arXiv subjects

Rafael Lopez-Mobilia

Publications and source records attributed to Rafael Lopez-Mobilia.

5 recordsLinked to original sources

arXiv2020

An exploration of the black hole entropy in Gauss-Bonnet gravity via the Weyl tensor

Penrose suggested that issues with the origin of the second law of thermodynamics and the remarkable homogeneous and isotropic nature of the universe on large scales can be resolved with a concept of an entropy for gravitational fields captured by the Weyl curvature tensor. This has led to various proposals for an entropy density for gravity constructed from the Weyl tensor. Most work investigating such entropy densities have been restricted to general relativity and little work has been done to them in modified theories of gravity. To remedy this, we investigate the simplest proposal for an entropy density in 5-dimensional Gauss-Bonnet gravity.

gr-qc↗

arXiv2020

A new phenomenological definition of entropy and application to black holes

Typically, the entropy of an isolated system in equilibrium is calculated by counting the number of accessible microstates, or in more general cases by using the Gibbs formula. In irreversible processes entropy spontaneously increases and this is understood from statistical arguments. We propose a new measure of entropy based on the level of irreversibility of a process. This formulation agrees in first approximation with the usual methods of calculating entropy and can be readily applied in the case of a black hole in the semiclassical regime.

cond-mat.stat-mech↗

arXiv2020

Proof of the quantum null energy condition for free fermionic field theories

The quantum null energy condition (QNEC) is a quantum generalization of the null energy condition which gives a lower bound on the null energy in terms of the second derivative of the von Neumann entropy or entanglement entropy of some region with respect to a null direction. The QNEC states that $\langle T_{kk}\rangle_{p}\geq lim_{A\rightarrow 0}\left(\frac{\hbar}{2πA}S_{out}^{\prime\prime}\right)$ where $S_{out}$ is the entanglement entropy restricted to one side of a codimension-2 surface $Σ$ which is deformed in the null direction about a neighborhood of point $p$ with area $A$. A proof of QNEC has been given before, which applies to free and super-renormalizable bosonic field theories, and to any points that lie on a stationary null surface. Using similar assumptions and methods, we prove the QNEC for fermionic field theories.

hep-th↗

arXiv2016

Primordial magnetic fields in the $f^{2}FF$ model in large field inflation under de Sitter and power law expansion

We use the $f^{2}FF$ model to study the generation of primordial magnetic fields (PMF) in the context of large field inflation (LFI), described by the potential, $V \sim M ϕ^{p}$. We compute the magnetic and electric spectra for all possible values of the model parameters under de Sitter and power law expansion. We show that scale invariant PMF are not obtained in LFI to first order in the slow roll approximation, if we impose the constraint $V(ϕ=0)\sim 0$. Alternatively, if these constraints are relaxed, the scale invariant PMF can be generated. The associated electric field energy can fall below the energy density of inflation, $ρ_{\rm{Inf}}$ for the ranges of comoving wavenumbers, $ k > 8 \times 10^{-7} \rm{Mpc^{-1}}$ and $ k > 4 \times 10^{-6} \rm{Mpc^{-1}}$ in de Sitter and power law (PL) expansion. Further, it can drop below $ρ_{\rm{Inf}}$ on the ranges, e-foldings $N > 51$, $p<1.66$, $p >2.03$, $l_0 > 3 \times 10^5 {M_{\rm{Pl}}}^{-1} (H_i < 3.3 \times 10^{-6} M_{\rm{Pl}})$, and $M > 2.8 \times 10^{-3} M_{\rm{Pl}}$. All of the above ranges fit with the observational constraints.

astro-ph.CO↗

arXiv2015

Primordial Magnetic Field Generated in Natural Infation

We study the simple gauge invariant model ${f^2}FF$ as a way to generate primordial magnetic fields (PMF) in Natural Inflation (NI). We compute both magnetic and electric spectra generated by the ${f^2}FF$ model in NI for different values of model parameters and find that both de Sitter and power law expansion lead to the same results at sufficiently large number of e-foldings. We also find that the necessary scale invariance property of the PMF cannot be obtained in NI in first order of slow roll limits under the constraint of inflationary potential, $V\left( 0 \right) \simeq 0$. Furthermore, if this constraint is relaxed to achieve scale invariance, then the model suffers from the backreaction problem for the co-moving wave number, $k \lesssim 8.0\times 10^{-7} \rm{Mpc^{-1}}$ and Hubble parameter, $H_i \gtrsim 1.25\times 10^{-3} \rm{M_{\rm{Pl}}}$. The former can be considered as a lower bound of $k$ and the later as an upper bound of $H_i$ for a model which is free from the backreaction problem. Further, we show that there is a narrow range of the height of the potential $Λ$ around ${Λ_{\min }} \approx 0.00874{M_{\rm{Pl}}}$ and of $k$ around ${k_{\min }} \sim 0.0173{\rm{Mp}}{\rm{c}^{ - 1}}$, at which the energy of the electric field can fall below the energy of the magnetic field. The range of $k$ lies within some observable scales. However, the relatively short range of $k$ presents a challenge to the viability of this model.

astro-ph.CO↗