246 research outputs found
Resonant Neutrino Spin-Flavor Precession and Supernova Nucleosynthesis and Dynamics
We discuss the effects of resonant spin-flavor precession (RSFP) of Majorana
neutrinos on heavy element nucleosynthesis in neutrino-heated supernova ejecta
and the dynamics of supernovae. In assessing the effects of RSFP, we explicitly
include matter-enhanced (MSW) resonant neutrino flavor conversion effects where
appropriate. We point out that for plausible ranges of neutrino magnetic
moments and proto-neutron star magnetic fields, spin-flavor conversion of
(or ) with a cosmologically significant mass (1--100 eV)
into a light could lead to an enhanced neutron excess in
neutrino-heated supernova ejecta. This could be beneficial for models of
-process nucleosynthesis associated with late-time neutrino-heated ejecta
from supernovae. Similar spin-flavor conversion of neutrinos at earlier epochs
could lead to an increased shock reheating rate and, concomitantly, a larger
supernova explosion energy. We show, however, that such increased neutrino
heating likely will be accompanied by an enhanced neutron excess which could
exacerbate the problem of the overproduction of the neutron number
nuclei in the supernova ejecta from this stage. In all of these scenarios, the
average energy will be increased over those predicted by supernova
models with no neutrino mixings. This may allow the SN1987a data to constrain
RSFP-based schemes.Comment: Latex file, 33 pages including 11 figures, uses psfig.sty, minor
changes about wording and clarification of the text, to be published in Phys.
Rev.
Resonant neutrino spin-flavor precession and supernova shock revival
A new mechanism of supernova shock revival is proposed, which involves
resonant spin--flavor precession of neutrinos with a transition magnetic moment
in the magnetic field of the supernova. The mechanism can be operative in
supernovae for transition magnetic moments as small as provided
the neutrino mass squared difference is in the range . It is shown that this mechanism can increase the
neutrino--induced shock reheating energy by about 60\%.Comment: 16 pages, latex, 2 figures. added few reference
Geophysical constraints on mirror matter within the Earth
We have performed a detailed investigation of geophysical constraints on the
possible admixture of mirror matter inside the Earth. On the basis of the
Preliminary Reference Earth Model (PREM) -- the `Standard Model' of the Earth's
interior -- we have developed a method which allows one to compute changes in
various quantities characterising the Earth (mass, moment of inertia, normal
mode frequencies etc.)due to the presence of mirror matter. As a result we have
been able to obtain for the first time the direct upper bounds on the possible
concentration of the mirror matter in the Earth. In terms of the ratio of the
mirror mass to the Earth mass a conservative upper bound is . We then analysed possible mechanisms (such as lunar and solar tidal
forces, meteorite impacts and earthquakes) of exciting mirror matter
oscillations around the Earth centre. Such oscillations could manifest
themselves through global variations of the gravitational acceleration at the
Earth's surface. We conclude that such variations are too small to be observed.
Our results are valid for other types of hypothetical matter coupled to
ordinary matter by gravitation only (e.g. the shadow matter of superstring
theories).Comment: 25 pages, in RevTeX, to appear in Phys.Rev.
Paradoxes of neutrino oscillations
Despite the theory of neutrino oscillations being rather old, some of its
basic issues are still being debated in the literature. We discuss, in the
framework of the wave packet approach, a number of such issues, including the
relevance of the "same energy" and "same momentum" assumptions, the role of
quantum-mechanical uncertainty relations in neutrino oscillations, the
dependence of the production/detection and propagation coherence conditions
that ensure the observability of neutrino oscillations on neutrino energy and
momentum uncertainties, the question of (in)dependence of the oscillation
probabilities on the neutrino production and detection processes, the
applicability limits of the stationary source approximation, and Lorentz
invariance of the oscillation probability. We also develop a novel approach to
calculation of the oscillation probability in the wave packet picture, based on
the summation/integration conventions different from the standard one, which
gives a new insight into the oscillation phenomenology. We discuss a number of
apparently paradoxical features of the theory of neutrino oscillations.Comment: LaTeX, 45 pages, no figures. v2: references adde
Leptogenesis via Collisions: Leaking Lepton Number to the Hidden Sector
We propose a lepto-baryogenesis mechanism in which the non-zero B-L of the
universe is produced in out-of-equilibrium, lepton number and CP violating
scattering processes that convert ordinary particles into particles of some
hidden sector. In particular, we consider the processes mediated by the heavy Majorana neutrinos of the seesaw
mechanism, where and are ordinary lepton and Higgs doublets and
, their hidden counterparts. Such a leptogenesis mechanism is
effective even if the reheating temperature is much smaller than the heavy
neutrino masses. In particular, it can be as low as GeV.Comment: 4 pages, revtex, 2 figures; as to appear in PRL, supplemented with an
additional remar
Mirror Matter as Self Interacting Dark Matter
It has been argued that the observed core density profile of galaxies is
inconsistent with having a dark matter particle that is collisionless and
alternative dark matter candidates which are self interacting may explain
observations better. One new class of self interacting dark matter that has
been proposed in the context mirror universe models of particle physics is the
mirror hydrogen atom whose stability is guaranteed by the conservation of
mirror baryon number. We show that the effective transport cross section for
mirror hydrogen atoms, has the right order of magnitude for solving the
``cuspy'' halo problem. Furthermore, the suppression of dissipation effects for
mirror atoms due to higher mirror mass scale prevents the mirror halo matter
from collapsing into a disk strengthening the argument for mirror matter as
galactic dark matter.Comment: 6 pages; some references adde
Exotic Smooth Structures on Small 4-Manifolds
Let M be either CP^2#3CP^2bar or 3CP^2#5CP^2bar. We construct the first
example of a simply-connected symplectic 4-manifold that is homeomorphic but
not diffeomorphic to M.Comment: 11 page
- …