215 research outputs found
Origin and Phenomenology of Weak-Doublet Spin-1 Bosons
We study phenomenological consequences of the Standard Model extension by the
new spin-1 fields with the internal quantum numbers of the electroweak Higgs
doublets. We show, that there are at least three different classes of theories,
all motivated by the hierarchy problem, which predict appearance of such vector
weak-doublets not far from the weak scale. The common feature for all the
models is the existence of an SU(3) gauge extension of the weak SU(2) group,
which is broken down to the latter at some energy scale around TeV. The Higgs
doublet then emerges as either a pseudo-Nambu-Goldstone boson of a global
remnant of SU(3), or as a symmetry partner of the true eaten-up Goldstone
boson. In the third class, the Higgs is a scalar component of a
high-dimensional SU(3) gauge field. The common phenomenological feature of
these theories is the existence of the electroweak doublet vectors (Z*,W*),
which in contrast to well-known Z' and W' bosons posses only anomalous
(magnetic moment type) couplings with ordinary light fermions. This fact leads
to some unique signatures for their detection at the hadron colliders.Comment: 7 pages, 5 figure
Nonequilibrium Neutrino Oscillations and Primordial Production of He-4
We studied nonequilibrium oscillations between left-handed electron neutrinos
and nonthermalized sterile neutrinos in medium for resonant and nonresonant
cases. The exact kinetic equations for neutrinos, written in terms of neutrino
density matrix in {\it momentum space} were analyzed. The evolution of neutrino
density matrix was numerically calculated. This allowed to study precisely the
evolution of the neutrino number densities, energy spectrum distortion and the
asymmetry between neutrinos and antineutrinos for each momentum mode. The
influence of nonequilibrium oscillations on the primordial production of He-4
was calculated. Cosmological constraints on the oscillation parameters were
obtained.Comment: LaTeX, 7 pages, 6 Postscript figures, figures are included in the
revised text (epsf.sty
Robust signatures of solar neutrino oscillation solutions
With the goal of identifying signatures that select specific neutrino
oscillation parameters, we test the robustness of global oscillation solutions
that fit all the available solar and reactor experimental data. We use three
global analysis strategies previously applied by different authors and also
determine the sensitivity of the oscillation solutions to the critical nuclear
fusion cross section, S_{17}(0), for the production of 8B. The favored
solutions are LMA, LOW, and VAC in order of g.o.f. The neutral current to
charged current ratio for SNO is predicted to be 3.5 +- 0.6 (1 sigma), which is
separated from the no-oscillation value of 1.0 by much more than the expected
experimental error. The predicted range of the day-night difference in charged
current rates is (8.2 +- 5.2)% and is strongly correlated with the day-night
effect for neutrino-electron scattering. A measurement by SNO of either a NC to
CC ratio > 3.3 or a day-night difference > 10%, would favor a small region of
the currently allowed LMA neutrino parameter space. The global oscillation
solutions predict a 7Be neutrino-electron scattering rate in BOREXINO and
KamLAND in the range 0.66 +- 0.04 of the BP00 standard solar model rate, a
prediction which can be used to test both the solar model and the neutrino
oscillation theory. Only the LOW solution predicts a large day-night effect(<
42%) in BOREXINO and KamLAND. For the KamLAND reactor experiment, the LMA
solution predicts 0.44 of the standard model rate; we evaluate 1 sigma and 3
sigma uncertainties and the first and second moments of the energy spectrum.Comment: Included predictions for KamLAND reactor experiment and updated to
include 1496 days of Super-Kamiokande observation
Model Independent Information On Solar Neutrino Oscillations
We present the results of a Bayesian analysis of solar neutrino data in terms
of nu_e->nu_{mu,tau} oscillations, independent from the Standard Solar Model
predictions for the solar neutrino fluxes. We show that such a model
independent analysis allows to constraint the values of the neutrino mixing
parameters in limited regions around the usual SMA, LMA, LOW and VO regions.
Furthermore, there is a strong indication in favor of large neutrino mixing and
large values of Delta m^2 (LMA region). We calculate also the allowed ranges of
the neutrino fluxes and we show that they are in good agreement with the
Standard Solar Model prediction. In particular, the ratio of the 8B flux with
its Standard Solar Model prediction is constrained in the interval [0.45,1.42]
with 99.73% probability. Finally, we show that the hypothesis of no neutrino
oscillations is strongly disfavored in a model independent way with respect to
the hypothesis of neutrino oscillations.Comment: 40 pages, 20 figures. Added references and improved figure
The breakdown of the Nagaoka phase in the 2D t-J model
In the limit of weak exchange, J, at low hole concentration, the ground state
of the 2D t-J model is believed to be ferromagnetic. We study the leading
instability of this Nagaoka state, which emerges with increasing J. Both exact
diagonalization of small clusters, and a semiclassical analytical calculation
of larger systems show that above a certain critical value of the exchange,
Nagaoka's state is unstable to phase separation. In a finite-size system a
bubble of antiferromagnetic Mott insulator appears in the ground state above
this threshold. The size of this bubble depends on the hole concentration and
scales as a power of the system size, N
Theta-13 as a Probe of Mu-Tau symmetry for Leptons
Many experiments are being planned to measure the neutrino mixing parameter
using reactor as well as accelerator neutrino beams. In this
note, the theoretical significance of a high precision measurement of this
parameter is discussed. It is emphasized that it will provide crucial
information about different ways to understand the origin of large atmospheric
neutrino mixing and move us closer towards determining the neutrino mass
matrix. For instance if exact symmetry in the
neutrino mass matrix is assumed to be the reason for maximal
mixing, one gets . Whether or can provide information about the way the
symmetry breaking manifests in the case of normal hierarchy. We also discuss
the same question for inverted hierarchy as well as possible gauge theories
with this symmetry.Comment: 12 pages; no figures; latex; more exact expressions given for some
parameters and minor typos corrected; paper accepted for publication in JHE
Exploring flavor structure of supersymmetry breaking from rare B decays and unitarity triangle
We study effects of supersymmetric particles in various rare B decay
processes as well as in the unitarity triangle analysis. We consider three
different supersymmetric models, the minimal supergravity, SU(5) SUSY GUT with
right-handed neutrinos, and the minimal supersymmetric standard model with U(2)
flavor symmetry. In the SU(5) SUSY GUT with right-handed neutrinos, we consider
two cases of the mass matrix of the right-handed neutrinos. We calculate direct
and mixing-induced CP asymmetries in the b to s gamma decay and CP asymmetry in
B_d to phi K_S as well as the B_s--anti-B_s mixing amplitude for the unitarity
triangle analysis in these models. We show that large deviations are possible
for the SU(5) SUSY GUT and the U(2) model. The pattern and correlations of
deviations from the standard model will be useful to discriminate the different
SUSY models in future B experiments.Comment: revtex4, 36 pages, 10 figure
Meson exchange currents in electromagnetic one-nucleon emission
The role of meson exchange currents (MEC) in electron- and photon-induced
one-nucleon emission processes is studied in a nonrelativistic model including
correlations and final state interactions. The nuclear current is the sum of a
one-body and of a two-body part. The two-body current includes pion seagull,
pion-in-flight and the isobar current contributions. Numerical results are
presented for the exclusive 16O(e,e'p)15N and 16O(\gamma,p)15N reactions. MEC
effects are in general rather small in (e,e'p), while in (\gamma,p) they are
always large and important to obtain a consistent description of (e,e'p) and
(\gamma,p) data, with the same spectroscopic factors. The calculated (\gamma,p)
cross sections are sensitive to short-range correlations at high values of the
recoil momentum, where MEC effects are larger and overwhelm the contribution of
correlations.Comment: 9 pages, 6 figure
Global Analysis with SNO: Toward the Solution of the Solar Neutrino Problem
We perform a global analysis of the latest solar neutrino data including the
SNO result on the CC-event rate. This result further favors the LMA solution of
the solar neutrino problem. The best fit values of parameters we find are:
\Delta m^2 = (4.8 - 5.0)10^{-5} eV^2, tan^2 \theta = 0.35 - 0.38, f_B = 1.08 -
1.12, and f_{hep} = 1 - 4. With respect to this best fit the LOW solution is
accepted at 90% C.L.. The Vacuum oscillation solution with \Delta m^2 = 1.4
10^{-10} eV^2, gives good fit of the data provided that the boron neutrino flux
is substantially smaller than the SSM flux (f_B \sim 0.5). The SMA solution is
accepted only at 3\sigma level. We find that vacuum oscillations to sterile
neutrino, VAC(sterile), with f_B \sim 0.5 also give rather good global fit of
the data. All other sterile solutions are strongly disfavored. We check the
quality of the fit by constructing the pull-off diagrams of observables.
Predictions for the day-night asymmetry, spectrum distortion and NC/CC ratio at
SNO are calculated. In the best fit points of the global solutions we find:
A_{DN}^{CC} \approx (7 - 8)% for LMA, \sim 3% for LOW, and (2 - 3)% for SMA. It
will be difficult to see the distortion of the spectrum expected for LMA as
well as LOW solutions. However, future SNO spectral data can significantly
affect the VAC and SMA solutions. We also calculate expectations for the
BOREXINO rate.Comment: 35 pages, latex, 9 figures; results of analysis slightly changed due
to different treatment of the hep neutrino flux; predictions for NC/CC ratio
and Borexino rate adde
Three Generation Neutrino Oscillation Parameters after SNO
We examine the solar neutrino problem in the context of the realistic three
neutrino mixing scenario including the SNO charged current (CC) rate. The two
independent mass squared differences and are taken to be in the solar and atmospheric ranges
respectively. We incorporate the constraints on m as obtained
by the SuperKamiokande atmospheric neutrino data and determine the allowed
values of , and from a combined
analysis of solar and CHOOZ data. Our aim is to probe the changes in the values
of the mass and mixing parameters with the inclusion of the SNO data as well as
the changes in the two-generation parameter region obtained from the solar
neutrino analysis with the inclusion of the third generation. We find that the
inclusion of the SNO CC rate in the combined solar + CHOOZ analysis puts a more
restrictive bound on . Since the allowed values of
are constrained to very small values by the CHOOZ experiment there is no
qualitative change over the two generation allowed regions in the plane. The best-fit comes in the LMA region and
no allowed area is obtained in the SMA region at 3 level from combined
solar and CHOOZ analysis.Comment: One reference added. Version to apprear in PR
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