297 research outputs found
Constraints on left-right symmetric models from the process
In left-right symmetric models, large contributions to the decay amplitude can arise from the mixing of the and gauge
bosons as well as from the charged Higgs boson. These amplitudes are enhanced
by the factor \mt/\mb compared to the contributions in the standard model. We
use the recent CLEO results on the radiative decay to place constraints on
the mixing angle and the mass of the charged Higgs boson
. Significant departures from the standard model predictions occur
when and/or when a few TeV.Comment: in LaTeX, 12 pages + 4 figures (available on request), BA-93-69,
UT-66
Continuous-distribution puddle model for conduction in trilayer graphene
An insulator-to-metal transition is observed in trilayer graphene based on
the temperature dependence of the resistance under different applied gate
voltages. At small gate voltages the resistance decreases with increasing
temperature due to the increase in carrier concentration resulting from thermal
excitation of electron-hole pairs. At large gate voltages excitation of
electron-hole pairs is suppressed, and the resistance increases with increasing
temperature because of the enhanced electron-phonon scattering. We find that
the simple model with overlapping conduction and valence bands, each with
quadratic dispersion relations, is unsatisfactory. Instead, we conclude that
impurities in the substrate that create local puddles of higher electron or
hole densities are responsible for the residual conductivity at low
temperatures. The best fit is obtained using a continuous distribution of
puddles. From the fit the average of the electron and hole effective masses can
be determined.Comment: 18 pages, 5 figure
Implications of a charged-current anomaly at HERA
We demonstrate that in the presence of mixing between different scalar
leptoquark multiplets it is possible to simultaneously account for the HERA
high- neutral current anomaly, and produce a charged current anomaly of
comparable magnitude. The reduced branching ratio to electrons and jets of the
lightest leptoquark state results in a significant weakening of the CDF/D0
limits on scalar leptoquarks; masses consistent with the HERA neutral current
excess are comfortably within the allowed range. We show that the possibilities
for such a successful mixed leptoquark scenario are quite limited, and we
investigate some aspects of their phenomenology.Comment: 10 pages Latex. Corrected 3-body decay width
Contact Interactions Involving Right-handed Neutrinos and SN1987A
We consider lepton-quark contact interactions in models with right-handed
neutrinos, and find that observational data from SN1987A restricts the scale of
such interactions to be at least TeV.Comment: 7 pages, latex, no figures. Minor corrections to match final version
to appear in Phys. Rev.
Finite Grand Unified Theories and the Quark Mixing Matrix
In N = 1 super Yang-Mills theories, under certain conditions satisfied by the
spectrum and the Yukawa couplings, the beta functions will vanish to all orders
in perturbation theory. We address the generation of realistic quark mixing
angles and masses in such finite Grand Unified Theories. Working in the context
of finite SUSY SU(5), we present several examples with realistic quark mixing
matrices. Non-Abelian discrete symmetries are found to be important in
satisfying the conditions for finiteness. Our realistic examples are based on
permutation symmetries and the tetrahedral symmetry . These examples
enable us to address questions such as the decay rate of the proton in finite
GUTs.Comment: 16 pages, LaTeX, typos correcte
Coupling Unification, GUT-Scale Baryogenesis and Neutron-Antineutron Oscillation in SO(10)
We show that unification of the three gauge couplings can be realized
consistently in a class of non-supersymmetric SO(10) models with a one-step
breaking to the Standard Model if a color-sextet scalar field survives down to
the TeV scale. Such scalars, which should be accessible to the LHC for direct
detection, arise naturally in SO(10) as remnants of the seesaw mechanism for
neutrino masses. The diquark couplings of these scalars lead to \Delta B = 2
baryon number violating processes such as neutron-antineutron oscillation. We
estimate the free neutron-antineutron transition time to be \tau_{n-\bar{n}}
\approx (10^9-10^{12}) sec., which is in the interesting range for next
generation n-\bar{n} oscillation experiments. These models also realize
naturally the recently proposed (B-L)-violating GUT scale baryogenesis which
survives to low temperatures unaffected by the electroweak sphaleron
interactions.Comment: 15 pages, 4 eps figures, references added, to appear in Phys. Lett.
Predictions for Proton Lifetime in Minimal Non-Supersymmetric SO(10) Models: An Update
We present our best estimates of the uncertainties due to heavy particle
threshold corrections on the unification scale , intermediate scale
and coupling constant Alpha_U in the minimal non-supersymmetric SO(10) models.
Using these , we update the predictions for proton life-time in these models.Comment: UMD-PP-94-117 ( 20 pages;latex; no figures
Muon anomalous magnetic moment, lepton flavor violation, and flavor changing neutral current processes in SUSY GUT with right-handed neutrino
Motivated by the large mixing angle solutions for the atmospheric and solar
neutrino anomalies, flavor changing neutral current processes and lepton flavor
violating processes as well as the muon anomalous magnetic moment are analyzed
in the framework of SU(5) SUSY GUT with right-handed neutrino. In order to
explain realistic mass relations for quarks and leptons, we take into account
effects of higher dimensional operators above the GUT scale. It is shown that
the supersymmetric (SUSY) contributions to the CP violation parameter in
mixing, , the branching ratio,
and the muon anomalous magnetic moment become large in a wide range of
parameter space. We also investigate correlations among these quantities.
Within the current experimental bound of , large
SUSY contributions are possible either in the muon anomalous magnetic moment or
in . In the former case, the favorable value of the recent muon
anomalous magnetic moment measurement at the BNL E821 experiment can be
accommodated. In the latter case, the allowed region of the Kobayashi-Maskawa
phase can be different from the prediction within the Standard Model (SM) and
therefore the measurements of the CP asymmetry of mode and
could discriminate this case from the SM. We also show that
the branching ratio can be close to the current
experimental upperbound and the mixing induced CP asymmetry of the radiative B
decay can be enhanced in the case where the neutrino parameters correspond to
the Mikheyev-Smirnov-Wolfenstein small mixing angle solution.Comment: 70 pages, 14 figure
Lepton Dipole Moments and Rare Decays in the CP-violating MSSM with Nonuniversal Soft-Supersymmetry Breaking
We investigate the muon anomalous magnetic dipole moment (MDM), the muon
electric dipole moment (EDM) and the lepton-flavour-violating decays of the
lepton, and , in the CP-violating
Minimal Supersymmetric Standard Model (MSSM) with nonuniversal
soft-supersymmetry breaking. We evaluate numerically the muon EDM and the
branching ratios and , after taking
into account the experimental constraints from the electron EDM and muon MDM.
Upon imposition of the experimental limits on our theoretical predictions for
the aforementioned branching ratios and the muon MDM, we obtain an upper bound
of about on the muon EDM which lies well within the
explorable reach of the proposed experiment at BNL.Comment: Latex, 26 pages, 8 figures, accepted for publication in Phys. Rev.
Rare Charm Decays in the Standard Model and Beyond
We perform a comprehensive study of a number of rare charm decays,
incorporating the first evaluation of the QCD corrections to the short distance
contributions, as well as examining the long range effects. For processes
mediated by the transitions, we show that sensitivity to
short distance physics exists in kinematic regions away from the vector meson
resonances that dominate the total rate. In particular, we find that
and are sensitive to non-universal
soft-breaking effects in the Minimal Supersymmetric Standard Model with
R-parity conservation. We separately study the sensitivity of these modes to
R-parity violating effects and derive new bounds on R-parity violating
couplings. We also obtain predictions for these decays within extensions of the
Standard Model, including extensions of the Higgs, gauge and fermion sectors,
as well as models of dynamical electroweak symmetry breaking.Comment: 45 pages, typos fixed, discussions adde
- âŠ