5,862 research outputs found
Theoretical Constraints on the Vacuum Oscillation Solution to the Solar Neutrino Problem
The vacuum oscillation (VO) solution to the solar anomaly requires an
extremely small neutrino mass splitting, Delta m^2_{sol}\leq 10^{-10} eV^2. We
study under which circumstances this small splitting (whatever its origin) is
or is not spoiled by radiative corrections. The results depend dramatically on
the type of neutrino spectrum. If m_1^2 \sim m_2^2 \geq m_3^2, radiative
corrections always induce too large mass splittings. Moreover, if m_1 and m_2
have equal signs, the solar mixing angle is driven by the renormalization group
evolution to very small values, incompatible with the VO scenario (however, the
results could be consistent with the small-angle MSW scenario). If m_1 and m_2
have opposite signs, the results are analogous, except for some small (though
interesting) windows in which the VO solution may be natural with moderate
fine-tuning. Finally, for a hierarchical spectrum of neutrinos, m_1^2 << m_2^2
<< m_3^2, radiative corrections are not dangerous, and therefore this scenario
is the only plausible one for the VO solution.Comment: 13 pages, LaTeX, 3 ps figures (psfig.sty
Model Independent Electromagnetic corrections in hadronic decays
The long distance correction to the total decay width of the decay is calculated in a model independent approach where a
discrimination of photons in the Bremmstrahlung process is assumed. This
correction is completely free of UV and IR singularities and moreover, it
satisfies electromagnetic gauge invariance. The result of this work can be
applied on the tau decays:
PAMELA's cosmic positron from decaying LSP in SO(10) SUSY GUT
We propose two viable scenarios explaining the recent observations on cosmic
positron excess. In both scenarios, the present relic density in the Universe
is assumed to be still supported by thermally produced WIMP or LSP (\chi). One
of the scenarios is based on two dark matter (DM) components (\chi,X) scenario,
and the other is on SO(10) SUSY GUT. In the two DM components scenario,
extremely small amount of non-thermally produced meta-stable DM component
[O(10^{-10}) < n_X /n_\chi] explains the cosmic positron excess. In the SO(10)
model, extremely small R-parity violation for LSP decay to e^\pm is naturally
achieved with a non-zero VEV of the superpartner of one right-handed neutrino
(\tilde{\nu}^c) and a global symmetry.Comment: 6 pages, Talks presented in PASCOS, SUSY, and COSMO/CosPA in 201
Stability Analysis of a Bose-Einstein Condensate Trapped in a Generic Potential
We investigate the dynamical behavior of the Gross-Pitaevskii equation for a
Bose-Einstein condensate trapped in a spherical power law potential restricted
to the repulsive case, from the dynamical system formalism point of view. A
five-dimensional dynamical system is found (due the symmetry of the
Gross-Pitaevskii equation interacting with a potential), where the Thomas-Fermi
approximation constrains the parameter space of solutions. We show that for
values of the power law exponent equal or smaller than 2 the system seems to be
stable. However, when the corresponding exponent is bigger than 2, the
instability of the system grows when the power law exponent grows, indicating
that large values of the aforementioned parameter can be related to a loss in
the number of particles from the condensed state. This fact can be used also to
show that the stability conditions of the condensate are highly sensitive to
the exponent associated with the external potential.Comment: 9 pages, 2 figure
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