495 research outputs found
Gravity induced neutrino-antineutrino oscillation: CPT and lepton number non-conservation under gravity
We introduce a new effect in the neutrino oscillation phase which shows the
neutrino-antineutrino oscillation is possible under gravity even if the rest
masses of the corresponding eigenstates are same. This is due to CPT violation
and possible to demonstrate if the neutrino mass eigenstates are expressed as a
combination of neutrino and antineutrino eigenstates, as of the neutral kaon
system, with the plausible breaking of lepton number conservation. For Majorana
neutrinos, this oscillation is expected to affect significantly the inner edge
of neutrino dominated accretion disks around a compact object by influencing
the neutrino sphere which controls the accretion dynamics, and then the related
type-II supernova evolution and the r-process nucleosynthesis. On the other
hand, in early universe, in presence of various lepton number violating
processes, this oscillation, we argue, might lead to neutrino asymmetry which
resulted baryogenesis from the B-L symmetry by electro-weak sphaleron
processes.Comment: 15 pages; Accepted for publication in Classical and Quantum Gravit
Predictive Power of Strong Coupling in Theories with Large Distance Modified Gravity
We consider theories that modify gravity at cosmological distances, and show
that any such theory must exhibit a strong coupling phenomenon, or else it is
either inconsistent or is already ruled out by the solar system observations.
We show that all the ghost-free theories that modify dynamics of spin-2
graviton on asymptotically flat backgrounds, automatically have this property.
Due to the strong coupling effect, modification of the gravitational force is
source-dependent, and for lighter sources sets in at shorter distances. This
universal feature makes modified gravity theories predictive and potentially
testable not only by cosmological observations, but also by precision
gravitational measurements at scales much shorter than the current cosmological
horizon. We give a simple parametrization of consistent large distance modified
gravity theories and their predicted deviations from the Einsteinian metric
near the gravitating sources.Comment: 12 pages, Latex, to be published in New Journal of Physic
Test of the Equivalence Principle Using a Rotating Torsion Balance
We used a continuously rotating torsion balance instrument to measure the
acceleration difference of beryllium and titanium test bodies towards sources
at a variety of distances. Our result Delta a=(0.6+/-3.1)x10^-15 m/s^2 improves
limits on equivalence-principle violations with ranges from 1 m to infinity by
an order of magnitude. The Eoetvoes parameter is eta=(0.3+/-1.8)x10^-13. By
analyzing our data for accelerations towards the center of the Milky Way we
find equal attractions of Be and Ti towards galactic dark matter, yielding
eta=(-4 +/- 7)x10^-5. Space-fixed differential accelerations in any direction
are limited to less than 8.8x10^-15 m/s^2 with 95% confidence.Comment: 4 pages, 4 figures; accepted for publication in PR
Positron-neutrino correlations in 32Ar and 33Ar Decays: Probes of Scalar weak currents and nuclear isospin mixing
The positron-neutrino correlation in the 0^+ \to 0^+ \beta decay of ^{32}Ar
was measured at ISOLDE by analyzing the effect of lepton recoil on the shape of
the narrow proton group following the superallowed decay. Our result is
consistent with the Standard Model prediction; for vanishing Fierz interference
we find a=0.9989 \pm 0.0052 \pm 0.0036. Our result leads to improved
constraints on scalar weak interactions. The positron-neutrino correlation in
^{33}Ar decay was measured in the same experiment; for vanishing Fierz
interference we find a=0.944 \pm 0.002 \pm 0.003. The ^{32}Ar and ^{33}Ar
correlations, in combination with precision measurements of the half-lives,
superallowed branching ratios and beta endpoint energies, will determine the
isospin impurities of the superallowed transitions. These will provide useful
tests of isospin-violation corrections used in deducing |V_{\rm ud}| which
currently indicates non-unitarity of the KM matrix.Comment: 15 pages, 6 figure
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