Search for semiclassical-gravity effects in relativistic stars

We discuss the possible influence of gravity in the neutronization process, $p^+ e^- \to n \nu_e$, which is particularly important as a cooling mechanism of neutron stars. Our approach is semiclassical in the sense that leptonic fields are quantized on a classical background spacetime, while neutrons and protons are treated as excited and unexcited nucleon states, respectively. We expect gravity to have some influence wherever the energy content carried by the in-state is barely above the neutron mass. In this case the emitted neutrinos would be soft enough to have a wavelength of the same order as the space curvature radius.Comment: 10 pages (REVTEX

Decay of protons and neutrons induced by acceleration

We investigate the decay of accelerated protons and neutrons. Calculations are carried out in the inertial and coaccelerated frames. Particle interpretation of these processes are quite different in each frame but the decay rates are verified to agree in both cases. For sake of simplicity our calculations are performed in a two-dimensional spacetime since our conclusions are not conceptually affected by this.Comment: 18 pages (REVTEX), 3 figure

Quantum versus classical instability of scalar fields in curved backgrounds

General-relativistic stable spacetimes can be made unstable under the presence of certain nonminimally coupled free scalar fields. In this paper, we analyze the evolution of linear scalar-field perturbations in spherically symmetric spacetimes and compare the classical stability analysis with a recently discussed quantum field one. In particular, it is shown that vacuum fluctuations lead to natural seeds for the unstable phase, whereas in the classical framework the presence of such seeds in the initial conditions must be assumed.Comment: 5 pages, 1 figure; condensed and revised version matching published on

Instability of nonminimally coupled scalar fields in the spacetime of slowly rotating compact objects

Nonminimally coupled free scalar fields may be unstable in the spacetime of compact objects. Such instability can be triggered by classical seeds or, more simply, by quantum fluctuations giving rise to the so-called {\em vacuum awakening effect}. Here, we investigate how the parameter space which characterizes the instability is affected when the object gains some rotation. For this purpose, we focus on the stability analysis of nonminimally coupled scalar fields in the spacetime of slowly spinning matter shells.Comment: 11 pages, 6 figure

Cosmological Acceleration Through Transition to Constant Scalar Curvature

As shown by Parker and Raval, quantum field theory in curved spacetime gives a possible mechanism for explaining the observed recent acceleration of the universe. This mechanism, which differs in its dynamics from quintessence models, causes the universe to make a transition to an accelerating expansion in which the scalar curvature, R, of spacetime remains constant. This transition occurs despite the fact that we set the renormalized cosmological constant to zero. We show that this model agrees very well with the current observed type-Ia supernova (SNe-Ia) data. There are no free parameters in this fit, as the relevant observables are determined independently by means of the current cosmic microwave background radiation (CMBR) data. We also give the predicted curves for number count tests and for the ratio, w(z), of the dark energy pressure to its density, as well as for dw(z)/dz versus w(z). These curves differ significantly from those obtained from a cosmological constant, and will be tested by planned future observations.Comment: 31 pages, 7 figures; to appear in ApJ. Corrected numerical results; described quantum basis of theory; 18 references added; 2 figures adde

Free massive particles with total energy E < mc^2 in curved spacetimes

We analyze free elementary particles with rest mass $m$ and total energy $E < m c^2$ in the Rindler wedge, outside Reissner-Nordstrom black holes and in the spacetime of relativistic (and non-relativistic) stars, and use Unruh-DeWitt-like detectors to calculate the associated particle detection rate in each case. The (mean) particle position is identified with the spatial average of the excitation probability of the detectors, which are supposed to cover the whole space. Our results are shown to be in harmony with General Relativity classical predictions. Eventually we reconcile our conclusions with Earth-based experiments which are in good agreement with $E \geq m c^2$.Comment: 12 pages (REVTEX), 12 figure

Awaking the vacuum with spheroidal shells

It has been shown that well-behaved spacetimes may induce the vacuum fluctuations of some nonminimally coupled free scalar fields to go through a phase of exponential growth. Here, we discuss this mechanism in the context of spheroidal thin shells emphasizing the consequences of deviations from spherical symmetry.Comment: 10 pages, 7 figures. Minor changes, version published on Phys. Rev.