Made available in DSpace on 2014-06-11T19:32:10Z (GMT). No. of bitstreams: 0 Previous issue date: 2011-02-28Bitstream added on 2014-06-13T18:43:08Z : No. of bitstreams: 1 landulfo_ags_dr_ift.pdf: 1384269 bytes, checksum: 63c70f6df185aec50583b1cc399bbf1b (MD5) / Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP) / Mesmo tratando a gravidade classicamente, a Teoria Quântica de Campos em Espaços Tempos Curvos (TQCEC) faz previsões impressionantes sobre o comportamento de campos quânticos na presença de campos gravitacionais. Entretanto, ao mesmo tempo em que nos revela efeitos surpreendentes, a TQCEC levanta uma série de questionamentos. O desenvolvimento de uma teoria na interface entre a teoria da relatividade, a mecânica quântica e a teoria da informação poderá não só lançar uma nova luz em tais questões como também nos permitir descobrir novos efeitos de gravitação quântica de baixas energias. Entretanto, os efeitos que a teoria da relatividade causa na teoria da informação quântica são não triviais já no espaço-tempo de Minkowski. Faz-se necessáaria portanto uma análise cuidadosa de tais efeitos já no contexto da relatividade especial. Sendo assim, estudamos primeiro o comportamento das desigualdades de Bell usando férmions de spin 1/2 e fótons quando os detetores que medem spin e polarização, respectivamente, movemse com certa velocidade. Além disso, usamos o limite de Holevo para estudar sistemas de comunicação quando as partes que trocam informação tem um movimento relativo. Como um desenvolvimento natural, estudamos diversos aspectos da teoria da informação quântica no contexto da teoria quântica de campos e, em particular, do efeito Unruh. Tais resultados nos permitiram prever o comportamento de qubits nas vizinhanças de um buraco negro de Schwarzschild / Although it treats gravity classically, the Quantum Field Theory in Curved Spacetimes (QFTCS) makes remarkable predictions about de behavior of quantum fields in the presence of gravitational fields. However, these striking discoveries raises several issues. The development of a theory at the interface between the theory of relativity, quantum mechanics and information theory could not only shed new light on such questions as well as allow us to uncover new low-energy quantum gravity effects. However, relativity affects quantum information theory in a highly non-trivial way already in Minkowski spacetime. Therefore, a careful analysis of these effects in the context of special relativity is needed. For this purpose, we begin investigating how the movement of the spin and polarization detectors influences the Bell inequalities using spin 1/2 fermions and photons, respectively. Then, we use the Holevo bound to investigate quantum communication channels when the parts that trade information have a relative motion. As a natural development, we use quantum field theory and, in particular, the Unruh effect to analyze several aspects of quantum information theory. This enables us to predict the behavior of qubits in the vicinity of a Schwarzschild black hole

Orientador: George Emanuel Avraam Matsas / Banca: Daniel Augusto Turolla Vanzella / Banca: Ernesto Galvão / Resumo: Não disponível / Abstract: When seeking inspiration for a future theory of quantum gravity, studying black holes is a promising ansatz, since they present us with several puzzles at the intersection of quantum theory and gravity. Among these is their entropy: although there are compelling arguments for its existence, its origin and statistical meaning remain a mystery. Previous work showed that at least some aspects of this phenomenon can be accounted for by the entanglement of quantum fields across the horizon: if a field is globally in a pure state, yet part of it is hidden behind the event horizon, then the reduced state of the remainder possesses non-zero entropy. This is the possibility we explore in the present work, in the simplest of settings: a ground-state escalar field, defined in three-dimensional, flat or unifromily curved space, and derive an expression for the entropy, which is evauated numerically. the results show that the entropy scales with the boundary area of the inaccessible region, a key feature of black hole entropy known as the area law. Furthermore. we conclude that the dominant contribution to the entropy is due to short-range interactions, and discuss some physical implications of this insight for the puzzle of black hole entropy / Mestre

Orientadores: Alberto Vazquez Saa, Marcus Aloízio Martinez de Aguiar / Dissertação (mestrado) - Universidade Estadual de Campinas, Instituto de Física Gleb Wataghin / Made available in DSpace on 2018-08-17T22:25:51Z (GMT). No. of bitstreams: 1 Freitas_GabrielBernardide_M.pdf: 1988646 bytes, checksum: 0b4661aa158c2d9e054e30fd044ba4d9 (MD5) Previous issue date: 2011 / Resumo: O objetivo deste trabalho é a investigação do efeito Greisen-Zatsepin-Kuzmin (GZK) na presença de buracos negros, contemplando, dessa forma, uma correção de natureza astrofísica à propagação de raios cósmicos de ultra-alta energia. Inicia-se com uma descrição das principais características dos dois elementos cruciais envolvidos no efeito: os raios cósmicos de ultra-alta energia e a radiação cósmica de fundo. Posteriormente, é feita uma revisão sistemática do efeito GZK, mostrando as interações mais relevantes e a abordagem utilizada para o cálculo das perdas de energia. Também é dada especial atenção às correções de natureza cosmológica que devem ser incorporadas ao considerar fontes de raios cósmicos muito distantes. Em seguida, analisa-se o problema na presença de um buraco negro. O estudo é feito considerando a situação mais simples: a radiação cósmica de fundo é tratada como um banho térmico no qual um buraco negro de Schwarzschild está imerso, constituindo um sistema cuja evolução pode ser tratada na aproximação quase estática (mudanças adiabáticas). Uma aproximação para as trajetórias de raios cósmicos nesse espaço-tempo é proposta, e a partir dela são calculadas as perdas de energia de cada partícula em função da distância de máxima aproximação em relação ao buraco negro. Finalmente, são apresentadas as conclusões do autor, e as perspectivas futuras de investigação são discutidas / Abstract: The aim of this work is the investigation of the Greisen-Zatsepin-Kuzmin (GZK) effect in the presence of black holes, thereby consisting of an astrophysical correction for the propagation of ultrahigh energy cosmic rays. Firstly, a description of the main features of the two crucial elements involved in the effect, the ultrahigh energy cosmic rays and the cosmic microwave background, is given. Then, a systematic review of the GZK effect is presented, showing the most relevant interactions and the approach used for the calculation of energy losses. Also, special attention is given to the cosmological corrections that must be incorporated when very far cosmic-ray sources are considered. After that, the problem is analysed in the presence of a black hole. The study is based upon the simplest situation: the cosmic microwave background is treated as a thermal bath in which a Schwarzschild black hole is immersed, constituting a system whose evolution can be treated in the quasi-static approximation (adiabatic changes). An approximation for the cosmic-ray particles¿ trajectories is proposed, and then used to calculate the energy loss for each particle as a function of the maximum approximation distance to the black hole. Finally, the author¿s conclusions are presented, as well as perspectives for future investigations / Mestrado / Relatividade e Gravitação / Mestre em Física

Orientadores: Alberto Vazquez Saa, Amir Ordacgi Caldeira / Tese (doutorado) - Universidade Estadual de Campinas, Instituto de Física Gleb Wataghin / Made available in DSpace on 2018-08-21T19:06:37Z (GMT). No. of bitstreams: 1 Santarelli_Raphael_D.pdf: 2666477 bytes, checksum: ddd17159cb8299eef7c96d47293f68ea (MD5) Previous issue date: 2012 / Resumo: O objetivo deste trabalho é testar a validade da Conjectura Fraca da Censura Cósmica em espaços-tempo com buracos negros. Essa conjectura foi proposta por Roger Penrose em 1969, e diz que singularidades resultantes de colapso gravitacional de matéria fisicamente razoável estão sempre envolvidas por um horizonte de eventos, ou seja, escondidas de um observador externo. Apesar de muitas evidências a favor dessa conjectura, ela nunca foi provada. Nossa meta é analisar se essa conjectura pode ser violada classicamente sob especificas circunstâncias. Começaremos com uma introdução ao assunto, apresentando os conceitos que nos serão úteis ao longo de nosso trabalho. Depois investigaremos os trabalhos anteriores na área, que visaram destruir o horizonte de eventos de um buraco negro, criando assim uma singularidade nua (visível), e consequentemente violando a conjectura. Por fim, apresentaremos nossos resultados, que podem ser divididos em duas partes: (i) generalização dos casos clássicos obtidos anteriormente, e demonstração, sob dadas condições, da violação da conjectura para um buraco negro de Kerr-Newman e (ii) análise da validade da conjectura para um buraco negro com cinco dimensões em um espaço-tempo assintoticamente AdS, dando assim uma contribuição para a correspondência AdS/CFT / Abstract: The aim of this work is to test the Weak Cosmic Censorship Conjecture in black holes. This conjecture was proposed by Roger Penrose in 1969, and it states that singularities arising from the gravitational collapse of physically reasonable matter are always involved by an event horizon, i.e., they are hidden from an external observer. Despite so much evidence in favor of this conjecture, it has never been proven. Our aim is to analyze if this conjecture can be violated classically under specific circumstances. We will start with an introduction to the subject, presenting the concepts that will be useful throughout the work. After that, we will investigate the previous studies in the field that tried to destroy the event horizon of a black hole, creating a naked (visible) singularity, and hence violating the conjecture. Lastly, we will present our results, which may be divided in two parts: (i) generalization of the classic cases previously obtained, and demonstration, under specific conditions, of the violation of the conjecture in a spacetime with a Kerr-Newman black hole and (ii) study of the validity of this conjecture with a five-dimensional rotating black hole in a asymptotically AdS spacetime, making a contribution to the AdS/CFT correspondence / Doutorado / Física / Doutor em Ciências

This dissertation deals with the following topics related to the magnetic activity of neutron stars and black holes: (I) Magnetic field evolution of neutron stars: We develop a numerical code which models the internal magnetic field evolution of neutron stars in axisymmetry. Our code includes the Hall drift and Ohmic effects in the crust, and the drift of superconducting flux tubes and superfluid vortices inside the liquid core. We enforce the correct hydromagnetic equilibrium in the core. We also model the elastic deformation of the crust and its feedback on the magnetic field evolution. We find that (i) The Hall attractor found by Gourgouliatos and Cumming in the crust also exists for B-fields which penetrate the core. (ii) If the flux tube drift is fast in the core, the pulsar magnetic fields are depleted on the Ohmic timescale (~150 Myr for hot neutron stars, or ~1.8 Gyr for cold neutron stars such as recycled pulsars, depending on impurity levels). (iii) The outward motion of superfluid vortices during the rapid spin-down of a young highly magnetized pulsar, can partially expel magnetic flux from the core when 𝐵 ≲ 10¹³ G. (II) Neutron star quakes and glitches: We develop a theoretical model to explain the remarkable null pulse coincident with the 2016 glitch in Vela rotation. We propose that a crustal quake associated with the glitch strongly disturbed the Vela magnetosphere and thus interrupted its radio emission. We develop the first numerical code which models the global dynamics of a neutron star quake. Our code resolves the elasto-dynamics of the entire crust and follows the evolution of Alfven waves excited in the magnetosphere. We find that Alfven waves launched by the quake become de-phased in the magnetosphere, and generate strong electric currents, capable of igniting electric discharge. Most likely, the discharge floods the magnetosphere with electron-positron plasma, quenching the pulsar radio emission. The observed ~0.2 s duration of the disturbance indicates that the crust is magnetically coupled to the superconducting core of the neutron star. (III) Pulsar magnetospheres and radio emission: We present an extreme high resolution kinetic plasma simulation of a pulsar magnetosphere using the Pigeon code. The simulation shows from first-principles how and where radio emission can be produced in pulsar magnetospheres. We observe the self-consistent formation of electric gaps which periodically ignite electron-positron discharge. The gaps form above the polar-cap, and in the bulk return-current. Discharge of the gaps excites electromagnetic modes which share several features with the radio emission of real pulsars. We also observe the excitation of plasma waves and charge bunches by streaming instabilities in the outer magnetosphere. (IV) Black hole magnetospheres and no-hair theorem: We explore the evolution of highly magnetized magnetospheres on Kerr black holes by performing general relativistic kinetic plasma simulations with the GRZeltron code, and general relativistic resistive magnetohydrodynamics simulations with the BHAC code. We show that a dipole magnetic field on the event horizon opens into a split-monopole and reconnects in a plasmoid-unstable current-sheet. The plasmoids are ejected from the magnetosphere, or swallowed by the black hole. The no-hair theorem is satisfied, in the sense that all components of the stress-energy tensor decay exponentially in time. We measure the decay time of magnetic flux on the event horizon for plasmoid-dominated reconnection in collisionless and collisional plasma.

The astrophysical origins of the rapid neutron-capture process (r-process), which gives rise to roughly half of the elements heavier than iron, has remained a mystery for almost 70 years. The likely violent events, which seed the r-process abundances in our solar system and galaxy, remain uncertain to this day. This is in part due to nuclear physics uncertainties associated with the r-process itself, but mainly due to uncertainties in astrophysics modeling. The discovery of the radioactively-powered kilonova emission from the neutron star merger event GW170817 confirmed the violent deaths of neutron stars as one key site of the r-process in the universe. However, other evidence appears to favor an additional r-process channel that more promptly follows star formation in the universe, such as core-collapse supernovae (CCSNe), i.e. the brilliant births of neutron stars. The two viable sites for the r-process are (1) core-collapse supernovae (CCSNe), which are explosions of massive stars at the end of their lives and (2) compact object mergers, which are violent collisions of stellar remnants formed at the endpoints of stellar evolution. Chapters 2 and 3 of this dissertation present general relativistic magnetohydrodynamic simulations of one potential r-process site associated with CCSNe: the neutrino-driven wind. These outflows are launched from the hot proto-neutron star (PNS) remnant by neutrino-heating above their surfaces, within seconds after the collapse of a massive star. However, previous work has shown that spherically symmetric winds from non-rotating PNS fail to achieve the requisite conditions for a robust r-process. Chapter 2 explores for the first time the combined effects of rapid rotation and strong gravity of the PNS on the wind properties. Chapter 3 explores the impact of a dynamically strong ordered magnetic field on the properties of non-rotating PNS winds. The wind in both cases is simulated in a controlled environment rather than as a part of a self-consistent global CCSNe simulation, to assess the viability of r-process nucleosynthesis as a function of PNS properties (neutrino energies/luminosities, rotation rate, magnetization). We find that rapid rotation allows for outflows that are ~10% more neutron-rich in the equatorial region, where the mass loss rate is roughly an order of magnitude higher than that of otherwise equivalent non-rotating models. The birth of very rapidly spinning neutron stars may thus be a site for the production of light r-process nuclei (38 < Z < 47). For PNSs with sufficiently strong magnetic fields (such that magnetic pressure exceeds gas pressure above the PNS surface), we find that equatorial outflows are trapped by the magnetic field in a region near the surface, and therefore receive additional neutrino heating relative to a freely-expanding unmagnetized wind. This allows a modest fraction of the wind material to achieves entropies high enough to synthesize 2nd peak r-process elements via an alpha-rich freeze-out mechanism. The final chapter explores the interplay between the r-process and the dynamics of compact object merger ejecta. Gravitational wave observatories are expected to detect several additional binary neutron star (BNS) and black hole-neutron star (BHNS) mergers in current and future observing runs, some of which may be accompanied by electromagnetic counterparts such as kilonovae. However, distinguishing more distant BNS from BHNS mergers based on their associated gamma-ray bursts (GRB), has proven tricky. This chapter presents a calculation of the effects of r-process heating on the dynamics of tidal ejecta from BNS and BHNS mergers. In particular we explore whether late-time fall-back of weakly bound debris created during the merger to the central black hole remnant, can explain the temporally extended X-ray emission observed following several merger GRB on timescales of several seconds to minutes. As a result of the different impact that r-process heating has depending on the composition of the ejecta and the mass of the black hole, a method to differentiate BHNS from BNS mergers, based on their extended X-ray emission, is proposed.

In this thesis, we consider three aspects of black holes. First, we examine a black hole boosted through a uniform magnetic field. We find that it can acquire an electric charge, just as a spinning black hole in an ambient magnetic field can, though the gravito-electrodynamics upstage naive arguments about screening electric fields in determining the value of the charge accrued. We study the chaotic behavior of the charged particles via their fractal basin boundaries. Second, we study the vanishing of Love numbers for black holes from a geometric perspective and connect it to the existence of quasinormal modes in de Sitter space. Behind each phenomenon is a ladder structure with a geometric/representation-theoretic origin which makes it possible to connect the asymptotic behavior of solutions at different boundaries. Third, we model the formation of a black hole in dRGT massive gravity in a de Sitter background with a collapsing homogeneous and pressureless ball of dust or ``star''. We focus on several choices of parameters corresponding to models of interest. We compute the position of the apparent horizon where it crosses the surface of the star, the Ricci curvature at the boundary, and the finite correction to the curvature of the apparent horizon due to the graviton mass. We argue that our collapsing solutions cannot be matched to a static, spherically symmetric vacuum solution at the star's surface, providing further evidence that physical black hole solutions in massive gravity are likely time-dependent.

The upcoming Laser Interferometer Space Antenna (LISA) is expected to detect gravitational waves (GWs) from massive black hole binaries (MBHB). Finding the electromagnetic (EM) counterparts for these GW events will be crucial for understanding how and where MBHBs merge, measuring their redshifts, constraining the Hubble constant and the graviton mass, and for other novel science applications. However, due to poor GW sky localization, multi-wavelength, time-dependent electromagnetic (EM) models are needed to identify the right host galaxy. This dissertation investigates electromagnetic (EM) signatures to accompany compact black hole binaries, specifically those that occur prior to, during, and following the merger, as well as those originating via self-lensing flares (SLFs). Chapter 2 considers equal-mass merging massive black hole binaries (MBHBs) embedded in a circumbinary disk (CBD), using high-resolution two-dimensional simulations, with a 𝚪-law equation of state, incorporating viscous heating, shock heating, and radiative cooling. Beginning from before the decoupling limit and transitioning through into post-merger, distinct EM features are identified before, during, and after the merger. The main result is that the MBHB produces strong thermal X-ray emission until 1-2 days prior to the merger. However, as the binary decouples from the CBD, the X-ray-bright minidisks rapidly shrink in size, become disrupted, and the accretion rate drops precipitously. As a result, the thermal X-ray luminosity drops by orders of magnitude, and the source remains X-ray dark for several days, regardless of any post-merger effects such as gravitational wave (GW) recoil or mass loss. Looking for this abrupt spectral change where the thermal X-ray disappears is a tell-tale EM signature of LISA mergers that does not require extensive pre-merger monitoring. Chapter 3 follows up on and extends the results of Chapter~\ref{chap:ch2} by investigating the effects to the EM spectrum for unequal-mass MBHBs via comparable simulations. This work corroborates the findings of a several order of magnitude drop in the thermal X-ray luminosity near the time of merger, but with delayed timing than found in an equal-mass system, while the source still remains X-ray dark for hours post-merger. The main result, however, is a new signature, a sharp spike in the thermal X-ray emission just before the tell-tale steep drop occurs. This adds an additional EM signature that can be used to identify EM counterparts of LISA's unequal MBHBs before the merger and potentially measure the mass ratio of the system through EM means. Finally, Chapter 4 addresses the EM signature of self-lensing flares (SLFs). SLFs are expected to be produced once or twice per orbit by an accreting MBHB, if the eclipsing MBHBs are observed close to edge-on. Again, using high-resolution two-dimensional viscous hydrodynamical simulations of a CBD embedding a MBHB, a very high-cadence output of these hydrodynamical simulation is used as inputs for a general-relativistic ray-tracing code to produce synthetic spectra and phase-folded light curves. The main results show a significant periodic amplification of the flux with the characteristic shape of a sharp flare with a central dip, as the foreground black hole (BH) transits across the minidisk and shadow of the background BH, respectively. These corroborate previous conclusions based on the microlensing approximation and analytical toy models of the emission geometry. A realistic concern with incorporating a physical disk was that the CBD might obscure our view of the SLF, considering they only appreciably occur for a near edge-on line of sight. However, this work shows that the CBD is in fact more a friend than foe in the detection, because while the CBD does indeed block other sources of emission that constitute noise, the bent trajectories of the light from the lensed minidisks remain visible even for these edge-on configurations.

We will consider the scenario of the co-rotation of a fluid star (in specific, a neutron star) and a black hole. The neutron star (or primary)is assumed to have constant angular velocity. The tidal effects on the primary are investigated. First, the centrally condensed approximation is applied, where both bodies are considered as point sources. In the second treatment, the primary is treated as an incompressible and homogeneous fluid mass, which in addition to its own gravity is subject to centrifugal and Coriolis forces, derived from fluid motions. The black hole (or secondary) is treated as a rigid sphere and can be regarded as a point mass. The equilibrium figure is derived. The problem is then adapted to include vorticity and a pseudo-Newtonian potential. The coalescence of neutron star - black hole binaries and their importance to gravitational wave detection is also discussed. / Mathematical Sciences / M. Sc. (Applied Mathematics)

Over recent years there has been an increase of the number of secure supermassive black hole (SMBH) detections. These SMBH measurements have lead astronomers to establish well defined empirical relationships between the SMBH mass and some of the properties of the host galaxy. The number of galaxies with SMBH mass measurements is currently limited to about 100. One approach of expanding the study of the SMBH is to use the empirical relations for estimating M[subscript(bh)] for larger samples of galaxies. The investigation of the SMBH population (or SMBH mass function) for large sample of galaxies in the nearby universe has helped to constrain the SMBH and the galaxy evolution. Previous estimates of the SMBH mass function at low redshift were produced mainly by combining the measurements of the galaxy luminosity or velocity function with one of the SMBH scaling relations. In the first part of the thesis I will present an independent construction of the nearby supermassive black hole mass function by applying the optical M[subscript(bh)]–L relation onto the Millennium Galaxy Catalogue (MGC). Additionally, in the second part I will provide photometric analysis of all UKIDSS galaxies for which SMBH masses have been measured. I will derive composite profiles of brightness, ellipticity and position angles of each galaxy. I will show that the Sérsic function fits the brightness profile of the majority of the elliptical galaxies and the bulge of disk galaxies and I will provide alternative multi-component fits when necessary. Then these photometric parameters will be used for constructing the M[subscript(bh)]–L relation in the near-IR and to investigate the M[subscript(bh)]–n relation. In the third part I will construct the near-IR SMBH mass function for the Galaxy and Mass Assembly (GAMA) survey. For this purpose I will apply the newly derived M[subscript(bh)]–L relation onto an elliptical subsample of K-band images. The advantage of this SMBH mass function is that during the M[subscript(bh)]–L construction I used the same quality images and techniques used on the GAMA survey. Apart from the M[subscript(bh)]–L relation, the M[subscript(bh)]–sigma relation was used as an alternative approach for a subsample of galaxies for which the velocity dispersions were available. Furthermore, I employed both local SMBH mass functions (MGC & GAMA) for estimating the SMBH mass density at redshift zero and accounted for the dependence of the total SMBH density on the look-back time by comparing with semi-analytic SMBH mass functions. Finally, from the SMBH mass density I estimated the baryon fraction that is locked into SMBHs.