14359365
Random phase approximation to neutrino energy losses from a relativistic electron-positron plasma
The process of $\nu \bar{\nu}$ radiation from a relativistic plasma of electrons and positrons is studied within the Random Phase Approximation.
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.
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.
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.
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.
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.
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.
115931245
Rare Decays with Missing Energy at SuperB
The study of rare B-decays at SuperB provides unique opportunities to understand the Standard Model and to constrain new physics. It is discussed the new physics potential of the B -> K\nu\nu and B -> K^*\nu\nu system from the proposed SuperB experiment with 75ab-1 of data (5 nominal years of data taking).
13891330
Spin foam models for quantum gravity
In this topical review, we review the present status of the spin foam formulation of non-perturbative (background-independent) quantum gravity. The topical review is divided into two parts. In the first part, we present a general introduction to the main ideas emphasizing their motivation from various perspectives. Riemannian three-dimensional gravity is used as a simple example to illustrate conceptual issues and the main goals of the approach. The main features of the various existing models for four-dimensional gravity are also presented here. We conclude with a discussion of important questions to be addressed in four dimensions (gauge invariance, discretization independence, etc). In the second part, we concentrate on the definition of the Barrett–Crane model. We present the main results obtained in this framework from a critical perspective. Finally, we review the combinatorial formulation of spin foam models based on the dual group field theory technology. We present the Barrett–Crane model in this framework and review the finiteness results obtained for both its Riemannian and its Lorentzian variants.
10753672
Energy and angular momentum radiated for non-head-on binary black hole collisions
We investigate the possible total radiated energy produced by a binary black hole system containing nonvanishing total angular momentum. For the scenarios considered we find that the total radiated energy does not exceed $1%.$ Additionally we explore the gravitational radiation field and the variation of angular momentum in the process. After the formation of the final black hole, the model uses the Robinson-Trautman (RT) spacetimes as background. The evolution of perturbed RT geometries is carried out numerically.
116396494
Status, open problems and prospects of the decay B^+ -> l^+ nu_l
The study of rare B-decays at SuperB provides unique opportunities to understand the Standard Model and constrain new physics. We discuss the new physics potential of the leptonic B^+ -> l^+ nu_l decays from the proposed SuperB experiment with 75ab-1 of data (5 nominal years of data taking).