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1
Zucchini, Sara. "Primordial black holes in string inflation." Master's thesis, Alma Mater Studiorum - Università di Bologna, 2018. http://amslaurea.unibo.it/17097/.
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In this thesis we consider the production of primordial black holes (PBH) in the context of single field inflation with the aim of describing a significant fraction of dark matter. In the models we consider, the inflaton is a string modulus and its potential is typical of type IIB fibre inflation. The potential presents a plateau at CMB scales and an extremely flat region on smaller scales. The background is analysed by solving the Friedmann's and the Klein-Gordon equations for the system. Perturbations are introduced through the usual Mukhanov-Sasaki equation for the gauge invariant curvature perturbations, whose solution allows us to find the primordial power spectrum which is then compared to observations. In the class of models considered there is an often occurring tension between the tilt of the scalar power spectrum and observations. We study this tension and propose mechanisms to minimise it. We modify the form of the fibre inflationary potential, modifying therefore the slope of the ultra slow-roll plateau. We find that a better agreement with the experimentally measured value of the spectral index can be reached. Therefore that tension between the value of the spectral index on CMB scale and the power spectrum enhancement on PBH scales can be explained as a consequence of the class of potential taken into account. This tension can be avoided in models that provide a different plateau form.
2
Pedrelli, Luca. "Inflation and primordial black holes in matter domination." Master's thesis, Alma Mater Studiorum - Università di Bologna, 2018. http://amslaurea.unibo.it/17095/.
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In this thesis we will study a new interpretation of dark matter in terms of Primordial Black Holes (PBHs), i.e. black holes that are believed to form when large density perturbations, produced during the inflationary epoch, reenter the horizon and collapse because of their own gravitational force. Black holes produced in this way are referred to as "Primordial" since their production mechanism has a primordial origin during inflation. These large density fluctuations are produced if the inflationary potential possesses enough tuning freedom to feature a slow-roll plateau followed by a near inflection point that greatly enhances the power spectrum of scalar perturbations. We examine PBH formation during a radiation dominated (RD) epoch and during a matter dominated (MD) epoch driven by a gravitationally coupled scalar field (modulus) which decays before Big Bang Nucleosynthesis in order to preserve its successful predictions. We will require in both cases that the produced PBHs constitute 100% of dark matter today. In the MD case, we find that the mass of the scalar field affects the enhancement required in the curvature power spectrum: for large modulus masses, this enhancement turns out to be smaller than the one in the RD case, meaning that in the case of horizon reentry during moduli domination the potential requires less tuning to produce the same amount of PBHs. Therefore, we focus on PBH production during a MD epoch. We then introduce a model of string inflation called "Fibre Inflation", that works particularly well for our purposes since it naturally leads to a post-inflationary epoch of MD driven by an axion-like modulus. In this model the inflationary potential has enough tuning freedom to induce a period of ultra slow-roll that enhances the density perturbations at the required PBH scales: we employ this potential to obtain a numerical estimate of the scalar power spectrum and the other inflationary observables.
3
Copparoni, Lorenzo. "Generating primordial black holes in non-canonical inflation." Master's thesis, Alma Mater Studiorum - Università di Bologna, 2021. http://amslaurea.unibo.it/23537/.
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Among the candidates for dark matter, Primordial Black Holes are extremely promising, as they do not require the introduction of new physics beyond the Standard Model of particle physics.
These objects can arise from the collapse of overdense regions generated by the curvature perturbation generated during inflation.
The probability distribution of these overdense regions is related to the power spectrum of the scalar perturbation which must be enhanced by compared to the perturbation at CMB scale
in order for the collapse to generate enough Primordial Black Holes to account for the dark mater budget we observe today.
In this thesis we discuss two possible amplification mechanism in non-canonical inflation, employing a decreasing sound speed.
In the first case we consider a model which starts in a slow-roll regime at CMB scale.
Later during inflation the field enters in a non-canonical regime and it approaches the k-inflation attractor.
During this kinetically driven transient phase the sound speed and the slow roll parameter $\epsilon$ decrease exponentially and the power spectrum of the curvature perturbation gets amplified.
We then consider a DBI model where we consider the presence of a gaussian spike in the warp factor, thus leading to the transition, from the canonical phase at CMB scales to a strongly non-canonical regime.
In this latter phase, the sound speed of perturbation is much smaller than 1, and leads to an amplification of the scalar perturbation power spectrum.
4
Erfani, Encieh [Verfasser]. "Inflation and Dark Matter Primordial Black Holes / Encieh Erfani." Bonn : Universitäts- und Landesbibliothek Bonn, 2012. http://d-nb.info/104408250X/34.
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Pedron, Nicola. "Gravitational waves from primordial black holes in string inflation." Master's thesis, Alma Mater Studiorum - Università di Bologna, 2021. http://amslaurea.unibo.it/23236/.
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We consider a model of inflation, called Fibre Inflation, derived from string theory in the framework of type IIB flux compactification and we study the production of primordial black holes due to the gravitational collapse of the curvature perturbations. They are a good candidate for dark matter and if their mass was between 10^-17 and 10^-13 solar masses then their contribution to the total dark matter abundance would be between 10% and 100%. The inflaton potential has enough tuning freedom to allow for a flat plateau at large field values, corresponding to the usual slow roll behaviour, and an inflection point near the minimum that enhances the scalar perturbations. It is the latter feature that greatly increases the density anisotropies from the usual δρ/ρ ~ 10^-5, typical of the CMB radiation, to δρ/ρ ~ 10^-1 due to a peak in the primordial power spectrum that allows for the formation of black holes. The latter is computed solving the Mukhanov-Sasaki equation numerically using the Hubble slow roll parameters extracted from the solutions to the Friedmann equations and the inflaton equation of motion. The formation of black holes is followed by the production of a stochastic background of secondary gravitational waves: in this thesis we compute their amplitude and compare it with current observational bounds and the sensitivities of earth- and space-based interferometers. Our result is within reach of experiments like DECIGO and BBO, hence in the future it will be possible to have a comparison between our theoretical results and observations.
6
Green, Anne M. "Constraining models of the early universe : inflation, primordial black holes and cosmic strings." Thesis, University of Sussex, 1998. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.263155.
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Giguere, Alexis. "Primordial black hole seeding from hybrid inflation : the direct integration approach." Thesis, Massachusetts Institute of Technology, 2013. http://hdl.handle.net/1721.1/88905.
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Thesis: S.B., Massachusetts Institute of Technology, Department of Physics, 2013.Cataloged from PDF version of thesis.
Includes bibliographical references (page 45).
We examine the notion that supermassive black holes at the centre of galaxies, such as the Milky Way, could have been seeded in the early universe by the mechanisms of hybrid inflation. Using luminosity data, we estimate the current density of supermassive black hole. We develop the formalism of the dierct integration method in hybrid inflation and obtain a power spectrum, which we try to relate to the literature. Our results do not directly show the plausibility of seeding supermassive black holes, but the shape of the power spectrum suggests that further work might yield positive results.
by Alexis Giguere.
S.B.
8
Longo, Mirko. "Stochastic effects in ultra slow-roll inflation." Master's thesis, Alma Mater Studiorum - Università di Bologna, 2018. http://amslaurea.unibo.it/17098/.
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In this work we apply the stochastic inflation formalism to backgrounds that deviate from standard slow-roll in a way that can lead to the production of primordial black holes. We analyse the effects of sudden transitions on the stochastic noise amplitude and its potential impact on the production of primordial black holes in single field inflation. We justify the claim that primordial black holes can be responsible for a significant fraction of the dark matter abundance today and estimate the required enhancement in the power spectrum. We introduce the Hamiltonian formalism and the coarse-graining of the quantum field and its momentum, allowing us to obtain a quantitative measure of the role of quantum diffusion in the production of primordial black holes. We mainly focus our analysis on a Starobinsky potential given that it is rich enough to allow for the dynamics of the scalar field during inflation to include an ultra slow-roll phase induced by a transition from a relatively large slow-roll parameter to a hierarchically smaller one. This has the effect of making the field perturbations undergo sudden transitions and rise from its ground state to an excited state.
We present two procedures that we employed when calculating the power spectrum: a numerical and an analytical one. Both methods show that stochastic effects are negligible at small scales where their amplitude is time dependent and vanishes at late times, and that for scales leaving the horizon after the ultra slow-roll phase the de Sitter estimate of $H^2/(4\pi^2)$ is approximately correct. We therefore demonstrate that the estimates in the literature are incomplete and that a revaluation of the role of stochastic effects on primordial black hole production is in order.
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Martineau, Killian. "Quelques aspects de cosmologie et de physique des trous noirs en gravitation quantique à boucles Detailed investigation of the duration of inflation in loop quantum cosmology for a Bianchi I universe with different inflaton potentials and initial conditions Some clarifications on the duration of inflation in loop quantum cosmology A first step towards the inflationary trans-Planckian problem treatment in loop quantum cosmology Scalar spectra of primordial perturbations in loop quantum cosmology Phenomenology of quantum reduced loop gravity in the isotropic cosmological sector Primordial Power Spectra from an Emergent Universe: Basic Results and Clarifications Fast radio bursts and the stochastic lifetime of black holes in quantum gravity Quantum fields in the background spacetime of a polymeric loop black hole Quasinormal modes of black holes in a toy-model for cumulative quantum gravity Seeing through the cosmological bounce: Footprints of the contracting phase and luminosity distance in bouncing models Dark matter as Planck relics without too exotic hypotheses A Status Report on the Phenomenology of Black Holes in Loop Quantum Gravity: Evaporation, Tunneling to White Holes, Dark Matter and Gravitational Waves." Thesis, Université Grenoble Alpes (ComUE), 2019. http://www.theses.fr/2019GREAY044.
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Cantonnée à la physique mathématique depuis des décennies, la gravitation quantique entre désormais dans le giron de la science expérimentale. Suivant cette mouvance nous considérons dans cette thèse trois cadres d’application de la gravitation quantique à boucles (LQG) : le système Univers, les trous noirs et les astroparticules. Le troisième n’est qu’esquissé tandis que les deux premiers sont présentés plus en détails.Le secteur cosmologique étant l’un des domaines les plus prometteurs pour tester et contraindre des théories de gravité quantique, le développement de différents modèles tentant d’appliquer les idées de la LQG à l’Univers primordial ne s’est pas fait attendre. Les travaux que nous présentons portent sur la phénoménologie associée à ces modèles; tant dans le secteur homogène (où nous nous focalisons notamment sur la durée de la phase d’inflation), que dans le secteur inhomogène (nous étudions ce coup-ci le devenir des spectres de puissance primordiaux). Ces études combinées nous permettent alors de préciser dans quelle mesure des effets de gravité quantique (à boucles) peuvent être observés dans les anisotropies du fond diffus cosmologique.D’autre part les trous noirs, non contents de faire partie des objets les plus étranges et les plus fascinants de l’Univers, constituent également des sondes privilégiées pour tester des théories de gravitation. Nous développons la phénoménologie associée à différents traitements des trous noirs en gravitation quantique à boucles. Celle-ci intervient sur une grande variété de fronts : de l’évaporation de Hawking aux ondes gravitationnelles, en passant par la matière noire. C’est sans nul doute un domaine riche et vaste.Finalement, l’existence d’une échelle de longueur minimale, prédite par la majorité des théories de gravité quantique, suggère une généralisation du principe d’incertitude de Heisenberg. Partant de ce constat nous présentons également dans ce manuscrit une méthodologie permettant de calculer une nouvelle relation de dispersion de la lumière à partir du principe d’incertitude généralisé le plus couramment répanduAfter decades of being confined to mathematical physics, quantum gravity now enters the field of experimental science. Following this trend, we consider throughout this thesis three implementation frameworks of Loop Quantum Gravity (LQG): the Universe as a system, black holes and astroparticles. The last one is only outlined while the first two are presented in more detail.Since the cosmological sector is one of the most promising areas for testing and constraining quantum gravity theories, it was not long before the development of different models attempting to apply the ideas of the LQG to the primordial Universe. The work we present deals with the phenomenology associated with these models; both in the homogeneous sector (where we focus particularly on the duration of the inflation phase), as in the inhomogeneous sector (where this time, we study the fate of the primordial power spectra). These combined studies then allow us to specify to what extent effects of (loop) quantum gravity can be observed in the anisotropies of the cosmic microwave background.On the other hand black holes, not content to be among the strangest and most fascinating objects of the Universe, are also prominent probes to test the theories of gravitation. We develop the phenomenology associated with different treatments of black holes in the loop quantum gravity framework, which intervenes on multiple levels: from the evaporation of Hawking to gravitational waves, including dark matter. This is undoubtedly a rich and vast area.Finally, the existence of a minimal length scale, predicted by the majority of quantum gravity theories, suggests a generalization of the Heisenberg uncertainty principle. On the basis of this observation, we also present in this manuscript a methodology to derive a new relation dispersion of light from the most widely used generalized uncertainty principle
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MacGibbon, Jane Helena. "Quark and gluon evaporation from primordial black holes." Thesis, University of Cambridge, 1988. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.279714.
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Hidalgo-Cuellar, Juan Carlos. "Primordial black holes in non-linear perturbation theory." Thesis, Queen Mary, University of London, 2009. http://qmro.qmul.ac.uk/xmlui/handle/123456789/495.
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The thesis begins with a study of the origin of non-linear cosmological fluctuations. In particular, a class of models of multiple field inflation are considered, with specific reference to those cases in which the non-Gaussian correlation functions are large. The analysis shows that perturbations from an almost massless auxiliary field generically produce large values of the non-linear parameter fNL. Next, the effects of including non-Gaussian correlation functions in the statistics of cosmological structure are explored. For this purpose, a non-Gaussian probability distribution function (PDF) for the curvature perturbationR is required. Such a PDF is derived from first principles in the context of quantum field theory, with n-point correlation functions as the only input. Under reasonable power-spectrum conditions, an explicit expression for the PDF is presented, with corrections to the Gaussian distribution from the three-point correlation function hRRRi. The method developed for the derivation of the non-Gaussian PDF is then used to explore two important problems in the physics of primordial black holes (PBHs). First, the non-Gaussian probability is used to compute corrections to the number of PBHs generated from the primordial curvature fluctuations. Particular characteristics of such corrections are explored for a variety of inflationary models. The non-Gaussian corrections explored consist exclusively of non-vanishing three-point correlation functions. The second application concerns new cosmological observables. The formation of PBHs is known to depend on two main physical characteristics: the strength of the gravitational field produced by the initial curvature inhomogeneity and the pressure gradient at the edge of the curvature configuration. The latter has so far been ignored in the estimation of the probability of PBH formation. We account for this by using two parameters to describe the profile: The amplitude of the inhomogeneity and its second radial derivative, both evaluated at the centre of the configuration. The method developed to derive the non-Gaussian PDF is modified to find the joint probability of these two parameters. We discuss the implications of the derived probability for the fraction of mass in the universe in the form of PBHs.
12
Young, Samuel Mark. "Constraining the early universe with primordial black holes." Thesis, University of Sussex, 2016. http://sro.sussex.ac.uk/id/eprint/64782/.
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Inflation is the leading candidate to explain the initial conditions for the Universe we see today. It consists of an epoch of accelerated expansion, and regularly solves many problems with the Big Bang theory. Non-Gaussianity of the primordial curvature perturbation can potentially be used to discriminate between competing models and provide an understanding of the mechanism of inflation. Whilst inflation is believed to have lasted at least 50 - 60 e-folds, constraints from sources such as the cosmic microwave background (CMB) or large-scale structure of the Universe (LSS) only span the largest 6 - 10 e-folds inside today's Hubble horizon, limiting our ability to constrain the early universe. Strong constraints on the non-Gaussianity on smaller scales. Primordial black holes (PBHs) represent a unique probe to study the small-scale early Universe, placing an upper limit on the primordial power spectrum spanning around 40 e-folds smaller than those visible in the CMB. PBHs are also a viable dark matter candidate. In this thesis, the effect of non-Gaussianity upon the abundance of PBHs, and the implications of such an effect are considered. It is shown that even smaller non-Gaussianity parameters can have a large effect on the constraints that can be placed on the primordial curvature perturbation power spectrum - which can become stronger or weaker by an order of magnitude. The effects of super-horizon curvature perturbation modes at the time of PBH formation are considered, and it is shown that these have little effect on the formation of a PBH, but can have an indirect effect on the abundance of PBHs due to modal coupling to horizon-scale modes in the presence of non-Gaussianity. By taking into account the effect of modal coupling to CMB-scale modes, many models can be ruled out as a mechanism to produce enough PBHs to constitute dark matter.
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Rossi, Dario. "Reissner-Nordström black holes and mass inflation." Bachelor's thesis, Alma Mater Studiorum - Università di Bologna, 2019. http://amslaurea.unibo.it/18370/.
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The existence and structure of black holes are derived from Einstein’s general theory of
relativity. Mass inflation (an increase in mass) is found when the internal structure of
black holes is studied. The objective of the present study is two-fold: (i) to obtain an
understanding of the nature of Reissner-Nordström black holes and (ii) examine the mass
inflation phenomenon. To do so, spherical symmetric solutions to Einstein’s field equations are analyzed.The Schwarzschild solution is analyzed to show the most basic result
of general relativity. The analytical (Kruskal) continuation of the Schwarzschild solution
and the mechanism of gravitational collapse are also discussed. The Reissner-Nordström
metric is then examined in detail analyzing both the general characteristics and the most
generic field equations for a body with spherical symmetry. Moreover two important applications are considered: the Vaidya solutions and the Dray-’t Hooft-Redmount (DTR)
relation. The mass inflation phenomenon is then formulated by formally integrating
Einstein’s field equations considering continuous infalling and outgoing radial fluxes of
gravitational radiation. To evaluate the growth rate of the gravitational mass, a formal
perturbation expansion in terms of the product of the flux luminosities is developed.
Finally, the possibility that the asymmetries occurring during a realistic collapse could
change the conclusions obtained for spherical symmetry is considered. The most striking
features of the physics behind black holes and the mass inflation phenomenon are shown.
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Russell, Megan S. B. Massachusetts Institute of Technology. "Formalism for the rapid evolution of primordial black holes." Thesis, Massachusetts Institute of Technology, 2010. http://hdl.handle.net/1721.1/111883.
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Thesis: S.B., Massachusetts Institute of Technology, Department of Physics, 2017.Cataloged from PDF version of thesis.
Includes bibliographical references (pages 47-48).
This thesis presents two different formalisms which can be used together to evolve a density perturbation produced during inflation forwards in time in the radiation-dominated era of the early universe. The first formalism, based on early work by Misner and Sharp, is for the evolution of a perfect fluid in spherical symmetry under its own gravity. This allows us to efficiently determine if a black hole will form, but due to the formation of a singularity, it does not allow us to extract the black hole's mass. The second, new, formalism allows us to evolve the density perturbation past the formation of a singularity until a time where we can reasonably extract the mass of the black hole. This new formalism has been designed to do this computation as rapidly as possible, improving over our previous methods. The limits of this new formalism are investigated, details regarding a numerical implementation of our code are discussed, and a proof of concept example is presented.
by Megan Russell.
S.B.
15
Russell, Megan S. B. Massachusetts Institute of Technology. "Formalism for the rapid evolution of primordial black holes." Thesis, Massachusetts Institute of Technology, 2017. http://hdl.handle.net/1721.1/111883.
Full textAbstract:
Thesis: S.B., Massachusetts Institute of Technology, Department of Physics, 2017.Cataloged from PDF version of thesis.
Includes bibliographical references (pages 47-48).
This thesis presents two different formalisms which can be used together to evolve a density perturbation produced during inflation forwards in time in the radiation-dominated era of the early universe. The first formalism, based on early work by Misner and Sharp, is for the evolution of a perfect fluid in spherical symmetry under its own gravity. This allows us to efficiently determine if a black hole will form, but due to the formation of a singularity, it does not allow us to extract the black hole's mass. The second, new, formalism allows us to evolve the density perturbation past the formation of a singularity until a time where we can reasonably extract the mass of the black hole. This new formalism has been designed to do this computation as rapidly as possible, improving over our previous methods. The limits of this new formalism are investigated, details regarding a numerical implementation of our code are discussed, and a proof of concept example is presented.
by Megan Russell.
S.B.
16
Chan, Jim Shung Fai. "On the universality of mass inflation inside black holes." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1998. http://www.collectionscanada.ca/obj/s4/f2/dsk2/tape15/PQDD_0011/NQ30593.pdf.
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Tashiro, Hiroyuki, and Naoshi Sugiyama. "Constraints on primordial black holes by distortions of the cosmic microwave background." American Physical Society, 2008. http://hdl.handle.net/2237/11310.
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Stomberg, Isak. "On the Possibility of Probing Early Matter Domination with Primordial Black Holes." Thesis, KTH, Fysik, 2021. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-297567.
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Primordial black holes (PBHs) are expected to form in the very early universe, and therefore, we could use them to probe preBBN times. Astrophysical observations permit the placement of bounds on the abundance of PBHs. Combining these bounds with predictions of PBH formation and the resulting PBH abundances, we explore the possibility to constrain an epoch of early matter domination (MD). For this analysis, we incorporate the recently obtained and most stringent bounds on PBHs from 21 cm observations. We assume density perturbations described by a nearpowerlaw form of the curvature power spectrum consistent with the Planck 2018 results and derive the corresponding PBH mass function using recent results from the literature. To place constraints on an early matterdominated (MD) epoch, we compare this with upto date bounds on PBHs, adding those from 21 cm astronomy, using a formalism to apply monochromatic constraints to extended mass functions. We find that 21 cm bounds on PBHs may probe early MD if it lasts for a duration of at least ∼ 12 efolds and ends at a reheating temperature T_min < T_reh ≲ 105.5 GeV, where Tmin depends on the duration of the MD, the spectral index ns, and αs. For optimistic assumptions, our derived limits on the spectral index ns extend into the Planck 2018 67% upper confidence region of n_s = 0.9649 ± 0.0042, nearly reaching its median n_s = 0.9649, if we neglect the running αs. Our bounds on the running α_s show that early MD is incompatible with positive running α_s ≳ 0.Primordiala svarta hål förutsäges ha skapats i det mycket tidiga universum. Ur detta förstår vi att dessa svarta hål ger oss en länk till universums tillstånd under deras skapelse och att vi genom studiet av primordiala svarta hål kan skymta detta tillstånd. Restriktioner på mängden primordiala svarta hål i universum kan beräknas utifrån astrofysiska observationer. Jämförelse av dessa restriktioner med teoretiska förutsägelser av vilka mängder av primordiala svarta hål som skapats vid olika tillstånd medger att vissa tillstånd utesluts. I detta arbete undersöker vi just detta samband och avser etablera huruvida de starkaste restriktionerna på primordiala svarta hål, speciellt från 21 cm observationer av universum, kan utesluta ett kosmologiskt scenario med tidig materiadominans. För att göra detta antar vi att störningar i den annars homogena energidensiteten kan beskrivas med hjälp av ett nästanstorleksoberoende potenssamband vars form ges av resultat från Planck kollaborationen 2018. Givet denna potenslag beräknar vi en form för de primordiala svarta hålens massdistribution medelst resultat från den vetenskapliga litteraturen. Vi jämför sedan dessa förutsägelser med de senaste mängdrestriktionerna på primordiala svarta hål, inkluderat dem från 21 cm observationer, för att erhålla nya begränsningar på tidig materiadominans. Vi tar i beaktande att massdistributionen av primordiala svarta hål inte är monokromatisk, utan utbredd. Resultatet av denna analys är att tidig materiadominans är inom räckhåll för att uteslutas medelst studier av primordiala svarta hål om perioden av materiadominans är längre än ∼ 12 efolds och att den slutar vid återuppvärmningstemperaturen T_min < T_reh ≲ 10^5.5 GeV, där Tmin beror på hur länge den tidiga materiadominansen varar, på det spektrala indexet ns och det spektrala indexets derivata αs. För optimistiska antaganden äventyrar dessa restriktioner på materiadominans resultat från Planck kollaborationen 2018 i det att det övre konfidensintervallet på det spektrala indexet n_s = 0.9649 ± 0.0042 är exkluderat, och att förändringen av detta index, α_s, inte kan vara positiv då vi låter storleksordningen minska.
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Suazo, Campos Matías Enrique. "The role of gas fragmentation in the formation of primordial supermassive black holes." Tesis, Universidad de Chile, 2018. http://repositorio.uchile.cl/handle/2250/170150.
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Tesis para optar al grado de Magíster en Ciencias, Mención AstronomíaEn la presente tesis estudio cómo el proceso de fragmentación afecta la formación de las semillas de agujeros negros supermasivos primordiales utilizando simulaciones cosmológicas hidrodinámicas. Éstos se caracterizan por habitar los centros de los cuásares más brillantes observados en épocas muy tempranas del Universo. Debido a las limitaciones observacionales y a la complejidad de las ecuaciones que gobiernan los fenómenos, las simulaciones computacionales resultan ser la mejor forma de entender como estas estructuras se formaron. En este trabajo se realizaron cincuenta simulaciones de baja resolución compuestas sólo de materia oscura con el fin de identificar los halos más prometedores para la formación de semillas masivas. Tres halos fueron elegidos con el fin de ser re-simulados con mayor resolución. El criterio de selección se basó en la rotación del halo y en la historia de fusión con otro halos. Lo anterior se realizó requiriendo que todos tuvieran una masa > 5 × 10⁷ Msun. Una vez escogidos los halos, se procedió a re-simularlos incluyéndose la física del gas, mayor resolución, y un fondo uniforme de radiación UV. Además se agregó un algoritmo para formar partículas sumidero, las cuales representan las estructuras no resueltas por el código. Los tres halos escogidos se re-simularon imponiendo dos condiciones de fondo UV: una de intensidad baja, J21 = 10, y otra de intensidad alta, J21 = 10000. Se observó que dos de las simulaciones bajo la influencia de un fondo de radiación UV de gran intensidad replicaron muy bien el modelo de colapso directo, en el cual el gas del halo colapsa directamente en un objeto muy masivo (> 10⁵ Msun). Estas simulaciones formaron una única partícula sumidero, la que alcanzó masas mayores a 10⁵ Msun hacia el final de la simulación. En ambos casos la tasa de acreción se mantuvo mayor a 0.1 Msun/yr durante todo el tiempo que se mantuvo corriendo la simulación y no se observó fragmentación en estos casos. Por el contrario, en la re-simulación de un halo formado como resultado de una gran cantidad de fusiones, una estructura espiral se formó en los 5 pársec centrales. Dicha estructura se fragmentó formando varias partículas sumidero. La primera que se formó alcanzó una masa cercana a los 10⁵ Msun, mientras que las demás alcanzaron masas intermedias entre 10³ Msun y 5 ×10⁴ Msun. Las simulaciones con un fondo de radiación UV de baja intensidad revelaron en todos los casos fragmentación y formación de varias partículas sumidero. En estos casos las partículas más masivas alcanzaron masas del orden de 10⁴ Msun, la cual es menor que en el caso anterior, pero sigue siendo relevante para la formación de semillas masivas. Como se formaron varias partículas sumidero en todos estos casos, éstas están más propensas a interactuar entre ellas, pudiendo fusionarse intensificando su tasa de acreción, lo cual efectivamente se observó. Finalmente se concluye que la fragmentación no es un impedimento para la formación de semillas masivas, y que la dinámica de los sistemas es relevante para la formación y evolución de las mismas.
FONDECYT regular 1181663 y Centro de Excelencia en Astrofísica y tecnologías afines(PFB-06) que incluye el uso del Cluster Geryon en el centro de Astro-Ingeniería UC. Powered@NLHP: Esta investigación fue parcialmente apoyada por la infraestructura de supercómputo del NLHPC (ECM-02)
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Escrivá, Mañas Alberto. "Numerical simulations of primordial black holes." Doctoral thesis, Universitat de Barcelona, 2021. http://hdl.handle.net/10803/672269.
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This thesis has been devoted to the study of the gravitational collapse of spherically symmetric perturbations on a Friedman-Robertson-Walker (FRW) universe filled by a perfect fluid. Large cosmological perturbations generated by inflation, are known to be statistically almost spherical. For this reason, this thesis aims to provide the conditions for Primordial Black Hole (PBH) formation due to the collapse of inflationary density fluctuations. PBHs are considered one of the best candidate for the missing dark matter (DM). To simulate the collapse of large spherical overdensities, it has been used a pseudo-spectral method which maps differential equations into an algebraic system. The numerical code developed, allows to outline the conditions for black hole formation with a greater than ever precision in some extreme cases. By using a combination of an excision technique and analytical estimations of accretion rates, it was found that the estimation of the black hole’s masses via a self-similar scaling law, gets worse and worse for larger and larger values. In addition, it was also found that the accretion of the BH masses relevant for the DM abundance, follows the law MBH,f roughly equal to 3MBH,i where, MBH,I is the initial mass of the BH at the time of apparent horizon formation and MBH,f is the final mass of the BH after the accretion process. In the case in which the fluid permeating the universe is of the form p equal to wρ, where p is the pressure, ρ is the density of the fluid and w is a constant, it is here shown that for w greater or equal to 1/3 the conditions for black hole formation, to a very good approximation, only depend upon the curvature of the local excess-mass (compaction function) around its peak value (δc), δc (the ”threshold” for PBH formation) and the equation of state of the collapsing fluid. This fact, has been used to build an analytical formula for δc in the case of w greater or equal to 1/3, which is accurate enough to be used for cosmological applications, conversely to previous attempts. For smaller w’s instead, the knowledge of the full shape of the compaction function is necessary, in contradiction to previous claims. Moreover, while the threshold for w greater or equal to 1/3 does not strongly depend from the full shape of the compaction function, in this thesis it is also shown that the BH mass does. While inflationary fluctuations are predominantly Gaussianly distributed at the cosmic microwave back-ground scales, those leading to PBH formation at smaller scales can have larger non-Gaussianities (NG). In the final part of this thesis, it was considered the effect (numerically and analytically) of those NG to the threshold for primordial black hole formation. By monitoring the non-gaussian parameter fNL, it was found that; i) for fNL roughly greater than 3.5, the population of PBH coming from false vacuum regions dominates over that coming from the collapse of large adiabatic overdensities; ii) the effect of the statistical dispersion of profiles is small in determining δc of the mean profile.Esta tesis pretende proporcionar las condiciones necesarias para la formación de Agujeros Negros Primordiales (PBHs) producidos por el colapso de perturbaciones cosmológicas. Los PBHs se consideran uno de los mejores candidatos para la materia oscura, cuya composición es todavía un misterio. Para simular el colapso de grandes sobredensidades esféricas y obtener las condiciones para la formación de un PBH, se ha utilizado un método pseudoespectral que mapea ecuaciones diferenciales en un sistema algebraico. En el caso en el que el fluido que impregna el universo se comporte como un fluido perfecto (p igual a wρ, donde p es la presión, ρ es la densidad del fluido y w es una constante), hemos comprobado que para w mayor o igual a 1/3 las condiciones para la formación de un agujero negro, en una muy buena aproximación, solo dependen de la curvatura del exceso de masa local (también llamado función de compactación) alrededor de su valor máximo (δc) , δc (el ” umbral ” para la formación de PBH) y la ecuación de estado del fluido que colapsa. Este remarcable resultado se ha utilizado para construir una fórmula analítica para δc en el caso de w mayor o igual a 1/3, que es lo suficientemente precisa como para usarse en aplicaciones cosmológicas. En cambio, para w más pequeños, es necesario conocer la forma completa de la función de compactación. Por otro lado, si bien es cierto que las fluctuaciones inflacionarias se distribuyen predominantemente de manera gaussiana en las escalas del fondo de microondas cósmicas, las que conducen a la formación de PBH a menores escalas pueden distribuirse de forma altamente no gaussiana (NG). En la parte final de esta tesis, se ha considerado el efecto de esas NGs en el umbral de formación de agujeros negros primordiales, tanto numérica como analíticamente.
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Savastano, Stefano. "Primordial dark matter halos from fifth-forces." Master's thesis, Alma Mater Studiorum - Università di Bologna, 2019. http://amslaurea.unibo.it/18143/.
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In this thesis we investigate a possible formation mechanism of non-linear structures, such as primordial black holes or similar screened objects, within a modified gravity framework. In particular, these structures can form during radiation era and provide the current dark matter component of the Universe. We refer to a model consisting of a long range attractive fifth-force stronger than gravity, mediated by a light scalar field $\phi$ - which could be in principle dynamical dark energy of Coupled Quintessence - interacting with a non-relativistic $\psi$-particle. The latter is coupled to radiation and matter species only via usual gravity.
By means of a dynamical system approach, we select the unique stable scaling solution of the phase space providing a radiation dominated era. Besides, after the introduction of the cosmological perturbation theory, we study the non-linear growth of the $\psi$ field density fluctuations in this epoch. The latter, being enhanced by the fifth interaction, in view of a field theory screening mechanisms that suppress the additional interaction, eventually collapse in stable and virialized structures, namely dark matter halos. We compare the theoretical predictions on the radius and the mass of the halos with experimental constraints on primordial black holes abundances, with an emphasis on their lensing signature in the solar mass window. In conclusion, we outline a viable scenario where the missing dark matter component of the universe might be completely supplied in form of dark halos.
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Montero, Camacho Paulo. "Searching the Cosmos: Ripples from Avant-Garde Cosmological Probes." The Ohio State University, 2019. http://rave.ohiolink.edu/etdc/view?acc_num=osu1562949205379439.
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Cutchin, Sean. "A Search for Astrophysical Radio Transients at Meter Wavelengths." Diss., Virginia Tech, 2011. http://hdl.handle.net/10919/29658.
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Astrophysical phenomena such as exploding primordial black holes (PBHs), gamma-ray bursts (GRBs), compact object mergers, and supernovae, are expected to produce a single pulse of electromagnetic radiation detectable at the low-frequency end of the radio spectrum. Detection of any of these pulses would be significant for the study of the objects themselves, their host environments, and the interstellar/intergalactic medium. Furthermore, a detection of a radio transient from an exploding PBH could be a signature of an extra spatial dimension, which would drastically alter our perception of spacetime. However, even upper limits on the existence of PBHs, from transient searches, would be important to discussions of cosmology.
We describe a method to carry out an agnostic single-dispersed-pulse search, and apply it to data collected with the Eight-meter-wavelength Transient Array (ETA). ETA is a radio telescope dedicated to searching for transient pulses. It consists of 12 crossed-dipole antenna stands with Galactic-noise-limited performance from 29-47 MHz. There is a vast amount of data collected from an ETA observation. It is therefore greatly beneficial to use a computer cluster, which works in parallel on different parts of a data set, in order to carry out a single-pulse search quickly and efficiently. Each spectrogram in a data set needs to be analyzed individually, without reference to the rest, in order to utilize a computer cluster's capabilities. The data reduction software has been developed for single-dispersed-pulse searches, and is described in this thesis. The data reduction involves sweeping through the collected data with a dedispersion routine assuming a range of dispersion measures. The resulting time series are searched with multiple matched filters for signals above a signal-to-noise threshold.
Applying the single pulse search to ~ 30 hours of ETA data did not yield a compelling detection of an astrophysical signal. However, from ≈ 5 hours of interference-free data we find an observational upper limit to the rate of exploding PBHs of r ≈ 4.8 × 10⁻⁷ pc⁻³ y⁻¹ for a PBH with a fireball Lorentz-factor f = 104.3. This limit is applicable to PBHs in the halo of the Galaxy to distances ≲ 2 kpc, and dispersion measures ≲ 80 pc cm⁻³ . We also find a source-agnostic rate limit ≲ 0.25 events y⁻¹ deg⁻² for pulses of duration < 3 s, and having apparent energy densities ≳ 2.6 × 10⁻²³ J m⁻² Hz⁻¹ at 38 MHz.Ph. D.
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Deshpande, Kshitija Bharat. "A Dedicated Search for Low Frequency Radio Transient Astrophysical Events using ETA." Thesis, Virginia Tech, 2009. http://hdl.handle.net/10919/35666.
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Astrophysical phenomena such as self-annihilation of primordial black holes (PBHs), gamma ray bursts (GRBs), and supernovae are expected to produce single dispersed pulses detectable in the low end of the radio spectrum. Analysis of these pulses could provide valuable information about the sources, and the surrounding and intervening medium. The Eight-meter-wavelength Transient Array (ETA) is a radio telescope dedicated to the search for these pulses in an 18 MHz bandwidth centered at 38 MHz. ETA consists of 10 dual-polarized active dipoles providing an all-sky field of view. This thesis describes the results of a search campaign using ETA, namely, a Crab giant pulse (CGP) search. CGPs are already known to exist, and thus provide an excellent diagnostic for system performance. We found 11 CGP candidates in 14 hours of data. Although there has not been a single compelling detection (signal-to-noise ratio > 6), our analysis shows that at least a few of these candidates may be CGPs. We also explain the analysis preparation for PBH and GRB searches. Additionally, we describe the instrument and a software "toolchain" developed for the analysis of data that includes calibration, radio frequency interference (RFI) mitigation, and incoherent dedispersion. A dispersed pulse simulation code was developed and used to test the toolchain. Finally, improvements are suggested.Master of Science
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Gomes, Joaquim António Maximiano. "Curvature perturbations from thermal inflation." Master's thesis, 2020. http://hdl.handle.net/10316/93899.
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Dissertação de Mestrado em Física apresentada à Faculdade de Ciências e TecnologiaUm período de inflação no início da história cósmica é agora tomado como paradigmático, visto este eliminar a aparente forte dependência da cosmologia padrão nas suas condições iniciais. Além disso, consegue explicar as pequenas heterogeneidades da radiação cósmica de fundo. Para além da época principal de inflação, algumas teorias supersimétricas preveem uma classe de campos escalares com um potencial extremamente plano, conhecidos como flatões. Estes campos podem levar a cabo um período secundário de inflação, mais curto que o primeiro, onde os referidos campos são mantidos num vácuo metastável por efeitos térmicos. Este período de inflação térmica pode diluir artefactos cosmológicos, como gravitinos e moduli, que podem ser produzidos em abundância durante o reaquecimento que segue a inflação principal. Visto que a inflação térmica ocorre depois da inflação primária ter terminado, esta pode levar à produção de perturbações na curvatura do espaço-tempo a escalas cosmológicas mais pequenas. Estas perturbações podem, em princípio, ter uma magnitude consideravelmente maior que as perturbações a larga escala observadas na radiação cósmica de fundo. Com efeito, perturbações suficientemente grandes podem colapsar diretamente em buracos negros quando reentram através do horizonte, na era de radiação. Estes buracos negros primordiais são, portanto, candidatos proeminentes a constituir (pelo menos uma parte) a matéria escura no universo. Na presente tese investigámos qual o espectro das perturbações da curvatura do espaço-tempo induzido pelas flutuações do flatão durante a inflação térmica. Um estudo recente considerou apenas flutuações quânticas do campo referido, desconsiderando praticamente os efeitos da temperatura. No entanto, mesmo que o flatão seja o fluido mais abundante durante este período, ele coexiste e interage com um banho térmico subdominante. Isto significa que o flatão deve exibir uma dinâmica de flutuação-dissipação que não pode ser descartada. Estas farão o flatão evoluir para um estado de equilíbrio térmico, desde que a taxa de interação seja superior à taxa de expansão de Hubble. Efetivamente, isto faz com que o flatão se comporte como um campo clássico estocástico em vez de como um campo quântico.Com isto em mente, estudámos a evolução das perturbações térmicas criadas pelo flatão na curvatura do espaço-tempo, à medida que este tende para o equilíbrio com o banho térmico. Calculámos o espectro das perturbações e descobrimos que estas são mais pequenas que o exposto no estudo puramente quântico estudado anteriormente na literatura. De facto, constatámos que a presença de um banho térmico suprime severamente a amplitude das perturbações da curvatura geradas durante a inflação térmica. Neste sentido, será difícil que uma população considerável de buracos negros primordiais tenha sido criada por perturbações na curvatura geradas durante esse período.
An early epoch of inflation in the cosmic history is now taken as paradigmatic since it eliminates the apparent fine-tuning of the standard cosmological model. Moreover, it can explain the small inhomogeneities of the cosmic microwave background. In addition to the main period of inflation, certain supersymmetric theories predict a class of scalar fields with an extremely flat potential, known as flatons. These fields can drive a shorter secondary inflationary period when they are held in a metastable vacuum state by thermal effects. Such a period of thermal inflation may dilute away any dangerous relics, such as gravitinos and moduli, that can be copiously produced during reheating, at the end of the first inflationary epoch. As thermal inflation occurs after the main inflation ends, it can produce perturbations in the curvature of space-time at smaller cosmological scales. Such perturbations could, in principle, have considerably larger amplitude than the large-scale perturbations observed in the cosmic microwave background. In fact, large enough perturbations could collapse directly into primordial black holes upon horizon re-entry in the radiation era. These astronomical objects are leading candidates for (at least a fraction of) the dark matter in the universe.In this thesis we have investigated the spectrum of space-time curvature perturbations during thermal inflation, generated by fluctuations of the flaton field. A recent study in the literature considered only quantum fluctuations of the said field, while thermal considerations were practically disregarded. However, even though the flaton is the dominant fluid during this period, it coexists and interacts with a subdominant radiation bath. As a result the flaton should exhibit fluctuation-dissipation dynamics that cannot be ignored. This will make the flaton evolve towards a state of thermal equilibrium, provided that the interaction rate exceeds the Hubble expansion rate. This effectively results in the flaton field behaving like a stochastic classical field instead of as a quantum field.With this in mind, we have studied the evolution of thermal perturbations produced by the flaton in the curvature of space-time, as it approaches equilibrium with a thermal bath. We have computed the power spectrum of the curvature perturbations and found that it is smaller than the purely quantum one previously studied in the literature. In fact, we have found that the presence of the radiation bath severely suppresses the amplitude of the curvature perturbations that may be created during thermal inflation. This makes it, therefore, very hard to form an appreciable primordial black hole population by curvature perturbations generated during this period.
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Ferraz, Paulo Bernardo Figueira da Silva. "Pion Superradiant Instabilities of Primordial Black Holes." Dissertação, 2019. https://hdl.handle.net/10216/124528.
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Ferraz, Paulo Bernardo Figueira da Silva. "Pion Superradiant Instabilities of Primordial Black Holes." Master's thesis, 2019. https://hdl.handle.net/10216/124528.
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Schleicher, Dominik R. G. [Verfasser]. "The early universe : probing primordial magnetic fields, dark matter models and the first supermassive black holes / put forward by Dominik R. G. Schleicher." 2009. http://d-nb.info/995782148/34.
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