This thesis is a study of the theory and phenomenology of trans-Planckian black holes, in TeV gravity extra-dimensional theories. The introduction starts with the motivation for this beyond the Standard Model scenario (chapter 1), a summary of the theoretical tools to formulate the theory, and a summary of the best bounds from experiment (chapter 2). In chapter 3, after setting up some notation and describing well known solutions in 4 + n-dimensional general relativity, we construct an approximate effective background for a brane charged rotating higher-dimensional black hole. This is achieved by solving Maxwell's equations perturbatively on the brane to obtain the electromagnetic field. A brief study of the effect of rotation on the absorption of classical particles is also provided. Chapter 4 is a review of methods to model black hole production focusing on the trapped surface method. A model for the mass and angular momentum loss into gravitational radiation is described. A detailed study of the effects of particle mass and charge, for fermions and scalars on the effective brane charged background, is presented in chapters 5 and 6. After coupling the fields to the background, the separated radial wave equations for both perturbations are obtained (chapter 5) and they are integrated using a detailed numerical method as well as analytic approximations (chapter 6). Similarly, a method is described to obtain high accuracy angular functions based on series expansions. We conclude the theoretical study by evaluating the Hawking spectra for various combinations of spin, mass, charge and rotation parameters, and discuss them comparatively. The last part of the thesis is on the implementation of the theoretical results in the new CHARYBDIS2 Monte Carlo simulation of black hole production and decay (chapter 7), and on the analysis of the phenomenological consequences (chapter 8). The main new features implemented in CHARYBDIS2 are: a full treatment of the spin-down phase using the angular and energy distributions of the associated Hawking radiation; an improved model for energy and angular momentum loss in the production process, and a wider range of options for the Planck-scale termination of the decay. The main conclusions of this thesis and an outlook on future directions are summarised in the final chapter.

The extension of the concepts of Newtonian cosmology to a universe consisting of a hierarchy of metagalaxies is fairly straightforward. However, in general relativistic cosmology, the construction of such a hierarchical universe is a difficult problem. It is the purpose of this work to examine some aspects of hierarchical cosmology in both the Newtonian and general relativistic cases. It is suggested that the metagalaxy may be a black hole or Schwarzschild object,(to account for the fact that no objects which could be identified as metagalaxies have been, as yet, observed. Some features of this concept are discussed. Tidal forces exerted on a metagalaxy, due to others distributed around it, are estimated in the Newtonian case. Such tidal forces may or may not be detectable, depending on the distance between metagalaxies. The interior of a metagalaxy is represented by a Fried-mann model, with given values of k and A. The Friedmann model is matched at the boundary to a Schwarzschild spacetime. The consequences of this and related calculations suggest that in most cases, a metagalaxy may be a black hole for only part of its lifetime, i.e., for other times, it may be optically detectable to an exterior observer. / Science, Faculty of / Physics and Astronomy, Department of / Graduate

No description available.

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.

In 1993, 't Hooft (1999 Nobel Prize winner in physics) proposed that quantum gravity requires that the information in a three dimensional world can be stored on a two dimensional manifold much like a hologram. This is known as the holographic principle, and since then this idea has changed the direction of researches in quantum gravity. A concrete realization of this idea in string theory was first discovered in 1997 by Maldacena in his famous anti de-Sitter/Conformal Field Theory\footnote{AdS/CFT for short. AdS stands for anti de-Sitter, and CFT is the acronym for Conformal Field Theory.} correspondence conjecture. The AdS/CFT correspondence states that some string theories on a certain manifold that contains AdS space, in some limits, are dual to a CFT living on the boundary of this manifold. Despite the rapid progress in studying the AdS/CFT, this proposal is still away from practical applications. Some of the reasons are the fact that the AdS (anti-de Sitter) spacetime is not likely the spacetime where we are living nowadays and the existence of extra dimensions (as one of the ingredients in string theory) is still under question. The Kerr/CFT correspondence which was proposed in 2008 by Strominger et al appears to be a more ``down to earth'' duality, compared to the AdS/CFT correspondence. Originally, this new correspondence states that the physics of extremal Kerr black holes which are rotating by the maximal angular velocity can be described by a two dimensional CFT living on the near horizon. In this thesis, after reviewing some concepts in Kerr/CFT correspondence, I present some of my research results which extend and support the correspondence for non-extremal rotating black holes. I discuss the extension of the Kerr/CFT correspondence for the rotating black holes in string theory, namely Kerr-Sen black holes, and the Kerr/CFT analysis for vector field perturbations near the horizon of Kerr black holes. It is recently conjectured that a generic non-extremal Kerr black hole could be holographically dual to a hidden conformal field theory in two dimensions. Furthermore, it is known that there are two CFT duals (pictures) to describe the charged rotating black holes which correspond to angular momentum $J$ and electric charge $Q$ of the black hole. Furthermore these two pictures can be incorporated by the CFT duals (general picture) that are generated by $SL(2,\mathbb{Z})$ modular group. The general conformal structure can be revealed by looking at a charged scalar wave equation with some appropriate values of frequency and charge. In this regard, we consider the wave equation of a charged massless scalar field in the background of Kerr-Sen black hole and show in the ``near region", the wave equation can be reproduced by the squared Casimir operator of a local $SL(2,\mathbb{R})_L \times SL(2,\mathbb{R})_R$ hidden conformal symmetry. We can find the exact agreement between macroscopic and microscopic physical quantities like entropy and absorption cross section of scalars for Kerr-Sen black hole. We then find an extension of the vector fields that in turn yields an extended local family of $SL(2,\mathbb{R})_L \times SL(2,\mathbb{R})_R$ hidden conformal symmetries, parameterized by one parameter. For some special values of the parameter, we find a copy of $SL(2,\mathbb{R})$ hidden conformal algebra for the charged Gibbons-Maeda-Garfinkle-Horowitz-Strominger black hole in the strong deflection limit. The generic non-extremal Kerr-Newman black holes are holographically dual to hidden conformal field theories in two different pictures. The two pictures can be merged together to the CFT duals in the general picture that are generated by $SL(2,\mathbb{Z})$ modular group. We find some extensions of the conformal symmetry generators that yield an extended local family of $SL(2,\mathbb{R})_L \times SL(2,\mathbb{R})_R$ hidden conformal symmetries for the Kerr-Newman black holes, parameterized by one deformation parameter. The family of deformed hidden conformal symmetry for Kerr-Newman black holes also provides a set of deformed hidden conformal generators for the charged Reissner-Nordstrom black holes. The set of deformed hidden conformal generators reduce to the hidden $SL(2,\mathbb{R})$ conformal generators for the Reissner-Nordstrom black hole for specific value of deformation parameter. We also find agreement between the macroscopic and microscopic entropy and absorption cross section of scalars for the Kerr-Newman black hole by considering the appropriate temperatures and central charges for the deformed CFTs. Also in this thesis, we derive an appropriate boundary action for the vector fields near the horizon of near extremal Kerr black hole. We then use the obtained boundary action to calculate the two-point function for the vector fields in Kerr/CFT correspondence. In performing this analysis we borrow a formula proposed in AdS/CFT, namely the equality between the bulk and boundary theories partition functions. We show the gauge-independent part of the two-point function is in agreement with what is expected from CFT.

We present the results of fully three dimensional, post-Newtonian hydrodynamical simulations of the dynamical evolution of mergers between compact stellar remnants (neutron stars and black holes). Although the code is essentially Newtonian, we simulate gravitational wave emission and the corresponding effect on the fluid flow via a post-Newtonian correction. Also, we use a modified Newtonian potential which reproduces certain aspects of the Schwarzschild and Kerr solutions to improve the physics in the vicinity of the black hole. Changes to the energy by neutrino/antineutrino emission are accounted for by an extensive neutrino leakage scheme. The hydrodynamical equations are integrated using the piecewise parabolic method (PPM) and the neutron star matter is described by a tabulated equation of state (EoS). Since the physics of matter at the extreme densities found in neutron stars is not yet certain, we compare results computed using two such tables to ascertain whether this uncertainty in the micro-physics extends to an uncertainty in the energy available to power a short-period gamma-ray burst. With an aim to including magnetic field physics to these simulations, we present a survey of approximate Riemann solvers which may be more easily extended to the system of equations of magnetohydrodynamics (MHD) than the exact or iterative Riemann solver used in the PPM scheme. Tests are performed using the linearised solver of Roe and the approximate Harten, Lax, van Leer and Einfeldt Riemann solvers (HLLE and HLLEM) with the PPM reconstruction scheme. Finally, we discuss the effectiveness of these approximate Riemann solvers in the simulation of mergers between compact stellar remnants.

We investigate the possibility that present-day galaxies and their dark matter halos contain a population of massive black holes (MBHs) that form by hierarchical merging of the black hole remnants of the first stars in the Universe. Some of the MBHs may be large enough or close enough to the centre of the galactic host that they merge within a Hubble time. We estimate to what extent this process could contribute to the mass of the super-massive black holes (SMBHs) observed in galactic centres today. The relation between SMBH and galactic bulge mass in our model displays the same slope as that found in observations. Many MBHs will not reach the centre of the host halo, however, but continue to orbit within it. In doing so MBHs may remain associated with remnants of the satellite halo systems of which they were previously a part. Using a semi-analytical approach that explicitly accounts for dynamical friction, tidal disruption and encounters with galactic disks, we follow the hierarchical merging of MBH systems and their subsequent dynamical evolution inside the respective host halos. In this context two types of dynamical processes are examined in more detail. We predict the mass and abundance of MBHs in present-day galactic halos and also estimate the MBH mass accretion rates considering two different accretion scenarios. On this basis we determine the bolometric, optical and X-ray luminosity functions for the accreting MBHs using thin disk and advection dominated accretion flow models. Our predicted MBH X-ray emissions are then compared with observations of ultra-luminous X-ray sources in galaxies. We find that the slope and normalisation of the predicted X-ray luminosity function are consistent with the observations. We also estimate the rate of gravitational wave events received from MBH mergers across all redshifts. At the end of their lives the first stars may explode in supernovae that are associated with gamma ray bursts (GRBs). Provided these are in principle detectable we have estimated the expected rate of events observed.

This third paper in the series modeling QSOs and AGN as clusters of accreting black holes studies the accretion flow within an externally supplied cluster. Significant radiation will be emitted by the cluster core, but the black holes in the outer halo, where the flow is considered spherically symmetric, will not contribute much to the overall luminosity of the source because of their large velocities relative to the infalling gas, and therefore their small accretion radii. As a result the scenario discussed in Paper I will refer to the cluster cores, rather than to entire clusters. This will steepen the high frequency region of the spectrum unless inverse Compton scattering is effective. In many cases accretion flow in the central part of the cluster will be optically thick to electron scattering resulting in a spectrum featuring optically thick radiative component in addition to power -law regimes. The fitting of these spectra to QSO and AGN observations is discussed, and application to 3C 273 is worked out as an example.

Thesis advisor: Kevin Bedell / Thesis advisor: Giovanni Fazio / One of the most exciting observational breakthrough in the past decades is the discovery of the tight correlations between supermassive black holes (SMBHs) and the galaxies they reside in the `host galaxies'. This finding is surprising, as the event horizon of a typical SMBH (about 10^8 solar masses) is about 3 times 10^8 km, while the galaxy is usually about 10^17 km across, a billion times larger. How could such a small object affect something so big? SMBHs appear to be at the center of most massive galaxies, and how they interact with the host galaxies has become a fundamental question in astrophysics. To understand how galaxies and SMBHs evolve together, we must first understand the statistical properties of these systems. Quasars, the bright manifestation of the most active SMBHs, serve as good candidate for this study. Using infrared space telescopes--Spitzer and Herschel, we discovered a population of `dust-rich' quasars at intermediate redshift (z about 1.5, about 9 billion years ago) in the Lockman Hole field. We study the statistical properties of these mid-infrared (MIR) and optically-selected quasars via optical and infrared observations. I present the MIR-selected quasar sample (Chapter 2), their addition to the completeness of optically-selected sample (Chapter 3), and their physical properties, i.e., their atomic emission and absorption features, SMBH masses, and Eddington ratios--an indicator of how fast the SMBH is growing (Chapter 4). We find a significant and constant (20%) fraction of extended objects previously missed optical color selection. The SMBH mass shows evidence of downsizing--they are more massive in the early universe, though their Eddington ratios remain constant to between now and about 11 billion years ago (0 lower than z lower than 3). In the past 7 billion years (z lower than 1), quasars with extended morphology show systematically lower Eddington ratios than the point-like quasars, indicating they have less active SMBHs. We also study the spectral energy distributions (SEDs) of a subsample of `cold-dust-rich' quasars (Chapter 5) that show evidence of ongoing star formation--an indicator of how fast the host galaxy is growing. These quasars are the younger and fainter counterparts of quasars previously observed in the sub-millimeter band, as both are bright in the far-infrared, where star formation dominates. For the most luminous cold-dust-rich quasars, however, their infrared SED suggests that the dust is heated by quasars, instead of star formation in the host galaxies. Chapter 6 gives a summary of this study and comment on the significance of the dust-rich quasars in bridging the gap between SMBHs with their host galaxies. Finally some avenues for future work are discussed. / Thesis (PhD) — Boston College, 2013. / Submitted to: Boston College. Graduate School of Arts and Sciences. / Discipline: Physics.

Quasars are amongst the most luminous objects known in the Universe and thus can be observed out to large distances and correspondingly early times in the history of the Universe. Luminous quasars are powered by accretion of matter onto supermassive black holes (10⁶ - 10¹⁰M⊙) and are situated in the centre of some of the most massive galaxies and are a crucial test of massive galaxy and supermassive black hole assembly and evolution models - proving hard to recreate using simulations. As well as being of intrinsic interest, the spectra of quasars contain information about the state of the intergalactic medium (IGM) in the vicinity of the quasar, and also cosmologically distributed material in the foreground, via absorption lines due to the intervening material. This allows studies of the IGM at high redshift along different sight lines, providing insight into the metallicity, temperature and homogeneity of the Universe. This thesis discusses a new method of finding high redshift quasars using new multi wavelength data from the Dark Energy Survey, the VISTA Hemisphere Survey and Wide-Field Infrared Survey Explorer. The beginning of the thesis focusses on developing an automated selection code for z > 6 quasars, including the automatic rejection of foreground contaminating sources such as instrumental artefacts, asteroids, galactic stars and lower redshift quasars and galaxies. Following on from my first discovery of a z = 6.1 quasar in the DES and VHS data, I have developed a robust selection method that allows me to go straight from candidates to spectroscopy without needing additional photometric follow up. The method uses a grid of quasar models with a range of reddening and a series of brown dwarf spectral energy distribution models to derive a X² statistical likelihood of an object being a quasar and an associated photometric redshift. This differs from previous methods in that it allows for automatic rejection of brown dwarf stars without requiring further data. My selection delivers a ranked candidate list which down weights astrophysical contaminants and imaging artefacts. The thesis then discusses extending this method to higher redshift and the discovery of two quasars at z = 6.75 and z = 6.9. Included with this is a discussion about spectroscopic reduction of near IR data and the properties which can be derived from it. The final part of the thesis uses the quasars I have found to study their environment such as the IGM which they are embedded in, I have been developing a robust method for measuring their hydrogen near zone sizes that can be compared to simulations.