Log in

Relevant bibliographies by topics / Scalar field theory / Dissertations / Theses

To see the other types of publications on this topic, follow the link: Scalar field theory.

Dissertations / Theses on the topic 'Scalar field theory'

Author: Grafiati

Published: 4 June 2021

Last updated: 30 July 2024

Create a spot-on reference in APA, MLA, Chicago, Harvard, and other styles

Select a source type:

Consult the top 50 dissertations / theses for your research on the topic 'Scalar field theory.'

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

Díaz, Calzadilla Pablo. "Scalar stars and effective field theory." Master's thesis, Alma Mater Studiorum - Università di Bologna, 2021. http://amslaurea.unibo.it/23167/.

Full text

Abstract:

The axion is one of the favored candidates to form the cold dark matter in the universe. This pseudo-scalar field may form compact objects called axion stars, whose physics is well captured by means of non-relativistic effective field theory coupled to Newtonian gravity. The interplay between gradient energy, self-interactions and gravity gives rise to both dilute and dense axion stars. While the existence of the dilute axion stars is well established, the situation is more complicated in the case of the so-called dense axion stars, an extra physically stable solution of the system of differential equations describing the dynamics of the axion field in the regime where self-interactions play an important role. The existence of the dense axion stars has not been settled in the literature. In this thesis, we discuss first the appropriate non-relativistic formalism for the study of these clumps by means of the various non-relativistic reductions found in the literature. We analyze the stability, for different sizes and number of particles, of these objects considering quartic self-interaction potentials. This allows us to corroborate the results for these cases already presented by other authors. We also go beyond the simplest case, by analyzing more complicated potentials describing with higher precision the axion self-interactions. By employing the correct non-relativistic axion effective field theory we show that the dense branch is an artefact of the non-relativistic reduction procedure.

APA, Harvard, Vancouver, ISO, and other styles

2

Thorne, Robert S. "Renormalizability of effective scalar field theory." Thesis, University of Oxford, 1993. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.358742.

Full text

APA, Harvard, Vancouver, ISO, and other styles

3

Smith, John D. "Scalar fields in quantum field theory and black holes." Thesis, University of Newcastle Upon Tyne, 1999. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.265489.

Full text

APA, Harvard, Vancouver, ISO, and other styles

4

Tassev, Svetlin Valentinov. "Quantum field theory of scalar cosmological perturbations." Thesis, Massachusetts Institute of Technology, 2005. http://hdl.handle.net/1721.1/32906.

Full text

Abstract:

Thesis (S.B.)--Massachusetts Institute of Technology, Dept. of Physics, 2005.
Includes bibliographical references (leaf 55).
Using canonical quantization we show that the spectrum of the scalar cosmological fluctuations as calculated until now is not correct. We derive the correct expression for the spectrum, and show that our correct treatment alleviates the fine-tuning problem in inflation.
by Svetlin Valentinov Tassev.
S.B.

APA, Harvard, Vancouver, ISO, and other styles

5

Stephanov, Mikhail Alexeevich. "Scalar-fermion theories on the lattice." Thesis, University of Oxford, 1994. http://ora.ox.ac.uk/objects/uuid:555a30de-2df9-4d39-b2dc-1974398911f7.

Full text

Abstract:

We study scalar-fermion models with Yukawa interaction on a space-time lat- tice. Such models can describe the Higgs sector of the Standard Model in the case when the Higgs particle is very heavy (few hundred GeV) and there are very heavy fermions whose masses are due to their Yukawa interactions with the Higgs field. We study a realistic model with four component scalar field as well as simplified models with one and two component scalar fields. We use a mean field approximation to calculate equations for critical lines in the large d (dimension of space-time) limit. These lines are in very good agreement with available Monte Carlo data for the models at d = 4. We calculate fermion correlation functions in the mean field and large d approximations to study properties of different phases in the lattice models. We find two distinct phases with vanishing expectation values of the scalar field. One (at small Yukawa coupling Y) contains massless fermions, while in the other (at large F) the fermions have masses larger than the scale given by the inverse lattice spacing. We find that in the latter phase fermions can form bosonic bound states. These states show up as poles in a four-fermion correlator. We discuss pos- sible continuum limits in the lattice scalar-fermion models. In particular, we show that a theory defined near the critical line separating the disordered phase from the phase with antiferromagnetic order is not unitary.

APA, Harvard, Vancouver, ISO, and other styles

6

Türköz, Ş. (Şemsettin). "Variational procedure for [phi]4-scalar field theory." Thesis, Massachusetts Institute of Technology, 1989. http://hdl.handle.net/1721.1/52913.

Full text

Abstract:

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Physics, 1990.
On t.p. "[phi]" is the original Greek letter.
Includes bibliographical references (leaves 81-83).
by Ş. Türköz.
Ph.D.

APA, Harvard, Vancouver, ISO, and other styles

7

Davies, Trevor Bamidelé. "Quadratic scalar-tensor gravity." Thesis, University of Aberdeen, 2017. http://digitool.abdn.ac.uk:80/webclient/DeliveryManager?pid=234075.

Full text

Abstract:

This thesis develops novel analytic models of scalar-tensor theories with quadratic coupling. In this framework, the coupling strength between scalar and matter is regulated in a way that allows the vacuum expectation value to vanish for low matter densities while becoming non-vanishingly large in the high-density regime. This results in significant deviations from the predictions of General Relativity in the strong-gravity regime. In astrophysics, we addressed the core-collapse supernova problem to account for the apparently missing energy required to explain the observed powerful explosions. We assumed a small, massless scalar gravitational field, thus allowing General Relativity to be recovered in the weak-gravity asymptotic limit. The non-trivial effects coming from the coupling function in the presence of a high-density field were analyzed at the instant of neutron star formation. Our results show that the scalar gravitational field evolves from a cosmological value to a new equilibrium via a Higgs-like mechanism. Additionally, the calculations associated with the gravitational binding energy shift and relevant relaxation timescale are explicitly shown. The full theory space of the model was also investigated for positive values of the coupling parameter. We studied a mechanism to address the stalled shock issue in core-collapse scenarios, which involved the application of sufficiently large positive values to the coupling parameter. Our results show that pulsating neutron stars act like optical cavities in which resonant scalar waves are parametrically amplified. It implies that the surface of a neutron star acts like an anti-phase reflector, releasing traveling scalar gravitational waves similar to an optical laser. In cosmology, the same framework was applied to a generic Friedman-Robertson-Walker universe involving general metric coupling and scalar potential functions. In cosmology, the same framework was applied to a generic Friedman-Robertson-Walker universe involving general metric coupling and scalar potential functions. We developed a mechanism which allowed the scalar field to be dynamically trapped, thus generating a potential capable of driving primordial inflation. Our results show that a trapped scalar field produces non-trivial dynamical consequences when applied to standard cosmology. Additionally, our analytic solutions for the generic inflationary behaviour, produce acceptable duration and e-foldings, thus recovering the Hubble parameter which is consistent with the present-day value. A feature of our cosmological model is that the universe can undergo several accelerating or decelerating phases, even though the scalar potential and metric coupling are monotonic functions overall. As this is important for the current dark energy problem, the quasi-static motion of the gravitational field induced by the scalar potential in the early universe, is investigated for a small value of the scalar field with normalized metric at the present time. Our results show that a variable Lambda Cold Dark Matter universe emerges naturally from the quadratic model.

APA, Harvard, Vancouver, ISO, and other styles

8

Hawley, Scott Hearne. "Scalar analogues of compact astrophysical systems /." Digital version accessible at:, 2000. http://wwwlib.umi.com/cr/utexas/main.

Full text

APA, Harvard, Vancouver, ISO, and other styles

9

Andersson, Mattias. "Scalar fields on star graphs." Thesis, Karlstads universitet, Avdelningen för fysik och elektroteknik, 2011. http://urn.kb.se/resolve?urn=urn:nbn:se:kau:diva-9139.

Full text

Abstract:

A star graph consists of a vertex to which a set of edges are connected. Such an object can be used to, among other things, model the electromagnetic properties of quantum wires. A scalar field theory is constructed on the star graph and its properties are investigated. It turns out that there exist Kirchoff's rules for the conserved charges in the system leading to restrictions of the possible type of boundary conditions at the vertex. Scale invariant boundary conditions are investigated in detail.
En stjärngraf består av en nod på vilken vilken ett antal kanter är anslutna. Ett sådant objekt kan bland annat användas till att modellera de elektromagnetiska egenskaperna hos kvanttrådar. En skalärfältsteori konstrueras på stjärngrafen och dess egenskaper undersöks. Det visar sig att det exisisterar en typ av Kirchoffs lagar för de konserverade laddningarna i systemet. Detta leder till restriktioner på vilka randvillkor som är möjliga vid noden. Skalinvarianta randvillkor undersöks i detalj.

APA, Harvard, Vancouver, ISO, and other styles

10

Schroeder, Christopher Robert. "Beyond the scalar Higgs, in lattice quantum field theory." Diss., [La Jolla] : University of California, San Diego, 2009. http://wwwlib.umi.com/cr/ucsd/fullcit?p3386720.

Full text

Abstract:

Thesis (Ph. D.)--University of California, San Diego, 2009.
Title from first page of PDF file (viewed January 19, 2010). Available via ProQuest Digital Dissertations. Vita. Includes bibliographical references (p. 87-93).

APA, Harvard, Vancouver, ISO, and other styles

11

Kent, Carl. "Quantum scalar field theory on anti-de Sitter space." Thesis, University of Sheffield, 2013. http://etheses.whiterose.ac.uk/4911/.

Full text

Abstract:

This thesis considers a real massive free quantum scalar field propagating with arbitrary coupling to $n$-dimensional anti-de Sitter space. Analytical expressions are found for the field modes and Feynman Green function. The condition for the equivalence of rotational vacuum states is also established. The rotational and thermal anti-commutator functions are then derived. A method is developed for computing the Hadamard renormalised vacuum and thermal expectation values of the quadratic field fluctuations and the stress-energy tensor. Results are obtained for $n=2$ to $n=11$, satisfying Wald's axioms and exhibiting the trace anomaly.

APA, Harvard, Vancouver, ISO, and other styles

12

Dick, Frank Albert. "Scalar field theories of nucleon interactions." Link to electronic thesis, 2007. http://www.wpi.edu/Pubs/ETD/Available/etd-042507-084002/.

Full text

Abstract:

Dissertation (Ph.D.) -- Worcester Polytechnic Institute.
Keywords: ladder approximation; inelastic process; Bethe-Salpeter; BSE; nucleon; scalar field; pion. Includes bibliographical references (p.161-163).

APA, Harvard, Vancouver, ISO, and other styles

13

Foster, Scott. "Singularity structure of scalar field cosmologies /." Title page, contents and abstract only, 1996. http://web4.library.adelaide.edu.au/theses/09PH/09phf757.pdf.

Full text

APA, Harvard, Vancouver, ISO, and other styles

14

Endres, Michael G. "Topics in lattice field theory /." Thesis, Connect to this title online; UW restricted, 2007. http://hdl.handle.net/1773/9713.

Full text

APA, Harvard, Vancouver, ISO, and other styles

15

Ding, Bingfeng. "Variational particle-antiparticle bound states in the scalar Yukawa model." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 2000. http://www.collectionscanada.ca/obj/s4/f2/dsk2/ftp02/NQ59128.pdf.

Full text

APA, Harvard, Vancouver, ISO, and other styles

16

Gratus, Jonathan. "Scalar fields and signature change in two dimensions." Thesis, Lancaster University, 1995. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.306889.

Full text

APA, Harvard, Vancouver, ISO, and other styles

17

Schelpe, Camilla Amadea Oxtoby. "The astrophysical signatures of chameleon-like scalar fields." Thesis, University of Cambridge, 2012. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.610180.

Full text

APA, Harvard, Vancouver, ISO, and other styles

18

Myers, Jason. "Equilibration of a scalar field theory: a comparison of methods." Master's thesis, University of Cape Town, 2014. http://hdl.handle.net/11427/9215.

Full text

Abstract:

Includes bibliographical references.
The Large Hadron Collider is a huge particle collider that, among other things, collides heavy ions together at massive energies. In such heavy ion collisions a new state of matter called the Quark Gluon Plasma (QGP) is formed where, in this state, quarks are no longer confined to hadrons but are free to move about. Studying this state is expected to lead to a far greater understanding of QCD as this is the only known state where one can find free quarks and gluons, the degrees of freedom of QCD. The QGP is known to be a very hot, very dense medium that is rapidly expanding, so one needs techniques that allow for the study of a Quantum Field Theory in an extreme and very dynamical environment.

APA, Harvard, Vancouver, ISO, and other styles

19

Kyllingstad, Lars Tandle. "Aspects of QCD thermodynamics through scalar field theory and NJL models." Doctoral thesis, Norges teknisk-naturvitenskapelige universitet, Institutt for fysikk, 2011. http://urn.kb.se/resolve?urn=urn:nbn:no:ntnu:diva-14532.

Full text

APA, Harvard, Vancouver, ISO, and other styles

20

Kujat, Jens. "Scalar fields in cosmology." Columbus, Ohio : Ohio State University, 2006. http://rave.ohiolink.edu/etdc/view?acc%5Fnum=osu1142978764.

Full text

APA, Harvard, Vancouver, ISO, and other styles

21

Vedula, Prakash. "Study of scalar transport in turbulent flows using direct numerical simulations." Diss., Georgia Institute of Technology, 2001. http://hdl.handle.net/1853/12119.

Full text

APA, Harvard, Vancouver, ISO, and other styles

22

Graham, Alexander Alan Hewetson. "Scalar fields in cosmology and black holes." Thesis, University of Cambridge, 2016. https://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.709524.

Full text

APA, Harvard, Vancouver, ISO, and other styles

23

Nilsen, Vebjorn. "Investigation of differentially diffusing scalars in isotropic decaying turbulence /." Thesis, Connect to this title online; UW restricted, 1998. http://hdl.handle.net/1773/7028.

Full text

APA, Harvard, Vancouver, ISO, and other styles

24

Stokley, Martin. "An investigation into particle and field ontologies for relativistic scalar fields in de Broglie-Bohm type theories." Thesis, University of Portsmouth, 2001. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.343394.

Full text

APA, Harvard, Vancouver, ISO, and other styles

25

Kommemi, Jonathan David. "The global structure of spherically symmetric charged scalar field spacetimes." Thesis, University of Cambridge, 2013. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.608282.

Full text

APA, Harvard, Vancouver, ISO, and other styles

26

Leith, Ben Maitland. "Scalar Fields and Alternatives in Cosmology and Black Holes." Thesis, University of Canterbury. Physics and Astronomy, 2007. http://hdl.handle.net/10092/1444.

Full text

Abstract:

Extensions to general relativity are often considered as possibilities in the quest for a quantum theory of gravity on one hand, or to resolve anomalies within cosmology on the other. Scalar fields, found in many areas of physics, are frequently studied in this context. This is partly due to their manifestation in the effective four dimensional theory of a number of underlying fundamental theories, most notably string theory. This thesis is concerned with the effects of scalar fields on cosmological and black hole solutions. By comparison, an analysis of an inhomogeneous cosmological model which requires no extensions to general relativity is also undertaken. In chapter three, examples of numerical solutions to black hole solutions, which have previously been shown to be linearly stable, are found. The model includes at least two scalar fields, non-minimally coupled to electromagnetism and hence possesses non-trivial contingent primary hair. We show that the extremal solutions have finite temperature for an arbitrary coupling constant. Chapter four investigates the effects of higher order curvature corrections and scalar fields on the late-time cosmological evolution. We find solutions which mimic many of the phenomenological features seen in the post-inflation Universe. The effects due to non-minimal scalar couplings to matter are also shown to be negligible in this context. Such solutions can be shown to be stable under homogeneous perturbations. Some restrictions on the value of the slope of the scalar coupling to the Gauss-Bonnet term are found to be necessary to avoid late-time superluminal behaviour and dominant energy condition violation. A number of observational tests are carried out in chapter five on a new approach to averaging the inhomogeneous Universe. In this "Fractal Bubble model" cosmic acceleration is realised as an apparent effect, due to quasilocal gravitational energy gradients. We show that a good fit can be found to three separate observations, the type Ia supernovae, the baryon acoustic oscillation scale and the angular scale of the sound horizon at last scattering. The best fit to the supernovae data is χ² ≃ 0:9 per degree of freedom, with a Hubble parameter at the present epoch of H0 = 61:7+1:4 -1:3 km sec⁻¹ Mpc⁻¹ , and a present epoch volume void fraction of 0:76 ± 0:05.

APA, Harvard, Vancouver, ISO, and other styles

27

Gardiner, Matthew Raymond. "Conserved charges, monodromy matrices and solitons in MKDV theory." Thesis, King's College London (University of London), 1999. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.322761.

Full text

APA, Harvard, Vancouver, ISO, and other styles

28

Zhu, Wenqi. "Out-of-core construction and simplification of Morse-Smale complexes /." View abstract or full-text, 2008. http://library.ust.hk/cgi/db/thesis.pl?CSED%202008%20ZHUW.

Full text

APA, Harvard, Vancouver, ISO, and other styles

29

Veraguth, Olivier J. "Conformal loop quantum gravity : avoiding the Barbero-Immirzi ambiguity with a scalar-tensor theory." Thesis, University of Aberdeen, 2017. http://digitool.abdn.ac.uk:80/webclient/DeliveryManager?pid=236513.

Full text

Abstract:

In the construction of Canonical Loop Quantum Gravity, General Relativity is rewritten in terms of the Ashtekar variables to simplify its quantisation. They consist of a densitised triad and a connection terms. The latter depends by definition and by construction on a free parameter β, called the Barbero–Immirzi parameter. This freedom is passed on to the quantum theory as it appears in the expressions of certain operators. Their discreet spectra depend on the arbitrary value of this parameter β, meaning that the scale of those spectra is not uniquely defined. To get around this ambiguity, we propose to consider a theory of Conformal Loop Quantum Gravity, by imposing a local conformal symmetry through the addition of a scalar field. We construct our theory starting from the usual Einstein–Hilbert action for General Relativity to which we add the action for the massless scalar field and rewrite it in terms of a new set of Ashtekar-like variables. They are constructed through a set of canonical transformations, which allow to move the Barbero–Immirzi parameter from the connection to the scalar variable. We then show that the theory can be quantised by fulfilling the conditions for a Dirac quantisation. Finally, we present some first elements of the quantum formalism. It is expected that with such a scalar-tensor theory, the quantum operators should not depend on the free parameter directly but rather on the dynamical scalar field, solving therefore the ambiguity.

APA, Harvard, Vancouver, ISO, and other styles

30

Chakraborty, Sankar. "Scalar, electromagnetic and elastic waves in periodic and certain broken-periodicity media /." free to MU campus, to others for purchase, 1997. http://wwwlib.umi.com/cr/mo/fullcit?p9842515.

Full text

APA, Harvard, Vancouver, ISO, and other styles

31

Bertan, Igor [Verfasser], and Ivo [Akademischer Betreuer] Sachs. "Quantum scalar field theory in AdS and the AdS/CFT correspondence / Igor Bertan ; Betreuer: Ivo Sachs." München : Universitätsbibliothek der Ludwig-Maximilians-Universität, 2019. http://d-nb.info/120201173X/34.

Full text

APA, Harvard, Vancouver, ISO, and other styles

32

Dasi, Lakshmi P. "The small-scale structure of passive scalar mixing in turbulent boundary layers." Diss., Available online, Georgia Institute of Technology, 2004, 2004. http://etd.gatech.edu/theses/available/etd-08132004-065041/.

Full text

Abstract:

Thesis (Ph. D.)--Civil and Environmental Engineering, Georgia Institute of Technology, 2006.
Cvitanovic, Predrag, Committee Member ; Roberts, Phillip, Committee Member ; Sturm, Terry, Committee Member ; Webster, Donald, Committee Chair ; Yeung, Pui-Kuen, Committee Member.

APA, Harvard, Vancouver, ISO, and other styles

33

Mohapi, Neo. "A study of spherical solutions in chameleon scalar-tensor theories." Thesis, Rhodes University, 2014. http://hdl.handle.net/10962/d1013315.

Full text

Abstract:

The equivalence principle has proven to be central to theories of gravity, with General Relativity being the simplest and most elegant theory to embody the principle. Most alternative theories of gravity struggle to satisfy the principle and still be distinct from GR. Extensions of cosmological and quantum theories question the irrefutably of the equivalence at every scale. The possibility of an equivalence principle violation at galactic scales would be an exciting prospect. In this thesis, we will carefully examine the equivalence principle through the study of chameleon scalar-tensor theories, this will include solutions for hypothetical stars known as boson stars. Such theories find varied application, especially in cosmology, where they model dark energy and inflation. The AWE hypothesis, is an instance of this. It is a nonuniversally coupled model in which violations of the equivalence principle on galactic scales may be apparent. We investigate spherically symmetric and static solutions within the framework of this theory. The constraints obtained from galactic rotation curves results in values of the couplings that show no significant violation of the equivalence principle or values consistent with a theory of dark energy

APA, Harvard, Vancouver, ISO, and other styles

34

Tighe, John Francis. "Derivative expansions of the exact renormalisation group and SU(NN) gauge theory." Thesis, University of Southampton, 2001. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.368120.

Full text

APA, Harvard, Vancouver, ISO, and other styles

35

Al-Kuwari, Hemyan A. "The use of the renormalization group equation in investigating the asymptotic behaviour of the effective potential in the scalar field and mass variables." Thesis, University of Sussex, 1996. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.307722.

Full text

APA, Harvard, Vancouver, ISO, and other styles

36

Sypsas, Spyridon. "Theoretical and observational constraints on brane inflation and study of scalar perturbations through the effective field theory formalism." Thesis, King's College London (University of London), 2014. https://kclpure.kcl.ac.uk/portal/en/theses/theoretical-and-observational-constraints-on-brane-inflation-and-study-of-scalar-perturbations-through-the-eective-field-theory-formalism(cd31253c-7a2e-4995-b600-1a6c948ae556).html.

Full text

Abstract:

In this thesis, we study observational signatures of cosmic (super)strings in the context of D brane inflation and properties of scalar inflaton perturbations on generic homogeneous inflating backgrounds. In the first part, we study the properties of cosmic superstrings produced at the end of inflation in two widely used effective models within a string theory framework, namely the D3/D7 and D3/¯D 3 models. For the D3/D7 model, we show that the symmetry breaking during the waterfall stage is anomalous and cancellation of this anomaly in combination with the moduli stabilisation procedure results in local axionic strings. In addition, we argue that the model is inconsistent with supergravity constraints on constant Fayet Iliopoulos terms. Moreover, we study radiative processes of cosmic superstrings on warped backgrounds. We argue that contrary to previous results in the literature, placing the string formation in a natural context such as D3/¯D 3 inflation, restricts the forms of possible radiation from these objects. Motivated by these string models, which inevitably result in the presence of heavy moduli fields during inflation, in the second part, we construct an effective field theory that captures the effects of massive scalars on the low energy dynamics of inflaton perturbations. We compute the energy scales that define the validity window of the Effective Field Theory (EFT) such as the scale where ultra violet (UV) degrees of freedom become operational and the scale where the EFT becomes strongly coupled. We show that the low energy operators related to heavy fields lift the strong coupling scale of the theory and result in a non linear dispersion relation for the light modes. Assuming that these modes cross the Hubble scale within the dispersive regime, we compute several observables and show how they are directly related with the scale of UV physics.

APA, Harvard, Vancouver, ISO, and other styles

37

Morgan, David C. "A Gaussian approximation to the effective potential." Thesis, University of British Columbia, 1987. http://hdl.handle.net/2429/26500.

Full text

Abstract:

This thesis investigates some of the properties of a variational approximation to scalar field theories: a trial wavefunctional which has a gaussian form is used as a ground state ansatz for an interacting scalar field theory - the expectation value of the Hamiltonian in this state is then minimized. This we call the Gaussian Approximation; the resulting effective potential we follow others by calling the Gaussian Effective Potential (GEP). An equivalent but more general finite temperature formalism is then reviewed and used for the calculations of the GEP in this thesis. Two scalar field theories are described: ϕ⁴ theory in four dimensions (ϕ⁴₄) and ϕ⁶ theory in three dimensions (ϕ⁶₃). After showing what the Gaussian Approximation does in terms of Feynman diagrams, renormalized GEP's are calculated for both theories. Dimensional Regularization is used in the renormalization and this this is especially convenient for the GEP in ϕ⁶₃ theory because it becomes trivially renor-malizable. It is noted that ϕ⁶₃ loses its infrared asymptotic freedom in the Gaussian Approximation. Finally, it is shown how a finite temperature GEP can be calculated by finding low and high temperature expansions of the temperature terms in ϕ⁶₃ theory.
Science, Faculty of
Physics and Astronomy, Department of
Graduate

APA, Harvard, Vancouver, ISO, and other styles

38

Wu, Rui Anzhong Wang. "Gravitational collapse and formation of black holes in the Brans-Dicke theory of gravity with (2+1) dimensions." Waco, Tex. : Baylor University, 2007. http://hdl.handle.net/2104/5115.

Full text

APA, Harvard, Vancouver, ISO, and other styles

39

Bilson, Matthew James. "Momentum and scalar transport in the straight pipe and rotating cylinder : a comparison of transport mechanisms /." St. Lucia, Qld, 2004. http://www.library.uq.edu.au/pdfserve.php?image=thesisabs/absthe17836.pdf.

Full text

APA, Harvard, Vancouver, ISO, and other styles

40

Capraro, Martin Horst. "Vacuum polarisation energies of two interacting scalar fields with a mass gap in (1 + 1) dimensions." Thesis, Stellenbosch : Stellenbosch University, 2014. http://hdl.handle.net/10019.1/95995.

Full text

Abstract:

Thesis (MSc)--Stellenbosch University, 2014.
ENGLISH ABSTRACT: The tools of perturbative Quantum Field Theory are by now a standard part of the theoretical physicist's arsenal. In this thesis we investigate the spectral method, an approach that uses tools from the quantum theory of scattering to calculate the O(~) corrections to fields. Speci cally, we investigate whether the approach can be extended to deal with two interacting scalar elds with a mass gap in (1+1) dimensions. To achieve this we need to verify the analyticity of the appropriate Jost function. All the machinery to do so is introduced during the course of the thesis. This includes the eld theoretic formalism which describes such a system, and the derivation of a number of di erential equations from which the density of states can be constructed. The numerical method is also outlined. Concrete results are presented to verify that the approach reproduces known results. Arguments related to Levinson's theorem are then presented that suggest that the Jost function is indeed analytic, with some caveats.
AFRIKAANSE OPSOMMING: Die gereedskap van perturbatiewe Kwantumveld-teorie is teen di e tyd al `n standaard-deel van die teoretiese sikus se werkskis. In hierdie tesis ondersoek ons die spektrale metode, `n benadering wat gereedskap van die kwantumteorie van verstrooing gebruik om die O(~) korreksie van velde te bereken. Ons ondersoek spesi ek of die metode uitgebrei kan word om toepaslik te wees in die geval van twee wisselwerkende skalaarvelde met `n massa-gaping in (1+1) dimensies. Vir hierdie doel moet ons bepaal of die toepaslike Jost-funksie analities is of nie. Al die masjinerie om dit te bepaal word deur die loop van hierdie tesis ingevoer. Dit sluit in die veld-teorietiese formalisme wat so `n stelsel beskryf, en die a eiding van `n aantal di erensiaal vergelykings wat gebruik kan word om die digtheid van toestande te konstrueer. Die numeriese metode word ook beskryf. Konkrete resultate wat bevestig dat die metode die korrekte antwoorde in `n analities bekende geval weergee, word verskaf. Argumente wat verband hou met Levinson se stelling word gebruik om te bevestig dat die Jost-funksie inderdaad analities is, met sekere voorbehoude.

APA, Harvard, Vancouver, ISO, and other styles

41

Leighton, Feifei Zhang. "Numerical modelling of shallow flows with horizontal density variation." Thesis, University of Oxford, 2005. http://ora.ox.ac.uk/objects/uuid:2ea7400f-9b2c-4052-961e-84446f501822.

Full text

Abstract:

A numerical model is presented of vertically homogeneous shallow flows with variable horizontal density. The governing equations represent mass and momentum conservation of a liquid-species mixture, and mass conservation of the species within a control volume. Here, the term species refers to material transported with the liquid flow. For example, when the species is taken to be suspended sediment, the model provides an idealised simulation of hyper-concentrated sediment-laden flows. The volumetric species concentration acts as an active scalar, allowing the species dynamics to influence the flow structure. The model can simulate flows driven by depth and density differences in the horizontal. The governing equations are written in a deviatoric, hyperbolic form to facilitate their solution by means of a Godunov-type finite volume scheme appropriate for flows containing sharp fronts. The deviatoric governing equations ensure that flux gradient and source terms are balanced (and there is no need for further numerical balancing). The numerical model is first verified for constant density cases, for which the governing equations reduce to the conventional coupled shallow water and species transport equations. Close agreement between numerical predictions and benchmark test solutions illustrate the model's ability to capture rapidly-varying flow features over uniform and non-uniform bathymetries. For variable-density cases, analytical steady-state solutions are derived for two simple cases, one with uniform bathymetry and the other with sinusoidal bathymetry. Detailed parameter studies are then undertaken to examine the effects of varying the initial density and depth in different regions. The shock-capturing scheme resolves all sharp features in the flow such as bore, shear waves, shock diamond like features, contact discontinuities and locally intense vortices. These interesting and novel nonlinear features are unique to variable density flows. The validated numerical model is applied to an idealised case of a hyperconcentrated sediment-laden debris-type flow along a tributary entering a river. The predicted evolution of the free surface flow field is qualitatively similar to observations of an actual debris flows into a river connected to the Upper Yangtze.

APA, Harvard, Vancouver, ISO, and other styles

42

Fermi, D. "A FUNCTIONAL ANALYTIC FRAMEWORK FOR LOCAL ZETA REGULARIZATION AND THE SCALAR CASIMIR EFFECT." Doctoral thesis, Università degli Studi di Milano, 2016. http://hdl.handle.net/2434/360961.

Full text

Abstract:

It is developed a functional analytic framework allowing to formulate a rigorous implementation of zeta regularization for a canonically quantized scalar field, living on an arbitrary spatial domain and interacting with a classical background potential. This framework relies on the construction of an infinite scale of graded Hilbert spaces associated to the real powers of some given, positive self-adjoint operator. When the latter is a Schr\"odinger-type differential operator, this formulation provides a natural language to study the integral kernels related to a large class of operators, fulfilling minimal regularity requirements; particular attention is devoted to the regularity of these kernels and to the construction of their analytic continuations with respect to some parameters. Within this framework, complex powers of the elliptic operator giving rise to the Klein-Gordon equation are used to define a zeta-regularized version of the Wightman field whose pointwise evaluation is well-posed. This regularized field determines regularized local observables (such as the stress-energy tensor), whose vacuum expectation values can be expressed in terms of the above mentioned integral kernels. This allows to make contact with the theory of the Casimir effect. Renormalization is achieved by analytic continuation, which is proved to give finite results for the previously mentioned expectation values in most cases of interest. Finally, to exhibit the computational efficiency of the above methods, some explicit examples are discussed.

APA, Harvard, Vancouver, ISO, and other styles

43

Guarnieri, Filippo. "Renormalization group flow of scalar models in gravity." Doctoral thesis, Humboldt-Universität zu Berlin, Mathematisch-Naturwissenschaftliche Fakultät I, 2014. http://dx.doi.org/10.18452/16976.

Full text

Abstract:

In dieser Doktorarbeit werden wir das Renormierungsproblem von Gravitationstheorien im Kontext der Renormierungsgruppe (RG) unter Anwendung von perturbativen und nicht-perturbativen Methoden untersuchen. Insbesondere werden wir uns auf verschiedene Gravitationsmodelle und Näherungen konzentrieren, in welchen die zentrale Rolle von einem skalaren Freiheitsgrad eingenommen wird. Wir konzentrieren uns besonders auf zwei Ansätze für Quantengravitation, die in letzter Zeit viel Aufmerksamkeit erhalten haben, nämlich den asymptotisch sicheren Fall der Gravitation und die Hořava-Lifshitz Quantengravitation. Das Prinzip der Asymptotischen Sicherheit beruht auf der Annahme, dass das hochenergetische Gravitationsregime von einem nicht-Gaußschen Fixpunkt bestimmt wird, der nicht-perturbative Renormierung und Endlichkeit der Korrelationsfunktionen sicherstellt. Wir werden die Existenz eines solchen nicht-trivialen Fixpunktes mit Hilfe der funktionalen Renormierungsgruppe untersuchen. Insbesondere werden wir den einzigen konformen Freiheitsgrad quantisieren. Die Frage nach der Existenz eines nicht-Gaußschen Fixpunktes in einem unendlich- dimensionalen Parameterraum, das heißt für eine generische f(R)-Theorie, kann jedoch nicht mit einem solchen konform reduzierten Model analysiert werden. Deshalb werden wir es untersuchen, indem wir eine skalare dynamische Äquivalentstheorie, das heißt eine generische Brans-Dicke Theorie in der lokal-Potential Näherung mit ω = 0, quantisieren. Schließlich werden wir mittels einer perturbativen RG Methode die asymptotische Freiheit der Hořava-Lifshitz Gravitationstheorie analysieren. Diese Gravitationstheorie beruht auf der Entstehung einer Anisotropie zwischen Raum und Zeit, die Newtons Konstante zu einer marginalen Koppelung werden lässt und explizit die Unitarität bewahrt. Insbesondere werden wir die Einschleifenkorrektur in 2+1 Dimensionen berechnen, indem wir nur den konformen Freiheitsgrad quantisieren.
In this Ph.D. thesis we will study the issue of renormalizability of gravitation in the context of the renormalization group (RG), employing both perturbative and non-perturbative techniques. In particular, we will focus on different gravitational models and approximations in which a central role is played by a scalar degree of freedom, since their RG flow is easier to analyze. We restrict our interest in particular to two quantum gravity approaches that have gained a lot of attention recently, namely the asymptotic safety scenario for gravity and the Hořava-Lifshitz quantum gravity. In the so-called asymptotic safety conjecture the high energy regime of gravity is controlled by a non-Gaussian fixed point which ensures non-perturbative renormalizability and finiteness of the correlation functions. We will then investigate the existence of such a non trivial fixed point using the functional renormalization group, a continuum version of the non-perturbative Wilson’s renormalization group. In particular we will quantize the sole conformal degree of freedom, which is an approximation that has been shown to lead to a qualitatively correct picture. The question of the existence of a non-Gaussian fixed point in an infinite-dimensional parameter space, that is for a generic f(R) theory, cannot however be studied using such a conformally reduced model. Hence we will study it by quantizing a dynamically equivalent scalar-tensor theory, i.e. a generic Brans-Dicke theory with ω = 0 in the local potential approximation. Finally, we will investigate, using a perturbative RG scheme, the asymptotic freedom of the Hořava-Lifshitz gravity, that is an approach based on the emergence of an anisotropy between space and time which lifts the Newton’s constant to a marginal coupling and explicitly preserves unitarity. In particular we will evaluate the one-loop correction in 2+1 dimensions quantizing only the conformal degree of freedom.

APA, Harvard, Vancouver, ISO, and other styles

44

Correia, Fagner Cintra [UNESP]. "The standard model effective field theory: integrating UV models via functional methods." Universidade Estadual Paulista (UNESP), 2017. http://hdl.handle.net/11449/151703.

Full text

Abstract:

Submitted by FAGNER CINTRA CORREIA null (ccorreia@ift.unesp.br) on 2017-09-24T14:11:35Z No. of bitstreams: 1 Correia_TeseIFT.pdf: 861574 bytes, checksum: 1829fcb0903e20303312d37d7c1e0ffc (MD5)
Approved for entry into archive by Monique Sasaki (sayumi_sasaki@hotmail.com) on 2017-09-27T19:37:47Z (GMT) No. of bitstreams: 1 correia_fc_dr_ift.pdf: 861574 bytes, checksum: 1829fcb0903e20303312d37d7c1e0ffc (MD5)
Made available in DSpace on 2017-09-27T19:37:47Z (GMT). No. of bitstreams: 1 correia_fc_dr_ift.pdf: 861574 bytes, checksum: 1829fcb0903e20303312d37d7c1e0ffc (MD5) Previous issue date: 2017-07-27
Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)
Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)
O Modelo Padrão Efetivo é apresentado como um método consistente de parametrizar Física Nova. Os conceitos de Matching e Power Counting são tratados, assim como a Expansão em Derivadas Covariantes introduzida como alternativa à construção do conjunto de operadores efetivos resultante de um modelo UV particular. A técnica de integração funcional é aplicada em casos que incluem o MP com Tripleto de Escalares e diferentes setores do modelo 3-3-1 na presença de Leptons pesados. Finalmente, o coeficiente de Wilson de dimensão-6 gerado a partir da integração de um quark-J pesado é limitado pelos valores recentes do parâmetro obliquo Y.
It will be presented the principles behind the use of the Standard Model Effective Field Theory as a consistent method to parametrize New Physics. The concepts of Matching and Power Counting are covered and a Covariant Derivative Expansion introduced to the construction of the operators set coming from the particular integrated UV model. The technique is applied in examples including the SM with a new Scalar Triplet and for different sectors of the 3-3-1 model in the presence of Heavy Leptons. Finally, the Wilson coefficient for a dimension-6 operator generated from the integration of a heavy J-quark is then compared with the measurements of the oblique Y parameter.
CNPq: 142492/2013-2
CAPES: 88881.132498/2016-01

APA, Harvard, Vancouver, ISO, and other styles

45

Correia, Fagner Cintra. "The standard model effective field theory : integrating UV models via functional methods /." São Paulo, 2017. http://hdl.handle.net/11449/151703.

Full text

Abstract:

Orientador: Vicente Pleitez
Resumo: O Modelo Padrão Efetivo é apresentado como um método consistente de parametrizar FísicaNova. Os conceitos de Matching e Power Counting são tratados, assim como a Expansão emDerivadas Covariantes introduzida como alternativa à construção do conjunto de operadoresefetivos resultante de um modelo UV particular. A técnica de integração funcional é aplicadaem casos que incluem o MP com Tripleto de Escalares e diferentes setores do modelo 3-3-1 napresença de Leptons pesados. Finalmente, o coeficiente de Wilson de dimensão-6 gerado a partirda integração de um quark-J pesado é limitado pelos valores recentes do parâmetro obliquo Y.
Doutor

APA, Harvard, Vancouver, ISO, and other styles

46

Wilhelm, Söderkvist Vermelin. "3+1 Approach to Cosmological Perturbations : Deriving the First Order Scalar Perturbations of the Einstein Field Equations." Thesis, Karlstads universitet, Fakulteten för hälsa, natur- och teknikvetenskap (from 2013), 2016. http://urn.kb.se/resolve?urn=urn:nbn:se:kau:diva-43257.

Full text

Abstract:

Experimental data suggest that the universe is homogeneous and isotropic on sufficiently large scales. An exact solution of the Einstein field equations exists for a homogeneous and isotropic universe, also known as a Friedmann-Lemaître-Robertson-Walker (FLRW) universe. However, this model is only a first approximation since we know that, locally, the universe has anisotropic and inhomogeneous structures such as galaxies and clusters of galaxies. In order to successfully introduce inhomogeneities and anisotropies to the model one uses perturbative methods. In cosmological perturbations the FLRW universe is considered the zeroth order term in a perturbation expansion and perturbation theory is used to derive higher order terms which one tries to match with observations. In this thesis I present a review of the main concepts of general relativity, discuss the 3+1 formalism which gives us the Einstein field equations in a useful form for the perturbative analysis, and lastly, I derive the first order scalar perturbations of the Einstein field equations.

APA, Harvard, Vancouver, ISO, and other styles

47

Gordon, Christopher. "Adiabatic and entropy perturbations in cosmology." Thesis, University of Portsmouth, 2001. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.369474.

Full text

APA, Harvard, Vancouver, ISO, and other styles

48

Alves, Júnior Francisco Artur Pinheiro. "Gerando modelos de dois campos escalares." Universidade Federal da Paraíba, 2012. http://tede.biblioteca.ufpb.br:8080/handle/tede/5745.

Full text

Abstract:

Made available in DSpace on 2015-05-14T12:14:11Z (GMT). No. of bitstreams: 1 arquivototal.pdf: 1469905 bytes, checksum: 95c9e3653497fa18a127fc9aae221421 (MD5) Previous issue date: 2012-09-28
Coordenação de Aperfeiçoamento de Pessoal de Nível Superior - CAPES
We focus this work in scalar field theory. We review the basic aspects of models containing one scalar field, like the 4, and the two scalars field theory, like the BNRT. We still review the deformation procedure, in order to generate new soluble one field models. The main result is concerned to a new procedure wich makes possible to generate new two field models and its static solutions.
Focamos este trabalho em teoria de campos escalares. Revisamos os aspectos básicos dos modelos contendo um campo, como o 4 e modelos contendo dois campos escalares, como o BNRT. Ainda, revisamos o procedimento de deformação, para gerar novos modelos solúveis com um campo escalar. Nosso principal resultado é um novo procedimento que possibilita a geração de modelos solúveis de dois campos escalares.

APA, Harvard, Vancouver, ISO, and other styles

49

Rodigast, Andreas. "Renormalisation in perturbative quantum gravity." Doctoral thesis, Humboldt-Universität zu Berlin, Mathematisch-Naturwissenschaftliche Fakultät I, 2012. http://dx.doi.org/10.18452/16571.

Full text

Abstract:

In dieser Arbeit berechnen wir die gravitativen Ein-Schleifen-Korrekturen zu den Propagatoren und Wechselwirkungen der Felder des Standardmodells der Elementarteilchenphysik. Wir betrachten hierzu ein höherdimensionales brane-world-Modell: Wärend die Gravitonen, die Austauchteilchen der Gravitationswechselwirkung, in der gesamten D-dimensionalen Raumzeit propagieren können, sind die Materiefelder an eine d-dimensionale Untermanigfaltigkeit (brane) gebunden. Um die divergenten Anteile der Ein-Schleifen-Diagramme zu bestimmen, entwickeln wir ein neues Regularisierungschema welches einerseits die Wardidentitäten der Yang-Mills-Theorie respektiert anderseits sensitiv für potenzartige Divergenzen ist. Wir berechnen die gravitativen Beiträge zu den beta-Funktionen der Yang-Mills-Eichtheorie, der quartischen Selbst-Wechselwirkung skalarer Felder und der Yukawa-Wechselwirkung zwischen Skalaren und Fermionen. Im physikalisch besonders interessanten Fall einer vier-dimensionalen Materie-brane verschwinden die gravitativen Beiträge zum Laufen der Yang-Mills-Kopplungskonstante. Die führenden Beiträge zum Laufen der anderen beiden Kopplungskonstanten sind positiv. Diese Ergebnisse sind unabhängig von der Anzahl der Extradimensionen in denen die Gravitonen propagieren können. Des Weiteren bestimmen wir alle gravitationsinduzierten Ein-Schleifen-Konterterme mit höheren kovarianten Ableitungen für skalare Felder, Dirac-Fermionen und Eichbosonen. Ein Vergleich dieser Konterterme mit den höheren Ableitungsoperatoren des Lee-Wick-Standardmodells zeigt, dass die Gravitationskorrekturen nicht auf letzte beschränkt sind. Eine Beziehung zwischen Quantengravitation und dem Lee-Wick-Standardmodell besteht somit nicht.
In this thesis, we derive the gravitational one-loop corrections to the propagators and interactions of the Standard Model field. We consider a higher dimensional brane world scenario: Here, gravitons can propagate in the whole D dimensional space-time whereas the matter fields are confined to a d dimensional sub-manifold (brane). In order to determine the divergent part of the one-loop diagrams, we develop a new regularisation scheme which is both sensitive for polynomial divergences and respects the Ward identities of the Yang-Mills theory. We calculate the gravitational contributions to the beta functions of non-Abelian gauge theories, the quartic scalar self-interaction and the Yukawa coupling between scalars and fermions. In the physically interesting case of a four dimensional matter brane, the gravitational contributions to the running of the Yang-Mills coupling constant vanish. The leading contributions to the other two couplings are positive. These results do not depend on the number of extra dimensions. We further compute the gravitationally induced one-loop counterterms with higher covariant derivatives for scalars, Dirac fermions and gauge bosons. In is shown that these counterterms do not coincide with the higher derivative terms in the Lee-Wick standard model. A possible connection between quantum gravity and the latter cannot be inferred.

APA, Harvard, Vancouver, ISO, and other styles

50

Ruy, Danilo Virges [UNESP]. "Estrutura hamiltoniana da hierarquia PIV." Universidade Estadual Paulista (UNESP), 2011. http://hdl.handle.net/11449/92036.

Full text

Abstract:

Made available in DSpace on 2014-06-11T19:25:34Z (GMT). No. of bitstreams: 0 Previous issue date: 2011-02-18Bitstream added on 2014-06-13T19:53:27Z : No. of bitstreams: 1 ruy_dv_me_ift.pdf: 500107 bytes, checksum: fef6f049175c290422f569aa7ad7e26e (MD5)
Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)
Esta dissertação trata da construção de hierarquias compatíveis com a equação PIV a partir dos modelos: AKNS, dois bósons e dois bósons quadráticos. Também são construidos os problema linear de Jimbo-Miwa dos três modelos e discutimos a hamiltoniana correspondente a equação PIV a partir do formalismo lagrangiano
This dissertation contains the construction of compatible hierarchies with the PIV equation from the models: AKNS, two-boson and quadratic two-boson. Also it is build the Jimbo-Miwa linear problem for the three models and we discuss the hamiltonian corresponding to fouth Painlevé equation from the Lagrangian formalism

APA, Harvard, Vancouver, ISO, and other styles

We offer discounts on all premium plans for authors whose works are included in thematic literature selections. Contact us to get a unique promo code!