Black hole collapse simulated by vacuum fluctuations with a moving semi-transparent mirror

Creation of scalar massless particles in two-dimensional Minkowski space-time--as predicted by the dynamical Casimir effect--is studied for the case of a semitransparent mirror initially at rest, then accelerating for some finite time, along a trajectory that simulates a black hole collapse (defined by Walker, and Carlitz and Willey), and finally moving with constant velocity. When the reflection and transmission coefficients are those in the model proposed by Barton, Calogeracos, and Nicolaevici [r(w)=-i\alpha/(\w+i\alpha) and s(w)=\w/(\w+i\alpha), with $\alpha\geq 0$], the Bogoliubov coefficients on the back side of the mirror can be computed exactly. This allows us to prove that, when $\alpha$ is very large (case of an ideal, perfectly reflecting mirror) a thermal emission of scalar massless particles obeying Bose-Einstein statistics is radiated from the mirror (a black body radiation), in accordance with results previously obtained in the literature. However, when $\alpha$ is finite (semitransparent mirror, a physically realistic situation) the striking result is obtained that the thermal emission of scalar massless particles obeys Fermi-Dirac statistics. We also show here that the reverse change of statistics takes place in a bidimensional fermionic model for massless particles, namely that the Fermi-Dirac statistics for the completely reflecting situation will turn into the Bose-Einstein statistics for a partially reflecting, physical mirror.Comment: 13 pages, no figures, version to appear in Physical Review

Qualitative study in Loop Quantum Cosmology

This work contains a detailed qualitative analysis, in General Relativity and in Loop Quantum Cosmology, of the dynamics in the associated phase space of a scalar field minimally coupled with gravity, whose potential mimics the dynamics of a perfect fluid with a linear Equation of State (EoS). Dealing with the orbits (solutions) of the system, we will see that there are analytic ones, which lead to the same dynamics as the perfect fluid, and our goal is to check their stability, depending on the value of the EoS parameter, i.e., to show whether the other orbits converge or diverge to these analytic solutions at early and late times.Comment: 12 pages, 7 figures. Version accepted for publication in CQ

Avantprojecte de llei sobre la filiació extramatrimonial. Edició crítica i estudi d'un avantprojecte de llei inèdit de la Comissió Jurídica Assessora de la Generalitat de Catalunya durant la Segona República

En aquest treball es publica l'edició crítica i l'estudi jurídic de l'Avantprojecte de llei sobre filiació extramatrimonial que elaborà la Comissió Jurídica Assessora de la Generalitat de Catalunya durant la Segona República espanyola, del qual fins ara només es tenia una notícia succinta gràcies als escrits de Ramon Maria Roca i Sastre, que fou un dels membres de la Comissió que destacadament participà en la seva elaboració.This paper presents a critical edition and the respective legal study of the Draft Bill of Law on Out-of-Wedlock Filiation, which was prepared by the Legal Advisory Commission of the Government of Catalonia during the Second Spanish Republic. Up to now, only a succinct knowledge of this text was available through the writings of Ramon Maria Roca i Sastre, a member of the Commission who played a prominent role in its drafting.En este trabajo se publica la edición crítica y el estudio jurídico del Anteproyecto de ley sobre filiación extramatrimonial elaborado por la Comissió Jurídica Assessora de laGeneralitat de Catalunya durante la Segunda República española, del que hasta la fecha solo se tenía una sucinta noticia gracias a los escritos de Ramon Maria Roca i Sastre, uno de los miembros de la Comissió que descatadamente participó en su elaboración

Els canvis de l'olfacte en l'embaràs

És cert el que es diu sobre el canvi de les olors en la dona embarassada

Generalized Yukawa couplings and matrix models

In this note we investigate U(N) gauge theories with matter in the fundamental and adjoint representations of the gauge group, interacting via generalized Yukawa terms of the form Tr[Q \Phi^n {\tilde Q}]. We find agreement between the matrix model and the gauge theory descriptions of these theories. The analysis leads to a partial description of the Higgs branch of the gauge theory. We argue that the transition between phases with different unbroken flavor symmetry groups is related to the appearance of cuts in the matrix model computation

Stochastic quantization and holographic Wilsonian renormalization group

We study relation between stochastic quantization and holographic Wilsonian renormalization group flow. Considering stochastic quantization of the boundary on-shell actions with the Dirichlet boundary condition for certain $AdS$ bulk gravity theories, we find that the radial flows of double trace deformations in the boundary effective actions are completely captured by stochastic time evolution with identification of the $AdS$ radial coordinate `$r$' with the stochastic time '$t$' as $r=t$. More precisely, we investigate Langevin dynamics and find an exact relation between radial flow of the double trace couplings and 2-point correlation functions in stochastic quantization. We also show that the radial evolution of double trace deformations in the boundary effective action and the stochastic time evolution of the Fokker-Planck action are the same. We demonstrate this relation with a couple of examples: (minimally coupled)massless scalar fields in $AdS_2$ and U(1) vector fields in $AdS_4$.Comment: 1+30 pages, a new subsection is added, references are adde