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.
118051961
Incompressibility of hot nuclear matter, general relativistic stellar collapse and shock propagation
Research into the effect of considering two extreme kinds of Skyrme-type nuclear interactions on the outcome of stellar core collapsing models have been carried out. Particular attention has been payed to dissociation effects generated by the shock. Neutrinos tansport is included via a Multigroup Trapping Scheme
119617684
Beta decay studies with the total absorption technique: Past, present and future
Measurements of beta decay reduced transition probabilities are particularly relevant in nuclei far from the stability line. It has been demonstrated that a proper measurement of this quantity requires the use of the total absorption technique, which has become a reliable tool in recent years, thanks to the increased efficiency of the associated spectrometers and the development of new analysis techniques. In this paper, we present a brief history of the past and present use of these detectors and how they might be developed in the future.
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.
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.
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.
118619230
Quantization of the Jackiw-Teitelboim model
We study the phase space structure of the Jackiw-Teitelboim model in its connection variables formulation where the gauge group of the field theory is given by local SL(2,R)[or SU(2) for the Euclidean model], i.e. the de Sitter group in two dimensions. In order to make the connection with two-dimensional gravity explicit, a partial gauge fixing of the de Sitter symmetry can be introduced that reduces it to space-time diffeomorphisms. This can be done in different ways. Having no local physical degrees of freedom, the reduced phase space of the model is finite dimensional. The simplicity of this gauge field theory allows for studying different avenues for quantization, which may use various (partial) gauge fixings. We show that reduction and quantization are noncommuting operations: the representation of basic variables as operators in a Hilbert space depends on the order chosen for the latter. Moreover, a representation that is natural in one case may not even be available in the other leading to inequivalent quantum theories.
118820970
Multiple-Event Probability in General-Relativistic Quantum Mechanics
We discuss the definition of quantum probability in the context of “timeless” general–relativistic quantum mechanics. In particular, we study the probability of sequences of events, or multi-event probability. In conventional quantum mechanics this can be obtained by means of the “wave function collapse” algorithm. We first point out certain difficulties of some natural definitions of multi-event probability, including the conditional probability widely considered in the literature. We then observe that multi-event probability can be reduced to single-event probability, by taking into account the quantum nature of the measuring apparatus. In fact, by exploiting the vonNeumann freedom of moving the quantum/classical boundary, one can always trade a sequence of non-commuting quantum measurements at different times, with an ensemble of simultaneous commuting measurements on the joint system+apparatus system. This observation permits a formulation of quantum theory based only on single-event probability, where the results of the “wave function collapse” algorithm can nevertheless be recovered. The discussion bears also on the nature of the quantum collapse.
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).
118421024
Two-dimensional topological field theories coupled to four-dimensional BF theory
Four-dimensional BF theory admits a natural coupling to extended sources supported on two-dimensional surfaces or string world sheets. Solutions of the theory are in one to one correspondence with solutions of Einstein equations with distributional matter (cosmic strings). We study new (topological field) theories that can be constructed by adding extra degrees of freedom to the two-dimensional world sheet. We show how two-dimensional Yang-Mills degrees of freedom can be added on the world sheet, producing in this way, an interactive (topological) theory of Yang-Mills fields with BF fields in four dimensions. We also show how a world sheet tetrad can be naturally added. As in the previous case the set of solutions of these theories are contained in the set of solutions of Einstein's equations if one allows distributional matter supported on two-dimensional surfaces. These theories are argued to be exactly quantizable. In the context of quantum gravity, one important motivation to study these models is to explore the possibility of constructing a background-independent quantum field theory where local degrees of freedom at low energies arise from global topological (world sheet) degrees of freedom at the fundamental level.
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.