57 research outputs found
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
Long Range Forces from the Cosmological Neutrino Background
The cosmological neutrino background will mediate long range forces between
objects. For a background of temperature T, the potential decreases as 1/r^5
for r >> 1/T and as 1/r for r << 1/T. These forces have large spin-dependent
components. If the neutrino background is nonrelativistic, the long range
forces are enhanced by a factor of the inverse neutrino velocity. These long
range forces may provide a method for observing the cosmological neutrino
background.Comment: 14 pages, LATEX, IUHET-249, IUNTC93-1
Beyond the Small-Angle Approximation For MBR Anisotropy from Seeds
In this paper we give a general expression for the energy shift of massless
particles travelling through the gravitational field of an arbitrary matter
distribution as calculated in the weak field limit in an asymptotically flat
space-time. It is {\it not} assumed that matter is non-relativistic. We
demonstrate the surprising result that if the matter is illuminated by a
uniform brightness background that the brightness pattern observed at a given
point in space-time (modulo a term dependent on the oberver's velocity) depends
only on the matter distribution on the observer's past light-cone. These
results apply directly to the cosmological MBR anisotropy pattern generated in
the immediate vicinity of of an object like a cosmic string or global texture.
We apply these results to cosmic strings, finding a correction to previously
published results for in the small-angle approximation. We also derive the
full-sky anisotropy pattern of a collapsing texture knot.Comment: 23 pages, FERMILAB-Pub-94/047-
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
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
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
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
Effects for atmospheric neutrino experiments from electron neutrino oscillations
The minimal interpretation of the atmospheric neutrino data suggests that the
muon neutrino oscillates into another species with a mixing angle close to the
maximal . In the Exact Parity Symmetric Model, both the muon and
electron neutrinos are expected to be maximally mixed with essentially sterile
partners ( and respectively). We examine the impact of
maximal oscillations on the atmospheric neutrino experiments.
We estimate that maximal oscillations will have effects on
atmospheric neutrino data for . For in this range, a slight but distinctive rise in the
ratio of muon-like to electron-like events is predicted for the low-energy
sample. Furthermore, the ratio of low-energy electron-like events with zenith
angles less than to those with zenith angles greater than
should be greater than 1.Comment: 11 pages, LaTeX, no figure
Neutrino flavor conversion in a neutrino background: single- versus multi-particle description
In the early Universe, or near a supernova core, neutrino flavor evolution
may be affected by coherent neutrino-neutrino scattering. We develop a
microscopic picture of this phenomenon. We show that coherent scattering does
not lead to the formation of entangled states in the neutrino ensemble and
therefore the evolution of the system can always be described by a set of
one-particle equations. We also show that the previously accepted formalism
overcounts the neutrino interaction energy; the correct one-particle evolution
equations for both active-active and active-sterile oscillations contain
additional terms. These additional terms modify the index of refraction of the
neutrino medium, but have no effect on oscillation physics.Comment: 12 pages, 3 figures, minor typos correcte
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.
- …