455 research outputs found
Nonminimal supersymmetric standard model with lepton number violation
We carry out a detailed analysis of the nonminimal supersymmetric standard
model with lepton number violation. The model contains a unique trilinear
lepton number violating term in the superpotential which can give rise to
neutrino masses at the tree level. We search for the gauged discrete symmetries
realized by cyclic groups which preserve the structure of the associated
trilinear superpotential of this model, and which satisfy the constraints of
the anomaly cancellation. The implications of this trilinear lepton number
violating term in the superpotential and the associated soft supersymmetry
breaking term on the phenomenology of the light neutrino masses and mixing is
studied in detail. We evaluate the tree and loop level contributions to the
neutrino mass matrix in this model. We search for possible suppression
mechanism which could explain large hierarchies and maximal mixing angles.Comment: Latex file, 43 pages, 2 figure
Study of a Neutrino Mass Texture Generated in Supergravity with Bilinear R-Parity Violation
We study a particular texture of the neutrino mass matrix generated in
supergravity with bilinear R-Parity violation. The relatively high value of
makes the one-loop contribution to the neutrino mass matrix as
important as the tree-level one. The atmospheric angle is nearly maximal, and
its deviation from maximal mixing is related to the smallness of the ratio
between the solar and atmospheric mass scales. There is also a common origin
for the small values of the solar and reactor angles, but the later is much
smaller due the large mass ratio between the lightest two neutrinos. There is a
high dependence of the neutrino mass differences on the scalar mass and
the gaugino mass , but a smaller one of the mixing angles on the same
sugra parameters. Measurements of branching ratios for the neutralino decays
can give important information on the parameters of the model. There are good
prospects at a future Linear Collider for these measurements, but a more
detailed analysis is necessary for the LHC.Comment: 21 pages, 9 figure
Silica in a Mars analog environment: Ka'u Desert, Kilauea Volcano, Hawaii
Airborne Visible/Near-Infrared Imaging Spectrometer (AVIRIS) data acquired over the Ka'u Desert are atmospherically corrected to ground reflectance and used to identify the mineralogic components of relatively young basaltic materials, including 250–700 and 200–400 year old lava flows, 1971 and 1974 flows, ash deposits, and solfatara incrustations. To provide context, a geologic surface units map is constructed, verified with field observations, and supported by laboratory analyses. AVIRIS spectral end-members are identified in the visible (0.4 to 1.2 μm) and short wave infrared (2.0 to 2.5 μm) wavelength ranges. Nearly all the spectral variability is controlled by the presence of ferrous and ferric iron in such minerals as pyroxene, olivine, hematite, goethite, and poorly crystalline iron oxides or glass. A broad, nearly ubiquitous absorption feature centered at 2.25 μm is attributed to opaline (amorphous, hydrated) silica and is found to correlate spatially with mapped geologic surface units. Laboratory analyses show the silica to be consistently present as a deposited phase, including incrustations downwind from solfatara vents, cementing agent for ash duricrusts, and thin coatings on the youngest lava flow surfaces. A second, Ti-rich upper coating on young flows also influences spectral behavior. This study demonstrates that secondary silica is mobile in the Ka'u Desert on a variety of time scales and spatial domains. The investigation from remote, field, and laboratory perspectives also mimics exploration of Mars using orbital and landed missions, with important implications for spectral characterization of coated basalts and formation of opaline silica in arid, acidic alteration environments
Nucleon decay in gauge unified models with intersecting D6-branes
Baryon number violation is discussed in gauge unified orbifold models of type
II string theory with intersecting Dirichlet branes. We consider setups of
D6-branes which extend along the flat Minkowski space-time directions and wrap
around 3-cycles of the internal 6-d manifold. The discussion is motivated by
the enhancement effect of low energy amplitudes anticipated for M-theory and
type II string theory models with matter modes localized at points of the
internal manifold. The conformal field theory formalism is used to evaluate the
open string amplitudes at tree level. We study the single baryon number
violating processes of dimension 6 and 5, involving four quarks and leptons and
in supersymmetry models, two pairs of matter fermions and superpartner
sfermions. The higher order processes associated with the baryon number
violating operators of dimension 7 and 9 are also examined, but in a
qualitative way. We discuss the low energy representation of string theory
amplitudes in terms of infinite series of poles associated to exchange of
string Regge resonance and compactification modes. The comparison of string
amplitudes with the equivalent field theory amplitudes is first studied in the
large compactification radius limit. Proceeding next to the finite
compactification radius case, we present a numerical study of the ratio of
string to field theory amplitudes based on semi-realistic gauge unified
non-supersymmetric and supersymmetric models employing the Z3 and Z2xZ2
orbifolds. We find a moderate enhancement of string amplitudes which becomes
manifest in the regime where the gauge symmetry breaking mass parameter exceeds
the compactification mass parameter, corresponding to a gauge unification in a
seven dimensional space-time.Comment: 63 pages revtex4. 8 postscript figures. 4 tables. Subsection II.B
revised. Several new references added. To appear in Physical Review
From the Bethe-Salpeter equation to non-relativistic approaches with effective two-body interactions
It is known that binding energies calculated from the Bethe-Salpeter equation
in ladder approximation can be reasonably well accounted for by an
energy-dependent interaction, at least for the lowest states. It is also known
that none of these approaches gives results close to what is obtained by using
the same interaction in the so-called instantaneous approximation, which is
often employed in non-relativistic calculations. However, a recently proposed
effective interaction was shown to account for the main features of both the
Bethe-Salpeter equation and the energy-dependent approach. In the present work,
a detailed comparison of these different methods for calculating binding
energies of a two-particle system is made. Some improvement, previously
incorporated for the zero-mass boson case in the derivation of the effective
interaction, is also employed for massive bosons. The constituent particles are
taken to be distinguishable and spinless. Different masses of the exchanged
boson (including a zero mass) as well as states with different angular momenta
are considered and the contribution of the crossed two-boson exchange diagram
is discussed. With this respect, the role played by the charge of the exchanged
boson is emphasized. It is shown that the main difference between the
Bethe-Salpeter results and the instantaneous approximation ones are not due to
relativity as often conjectured.Comment: 38 pages, 12 eps figures, uses elsart.cls (included
On photoexcitation of baryon antidecuplet
We show that the photoexcitation of the baryon antidecuplet, suggested by the
soliton classification of low-lying baryons, is strongly suppressed on the
proton target. The process occurs mostly on the neutron target. This
qualitative prediction can be useful in identifying the non-exotic members of
the antidecuplet in the known baryon spectrum. We also analyze the
interrelation between photocouplings of various baryon multiplets in the
soliton picture and in the nonrelativistic quark model.Comment: 9 pages, one Latex figur
Silica coatings on young Hawaiian basalts: Constraints on formation mechanism from silicon isotopes
Young basalts from Kilauea, on the big island of Hawai’i, frequently feature visually striking, white, orange and blue
coatings, consisting of a 10-50 μm layer of amorphous silica, capped, in some cases, by a ~1 μm layer of Fe-Ti oxide [1].
The coatings provide an opportunity to study the early onset of acid-sulfate weathering, a process common to many volcanic
environments. Silicon isotopes fractionate with the precipitation of clays and opaline silica, and have been
demonstrated to be an indicator of weathering intensity [2,3]. Here we report in situ measurements of δ^(30)_Si of the silica
coatings and their implications for coating formation
Photoproduction and Radiative Decay of Spin 1/2 and 3/2 Pentaquarks
We study photoproduction and radiative decays of pentauqarks paying
particular attention to the differences between spin-1/2 and spin-3/2, positive
and negative parities of pentaquarks. Detailed study of these processes can not
only give crucial information about the spin, but also the parity of
pentaquarks.Comment: 14 pages, 7 figure
Octet, decuplet and antidecuplet magnetic moments in the chiral quark soliton model revisited
We reanalyse the magnetic moments of the baryon octet, decuplet, and
antidecuplet within the framework of the chiral quark-soliton model, with SU(3)
symmetry breaking taken into account. We consider the contributions of the
mixing of higher representations to the magnetic moment operator arising from
the SU(3) symmetry breaking. Dynamical parameters of the model are fixed by
experimental data for the magnetic moments of the baryon octet and from the
masses of the octet, decuplet and of . The magnetic moment of
depends rather strongly on the pion-nucleon sigma term and reads
to for and 75 MeV
respectively. The recently reported mass of is
compatible with MeV. As a byproduct the strange magnetic
moment of the nucleon is obtained with a value of n.m.Comment: RevTeX is used. 12 pages, 3 figures, final version for publication in
Phys. Rev.
Effects of R-parity violation on direct CP violation in B decays and extraction of
In the standard model, direct CP-violating asymmetries for are roughly 2% based on perturbative calculation. Rescattering effects might
enhance it to at most (20-25)%. We show that lepton-number-violating couplings
in supersymmetric models without R-parity are capable of inducing as large as
100% CP asymmetry in this channel. Such effects drastically modify the allowed
range of the CKM parameter arising from the combinations of the
observed charged and neutral B decays in the modes. With a multichannel
analysis in B decays, one can either discover this exciting new physics, or
significantly improve the existing constraints on it.Comment: Latex, 5 pages; minor changes, to appear in Phys Rev Let
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