11,456 research outputs found
Gravitational helicity interaction
For gravitational deflections of massless particles of given helicity from a
classical rotating body, we describe the general relativity corrections to the
geometric optics approximation. We compute the corresponding scattering cross
sections for neutrinos, photons and gravitons to lowest order in the
gravitational coupling constant. We find that the helicity coupling to
spacetime geometry modifies the ray deflection formula of the geometric optics,
so that rays of different helicity are deflected by different amounts. We also
discuss the validity range of the Born approximation.Comment: 16 pages, 1 figure, to be published in Nuclear Physics
Mutual cosideration of and in supersymmetric SO(10) grand unification
We compare the branching ratios for and
in terms of constraining the parameter space in
supersymmetric SO(10) grand unification models where supersymmetry is broken
softly near the Planck scale by generationally symmetric operators. We observe
two general cases. One with small and the other one with large
having third generation Yukawa coupling unification at the GUT
scale. \newline\indent We show that for small the branching ratio
constraints allow only a smaller region of parameter space for compared
to for gluino mass \alt 500 GeV.
With large , we find acceptable regions of parameter space with
\left|\mu \right|\alt 1 TeV only for . The dominant constraint on
large with parameter space is found to be given by the
branching ratio, while for large with it is found to be given by the branching ratio. In
many of these acceptable regions, we find that the
branching ratio is predicted to be within one order of magnitude of its current
experimental bound. We also show that the usually neglected gluino mediated
diagrams in can not be ignored in some regions of
parameter space, especially for large scenarios when the gluino
mass is near its lower experimental bound.Comment: 14 pages (Latex), 4 PS figs (uuencoded, epsf.tex), slight
modification in text, as to appear in Physics Letters
Role of Long-Range Correlations on the Quenching of Spectroscopic Factors
We consider the proton and neutron quasiparticle orbits around the
closed-shell 56Ni and 48Ca isotopes. It is found that large model spaces
(beyond the capability of shell-model applications) are necessary for
predicting the quenchings of spectroscopic factors.
The particle-vibration coupling is identified as the principal mechanism.
Additional correlations--due to configuration with several particle-hole
excitations--are estimated using shell-model calculations and generate an extra
reduction which is < ~4% for most quasiparticle states. The theoretical
calculations nicely agree with (e,e'p) and heavy ion knock-out experiments.
These results open a new path for a microscopic understanding of the
shell-model.Comment: Minor comments added and typos corrected. Accepted for publication on
Phys. Rev. Let
Effects of an intermediate scale in SUSY grand unification
We discuss the production of lepton flavor violation and EDMs and the
viability of the unification hypothesis in SUSY grand unification with
an intermediate gauge symmetry breaking scale.Comment: 3 pages (Latex, esprc2.sty used), talk given at 4th International
Conference on Supersymmetry (SUSY '96, College Park, MD, May 29 - June 1,
1996
Optical phase coherent timing of the Crab nebula pulsar with Iqueye at the ESO New Technology Telescope
The Crab nebula pulsar was observed in 2009 January and December with a novel
very fast optical photon counter, Iqueye, mounted at the ESO 3.5 m New
Technology Telescope. Thanks to the exquisite quality of the Iqueye data, we
computed accurate phase coherent timing solutions for the two observing runs
and over the entire year 2009. Our statistical uncertainty on the determination
of the phase of the main pulse and the rotational period of the pulsar for
short (a few days) time intervals are s and ~0.5 ps,
respectively. Comparison with the Jodrell Bank radio ephemerides shows that the
optical pulse leads the radio one by ~240 s in January and ~160 s in
December, in agreement with a number of other measurements performed after
1996. A third-order polynomial fit adequately describes the spin-down for the
2009 January plus December optical observations. The phase noise is consistent
with being Gaussian distributed with a dispersion of s in most observations, in agreement with theoretical expectations for
photon noise-induced phase variability.Comment: 10 pages, 5 figures. Accepted for publication in Monthly Notices of
the Royal Astronomical Societ
Neutrino masses and flavor symmetries
The problem of neutrino masses and mixing angles is analysed in a class of
supersymmetric grand unified models, with SO(10) gauge symmetry and global U(2)
flavour symmetry. Adopting the seesaw mechanism for the generation of the
neutrino masses, one obtains a mass matrix for the left-handed neutrinos which
is directly related to the parameters of the charged sector, while the unknown
parameters of the right-handed Majorana mass matrix are inglobed in a single
factor.Comment: 17 pages, 1 eps figure, uses graphicx.sty, LaTeX 2e, to be published
on "Il Nuovo Cimento
QCD Radiative Corrections to the Leptonic Decay Rate of the B_c Meson
The QCD radiative corrections to the leptonic decay rate of the meson
are calculated using the formalism of nonrelativistic QCD (NRQCD) to separate
short-distance and long-distance effects. The decay constant is factored
into a sum of NRQCD matrix elements each multiplied by a short-distance
coefficient. The short-distance coefficient for the leading matrix element is
calculated to order by matching a perturbative calculation in full
QCD with the corresponding perturbative calculation in NRQCD. This
short-distance correction decreases the leptonic decay rate by approximately
.Comment: Changed Eq. 2 to read 1/(8 \pi), put in a missing i M_{B_c} in Eq.
18, and put in a normalisation factor of 2 M_{B_c} in Eq. 19
The History of the Mysterious Eclipses of KH 15D: Asiago Observatory, 1967-1982
We are gathering archival observations to determine the photometric history
of the unique and unexplained eclipses of the pre-main-sequence star KH 15D.
Here we present a light curve from 1967-1982, based on photographic plates from
Asiago Observatory. During this time, the system alternated periodically
between bright and faint states, as observed today. However, the bright state
was 0.9 mag brighter than the modern value, and the fractional variation
between bright and faint states (Delta I = 0.7 mag) was smaller than observed
today (3.5 mag). A possible explanation for these findings is that the system
contains a second star that was previously blended with the eclipsing star, but
is now completely obscured.Comment: Accepted to AJ. 24 pages, 10 figures, 2 tables. v2: Phase error
corrected in figures 8 and 1
Supersymmetry phenomenology beyond the MSSM after 5/fb of LHC data
We briefly review the status of motivated beyond-the-MSSM phenomenology in
the light of the LHC searches to date. In particular, we discuss the conceptual
consequences of the exclusion bounds, of the hint for a Higgs boson at about
125 GeV, and of interpreting the excess of direct CP violation in the charm
sector as a signal of New Physics. We try to go into the various topics in a
compact way while providing a relatively rich list of references, with
particular attention to the most recent developments.Comment: 20 pages + refs. v2: minor modifications, published versio
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