Hawking Radiation and Black Hole Gravitational Back Reaction - A Quantum Geometrodynamical Simplified Model

The purpose of this paper is to analyse the back reaction problem, between Hawking radiation and the black hole, in a simplified model for the black hole evaporation in the quantum geometrodynamics context. The idea is to transcribe the most important characteristics of the Wheeler-DeWitt equation into a Schrödinger’s type of equation. Subsequently, we consider Hawking radiation and black hole quantum states evolution under the influence of a potential that includes back reaction. Finally, entropy is estimated as a measure of the entanglement between the black hole and Hawking radiation states in this model.info:eu-repo/semantics/publishedVersio

Schwarzschild 1/r1/r-singularity is not permissible in ghost free quadratic curvature infinite derivative gravity

In this paper we will study the complete equations of motion for a ghost free quadratic curvature infinite derivative gravity. We will argue that within the scale of non-locality, Schwarzschild-type singular metric solution is not {\it permissible}. Therefore, Schwarzschild-type vacuum solution which is a prediction in Einstein-Hilbert gravity may {\it not} persist within the region of non-locality. We will also show that just quadratic curvature gravity, without infinite derivatives, always allows Schwarzschild-type singular metric solution.Comment: 10 pages, title changed, discussion added, references updated, version accepted in PR

Gravitational waves in α−\alpha-attractors

We study inflation in the $\alpha-$attractor model under a non-slow-roll dynamics with an ansatz proposed by Gong \& Sasaki \cite{Gong:2015ypa} of assuming $N=N\left(\phi\right)$. Under this approach, we construct a class of local shapes of inflaton potential that are different from the T-models. We find this type of inflationary scenario predicts an attractor at $n_{s}\sim0.967$ and $r\sim0.00055$. In our approach, the non-slow-roll inflaton dynamics are related to the $\alpha-$parameter which is the curvature of K\"ahler geometry in the SUGRA embedding of this model.Comment: 6 pages, 2 figures. Contribution to the proceedings of "The Fourtheenth Marcel Grossmann Meeting on General Relativity", University of Rome "La Sapienza", Rome, July 12-18, 2015, based on a talk delivered at the ST4 parallel sessio

Towards a unitary formulation of quantum field theory in curved space-time II: the case of Schwarzschild black hole

We argue that the origin of unitarity violation and information loss paradox in our understanding of black holes (BH) lies in the standard way of doing quantum field theory in curved space-time (QFTCS), which is heavily biased on intuition borrowed from classical General Relativity. In this paper, with the quantum first approach, we formulate a so-called direct sum QFT (DQFT) in BH space-time based on a novel formulation of discrete space-time transformations in gravity that potentially restores unitarity. By invoking the quantum effects associated with the gravitational backreaction, we show that the Hawking quanta emerging outside of the Schwarzschild radius ($r_S=2GM$) cannot be independent of the quanta that continue to be inside $r_S$. This enables the information to be carried by Hawking quanta, but in the BH DQFT formalism, we do not get any firewalls. Furthermore, BH DQFT does not create any entanglement between interior and exterior Hawking quanta which implies there is no entanglement entropy and the BH evaporation happens involving only pure states. Finally, we discuss the ways our framework leaves important clues for formulating a scattering matrix and probing the nature of quantum gravity.Comment: 31 pages, 4 figures. Any comments are welcom

Non-slow-roll dynamics in α−\alpha-attractors

In this paper we consider the $\alpha-$attractor model and study inflation under a non-slow-roll dynamics. More precisely, we follow the approach recently proposed by Gong and Sasaki \cite{Gong:2015ypa} by means of assuming $N=N\left(\phi\right)$. Within this framework we obtain a family of functions describing the local shape of the potential during inflation. We study a specific model and find an inflationary scenario predicting an attractor at $n_{s}\approx0.967$ and $r\approx5.5\times10^{-4}$. We further show that considering a non-slow-roll dynamics, the $\alpha-$attractor model can be broaden to a wider class of models that remain compatible with value of $r<0.1$. We further explore the model parameter space with respect to large and small field inflation and conclude that the inflaton dynamics is connected to the $\alpha-$ parameter, which is also related to the K\"ahler manifold curvature in the supergravity (SUGRA) embedding of this model. We also comment on the stabilization of the inflaton's trajectory.Comment: 17 pages, 6 figures, version accepted in JCA

A varying Dark Energy effective speed of sound parameter in the phantom Universe

We analyse the phenomenological effects of a varying Dark Energy (DE) effective speed of sound parameter, $c^{2}_{\textrm{sd}}$, on the cosmological perturbations of three phantom DE models. Each of these models induce a particular abrupt future event known as Big Rip (BR), Little Rip (LR), and Little Sibling of the Big Rip (LSBR). In this class of abrupt events, all the bound structures in the Universe would be ripped apart at a finite cosmic time. We compute the evolution of the perturbations, $f\sigma_{8}$ growth rate and forecast the current matter power spectrum. We vary the $c^{2}_{\textrm{sd}}$ parameter in the interval $[0,1]$ and compute the relative deviation with respect $c^{2}_{\textrm{sd}}=1$. In addition, we analyse the effect of gravitational potential sign flip that occurs at very large scale factors as compared with the current one.Comment: 15 pages, 6 figures. Improved version with an extended physical discussion. Version published in EPJ

Towards resolution of anisotropic cosmological singularity in infinite derivative gravity

In this paper, we will show that the equations of motion of the quadratic in curvature, ghost free, infinite derivative theory of gravity will not permit an anisotropic collapse of a homogeneous Universe for a Kasner-type vacuum solution.Comment: 8 pages. arXiv admin note: substantial text overlap with arXiv:1803.0030

Cosmic infinity: a dynamical system approach

Dynamical system techniques are extremely useful to study cosmology. It turns out that in most of the cases, we deal with finite isolated fixed points corresponding to a given cosmological epoch. However, it is equally important to analyse the asymptotic behaviour of the universe. On this paper, we show how this can be carried out for 3-forms model. In fact, we show that there are fixed points at infinity mainly by introducing appropriate compactifications and defining a new time variable that washes away any potential divergence of the system. The richness of 3-form models allows us as well to identify normally hyperbolic non-isolated fixed points. We apply this analysis to three physically interesting situations: (i) a pre-inflationary era; (ii) an inflationary era; (iii) the late-time dark matter/dark energy epoch.The work of MBL is supported by the Portuguese Agency Fundação para a Ciência e Tecnologia through an Investigador FCT Research contract, with refer- ence IF/01442/2013/ CP1196/CT0001. MBL and JMorais wish to acknowledge the sup- port from the Basque government Grant No. IT592-13 (Spain), FONDOS FEDER under grant FIS2014-57956-P (Spanish government) and the COST Action CA15117 (CANTATA). JMorais is also thankful to UPV/EHU for a PhD fellowship. This research work is supported by the grant UID/MAT/00212/2013.info:eu-repo/semantics/publishedVersio

Interacting 3-form dark energy models: distinguishing interactions and avoiding the Little Sibling of the Big Rip

In this paper we consider 3-form dark energy (DE) models with interactions in the dark sector. We aim to distinguish the phenomenological interactions that are defined through the dark matter (DM) and the DE energy densities. We do our analysis mainly in two stages. In the first stage, we identify the non-interacting 3-form DE model which generically leads to an abrupt late-time cosmological event which is known as the little sibling of the Big Rip (LSBR). We classify the interactions which can possibly avoid this late-time abrupt event. We also study the parameter space of the model that is consistent with the interaction between DM and DE energy densities at present as indicated by recent studies based on BAO and SDSS data. In the later stage, we observationally distinguish those interactions using the statefinder hierarchy parameters {S3(1),S4 (1)},{S3 (1),S5 (1)} . We also compute the growth factor parameter ε(z) for the various interactions we consider herein and use the composite null diagnostic (CND) {S3(1), ε(z)} as a tool to characterise those interactions by measuring their departures from the concordance model. In addition, we make a preliminary analysis of our model in light of the recently released data by SDSS~III on the measurement of the linear growth rate of structure.info:eu-repo/semantics/publishedVersio

Desenvolvimento de processo de fabrico aditivo robotizado

O crescimento das tecnologias de fabrico aditivo tem comprovado que cada vez mais estas deixaram de ser apenas consideradas para a fabricação de protótipos, passando a estar no leque de escolhas quando há a necessidade de criar um componente final. Vantagens como a elevada liberdade geométrica, que permite a criação de componentes otimizados com formas que dificilmente seriam possíveis de obter com qualquer outro processo convencional ou a competitividade na produção de pequenas séries, tornam o fabrico aditivo numa opção a ter em conta. O trabalho desenvolvido neste projeto tem como objetivo o estudo de diferentes processos de fabrico aditivo que recorrem a metais como matéria-prima, com especial ênfase no processo de fabrico aditivo com recurso à tecnologia MIG/MAG como fonte de material de adição e a um braço robotizado como meio de deslocação da tocha do equipamento MIG/MAG. Este é um processo de fabrico aditivo com elevada taxa de deposição, o que permite a obtenção de componentes de grande volume de material. Após uma primeira parte de pesquisa bibliográfica, foram idealizados e concebidos diversos mecanismos necessários à implementação do processo fabrico aditivo robotizado. Procedeu-se ao fabrico de componentes-teste com base nessa tecnologia como validação da exequibilidade do processo, no qual se recorreu a vários parâmetros de soldadura e de velocidade de deslocação da tocha, sendo posteriormente realizados ensaios laboratoriais de análise de mecânica dos componentes. Os ensaios laboratoriais confirmaram a capacidade desta tecnologia na criação de componentes com um bom nível global de homogeneização da sua estrutura bem como uma boa interligação entre camadas sem uma presença significativa de inclusões ou defeitos