414 research outputs found
Parity-Violating Electron Scattering as a Probe of Supersymmetry
We compute the one-loop supersymmetric (SUSY) contributions to the weak
charges of the electron () and proton () using the Minimal
Supersymmetric Standard Model (MSSM). These vector couplings of the
-boson to fermions will be determined in two fixed-target,
parity-violating electron scattering experiments. The SUSY loop contributions
to and can be substantial, leading to several percent
corrections to the Standard Model values for these quantities. We show that the
relative signs of the SUSY loop effects on and are correlated
and positive over nearly all of the MSSM parameter space, whereas inclusion of
R-parity nonconserving interactions can lead to opposite sign relative shifts
in the weak charges. Thus, a comparison of and measurements
could help distinguish between different SUSY scenarios.Comment: 4 pages, 2 figure
Probing Supersymmetry with Neutral Current Scattering Experiments
We compute the supersymmetric contributions to the weak charges of the
electron and proton in the framework of Minimal Supersymmetric Standard Model.
We also consider the ratio of neutral current to charged current cross
sections, R_nu and R_nubar at nu (nubar)-nucleus deep inelastic scattering, and
compare the supersymmetric corrections with the deviations of these quantities
from the Standard Model predictions implied by the recent NuTeV measurement.Comment: 4 pages, contribution to the proceedings of CIPANP 2003 (May, 2003),
New York Cit
Radiative corrections in neutrino-deuterium disintegration
The radiative corrections of order alpha for the charged- and neutral-current neutrino-deuterium disintegration for energies relevant to the SNO experiment are evaluated. Particular attention is paid to the issue of the bremsstrahlung detection threshold. It is shown that the radiative corrections to the total cross section for the charged current reaction are independent of that threshold, as they must be for consistency, and amount to a slowly decreasing function of the neutrino energy E-nu, varying from about 4% at low energies to 3% at the end of the B-8 spectrum. The differential cross section corrections, on the other hand, do depend on the bremsstrahlung detection threshold. Various choices of the threshold are discussed. It is shown that for a realistic choice of the threshold and for the actual electron energy threshold of the SNO detector, the deduced B-8 nu(e) flux should be decreased by about 2%. The radiative corrections to the neutral-current reaction are also evaluated
Parity-Violating Electron Scattering from the Pion-Correlated Relativistic Fermi Gas
Parity-violating quasielastic electron scattering is studied within the
context of the relativistic Fermi gas and its extensions to include the effects
of pionic correlations and meson-exchange currents. The work builds on previous
studies using the same model; here the part of the parity-violating asymmetry
that contains axial-vector hadronic currents is developed in detail using those
previous studies and a link is provided to the transverse vector-isovector
response. Various integrated observables are constructed from the differential
asymmetry. These include an asymmetry averaged over the quasielastic peak, as
well as the difference of the asymmetry integrated to the left and right of the
peak -- the latter is shown to be optimal for bringing out the nature of the
pionic correlations. Special weighted integrals involving the differential
asymmetry and electromagnetic cross section, based on the concepts of y-scaling
and sum rules, are constructed and shown to be suited to studies of the
single-nucleon form factor content in the problem, in particular, to
determinations of the isovector/axial-vector and electric strangeness form
factors. Comparisons are also made with recent predictions made on the basis of
relativistic mean-field theory.Comment: 28 pages, LATeX, 13 figures (tar-compressed postscript files,
available from the authors), MIT preprint CTP#222
Supersymmetric Effects in Parity-Violating Deep Inelastic Electron-Nucleus Scattering
We compute the supersymmetric (SUSY) corrections to the parity-violating,
deep inelastic electron-deuteron asymmetry. Working with the Minimal
Supersymmetric Standard Model (MSSM) we consider two cases: R parity conserving
and R parity-violating. Under these scenarios, we compare the SUSY effects with
those entering other parity-violating observables. For both cases of the MSSM,
we find that the magnitude of the SUSY corrections can be as large as about 1%
and that they are strongly correlated with the effects on other
parity-violating observables. A comparison of various low-energy
parity-violating observables thus provides a potentially interesting probe of
SUSY.Comment: 12 pages, 5 figure
Pion Leptonic Decays and Supersymmetry
We compute supersymmetric contributions to pion leptonic (\pi_{l2}) decays in
the Minimal Supersymmetric Standard Model (MSSM). When R-parity is conserved,
the largest contributions to the ratio R_{e/\mu} = \Gamma[ \pi^+ \to e^+
\nu_e(\gamma)]/\Gamma[ \pi^+ \to \mu^+ \nu_\mu(\gamma)] arise from one-loop
(V-A)x(V-A) corrections. These contributions can be potentially as large as the
sensitivities of upcoming experiments; if measured, they would imply
significant bounds on the chargino and slepton sectors complementary to current
collider limits. We also analyze R-parity violating interactions, which may
produce a detectable deviation in R_{e/\mu} while remaining consistent with all
other precision observables.Comment: 12 pages, 11 figures; included additional electroweak constraints in
analysis, simplified abstract, ref. adde
Probing Nucleon Strangeness with Neutrinos: Nuclear Model Dependences
The extraction of the nucleon's strangeness axial charge, Delta_s, from
inclusive, quasielastic neutral current neutrino cross sections is studied
within the framework of the plane-wave impulse approximation. We find that the
value of Delta_s can depend significantly on the choice of nuclear model used
in analyzing the quasielastic cross section. This model-dependence may be
reduced by one order of magnitude when Delta_s is extracted from the ratio of
total proton to neutron yields. We apply this analysis to the interpretation of
low-energy neutrino cross sections and arrive at a nuclear theory uncertainty
of plus/minus 0.03 on the value of Delta_s expected to be determined from the
ratio of proton and neutron yields measured by the LSND collaboration. This
error compares favorably with estimates of the SU(3)-breaking uncertainty in
the value of Delta_s extracted from inclusive, polarized deep-inelastic
structure function measurements. We also point out several general features of
the quasielastic neutral current neutrino cross section and compare them with
the analogous features in inclusive, quasielastic electron scattering.Comment: 40 pages (including 11 postscript figures), uses REVTeX and
epsfig.st
Parity-violating longitudinal response
The longitudinal quasielastic parity-violating electron scattering response
is explored within the context of a model that builds antisymmetrized RPA-HF
correlations on a relativistic Fermi gas basis. The large sensitivity to
nuclear dynamics of this observable, found in previous studies where only
pionic correlations were included, is shown to survive in the present model
where the effects from pion, rho, sigma and omega exchange in a version of the
Bonn potential are incorporated. Through an intricate diagrammatic
cancellation/filtration mechanism the longitudinal parity-violating response
turns out to be close to the one obtained in first-order perturbation theory
with the pion alone. Finally, in accord with our previous work, the
parity-violating response is seen to display appreciable sensitivity to the
electric strangeness content of the nucleon, especially at high momentum
transfer.Comment: 13 pages, uses REVTeX and epsfig, 10 postscript figures; a postscript
version of the paper is available by anonymous ftp at
ftp://carmen.to.infn.it/pub/barbaro/papers/951
Electroweak Beautygenesis: From b {\to} s CP-violation to the Cosmic Baryon Asymmetry
We address the possibility that CP-violation in mixing may
help explain the origin of the cosmic baryon asymmetry. We propose a new
baryogenesis mechanism - "Electroweak Beautygenesis" - explicitly showing that
these two CP-violating phenomena can be sourced by a common CP-phase. As an
illustration, we work in the Two-Higgs-Doublet model. Because the relevant
CP-phase is flavor off-diagonal, this mechanism is less severely constrained by
null results of electric dipole moment searches than other scenarios. We show
how measurements of flavor observables by the D0, CDF, and LHCb collaborations
test this scenario.Comment: 4 pages, 1 figure, 1 tabl
Neutrinoless Double Beta Decay and Lepton Flavor Violation
We point out that extensions of the Standard Model with low scale (~TeV)
lepton number violation (LNV) generally lead to a pattern of lepton flavor
violation (LFV) experimentally distinguishable from the one implied by models
with GUT scale LNV. As a consequence, muon LFV processes provide a powerful
diagnostic tool to determine whether or not the effective neutrino mass can be
deduced from the rate of neutrinoless double beta decay. We discuss the role of
\mu -> e \gamma and \mu -> e conversion in nuclei, which will be studied with
high sensitivity in forthcoming experiments.Comment: 4 pages, 3 figure
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