14718218
Nucleon–nucleon effective potential in dense matter including rho-meson exchange
Abstract We obtain the RPA summed one-meson exchange potential between nucleons in symmetric nuclear matter at zero temperature, from a model which includes ρ , σ , ω and π mesons. The behavior of rho mesons inside the medium is first discussed using different schemes to extract a finite contribution from the vacuum polarization. These schemes give qualitatively different results for the in-medium rho mass. The results are discussed in connection with the nonrenormalizability of the model. We next study the modified potential as density increases. In the intermediate-distance range, it is qualitatively modified by matter and vacuum effects. In the long-distance range ( r >2 fm), one observes the presence of oscillations, which are not present in free space. Features on this distance range are insensitive to the renormalization scheme.
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.
119094287
Equilibrium properties of self-interacting neutrinos in the quasi-particle approach
In this work, a neutrino gas in equilibrium is studied both at T = 0 and at finite temperature. Neutrinos are treated as massive Dirac quasi-particles with two generations. We include self-interactions among the neutrinos via neutral currents, as well as the interaction with a background of matter. To obtain the equilibrium properties, we use Wigner function techniques. To account for corrections beyond the Hartree approximation, we also introduce correlation functions. We prove that, under the quasi-particle approximation, these correlation functions can be expressed as products of Wigner functions. We analyse the main properties of the neutrino eigenmodes in the medium, such as effective masses and mixing angle. We show that the formulae describing these quantities will differ with respect to the case with no self-interactions.
119371304
Neutrino-nucleon scattering rate in proto-neutron star matter
Abstract:We present a calculation of the neutrino-nucleon scattering cross-section which takes into account the nuclear correlations in the relativistic random phase approximation (RPA). Our approach is based on a quantum-hadrodynamics model with exchange of σ, ω, π, ρ and δ mesons. In view of applications to neutrino transport in the final stages of supernova explosion and proto-neutron star cooling, we study the evolution of the neutrino mean free path as a function of density, proton-neutron asymmetry and temperature. Special attention was paid to the issues of renormalization of the Dirac sea, residual interactions in the tensor channel, coupling to the delta-meson and meson mixing. In contrast with the results of other authors, we find that the neutral-current process is not sensitive to the strength g' of the residual contact interaction. As a consequence, it is found that RPA corrections with respect to the mean-field approximation amount to only 10% to 15% at high density.
14718218
Nucleon–nucleon effective potential in dense matter including rho-meson exchange
Abstract We obtain the RPA summed one-meson exchange potential between nucleons in symmetric nuclear matter at zero temperature, from a model which includes ρ , σ , ω and π mesons. The behavior of rho mesons inside the medium is first discussed using different schemes to extract a finite contribution from the vacuum polarization. These schemes give qualitatively different results for the in-medium rho mass. The results are discussed in connection with the nonrenormalizability of the model. We next study the modified potential as density increases. In the intermediate-distance range, it is qualitatively modified by matter and vacuum effects. In the long-distance range ( r >2 fm), one observes the presence of oscillations, which are not present in free space. Features on this distance range are insensitive to the renormalization scheme.
119425946
Direct URCA process in neutron stars with strong magnetic fields
We calculate the emissivity for the direct URCA process in strongly magnetized, degenerate matter in neutron stars, under β-equilibrium. We show that, if the magnetic field is large enough for protons and electrons to be confined to their ground Landau levels, the field-free threshold condition on proton concentration no longer holds, and direct URCA reactions are open for an arbitrary proton concentration. Direct URCA process leads to an early phase of fast neutron star cooling. This circumstance allows us to constrain the initial magnetic field inside observed pulsars.
118474
Spin foam quantization and anomalies
The most common spin foam models of gravity are widely believed to be discrete path integral quantizations of the Plebanski action. However, their derivation in present formulations is incomplete and lower dimensional simplex amplitudes are left open to choice. Since their large-spin behavior determines the convergence properties of the state-sum, this gap has to be closed before any reliable conclusion about finiteness can be reached. It is shown that these amplitudes are directly related to the path integral measure and can in principle be derived from it, requiring detailed knowledge of the constraint algebra and gauge fixing. In a related manner, minimal requirements of background independence provide non trivial restrictions on the form of an anomaly free measure. Many models in the literature do not satisfy these requirements. A simple model satisfying the above consistency requirements is presented which can be thought of as a spin foam quantization of the Husain–Kuchař model.
118582103
Rare B Decays Potential of SuperB
The study of rare B-decays at SuperB provides unique opportunities to understand the Standard Model and constrain new physics. It is discussed the new physics potential of the B -> K nu nu_bar and B -> K^{\ast} nu nu_bar system from the proposed SuperB experiment with 75ab-1 of data (5 nominal years of data taking).
33010210
Spin foam model for Lorentzian general relativity
We present a spin foam formulation of Lorentzian quantum general relativity. The theory is based on a simple generalization of a Euclidean model defined in terms of a field theory over a group. Its vertex amplitude turns out to be the one recently introduced by Barrett and Crane. As in the case of its Euclidean relatives, the model fully implements the desired sum over 2-complexes which encodes the local degrees of freedom of the theory.
119281747
Regular isolated black holes
We review a recently introduced1 approach to study spacetimes which contain an isolated black hole. We allow for gravitational radiation to fall through the event horizon and/or to be radiated at infinity. The crucial idea in our setting is the introduction of physical coordinates that have the meaning of being null hypersurfaces near the horizon and in a neighborhood of future null infinity. These spacetimes have remarkable properties, as for example a generalized notion of surface gravity κH.
123007558
Spin foam quantization of SO(4) Plebanski's action
The goal of this work is two-fold. In the first part of this paper we regard classical Plebanski's action as a BF action supplemented by constraints. We introduce a spin foam model for Riemannian general relativity by systematically implementing these constraints as restrictions on paths in the state-sum of the BF theory. The spin foam model obtained is precisely the Barrett-Crane model. This provides a clear-cut connection of the model with a simplicial action. 
In the second part of the paper we study the quantization of the effective action corresponding to the degenerate sectors of Plebanski's theory and obtain a very simple spin foam model. This model turns out to be precisely the one introduced by De Pietri et al. as an alternative to the one proposed by Barrett and Crane.