39400765
Black hole evaporation in a thermalized final-state projection model
We propose a modified version of the Horowitz-Maldacena final-state boundary condition based upon a matter-radiation thermalization hypothesis on the Black Hole interior, which translates into a particular entangled state with thermal Schmidt coefficients. We investigate the consequences of this proposal for matter entering the horizon, as described by a Canonical density matrix characterized by the matter temperature T. The emitted radiation is explicitly calculated and is shown to follow a thermal spectrum with an effective temperature T{sub eff}. We analyze the evaporation process in the quasistatic approximation, highlighting important differences in the late stages with respect to the usual semiclassical evolution, and calculate the fidelity of the emitted Hawking radiation relative to the infalling matter.
122640455
A study of meson dynamics in relativistic models of nuclear matter
Abstract We analyze the dynamics of mesons in nuclear matter, as resulting from two relativistic models for the meson-nucleon interaction (σ and Walecka model). The covariant Wigner function techniques are used in order to describe a plasma of nucleons in thermodynamical equilibrium, and to analyze the quasi-meson spectra in the medium. The models are solved in the mean-field and Hartree approximations, as first-order approximations to the solution of a hierarchy of kinetic equations describing the collective behaviour of the plasma. The small perturbations around both ground states give, in every case, the dispersion relations for the mesons. A numerical study of the different branches and the evolution of the quasi-meson masses with density is performed. This analysis shows that the mean-field ground state is unstable in some density ranges and should evolve towards a new spatially-structured state. We also show that vacuum polarization effects eliminate such instabilities, although they introduce a new instability related to “tachyonic modes”, arising at large momenta. For such momenta, the structural properties of the nucleon should be taken into account. We show that the “tachyonic instability” disappears with the introduction of a simple monopolar form factor for the nucleon. Finally, we study the linear response of the plasma and analyze the screening effects on the interaction.
176593914
Screening in Relativistic Dense Matter
16895941
Relativistic direct Urca processes in cooling neutron stars
Abstract We derive a relativistic expression for neutrino energy losses caused by the direct Urca processes in degenerate baryon matter of neutron stars. We use two different ways to calculate the emissivity caused by the reactions to our interest. First we perform a standard calculation by Fermi's “golden” rule. The second calculation, resulting in the same expression, is performed with the aid of polarization functions of the medium. Our result for neutrino energy losses strongly differs from previous nonrelativistic results. We also discuss nonconservation of the baryon vector current in reactions through weak charged currents in the medium, when the asymmetry between protons and neutrons is considered. The above effects, not discussed in the literature before, substantially modify the polarization functions responsible for the induced weak charged currents in baryon matter.
52247000
Neutrino oscillation and stellar collapse.
The effects of neutrino oscillations on the equation of state of supernova matter are explored with simple arguments. Its influence on the dynamics of the collapse is analyzed. We find the most dramatic results in the numerical flux of neutrinos, which appears almost proportional to the number of generations participating in the oscillation.
119585017
Linear response and Friedel oscillations of the pion field in relativistic nuclear matter
Abstract This paper is concerned with the study of the linear response and the screening effects on the pion field in nuclear matter. The linear response of a relativistic plasma of nucleons interacting through the exchange of scalar (σ) and vector-isoscalar (ω) mesons in the framework of a QHD model is analyzed. The pions are assumed to be coupled to nucleons through the usual isospin invariant lagrangian. For the sake of comparison, we consider also a lagrangian that predicts reasonable low-energy πN scattering amplitudes in vacuum. It is obtained by adding a non-linear σπ coupling term to the QHD lagrangian. The ω- and σ-nucleon coupling constants are fixed in such a way that saturation is attained in the Hartree approximation near the nuclear density, while the πN coupling constant is taken from scattering data. The linear response formalism is introduced, and the quasi-pion propagator is computed in a self-consistent one-loop approximation. From these results, we analyze the screening effects on an external perturbing field. In the case of an uniform perturbing field, we obtain the behaviour of the effective πN coupling constant as a function of the density. Also, we study the effective field in the plasma created by a point-like baryonic source at rest. In vacuum, this field is given by the usual Yukawa expression. However, inside the matter, the form of the field is strongly modified by screening effects. In the non-degenerate case, the field exhibits exponentially damped oscillations, while in the degenerate case it shows Friedel-type oscillations, damped as the third power of the distance. Nevertheless, in both cases the effective field is strongly reduced as compared to the vacuum case (in the degenerate case, at least up to distances ∼10 fm). As a consequence, the range of the hard-core of the interaction inside the plasma remains smaller than the mean interparticle distance in all the meaningful range of densities. This behaviour is dominated by the analytic structure of the polarization tensor, and is rather insensitive to the model for the πN interaction.
10874262
Observables in quantum gravity
We study a family of physical observable quantities in quantum gravity. We denote them W functions, or n-net functions. They represent transition amplitudes between quantum states of the geometry, are analogous to the n-point functions in quantum field theory, but depend on spin networks with n connected components. In particular, they include the three-geometry to three-geometry transition amplitude. The W functions are scalar under four-dimensional diffeomorphism, and fully gauge invariant. They capture the physical content of the quantum gravitational theory. We show that W functions are the natural n-point functions of the field theoretical formulation of the gravitational spin foam models. They can be computed from a perturbation expansion, which can be interpreted as a sum-over-four-geometries. Therefore the W functions bridge between the canonical (loop) and the covariant (spinfoam) formulations of quantum gravity. Following Wightman, the physical Hilbert space of the theory can be reconstructed from the W functions, if a suitable positivity condition is satisfied. We compute explicitly the W functions in a "free" model in which the interaction giving the gravitational vertex is shut off, and we show that, in this simple case, we have positivity, the physical Hilbert space of the theory can be constructed explicitly and the theory admits a well defined interpretation in terms of diffeomorphism invariant transition amplitudes between quantized geometries.
21084326
Quantization of strings and branes coupled to BF theory
BF theory is a topological theory that can be seen as a natural generalization of 3-dimensional gravity to arbitrary dimensions. Here we show that the coupling to point particles that is natural in three dimensions generalizes in a direct way to BF theory in d dimensions coupled to (d − 3)branes. In the resulting model, the connection is flat except along the membrane world-sheet, where it has a conical singularity whose strength is proportional to the membrane tension. As a step towards canonically quantizing these models, we show that a basis of kinematical states is given by ‘membrane spin networks’, which are spin networks equipped with extra data where their edges end on a brane.
122105103
Quasilocal first law for black hole thermodynamics
We first show that stationary black holes satisfy an extremely simple local form of the first law \delta E=\kappa(l) \delta A/(8 \pi) where the thermodynamical energy E=A/(8\pi l) and (local) surface gravity \kappa(l)=1/l, where A is the horizon area and l is a proper length characterizing the distance to the horizon of a preferred family of local observers suitable for thermodynamical considerations. Our construction is extended to the more general framework of isolated horizons. The local surface gravity is universal. This has important implications for semiclassical considerations of black hole physics as well as for the fundamental quantum description arising in the context of loop quantum gravity.
16594811
Higher spin gravity in 3D: Black holes, global charges and thermodynamics
Abstract Global charges and thermodynamic properties of three-dimensional higher spin black holes that have been recently found in the literature are revisited. Since these solutions possess a relaxed asymptotically AdS behavior, following the canonical approach, it is shown that the global charges, and in particular the energy, acquire explicit nontrivial contributions given by nonlinear terms in the deviations with respect to the reference background. It is also found that there are cases for which the first law of thermodynamics can be readily worked out in the canonical ensemble, i.e., without work terms associated to the presence of higher spin fields, and remarkably, the semiclassical higher spin black hole entropy is exactly reproduced from Cardy formula.
122318174
Charmless Hadronic Three Body B Decays at BaBar
We report on recent measurements of branching fractions and CP violation observables of selected charmless hadronic B decays obtained from data collected with the BABAR detector at the PEP-II asymmetric-energy collider, operating at the ϒ(4S) resonance.