. I conclude with limitations of EFT methods and some perspectives on what new work may be achieved with these EFTs.
18
Schritt, Dimitri. "Symmetries in quantum and classical field theories." Thesis, University of Canterbury. Physics and Astronomy, 2013. http://hdl.handle.net/10092/8032.
Full textAbstract:
The initial chapter of the thesis provides a review of Weinberg’s formalism for the derivation of quantum fields. The formalism is extended to allow for the derivation of quantum fields with more than one spin degree of freedom. It is conjectured that it may be possible to construct massive bosonic quantum field theories of any desired spin j that are consistent and unitary at all energies without the need for regulator terms by including j + 1
spin degrees of freedom: j, j - 1, down to j - j. The concept is then demonstrated in two subsequent chapters by the derivation of a quantum field with spin one and spin zero degrees of freedom followed the derivation of a quantum field with spin two, spin one, and spin zero degrees of freedom. Both field theories are found to be consistent and unitary at all energies without the need for regulator terms. The final two chapters are on unrelated topics. The penultimate chapter provides an explicit derivation of quantum fields for massless particles of spin one-half. In the final chapter, a derivation of the free-space Proca and Maxwell equations is provided via a consistent identification of the linear combinations of the classical fields of the (1,0) and (0,1) representations of the orthochronous
Lorentz group.
19
Neves, Rui Gomes Mendona. "Conformal field theories on random surfaces and the non-critical string." Thesis, Durham University, 1997. http://etheses.dur.ac.uk/4750/.
Full textAbstract:
Recently, it has become increasingly clear that boundaries play a significant role in the understanding of the non-perturbative phase of the dynamics of strings. In this thesis we propose to study the effects of boundaries in non-critical string theory. We thus analyse boundary conformal field theories on random surfaces using the conformal gauge approach of David, Distler and Kawai. The crucial point is the choice of boundary conditions on the Liouville field. We discuss the Weyl anomaly cancellation for Polyakov's non-critical open bosonic string with Neumann, Dirichlet and free boundary conditions. Dirichlet boundary conditions on the Liouville field imply that the metric is discontinuous as the boundary is approached. We consider the semi-classical limit and argue how it singles out the free boundary conditions for the Liouville held. We define the open string susceptibility, the anomalous gravitational scaling dimensions and a new Yang-Mills Feynman mass critical exponent. Finally, we consider an application to the theory of non-critical dual membranes. We show that the strength of the leading stringy non-perturbative effects is of the order e(^-o(1/βst)), a result that mimics those found in critical string theory and in matrix models. We show how this restricts the space of consistent theories. We also identify non-critical one dimensional D-instantons as dynamical objects which exchange closed string states and calculate the order of their size. The extension to the minimal c ≤ 1 boundary conformal models is also briefly discussed.
20
Roy, Alan A. "Aspects of renormalisation in some quantum field theories." Thesis, Rhodes University, 1998. http://hdl.handle.net/10962/d1005214.
Full textAbstract:
Renormalisation is an important aspect of Quantum Field Theory. It is used to create physically meaningful theories and some major developments took place in the 1970's and onwards. We consider Renormalisation in its application to the theories of ψ⁴ , Quantum Electrodynamics, Quantum Chromodynamics and the Background Field Method. Feynman diagrams are used to illustrate many of the concepts.
21
Petrov, Dmitri. "Novel approaches to numerical solutions of quantum field theories /." View online version; access limited to Brown University users, 2005. http://wwwlib.umi.com/dissertations/fullcit/3174659.
Full text
22
Söderberg, Alexander. "Renormalization in Field Theories." Thesis, Uppsala universitet, Teoretisk fysik, 2015. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-251561.
Full textAbstract:
Several different approaches to renormalization are studied. The Callan-Symanzik equation is derived and we study its beta functions. An effective potential for the Coleman-Weinberg model is studied to find that the beta function is positive and that spontaneous symmetry breaking will occur if we expand around the classical field. Lastly we renormalize a non-abelian gaugetheory to find that the beta function in QCD is negative.
23
Katona, Gregory. "Field Theoretic Lagrangian From Off-Shell Supermultiplet Gauge Quotients." Doctoral diss., University of Central Florida, 2013. http://digital.library.ucf.edu/cdm/ref/collection/ETD/id/5958.
Full textAbstract:
Recent efforts to classify off-shell representations of supersymmetry without a central charge have focused upon directed, supermultiplet graphs of hypercubic topology known as Adinkras. These encodings of Super Poincare algebras, depict every generator of a chosen supersymmetry as a node-pair transformtion between fermionic / bosonic component
fields. This research thesis is a culmination of investigating novel diagrammatic sums of gauge quotients by supersymmetric images of other Adinkras, and the correlated building of field theoretic worldline Lagrangians to accommodate both classical and quantum venues. We find Ref [40], that such gauge quotients do not yield other stand alone or ”proper” Adinkras as afore sighted, nor can they be decomposed into supermultiplet sums, but are rather a connected ”Adinkraic network”. Their iteration, analogous to Weyl's construction for producing all finite-dimensional unitary representations in Lie algebras, sets off chains of algebraic paradigms in discrete-graph and continuous-field variables, the links of which feature distinct, supersymmetric Lagrangian templates. Collectively, these Adiankraic series air new symbolic genera for equation to phase moments in Feynman path integrals. Guided in this light, we proceed by constructing Lagrangians actions for the N = 3 supermultiplet YI /(iDI X) for I = 1, 2, 3, where YI and X are standard, Salam-Strathdee superfields: YI fermionic and X bosonic. The system, bilinear in the component fields exhibits a total of thirteen free parameters, seven of which specify Zeeman-like coupling to external background (magnetic) fluxes. All but special subsets of this parameter space describe aperiodic oscillatory responses, some of which are found to be surprisingly controlled by the golden ratio, ? ? 1.61803, Ref [52]. It is further determined that these Lagrangians allow an N = 3 ? 4 supersymmetric extension to the Chiral-Chiral and Chiral-twisted-
Chiral multiplet, while a subset admits two inequivalent such extensions. In a natural progression, a continuum of observably and usefully inequivalent, finite-dimensional off-shell
representations of worldline N = 4 extended supersymmetry are explored, that are variate
from one another but in the value of a tuning parameter, Ref [53]. Their dynamics turns
out to be nontrivial already when restricting to just bilinear Lagrangians. In particular, we
find a 34-parameter family of bilinear Lagrangians that couple two differently tuned supermultiplets to each other and to external magnetic fluxes, where the explicit parameter dependence is unremovable by any field redefinition and is therefore observable. This offers the evaluation of X-phase sensitive, off-shell path integrals with promising correlations
to group product decompositions and to deriving source emergences of higher-order background flux-forms on 2-dimensional manifolds, the stacks of which comprise space-time volumes. Application to nonlinear sigma models would naturally follow, having potential use in M- and F- string theories.<br>Ph.D.<br>Doctorate<br>Physics<br>Sciences<br>Physics
24
Catterall, Simon Marcus. "Numerical studies of field theories on random lattices." Thesis, University of Oxford, 1988. http://ora.ox.ac.uk/objects/uuid:48c22ec6-0096-4a2c-be45-cbb20ba7a5b6.
Full textAbstract:
In this thesis we shall be concerned with the study of models which arise as a consequence of adopting discrete regularisations for various Euclidean space quantum field theories. Specifically, we employ a random triangulation of the continuum space, and define the fields only over nodes or links of the mesh. Lattice field theories, together with the Renormalisation Group, are introduced in the first chapter. Continuum physics is shown to depend on the positions and stabilities of zeroes of the β-function, which in turn requires a knowledge of the critical behaviour of the associated statistical model. In Chapter 2. we examine a theory of Dirac fermions in 2 + 1 dimensions on a random lattice. We investigate the behaviour of the 2-pt function and fermion condensate in the absence of any background gauge field. The results indicate certain doubling problems, generic to regular lattice formulations of fermion field theories, are evaded, at least at tree graph level. We then go on to examine the fermion vacuum currents in the presence of background fields with non-zero winding number. We are able to demonstrate the existence of a Chern-Simon's topological term in the gauge field effective action which yields parity violating vacuum currents. The magnitude of these are in agreement with certain continuum calculations. The final chapter concerns the properties of random surfaces. The particular class of models chosen originate as discretisations of Polyakov's string. The partition function is approximated by a sum over all possible random triangulations and an integral over vertex positions. The sum over random lattices is intended to mimick the functional integral over intrinsic metrics encountered in the continuum, and the model may also be pictured as 2D quantum gravity coupled to a scalar field. We consider the phase structure of the models when two forms of extrinsic curvature are added to the standard action. Monte-Carlo simulation indicates that with one type of curvature term a strong 2<sup>nd</sup> order phase transition exists at finite coupling, leading to a new continuum limit for the model possessing long-range correlation properties. With the other type a much weaker higher order transition is observed. In this case the surface will be crumpled at long distance. We discuss the implications of these results for continuum surfaces.
25
McCloud, Paul James. "Symmetry in classical and quantum field theory : an application of the theory of jets." Thesis, King's College London (University of London), 1995. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.321679.
Full text
26
Flachi, Antonino. "Quantum field theory on brane backgrounds." Thesis, University of Newcastle Upon Tyne, 2001. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.366586.
Full text
27
Tourkine, Piotr. "Results in perturbative quantum supergravity from string theory." Thesis, Paris 6, 2014. http://www.theses.fr/2014PA066295/document.
Full textAbstract:
Les théories de supergravité sont des extensions supersymmetriques de la relativité générale (RG) d'Einstein. Leur comportement ultraviolet (UV) est meilleur que celui de la RG car les contributions bosoniques et fermioniques se compensent dans les diagrammes en boucles. La supergravité maximale a le meilleur comportement UV, toutefois les prédictions les plus précises venant aussi bien de la théorie des champs que de la théorie des cordes indiquent que la théorie devrait elle aussi souffrir de divergences UV, à partir de 7 boucles. Cette question ouverte constitue un cadre dans lequel peut être problématisés ma thèse. En général, l'approche que j'ai suivie consiste à étudier les amplitudes de diffusion en théorie des cordes dans la limite ou la longueur de la corde devient nulle; on s'attend ainsi à retrouver les amplitudes de diffusion de supergravité. Curieusement, on sait très peu de choses sur cette limite au délà d'une boucle. Une part importante de mon travail thèse a consisté à développer des outils mathématiques basés sur la géométrie tropicale pour décrire cette limite en genre deux et au délà. Afin de tester la précision des prédiction de la théorie des cordes, dans ma thèse j'ai aussi travaillé sur le comportement UV des théories de supergravité demi-maximale. Nous avons montré un théorème de non-renormalisation qui expliqué l'absence de divgerence à 3 boucles et en prédit une à 4 boucles. Enfin je me suis intéressé aux techniques utilisées en théorie des champs pour calculer ces amplitudes à haut nombre de boucles en théorie des champs, et notament à la "double copie BCJ", dont avons proposé la première analyse à une boucle depuis la théorie des cordes<br>Supergravity theories are supersymmetric extensions of General Relativity (GR). They have a better ultraviolet (UV) behavior than GR, due to cancellations between bosons and fermions in loop diagrams. Maximal supergravity is a candidate for a UV finite point-like theory of quantum gravity. Nowadays, the most advanced understanding coming from field theory and string theory indicate that the theory should not be UV finite, and that the first UV divergences should appear at the 7-loop order. This open question constitutes a background in which my PhD thesis can be problematized.In this thesis, our approach consists in using string theory scattering amplitudes and study their point-like limit, in which supergravity amplitudes are expected to be recovered. Very little is known beyond one loop on this limit and in this manuscript I describe first how a recent field of mathematics, tropical geometry, may be used in this process, and mention some applications and open issues.Another way to cross-check the predictions of string theory on the UV behavior of maximal supergravity consists in performing the same analysis in theories of reduced supersymmetry.I discuss the case of half-maximal supergravity theories, and show a non-renormalization theorem in heterotic string which explains the vanishing of the 3-loop divergence of this theory and predicts a 4-loop divergence.The last aspect of my work is focused on a string theoretic understanding on the techniques used in field theory to compute higher loop amplitudes. I describe the first analysis of the so called BCJ double copy construction at one-loop from string theory, and partly explain the origin of the BCJ prescription
28
Klaczynski, Lutz. "Haag's theorem in renormalisable quantum field theories." Doctoral thesis, Humboldt-Universität zu Berlin, Mathematisch-Naturwissenschaftliche Fakultät, 2016. http://dx.doi.org/10.18452/17448.
Full textAbstract:
Wir betrachten eine Reihe von Trivialitäts- resultaten und No-Go-Theoremen aus der Axiomatischen Quantenfeldtheorie. Von besonderem Interesse ist Haags Theorem. Im Wesentlichen sagt es aus, dass der unitäre Intertwiner des Wechselwirkungsbildes nicht existiert oder trivial ist. Als wichtigste Voraussetzung von Haags Theorem arbeiten wir die unitäre Äquivalenz heraus und unterziehen die kanonische Störungstheorie skalarer Felder einer Kritik um zu argumentieren, dass die kanonisch renormierte Quantenfeldtheorie Haags Theorem umgeht, da sie genau diese Bedingung nicht erfüllt. Der Hopfalgebraische Zugang zur perturbativen Quantenfeldtheorie bietet die Möglichkeit, Dyson-Schwinger-und Renormierungsgruppengleichungen mathematisch sauber herzuleiten, wenn auch mit rein kombinatorischem Ausgangspunkt. Wir präsentieren eine Beschreibung dieser Methode und diskutieren eine gewöhnliche Differentialgleichung für die anomale Dimension des Photons. Eine Spielzeugmodellversion dieser Gleichung lässt sich exakt lösen; ihre Lösung weist eine interessante nichtstörunsgtheoretische Eigenschaft auf, deren Auswirkungen auf die laufende Kopplung und die Selbstenergie des Photons wir untersuchen. Solche nichtperturbativen Beiträge mögen die Existenz eines Landau-Pols ausschliessen, ein Sachverhalt, den wir ebenfalls diskutieren. Unter der Arbeitshypothese, dass die anomale Dimension eines Quantenfeldes in die Klasse der resurgenten Funktionen fällt, studieren wir, welche Bedingungen die Dyson-Schwinger-und Renormierungsgruppengleichungen an ihre Transreihe stellen. Wir stellen fest, dass diese unter bestimmten Bedingungen kodieren, wie der perturbative Sektor den nichtperturbativen vollständig determiniert.<br>We review a package of triviality results and no-go theorems in axiomatic quantum field theory. Of particular interest is Haag''s theorem. It essentially says that the unitary intertwiner of the interaction picture does not exist unless it is trivial. We single out unitary equivalence as the most salient provision of Haag''s theorem and critique canonical perturbation theory for scalar fields to argue that canonically renormalised quantum field theory bypasses Haag''s theorem by violating this very assumption. The Hopf-algebraic approach to perturbative quantum field theory allows us to derive Dyson-Schwinger equations and the Callan-Symanzik equation in a mathematically sound way, albeit starting with a purely combinatorial setting. We present a pedagogical account of this method and discuss an ordinary differential equation for the anomalous dimension of the photon. A toy model version of this equation can be solved exactly; its solution exhibits an interesting nonperturbative feature whose effect on the running coupling and the self-energy of the photon we investigate. Such nonperturbative contributions may exclude the existence of a Landau pole, an issue that we also discuss. On the working hypothesis that the anomalous dimension of a quantum field falls into the class of resurgent functions, we study what conditions Dyson-Schwinger and renormalisation group equations impose on its resurgent transseries. We find that under certain conditions, they encode how the perturbative sector determines the nonperturbative one completely.
29
Mayger, E. M. "Superspace calculations and techniques for non-linear field theories." Thesis, University of Cambridge, 1986. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.384546.
Full text
30
Gómez, Subils Javier. "Non-perturbative Aspects of Quantum Field Theories from Holography." Doctoral thesis, Universitat de Barcelona, 2021. http://hdl.handle.net/10803/672276.
Full textAbstract:
In this thesis we have employed the holographic duality to study the non-perturbative regime of a one-parameter family of theories with multi-scale dynamics. Normally, this (super)string theory motivated duality identifies gauge theories in flat space with string theories in a certain curved spacetime. Its relevance roots in its ability to relate the strongly-coupled regime of gauge theories with classical gravity governed by Einstein's equations. In the Introduction of the thesis, we have reviewed the main string theory ingredients that we used throughout the thesis and revisited some of the previous results which are the starting point of out study.
In Chapter 2, we gather the explicit form of the supergravity solutions whose dual are the gauge theories of interest. These are three-dimensional gauge theories. Generically, they share the same physics at high energies, given by Yang-Mills and Chern-Simons interactions. Remarkably, when the low energy regime of the theories is studied, a rich variety of non-perturbative phenomenology is discovered.
In particular, for a generic value of the parameter distinguishing the theories, they develop a mass gap in their spectrum. However, the two theories which are obtained at the limiting values of the parameter are special. On the one hand, the theory flows towards an infrarred fixed point, dual to a Conformal Field Theory. On the other hand, a confining theory is obtained, in the sense that the potential felt between quarks grows linearly with the distance between them for large separations.
All these phenomena, together with the computation of the spectrum of spin-0 and spin-2 states, are studied in Chapter 3. The fact that in this system the Renormalisation Group flow can pass close to a Conformal Field Theory motivated the search of a light dilaton in the spectrum. But such light state was not found, the reason for that being that the values of the source and the vacuum expectation value that prevented the flow from finishing at the fixed point where of the same order.
On top of that, in this Chapter some entanglement entropy measures were studied. This last investigation was motivated by the fact that in the literature some quantities extracted from such magnitudes where proposed as a probe for confinement. Our results show that, when these quantities are considered in our system, they are not able to discriminate between confining and non-confining gapped theories.
Not only did we consider the theories at zero temperature case, but we also studied thermal states by constructing numerical black brane solutions in the gravity side. Black branes are very much like black holes, with the peculiarity that their surface extends in non-compact directions. Such solutions are discussed in Chapter 4. As a result, we understood their phase diagram, exhibiting a rich structure endowed with first and second order phase transitions, as well as a triple point where three phases coexist and a critical point where the second order phase transition takes place.
Intrigued by the effect that the proximity of a Conformal Field Theory could have in the Renormalisation Group flow of a field theory, in Chapter 5 we carried out a study on complex Conformal Field Theories. We proposed their holographic dual, and analysed some of their properties in the strongly-coupled case.
Finally, in Chapter 6, we studied transport coefficients in holographic theories which model Quantum Chromodynamics. We concluded that the holographic results are quite different from the ones obtained using perturbative techniques. These studies could have phenomenological consequences and find their application in astrophysical observations concerning neutron stars.<br>En esta tesis hemos utilizado la dualidad holográfica para entender el régimen no perturbativo de una familia uni-paramétrica de teorías con múltiples escalas. Primeramente, hemos repasado los ingredientes esenciales que necesitamos de teoría de cuerdas. A la vez, hemos introducimos algunos resultados previos que son el punto de partida de nuestras investigaciones.
Tras dicha introducción, se recogen todas las soluciones de supergravedad duales a las teorías en tres dimensiones que estudiamos. Genéricamente, comparten la misma física a altas energías pero a bajas energías muestran una rica fenomenología. En particular, desarrollan un salto de masa en su espectro. Curiosamente, las teorías correspondientes a tomar los valores límites del parámetro son especiales. En un caso, la teoría fluye a una teoría de campos conforme. En el otro se obtiene una teoría confinante, con potencial lineal entre quarks.
También se calcula el espectro de estados con espín 0 y espín 2. Además, se analizan diferentes medidas de entrelazamiento cuántico que en nuestro caso no son capaces de discriminar entre teorías con confinamiento y teorías con un salto de masa. Esto contrasta con algunas propuestas que se encuentran en la literatura.
Adicionalmente hemos construido numéricamente soluciones de branas negras, que describen estados térmicos de las teorías. Hemos descubierto un diagrama de fases muy rico, con transiciones de fase de primer y segundo orden, junto a un punto crítico y un punto triple.
Interesados por el efecto que una teoría conforme de campos pudiera tener si es cercana al flujo del grupo de renormalización de otra teoría, en el Capítulo 5 nos adentramos en el estudio de teorías conformes de campos complejas, dando su el dual holográfico.
Finalmente, se calculan coeficientes de transporte en teorías holográficas que modelan Cromodinámica Quántica y que podrían tener consecuencias fenomenológicas en observaciones referentes a estrellas de neutrones.
31
Buchberger, Igor. "Strings, Gravitons, and Effective Field Theories." Doctoral thesis, Karlstads universitet, Institutionen för ingenjörsvetenskap och fysik, 2016. http://urn.kb.se/resolve?urn=urn:nbn:se:kau:diva-41912.
Full textAbstract:
This thesis concerns a range of aspects of theoretical physics. It is composed of two parts. In the first part we motivate our line of research, and introduce and discuss the relevant concepts. In the second part, four research papers are collected. The first paper deals with a possible extension of general relativity, namely the recently discovered classically consistent bimetric theory. In this paper we study the behavior of perturbations of the metric(s) around cosmologically viable background solutions. In the second paper, we explore possibilities for particle physics with low-scale supersymmetry. In particular we consider the addition of supersymmetric higher-dimensional operators to the minimal supersymmetric standard model, and study collider phenomenology in this class of models. The third paper deals with a possible extension of the notion of Lie algebras within category theory. Considering Lie algebras as objects in additive symmetric ribbon categories we define the proper Killing form morphism and explore its role towards a structure theory of Lie algebras in this setting. Finally, the last paper is concerned with the computation of string amplitudes in four dimensional models with reduced supersymmetry. In particular, we develop general techniques to compute amplitudes involving gauge bosons and gravitons and explicitly compute the corresponding three- and four-point functions. On the one hand, these results can be used to extract important pieces of the effective actions that string theory dictates, on the other they can be used as a tool to compute the corresponding field theory amplitudes.<br>Over the last twenty years there have been spectacular observations and experimental achievements in fundamental physics. Nevertheless all the physical phenomena observed so far can still be explained in terms of two old models, namely the Standard Model of particle physics and the ΛCDM cosmological model. These models are based on profoundly different theories, quantum field theory and the general theory of relativity. There are many reasons to believe that the SM and the ΛCDM are effective models, that is they are valid at the energy scales probed so far but need to be extended and generalized to account of phenomena at higher energies. There are several proposals to extend these models and one promising theory that unifies all the fundamental interactions of nature: string theory. With the research documented in this thesis we contribute with four tiny drops to the filling of the fundamental physics research pot. When the pot will be saturated, the next fundamental discovery will take place.
32
Grosse, Harald, Thomas Krajewski, Raimar Wulkenhaar, and grosse@doppler thp univie ac at. "Renormalization of Noncommutative Yang-Mills Theories: A Simple Example." ESI preprints, 2000. ftp://ftp.esi.ac.at/pub/Preprints/esi914.ps.
Full text
33
Bouatta, Nazim. "String field theory, non-commutativity and higher spins." Doctoral thesis, Universite Libre de Bruxelles, 2008. http://hdl.handle.net/2013/ULB-DIPOT:oai:dipot.ulb.ac.be:2013/210481.
Full textAbstract:
In Chapter 1, we give an introduction to the topic of open string field theory. The concepts presented include gauge invariance, tachyon condensation, as well as the star product.<p>In Chapter 2, we give a brief review of vacuum string field theory (VSFT), an approach to open string field theory around the stable vacuum of the tachyon. We discuss the sliver state explaining its role as projector in the space of half-string basis. We review the construction of D-brane solutions in vacuum string field theory. We show that in the sliver basis the star product correspond to a matrix product. <p>Using the material introduced in the previous chapters, in Chapter 3 we establish a translation dictionary between open and closed strings, starting from open string field theory. Under this correspondence, we show that (off--shell) level--matched closed string states are represented by star algebra projectors in open string field theory. As an outcome of our identification, we show that boundary states, which in closed string theory represent D-branes, correspond to the identity string field in the open string side. <p>We then turn to noncommutative field theories. In Chapter 4, we introduce the framework in which we will work. The tools introduced are solitons, projectors, and partial isometries.<p>The ideas of Chapter 4 are applied to specific examples in Chapter 5, where we present new solutions of noncommutative gauge theories in which coincident vortices expand into circular shells. As the theories are noncommutative, the naive definition of the locations of the vortices and shells is gauge-dependent, and so we define and calculate the profiles of these solutions using the gauge-invariant noncommutative Wilson lines introduced by Gross and Nekrasov. We find that charge 2 vortex solutions are characterized by two positions and a single nonnegative real number, which we demonstrate is the radius of the shell. We find that the radius is identically zero in all 2-dimensional solutions. If one considers solutions that depend on an additional commutative direction, then there are time-dependent solutions in which the radius oscillates, resembling a braneworld description of a cyclic universe. There are also smooth BIon-like space-dependent solutions in which the shell expands to infinity, describing a vortex ending on a domain wall.<p>In Chapter 6, we review the Fronsdal models for free high-spin fields that exhibit peculiar properties. We discuss the triplet structure of totally symmetric tensors of the free String Field Theory and their generalization to AdS background.<p>In Chapter 7, in the context of massless higher spin gauge fields in constant curvature spaces discussed in chapter 6, we compute the surface charges which generalize the electric charge for spin one, the color charges in Yang-Mills theories and the energy-momentum and the angular momentum for asymptotically flat gravitational fields. We show that there is a one-to-one map from surface charges onto divergence free Killing tensors. These Killing tensors are computed by relating them to a cohomology group of the first quantized BRST model underlying the Fronsdal action.<p><p><br>Doctorat en Sciences<br>info:eu-repo/semantics/nonPublished
34
Ardekani, Armin. "Monte Carlo studies of two dimensional field theories /." Title page, table of contents and introduction only, 1998. http://web4.library.adelaide.edu.au/theses/09PH/09pha676.pdf.
Full text
35
Wu, Ruoxu. "Notes on Some (0,2) Supersymmetric Theories in Two Dimensions." Diss., Virginia Tech, 2017. http://hdl.handle.net/10919/77921.
Full textAbstract:
This thesis is devoted to a discussion of two-dimensional theories with (0,2) supersymmetry. Examples of two-dimensional (0,2) gauged linear sigma models (GLSMs) are constructed for various spaces including Grassmannians, complete intersections in Grassmannians, and non-complete intersections such as Pfaffians. Generalizations of (2,2) Toda dual theories to (0,2) Toda-like theories are also discussed and some examples are given, including products of projective spaces and del Pezzo surfaces. Correlation functions are computed to show the examples are the correct mirror models.<br>Ph. D.
36
Ludwig, Thomas. "Wick Rotation for Quantum Field Theories on Degenerate Moyal Space." Doctoral thesis, Universitätsbibliothek Leipzig, 2013. http://nbn-resolving.de/urn:nbn:de:bsz:15-qucosa-118795.
Full textAbstract:
In dieser Arbeit wird die analytische Fortsetzung von Quantenfeldtheorien auf dem nichtkommutativen Euklidischen Moyal-Raum mit kommutativer Zeit zu entsprechenden Moyal-Minkowski Raumzeit (Wick Rotation) erarbeitet. Dabei sind diese Moyal-Räume durch eine konstante Nichtkommutativiät
gegeben. Einerseits wird die Wick Rotation im Kontext der algebraischen Quantenfeldtheorie, ausgehend von einer Arbeit von Schlingemann, hergeleitet. Von einem Netz Euklidischer Observablen wird die Lorentz’sche Theorie durch alle Bilder der fortgesetzten Poincare Gruppenwirkung auf der Zeit-Null Schicht erhalten. Dabei wird gezeigt, dass die Vorgänge der nichtkommutativen Deformation und der Wick Rotation kommutieren. Andererseits ist so eine analytische Fortsetzung ebenfalls für Quantenfeldtheorien, die durch einen Satz von Schwingerfunktionen definiert ist, möglich. Durch die Gültigkeit einer Kombination aus Wachstumsbedinungen, die aus der Wick Rotation von Osterwalder und Schrader bekannt sind, kann der Übergang zu einer deformierten Wightman-Theorie gezeigt werden. Abschließend beinhaltet diese Arbeit ergänzende
Resultate zu den physikalischen Eigenschaften der Kovarianz und der Lokalität.
37
Lechner, Gandalf. "On the construction of quantum field theories with factorizing S-matrices." Doctoral thesis, [S.l.] : [s.n.], 2006. http://webdoc.sub.gwdg.de/diss/2006/lechner.
Full text
38
He, Yang-Hui 1975. "On algebraic singularities, finite graphs and D-brane gauge theories : a string theoretic perspective -- with a digression on string field theory." Thesis, Massachusetts Institute of Technology, 2002. http://hdl.handle.net/1721.1/8490.
Full textAbstract:
Thesis (Ph.D.)--Massachusetts Institute of Technology, Dept. of Physics, 2002.<br>Includes bibliographical references (p. 601-634).<br>In this thesis we shall address certain beautiful inter-relations between the construction of 4-dimensional supersymmetric gauge theories and resolution of algebraic singularities, from the perspective of String Theory. We review in detail the requisite background in both the mathematics, such as orbifolds, symplectic quotients and quiver representations, as well as the physics, such as gauged linear sigma models, geometrical engineering, Hanany-Witten setups and D-brane probes. We present the work of the author in the past 4 years at the Centre for Theoretical Physics, on aspects of the world-volume gauge dynamics using D-brane resolutions of various Calabi-Yau singularities, notably Gorenstein quotients and toric singularities. Attention will be paid to the general methodology of contructing gauge theories for these singular backgrounds, with and without the presence of the NS-NS B-field, as well as the T-duals to brane setups and branes wrapping cycles in the mirror geometry. Applications of such diverse and elegant mathematics as crepant resolution of algebraic singularities, representation of finite groups and finite graphs, modular invariants of affine Lie algebras, etc. will naturally arise. Various viewpoints and generalisations of McKay's Correspondence will also be considered. As a final digression, the author's work in Witten's cubic bosonic open string field theory, will also be included.<br>by Yahg-Hui He.<br>Ph.D.
39
Källén, Johan. "Twisting and Gluing : On Topological Field Theories, Sigma Models and Vertex Algebras." Doctoral thesis, Uppsala universitet, Teoretisk fysik, 2012. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-173225.
Full textAbstract:
This thesis consists of two parts, which can be read separately. In the first part we study aspects of topological field theories. We show how to topologically twist three-dimensional N=2 supersymmetric Chern-Simons theory using a contact structure on the underlying manifold. This gives us a formulation of Chern-Simons theory together with a set of auxiliary fields and an odd symmetry. For Seifert manifolds, we show how to use this odd symmetry to localize the path integral of Chern-Simons theory. The formulation of three-dimensional Chern-Simons theory using a contact structure admits natural generalizations to higher dimensions. We introduce and study these theories. The focus is on the five-dimensional theory, which can be understood as a topologically twisted version of N=1 supersymmetric Yang-Mills theory. When formulated on contact manifolds that are circle fibrations over a symplectic manifold, it localizes to contact instantons. For the theory on the five-sphere, we show that the perturbative part of the partition function is given by a matrix model. In the second part of the thesis, we study supersymmetric sigma models in the Hamiltonian formalism, both in a classical and in a quantum mechanical setup. We argue that the so called Chiral de Rham complex, which is a sheaf of vertex algebras, is a natural framework to understand quantum aspects of supersymmetric sigma models in the Hamiltonian formalism. We show how a class of currents which generate symmetry algebras for the classical sigma model can be defined within the Chiral de Rham complex framework, and for a six-dimensional Calabi-Yau manifold we calculate the equal-time commutators between the currents and show that they generate the Odake algebra.
40
Mattsson, Peter Aake. "Integrable quantum field theories, in the bulk and with a boundary." Thesis, Durham University, 2000. http://etheses.dur.ac.uk/4225/.
Full textAbstract:
In this thesis, we consider the massive field theories in 1+1 dimensions known as affine Toda quantum field theories. These have the special property that they possess an infinite number of conserved quantities, a feature which greatly simplifies their study, and makes extracting exact information about them a tractable problem. We consider these theories both in the full space (the bulk) and in the half space bounded by an impenetrable boundary at x = 0. In particular, we consider their fundamental objects: the scattering matrices in the bulk, and the reflection factors at the boundary, both of which can be found in a closed form. In Chapter 1, we provide a general introduction to the topic before going on, in Chapter 2, to consider the simplest ATFT—the sine-Gordon model—with a boundary. We begin by studying the classical limit, finding quite a clear picture of the boundary structure we can expect in the quantum case, which is introduced in Chapter 3. We obtain the bound-state structure for all integrable boundary conditions, as well as the corresponding reflection factors. This structure turns out to be much richer than had hitherto been imagined. We then consider more general ATFTs in the bulk. The sine-Gordon model is based on a(^(1))(_1), but there is an ATFT for any semi-simple Lie algebra. This underlying structure is known to show up in their S-matrices, but the path back to the parameters in the Lagrangian is still unclear. We investigate this, our main result being the discovery of a "generalised bootstrap" equation which explicitly encodes the Lie algebra into the S-matrix. This leads to a number of new S-matrix identities, as well as a generalisation of the idea that the conserved charges of the theory form an eigenvector of the Cartan matrix. Finally our results are summarised in Chapter 5, and possible directions for further study are highlighted.
41
Sadofyev, Andrey, and Srimoyee Sen. "Chiral anomalous dispersion." SPRINGER, 2018. http://hdl.handle.net/10150/627127.
Full textAbstract:
The linearized Einstein equation describing graviton propagation through a chiral medium appears to be helicity dependent. We analyze features of the corresponding spectrum in a collision-less regime above a flat background. In the long wave-length limit, circularly polarized metric perturbations travel with a helicity dependent group velocity that can turn negative giving rise to a new type of an anomalous dispersion. We further show that this chiral anomalous dispersion is a general feature of polarized modes propagating through chiral plasmas extending our result to the electromagnetic sector.
42
Mori, Yuto. "Path optimization with neural network for sign problem in quantum field theories." Doctoral thesis, Kyoto University, 2021. http://hdl.handle.net/2433/263466.
Full text
43
Fischer, Michael. "Non-adiabatic quantum molecular dynamics: - Benchmark systems in strong laser fields - Approximate electron-nuclear correlations." Doctoral thesis, Saechsische Landesbibliothek- Staats- und Universitaetsbibliothek Dresden, 2014. http://nbn-resolving.de/urn:nbn:de:bsz:14-qucosa-148848.
Full textAbstract:
The non-adiabatic quantum molecular dynamics (NA-QMD) method couples self-consistently classical nuclear motion with time-dependent density functional theory (TDDFT) in basis expansion for the electron dynamics. It has become a versatile approach to study the dynamics of atoms, molecules and clusters in a wide range of scenarios. This work presents applications of the NA-QMD method to important benchmark systems and its systematic extension to include quantum effects in the nuclear motion.
Regarding the first objective, a complete study of the strong-field ionization and dissociation dynamics of nature’s simplest molecule H2+ is performed. By including all electronic and nuclear degrees of freedom and all reaction channels, molecular rotation is shown to play an important role in the ionization process. In addition, strong orientation effects in the energy deposition process of the Buckminster fullerene C60 in short intense laser pulses are surprisingly found in full dimensional calculations. Their consequences on the subsequent nuclear relaxation dynamics shed new light on available experimental data and future experiments are proposed to confirm the detailed predictions.
Regarding the second objective, the NA-QMD formalism is basically extended to take electron-nuclear correlations into account. This extension is achieved by means of a trajectory surface hopping scheme in the adiabatic Kohn-Sham framework. First studied examples from collision physics and photochemistry illustrate the relevance and importance of quantum effects in the nuclear dynamics.
44
Baume, Florent [Verfasser], and Eran [Akademischer Betreuer] Palti. "Constraints on Four Dimensional Effective Field Theories From String and F-theory / Florent Baume ; Betreuer: Eran Palti." Heidelberg : Universitätsbibliothek Heidelberg, 2017. http://d-nb.info/1180986490/34.
Full text
45
Slizovskiy, Sergey. "Yang-Mills Theory in Gauge-Invariant Variables and Geometric Formulation of Quantum Field Theories." Doctoral thesis, Uppsala universitet, Teoretisk fysik, 2010. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-129670.
Full textAbstract:
In Part I we are dealing with effective description of Yang-Mills theories based on gauge-invarint variables. For pure Yang-Mills we study the spin-charge separation varibles. The dynamics in these variables resembles the Skyrme-Faddeev model. Thus the spin-charge separation is an important intermediate step between the fundamental Yang-Mills theory and the low-energy effective models, used to model the low-energy dynamics of gluons. Similar methods may be useful for describing the Electroweak sector of the Standard Model in terms of gauge-invariant field variables called supercurrents. We study the geometric structure of spin-charge separation in 4D Euclidean space (paper III) and elaborate onconnection with gravity toy model. Such reinterpretation gives a way to see how effective flat background metric is created in toy gravity model by studying the appearance of dimension-2 condensate in the Yang-Mills (paper IV). For Electroweak theory we derive the effective gauge-invariant Lagrangian by doing the Kaluza-Klein reduction of higher-dimensional gravity with 3-brane, thus making explicit the geometric interpretation for gauge-invariant supercurrents. The analogy is then made more precise in the framework of exact supergravity solutions. Thus, we interpret the Higgs effect as spontaneous breaking of Kaluza-Klein gauge symmetry and this leads to interpretation of Higgs field as a dilaton (papers I and II). In Part II of the thesis we study rather simple field theories, called “geometric” or “instantonic”. Their defining property is exact localization on finite-dimensional spaces – the moduli spaces of instantons. These theories allow to account exactly for non-linearity of space of fields, in this respect they go beyond the standard Gaussian perturbation theory. In paper V we show how to construct a geometric theory of chiral boson by embedding it into the geometric field theory. In Paper VI we elaborate on the simplest geometric field theory – the supersymmetric Quantum Mechanics and construct new non-perturbative topological observables that have a transparent meaning both in geometric and in the Hamiltonian formalisms. In Paper VII we are motivated by making perturbations away from the simple instantonic limit. For that we need to carefully define the observables that are quadratic in momenta and develop the way to compute them in geometric framework. These correspond geometrically to bivector fields (or, in general, the polyvector fields). We investigate the local limit of polyvector fields and compare the geometric calculation with free-field approach.
46
Riederer, Stéphane Jean. "D-theory formulation of quantum field theories and application to CP(N-1) models /." [S.l.] : [s.n.], 2006. http://www.zb.unibe.ch/download/eldiss/06riederer_sj.pdf.
Full text
47
Carrozza, Sylvain. "Tensorial methods and renormalization in Group Field Theories." Thesis, Paris 11, 2013. http://www.theses.fr/2013PA112147/document.
Full textAbstract:
Cette thèse présente une étude détaillée de la structure de théories appelées GFT ("Group Field Theory" en anglais),à travers le prisme de la renormalisation. Ce sont des théories des champs issues de divers travaux en gravité quantique, parmi lesquels la gravité quantique à boucles et les modèles de matrices ou de tenseurs. Elles sont interprétées comme desmodèles d'espaces-temps quantiques, dans le sens où elles génèrent des amplitudes de Feynman indexées par des triangulations,qui interpolent les états spatiaux de la gravité quantique à boucles. Afin d'établir ces modèles comme des théories deschamps rigoureusement définies, puis de comprendre leurs conséquences dans l'infrarouge, il est primordial de comprendre leur renormalisation. C'est à cette tâche que cette thèse s'attèle, grâce à des méthodes tensorielles développées récemment,et dans deux directions complémentaires. Premièrement, de nouveaux résultats sur l'expansion asymptotique (en le cut-off) des modèles colorés de Boulatov-Ooguri sont démontrés, donnant accès à un régime non-perturbatif dans lequel une infinité de degrés de liberté contribue. Secondement, un formalisme général pour la renormalisation des GFTs dites tensorielles (TGFTs) et avec invariance de jauge est mis au point. Parmi ces théories, une TGFT en trois dimensions et basée sur le groupe de jauge SU(2) se révèle être juste renormalisable, ce qui ouvre la voie à l'application de ce formalisme à la gravité quantique<br>In this thesis, we study the structure of Group Field Theories (GFTs) from the point of view of renormalization theory.Such quantum field theories are found in approaches to quantum gravity related to Loop Quantum Gravity (LQG) on the one hand,and to matrix models and tensor models on the other hand. They model quantum space-time, in the sense that their Feynman amplitudes label triangulations, which can be understood as transition amplitudes between LQG spin network states. The question of renormalizability is crucial if one wants to establish interesting GFTs as well-defined (perturbative) quantum field theories, and in a second step connect them to known infrared gravitational physics. Relying on recently developed tensorial tools, this thesis explores the GFT formalism in two complementary directions. First, new results on the large cut-off expansion of the colored Boulatov-Ooguri models allow to explore further a non-perturbative regime in which infinitely many degrees of freedom contribute. The second set of results provide a new rigorous framework for the renormalization of so-called Tensorial GFTs (TGFTs) with gauge invariance condition. In particular, a non-trivial 3d TGFT with gauge group SU(2) is proven just-renormalizable at the perturbative level, hence opening the way to applications of the formalism to (3d Euclidean) quantum gravity
48
Wojtas, David Heinrich. "Suppressing Discretization Error in Langevin Simulations of (2+1)-dimensional Field Theories." Thesis, University of Canterbury. Physics and Astronomy, 2006. http://hdl.handle.net/10092/1294.
Full textAbstract:
Lattice simulations are a popular tool for studying the non-perturbative physics of nonlinear field theories. To perform accurate lattice simulations, a careful account of the discretization error is necessary. Spatial discretization error as a result of lattice spacing dependence in Langevin simulations of anisotropic (2 + 1)-dimensional classical scalar field theories is studied. A transfer integral operator (TIO) method and a one-loop renormalization (1LR) procedure are used to formulate effective potentials. The effective potentials contain counterterms which are intended to suppress the lattice spacing dependence. The two effective potentials were tested numerically in the case of a phi-4 model. A high accuracy modified Euler method was used to evolve a phenomenological Langevin equation. Large scale Langevin simulations were performed in parameter ranges determined to be appropriate. Attempts at extracting correlation lengths as a means of determining effectiveness of each method were not successful. Lattice sizes used in this study were not of a sufficient size to obtain an accurate representation of thermal equilibrium. As an alternative, the initial behaviour of the ensemble field average was observed. Results for the TIO method showed that it was successful at suppressing lattice spacing dependence in a mean field limit. Results for the 1LR method showed that it performed poorly.
49
Delporte, Nicolas. "Tensor Field Theories : Renormalization and Random Geometry." Thesis, université Paris-Saclay, 2020. http://www.theses.fr/2020UPASP011.
Full textAbstract:
Cette thèse se scinde en deux volets, avec vue sur la renormalisation de théorie quantique des champs.Le premier volet traite de trois modèles tensoriels en trois dimensions, un quartique fermionique de rang 3 et deux sextiques bosonique, de rangs 3 et 5. On se base sur l'expansion melonique à grand N des théories tensorielles. Pour le premier modèle, invariant sous le groupe U(N)³, on calcule le flot du groupe de renormalisation des deux couplages meloniques et on dresse le diagramme des phases du vide de la théorie, en étudiant sa reformulation par un champ intermédiaire matriciel diagonalisable. Observant une brisure spontanée de la symétrie discrète chirale, la comparaison avec le modèle de Gross-Neveu tri-dimensionel est faite. Au-delà de la phase symétrique U(N)³ sans masse, on note aussi une phase massive de même symétrie et une autre où la symétrie est brisée vers U(N²) x U(N/2) x U(N/2). Un modèle matriciel de symétrie U(N) x U(N²), présentant les mêmes caractéristiques, est aussi considéré.Dans les deux autres modèles tensoriels, de groupes de symétrie U(N)³ et O(N)⁵, un couplage non-melonique (la ``roue") adjoint d'une puissance de N optimale nous conduit à une expansion melonique généralisée. Les termes cinétiques sont pris de courte ou longue portée et on étudie, à grand N, perturbativement les différents groupes de renormalisation des couplages d'ordre 6, jusqu'à quatre boucles. Tandis que le modèle de rang 5 ne présente pas de point fixe non-trivial, celui de rang 3 possède deux points fixes non-triviaux réels de type Wilson-Fisher dans le cas à courte portée et une ligne de points fixes dans l'autre. On obtient enfin les dimensions conformes réelles des opérateurs primaires bilinéaires en le champ fondamental.Le second volet établit les premiers résultats de renormalisation constructive multi-échelle pour un modèle scalaire quartique sur des arbres de Galton-Watson critiques, avec un terme cinétique à longue portée. Au point critique, l'émergence d'une spine infinie fournit un espace de dimension effective 4/3 sur lequel calculer des fonctions de corrélations moyennées. Cela formalise la notion de théorie des champs sur une géométrie aléatoire. Nous utilisons dans notre approche des bornes probabilistes sur le noyau de la chaleur dans un graphe aléatoire. On esquisse pour terminer l'extension du formalisme à des fermions et à une spine compactifiée<br>This thesis divides into two parts, focusing on the renormalization of quantum field theories. The first part considers three tensor models in three dimensions, a fermionic quartic with tensors of rank-3 and two bosonic sextic, of ranks 3 and 5. We rely upon the large-N melonic expansion of tensor models. For the first model, invariant under U(N)³, we compute the renormalization group flow of the two melonic couplings and establish the vacuum phase diagram, from a reformulation with a diagonalizable matrix intermediate field. Noting a spontaneous symmetry breaking of the discrete chiral symmetry, the comparison with the three-dimensional Gross-Neveu model is made. Beyond the massless U(N)³ symmetric phase, we also observe a massive phase of same symmetry and another where the symmetry breaks into U(N²) x U(N/2) x U(N/2). A matrix model invariant under U(N) x U(N²), sharing the same properties, is also studied.For the two other tensor models, with symmetry groups U(N)³ and O(N)⁵, a non-melonic coupling (the ``wheel") with an optimal scaling in N drives us to a generalized melonic expansion. The kinetic terms are taken of short and long range, and we analyze perturbatively, at large-N, the renormalization group flows of the sextic couplings up to four loops. While the rank-5 model doesn't present any non-trivial fixed point, that of rank 3 displays two real non-trivial Wilson-Fisher fixed points in the short-range case and a line of fixed points in the other. We finally obtain the real conformal dimensions of the primary operators bilinear in the fundamental field.In the second part, we establish the first results of constructive multi-scale renormalization for a quartic scalar field on critical Galton-Watson trees, with a long-range kinetic term. At the critical point, an emergent infinite spine provides a space of effective dimension 4/3 on which to compute averaged correlation fonctions. This approach formalizes the notion of a quantum field theory on a random geometry. We use known probabilistic bounds on the heat-kernel on a random graph. At the end, we sketch the extension of the formalism to fermions and to a compactified spine
50
Bond, Andrew David. "Weakly coupled fixed points and interacting ultraviolet completions of vanilla quantum field theories, or, Better asymptotically safe than asymptotically sorry." Thesis, University of Sussex, 2018. http://sro.sussex.ac.uk/id/eprint/80674/.
Full textAbstract:
The renormalisation group is a crucial tool for understanding scale-dependent quantum field theories. Renormalisation group fixed points correspond to theories where scale invariance is restored at the quantum level, and may provide high- or low-energy limits for more general quantum field theories. In particular, those reached in the ultraviolet allow theories to be defined microscopically, a scenario known as asymptotic safety. In this work I investigate fixed points of conventional four-dimensional, at-space, perturbatively renormalisable, local quantum field theories. Focusing on weakly interacting fixed points the problem becomes amenable to perturbation theory. The approach is twofold: on the one hand to understand general conditions for the existence of such fixed points, and on the other to construct theories which introduce new features compared to previous examples. To understand perturbative fixed points, general calculations for theories of this type are exploited. It is established, for gauge theories, interacting fixed points may be nonzero in gauge couplings alone, or in gauge and Yukawa couplings. Deriving novel group theory bounds it is established that only the latter may possibly be ultraviolet. Additionally it is shown that theories without gauge interactions cannot possess weakly coupled fixed points, and the connexion between this fact and the impossibility of such theories being asymptotically free is highlighted. Two explicit families of examples are presented: a theory with semisimple gauge group is analysed in detail, containing many new fixed points, a rich phase structure, and asymptotically safe regions of parameter space, and a separate supersymmetric model with an ultraviolet fixed point, providing the first known explicit example of an asymptotically safe supersymmetric gauge theory.