Generational Mass Splitting of Neutrinos in High Temperature SU(2)L⊗U(1)SU(2)_{\scriptscriptstyle{L}}\otimes U(1) Gauge Theory

We calculate the generational mass splitting of neutrinos in high temperature $SU(2)_{\scriptscriptstyle{L}}\otimes U(1)$ gauge theory when the temperature is above $250$ GeV and the gauge symmetry is restored. We consider the case of neutrinos that are massless at tree level as well as the case of neutrinos with tree-level mass and large mixing.Comment: 12 Pages, JHU-TIPAC-940008/INFNCA-TH-94-

Heavy sterile neutrinos - what they can be and what they can't

We review current astrophysical bounds on MeV sterile neutrinos, and then we discuss why a sterile keV neutrino is a natural warm dark matter candidate.Comment: 4 pages, 2 figures, talk given at Frontiers in Particle Astrophysics and Cosmology held at San Feli

Neutrino oscillations and Big Bang Nucleosynthesis

We outline how relic neutrino asymmetries may be generated in the early universe via active-sterile neutrino oscillations. We discuss possible consequences for big bang nucleosynthesis, within the context of a particular 4-neutrino model.Comment: 6 pages. Talk given at NuFACT'01 workshop, Tsukuba, Japan (May 2001

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

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

Fermion and Anti-Fermion Effective Masses in High Temperature Gauge Theories in CPCP-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 $CP$-asymmetric fermionic background. In particular we consider the case of left-handed leptons in the $SU(2)\otimes U(1)$ theory when the temperature is above $250$ GeV and the gauge symmetry is restored.Comment: 13 pages, TIPAC-93001

Nonequilibrium Neutrino Oscillations in the Early Universe with an Inverted Neutrino-Mass Hierarchy

The annihilation of electron-positron pairs around one second after the big bang distorts the Fermi-Dirac spectrum of neutrino energies. We determine the distortions assuming neutrino mixing with an inverted neutrino-mass hierarchy. Nonequilibrium thermodynamics, the Boltzmann equation, and numerical integration are used to achieve the results. The various types of neutrino behavior are established as a function of masses and mixing angles.Comment: 9 pages in Latex with 6 figures (10 postscript files

\nu_\mu<->\nu_\tau vs \nu_\mu<->\nu_s solutions for the atmospheric neutrino problem

The $\nu_\mu \leftrightarrow\nu_\tau$ and $\nu_\mu \leftrightarrow\nu_s$ solutions to the atmospheric neutrino problem are compared with Superkamiokande data. Both the solutions with a large mixing angle seem to be consistent with the data.Comment: 5 pages (uses espcrc2.sty) including 8 figures (uses epsf):contribution to the proceedings of Neutrino 98, Takayama, Japan, 4-9 June, 199

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