62 research outputs found
Mass of perfect fluid black shells
The spherically symmetric singular perfect fluid shells are considered for
the case of their radii being equal to the event horizon (the black shells). We
study their observable masses, depending at least on the three parameters,
viz., the square speed of sound in the shell, instantaneous radial velocity of
the shell at a moment when it reaches the horizon, and integration constant
related to surface mass density. We discuss the features of black shells
depending on an equation of state.Comment: 1 figure, LaTeX; final version + FA
The effect of very low energy solar neutrinos on the MSW mechanism
We study some implications on standard matter oscillations of solar neutrinos
induced by a background of extremely low energy thermal neutrinos trapped
inside the Sun by means of coherent refractive interactions. Possible
experimental tests are envisaged and current data on solar neutrinos detected
at Earth are briefly discussed.Comment: RevTex4, 4 pages, no figure
Fermion and Anti-Fermion Effective Masses in High Temperature Gauge Theories in -Asymmetric Background
We calculate the splitting between fermion and anti-fermion effective masses
in high temperature gauge theories in the presence of a non-vanishing chemical
potential due to the -asymmetric fermionic background. In particular we
consider the case of left-handed leptons in the theory when
the temperature is above GeV and the gauge symmetry is restored.Comment: 13 pages, TIPAC-93001
Radiative transitions of high energy neutrino in dense matter
The quantum theory of the ``spin light'' (electromagnetic radiation emitted
by a massive neutrino propagating in dense matter due to the weak interaction
of a neutrino with background fermions) is developed. In contrast to the
Cherenkov radiation, this effect does not disappear even if the medium
refractive index is assumed to be equal to unity. The formulas for the
transition rate and the total radiation power are obtained. It is found out
that radiation of photons is possible only when the sign of the particle
helicity is opposite to that of the effective potential describing the
interaction of a neutrino (antineutrino) with the background medium. Due to the
radiative self-polarization the radiating particle can change its helicity. As
a result, the active left-handed polarized neutrino (right-handed polarized
antineutrino) converting to the state with inverse helicity can become
practically ``sterile''. Since the sign of the effective potential depends on
the neutrino flavor and the matter structure, the ``spin light'' can change a
ratio of active neutrinos of different flavors. In the ultra relativistic
approach, the radiated photons averaged energy is equal to one third of the
initial neutrino energy, and two thirds of the energy are carried out by the
final ``sterile'' neutrinos. This fact can be important for the understanding
of the ``dark matter'' formation mechanism on the early stages of evolution of
the Universe.Comment: 7 pages, latex, one misprint in eq. 12 correcte
Neutrino self-energy and dispersion in a medium with magnetic field
We calculate the one-loop thermal self-energy of a neutrino in a constant and
homogeneous magnetic field to all orders in the magnetic field strength using
Schwinger's proper time method. We obtain the dispersion relation under various
conditions.Comment: 17 pp, RevTeX, one figur
Electromagnetic duality in general relativity
By resolving the Riemann curvature relative to a unit timelike vector into
electric and magnetic parts, we consider duality relations analogous to the
electromagnetic theory. It turns out that the duality symmetry of the Einstein
action implies the Einstein vacuum equation without the cosmological term. The
vacuum equation is invariant under interchange of active and passive electric
parts giving rise to the same vacuum solutions but the gravitational constant
changes sign. Further by modifying the equation it is possible to construct
interesting dual solutions to vacuum as well as to flat spacetimes.Comment: 18 pages, LaTEX versio
Bimodal Coherence in Dense Self-Interacting Neutrino Gases
Analytical solutions are obtained to the nonlinear equations describing
neutrino oscillations when explicit neutrino-antineutrino asymmetries are
present. Such a system occurs in the early Universe if neutrinos have a
non-zero chemical potential. Solutions to the equations lead to a new type of
coherent behavior governed by two modes. These bimodal solutions provide new
insights into dense neutrino gases and into neutrino oscillations in the early
Universe, thereby allowing one to surmise the flavor behavior of neutrinos with
a non-zero chemical potential.Comment: 21 pages in Latex, 11 figures packaged in one Postscript file.
Figures also obtainable as 20 gif files at
http://www.sci.ccny.cuny.edu/~ssamuel/bimodalfigs.html Revision on 4/19/96
was to pack the figures more sensibly. This paper is to appear in a May issue
of Phys. Rev.
On the observability of the neutrino charge radius
It is shown that the probe-independent charge radius of the neutrino is a
physical observable; as such, it may be extracted from experiment, at least in
principle. This is accomplished by expressing a set of experimental
neutrino-electron cross-sections in terms of the finite charge radius and two
additional gauge- and renormalization-group-invariant quantities, corresponding
to the electroweak effective charge and mixing angle.Comment: 10 pages, 1 figure; a typo in Eq.1 corrected, some comments adde
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.Comment: 21 pages, Latex, uses axodraw.sty (typos corrected; two references
added. To appear in Phys. Rev. D
On the indistinguishibility of Majorana- from Dirac-neutrino propagation in a stellar medium
We study, in the framework of the Standard Model, the propagation of (pure)
Majorana neutrinos in a typical stellar medium and show that Majorana neutrino
matter oscillations are completely indistinguishable from Dirac ones, even if
in the case of no family mixing Majorana neutrinos can be distinguished from
Dirac ones in the non-relativistic limit. Moreover, if CP violation is present,
an effective phase arises in the effective mixing matrix but, due to a symmetry
of the Majorana fields, this cannot be univocally determinedComment: 11 pages, Latex, 2 figures available upon request; to be published in
Il Nuovo Cimento
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