Vacuum polarization by topological defects in de Sitter spacetime

In this paper we investigate the vacuum polarization effects associated with a massive quantum scalar field in de Sitter spacetime in the presence of gravitational topological defects. Specifically we calculate the vacuum expectation value of the field square, $$. Because this investigation has been developed in a pure de Sitter space, here we are mainly interested on the effects induced by the presence of the defects.Comment: Talk presented at the 1st. Mediterranean Conference on Classical and Quantum Gravity (MCCQG

Theory of the Fermi Arcs, the Pseudogap, TcT_c and the Anisotropy in k-space of Cuprate Superconductors

The appearance of the Fermi arcs or gapless regions at the nodes of the Fermi surface just above the critical temperature is described through self-consistent calculations in an electronic disordered medium. We develop a model for cuprate superconductors based on an array of Josephson junctions formed by grains of inhomogeneous electronic density derived from a phase separation transition. This approach provides physical insights to the most important properties of these materials like the pseudogap phase as forming by the onset of local (intragrain) superconducting amplitudes and the zero resistivity critical temperature $T_c$ due to phase coherence activated by Josephson coupling. The formation of the Fermi arcs and the dichotomy in k-space follows from the direction dependence of the junctions tunneling current on the d-wave symmetry on the $CuO_2$ planes. We show that this semi-phenomenological approach reproduces also the main future of the cuprates phase diagram.Comment: 5 pages 7 fig

Reply to "Comment on 'Gravitating Magnetic Monopole in the Global Monopole Spacetime' "

In this Reply I present some arguments in favor of the stability of the topological defect composed by global and magnetic monopoles.Comment: 1 page, no figures. Revised version improves the theoretical analysis about electrostatic self-interaction in the global monopole spacetim

Wave Scattering through Classically Chaotic Cavities in the Presence of Absorption: An Information-Theoretic Model

We propose an information-theoretic model for the transport of waves through a chaotic cavity in the presence of absorption. The entropy of the S-matrix statistical distribution is maximized, with the constraint $=\alpha n$: n is the dimensionality of S, and $0\leq \alpha \leq 1, \alpha =0(1)$ meaning complete (no) absorption. For strong absorption our result agrees with a number of analytical calculations already given in the literature. In that limit, the distribution of the individual (angular) transmission and reflection coefficients becomes exponential -Rayleigh statistics- even for n=1. For $n\gg 1$ Rayleigh statistics is attained even with no absorption; here we extend the study to $\alpha <1$. The model is compared with random-matrix-theory numerical simulations: it describes the problem very well for strong absorption, but fails for moderate and weak absorptions. Thus, in the latter regime, some important physical constraint is missing in the construction of the model.Comment: 4 pages, latex, 3 ps figure