arXiv subjects

Jose F. Nieves

Publications and source records attributed to Jose F. Nieves.

32 records · Page 2Linked to original sources

arXiv1998

Photogravitational processes

In the linearized theory of gravity coupled to the electromagnetic field, we calculate the cross sections of two processes in which both the gravitational and electromagnetic interactions play a role. Those processes, in which a graviton is produced in the final state, are: (a) the photoproduction of gravitons off electrons and (b) the production of a photon and a graviton from electron-positron annihilation. The motivation and outlook for these calculations are discussed.

hep-ph↗

arXiv1998

Gravitational coupling of neutrinos in a medium

In a medium that contains electrons but not the other charged leptons, such as normal matter, the gravitational interactions of neutrinos are not the same for all the neutrino flavors. We calculate the leading order matter-induced corrections to the neutrino gravitational interactions in such a medium and consider some of their physical implications.

hep-ph↗

arXiv1997

Optical Activity of a Neutrino Gas

For photons that propagate through a gas of neutrinos with a non-zero chemical potential, the left-handed and right-handed polarization modes acquire different dispersion relations. This is due to the CP and CPT-odd terms induced by such a background on the photon self-energy. We present a detailed calculation of this effect, which does not depend on any physical assumptions beyond those of the standard electroweak model. Some possible cosmological and astrophysical implications of our results are considered in several contexts, including the recent discussions regarding the rotation of the plane of polarization of electromagnetic waves over cosmological distances.

hep-ph↗

arXiv1997

Nucleon effects on the photon dispersion relations in matter

We calculate the nucleon contribution to the photon self-energy in a plasma, including the effect of the anomalous magnetic moment of the nucleons. General formulas for the transverse and longitudinal components of the self-energy are obtained and we give explicit results in various limits of physical interest. The formulas are relevant for the study of the photon dispersion relations and the dynamical susceptibility in a nuclear medium such as the core of a supernova, and has implications with regard to the recent suggestion that the Cerenkov process $ν\to νγ$ can take place in such a system.

hep-ph↗

arXiv1997

Nucleon contribution to the neutrino electromagnetic vertex in matter

We calculate the nucleon contribution to the electromagnetic vertex of a neutrino in a background of particles, including the effect of the anomalous magnetic moment of the nucleons. Explicit formulas for the form factors are given in various physical limits of practical interest. Several applications of the results are mentioned, including the effect of an external magnetic field on the dispersion relation of a neutrino in matter.

hep-ph↗

arXiv1997

Radiative neutrino decay in hot media

We calculate the rate for the radiative neutrino decay in a thermal background of electrons and photons, taking into account the effect of the stimulated emission of photons in the thermal bath. We show that the rate is enhanced by a large factor relative to the rate for the corresponding process in the vacuum.

hep-ph↗

arXiv1996

Electromagnetic properties of neutral and charged spin 1 particles

The structure of the electromagnetic vertex of spin-1 particles are studied in a general way, for the diagonal as well as the off-diagonal couplings. In each case, we consider in detail the consequences of gauge invariance and the space-time discrete symmetries, paying particular attention to the implications for the couplings of the photon to neutral gauge bosons, which arise in higher orders. Several general results concerning the static electromagnetic properties of neutral bosons are derived, analogous to the results that are well known in the case of neutral spin-1/2 particles.

hep-ph↗

arXiv1996

Chirality-preserving neutrino oscillations in an external magnetic field

Neutrinos propagating in matter acquire an effective electromagnetic vertex induced by their weak interactions with the charged particles in the background. In the presence of an external magnetic field the induced vertex affects the flavor transformations of mixed neutrinos in a way that, in contrast to the oscillations driven by an intrinsic magnetic moment interaction, preserve chirality. We derive the evolution equation for this case and discuss some of the physical consequences in environments such as a supernova. For small values of the square mass difference the resonance for neutrinos and antineutrinos occur within regions which are close. In that case, the resonance condition becomes independent of the vacuum parameters and is approximately the same for both.

hep-ph↗

arXiv1995

Cherenkov radiation by massless neutrinos

Due to their weak interactions, neutrinos can polarize a medium and acquire an induced charge. We consider the Cherenkov radiation emitted by neutrinos due to their effective electromagnetic interactions as they pass through a polarizable medium. The effect exists even for massless, chiral neutrinos, where no physics beyond the standard model needs to be assumed.

hep-ph↗

arXiv1995

Remarks on the Coulomb and Covariant Gauges in Finite Temperature QED

We compare the use of the Coulomb gauge in finite temperature QED with a recently proposed prescription for covariant gauges, in which only the transverse photon degrees of freedom are thermalized. Using the Landau rule as a guide, we clarify the relation between the retarded electron self-energy and the elements of the self-energy matrix in the real-time formulation of . The general results are illustrated by means of the one-loop expressions for the electron self-energy in a QED plasma.

hep-ph↗

arXiv1995

Damping Rate of a Fermion in a Medium

We examine the relation between the damping rate of a massless, chiral fermion that propagates in a medium, and the rate $Γ$ of approach to equilibrium. It is proven that these quantities are equal, by showing that they are given by the same formula in terms of the imaginary part of the self-energy evaluated at the energy of the propagating fermion mode. This result is valid provided $Γ$ is defined by using the appropriate wave functions of the mode.

hep-ph↗

arXiv1995

Thermal Self-Energies at Zero Momentum

In general the zero momentum limit of thermal self-energies calculated in perturbation theory depends on the order in which the time and the space components of the momentum are taken to zero. We show that this is an artifact of the perturbative calculation, and in fact the non-analyticity of the one-loop self-energy disappears when it is calculated with improved vertices and/or improved propagators that incorporate the imaginary part of the self-energy.

hep-ph↗

arXiv1994

The Third Electromagnetic Constant of an Isotropic Medium:

In addition to the dielectric and magnetic permeability constants, another constant is generally needed to describe the electrodynamic properties of a linear isotropic medium. We discuss why the need for the third constant arises and what sort of physical situations can give rise to a non-zero value for it. This additional constant, which we call the {\em ``Activity Constant''} and denote by $ζ$, can explain optical activity and other phenomena from a purely macroscopic and phenomenological point of view.

hep-ph↗

arXiv1993

Induced Charge of Neutrinos in a Medium

Neutrinos can polarize a medium due to their weak interaction. This can manifest itself as an effective induced charge of the neutrino. We show how it is related to the Debye screening length in a plasma, first using the results of the 1-loop calculation of the neutrino electromagnetic vertex and then in general to all orders in $e$ and to leading order in the Fermi coupling. We also discuss how the results are modified if the neutrinos have mass -- either Dirac or Majorana type.

hep-ph↗