8,112 research outputs found
New vector-scalar contributions to neutrinoless double beta decay and constraints on R-parity violation
We show that in minimal supersymmetric standard model (MSSM) with R-parity
breaking as well as in the left-right symmetric model, there are new observable
contributions to neutrinoless double beta decay arising from hitherto
overlooked diagrams involving the exchange of one W boson and one scalar boson.
In particular, in the case of MSSM, the present experimental bounds on
neutrinoless double beta decay lifetime improves the limits on certain R-parity
violating couplings by about two orders of magnitude. It is shown that similar
diagrams also lead to enhanced rates for conversion in
nuclei, which are in the range accessible to ongoing experiments.Comment: Latex file; 9 pages; 3 figures available on reques
Supernova Constraints on a Superlight Gravitino
In supergravity models with low supersymmetry breaking scale the gravitinos
can be superlight with mass in the micro-eV to keV range. In such a case,
gravitino emission provides a new cooling mechanism for protoneutron stars and
therefore can provide constraints on the mass of the superlight gravitino. This
happens because the coupling to matter of superlight gravitinos is dominated by
its goldstino component, whose coupling to matter is inversely proportional to
the scale of supersymmetry breaking and increases as the gravitino mass
decreases. Present observations therefore provide lower limits on the gravitino
mass. Using recently revised goldstino couplings, we find that the two dominant
processes in supernova cooling are and
. They lead to lower limits on the
supersymmetry breaking scale from 160 to 500 GeV for core
temperatures 30 to 60 MeV and electron chemical potentials 200 to 300 MeV. The
corresponding lower limits on the gravitino mass are eV.Comment: Latex 6 pages; one figure; UTEXAS-HEP-97-19, UMD-PP-98-07,
SMU-HEP-97-1
Seesaw Right Handed Neutrino as the Sterile Neutrino for LSND
We show that a double seesaw framework for neutrino masses with
exchange symmetry can lead to one of the righthanded seesaw partners of the
light neutrinos being massless. This can play the role of a light sterile
neutrino, giving a model that explains the LSND results. We get a very
economical scheme, which makes it possible to predict the full
neutrino mass matrix if CP is conserved. Once CP violation is included, effect
of the LSND mass range sterile neutrino is to eliminate the lower bound on
neutrinoless double beta decay rate which exists for the three neutrino case
with inverted mass hierarchy. The same strategy can also be used to generate a
natural model for LSND, which is also equally predictive for the CP
conserving case in the limit of exact symmetry.Comment: 13 pages and one figure; model extended to 3+2 cas
Two Higgs Bi-doublet Model With Spontaneous P and CP Violation and Decoupling Limit to Two Higgs Doublet Model
The two Higgs bi-doublet left-right symmetric model (2HBDM) as a simple
extension of the minimal left-right symmetric model with a single Higgs
bi-doublet is motivated to realize both spontaneous P and CP violation while
consistent with the low energy phenomenology without significant fine tuning.
By carefully investigating the Higgs potential of the model, we find that
sizable CP-violating phases are allowed after the spontaneous symmetry
breaking. The mass spectra of the extra scalars in the 2HBDM are significantly
different from the ones in the minimal left-right symmetric model. In
particular, we demonstrate in the decoupling limit when the right-handed gauge
symmetry breaking scale is much higher than the electroweak scale, the 2HBDM
decouples into general two Higgs doublet model (2HDM) with spontaneous CP
violation and has rich induced sources of CP violation. We show that in the
decoupling limit, it contains extra light Higgs bosons with masses around
electroweak scale, which can be directly searched at the ongoing LHC and future
ILC experiments.Comment: 19 pages, discussions on fine-tuning problem added. Version to appear
in Phys.Rev.
Minimal Seesaw as an Ultraviolet Insensitive Cure for the Problems of Anomaly Mediation
We show that an intermediate scale supersymmetric left-right seesaw scenario
with automatic R-parity conservation can cure the problem of tachyonic slepton
masses that arises when supersymmetry is broken by anomaly mediation, while
preserving ultraviolet insensitivity. The reason for this is the existence of
light B - L = 2 higgses with yukawa couplings to the charged leptons. We find
these theories to have distinct predictions compared to the usual mSUGRA and
gauge mediated models as well as the minimal AMSB models. Such predictions
include a condensed gaugino mass spectrum and possibly a correspondingly
condensed sfermion spectrum.Comment: 19 pages, 1 figur
MeV Right-handed Neutrinos and Dark Matter
We consider the possibility of having a MeV right-handed neutrino as a dark
matter constituent. The initial reason for this study was the 511 keV spectral
line observed by the satellite experiment INTEGRAL: could it be due to an
interaction between dark matter and baryons? Independently of this, we find a
number of constraints on the assumed right-handed interactions. They arise in
particular from the measurements by solar neutrino experiments. We come to the
conclusion that such particles interactions are possible, and could reproduce
the peculiar angular distribution, but not the rate of the INTEGRAL signal.
However, we stress that solar neutrino experiments are susceptible to provide
further constraints in the future.Comment: 7 pages, figure 1 changed, added reference
Effects of Decays of Tau Neutrinos Near A Supernova
We revisit the constraints implied by SN 1987 A observations on the decay
rate of a multi-MeV decaying into the visible channel , if its lifetime is more than 10 {\it sec.}. We
discuss its implication for the minimal left-right symmetric model with see-saw
mechanism for neutrino masses. We also speculate on the possible formation of a
``giant Capacitor" in intergalactic space due to the decay of "neutronization"
's and spin allignment possibility in the supernova.Comment: 29 Pages, Tex file, UMDHEP 94-4
Searching for Strongly Interacting Massive Particles (SIMPs)
We consider laboratory experiments that can detect stable, neutral strongly
interacting massive particles (SIMPs). We explore the SIMP annihilation cross
section from its minimum value (restricted by cosmological bounds) to the barn
range, and vary the mass values from a GeV to a TeV. We calculate, as a
function of the SIMP-nucleon cross section, the minimum nucleon number A for
which there should be binding in a nucleus. We consider accelerator mass
spectrometry with a gold (A=200) target, and compute the likely abundance of
anomalous gold nuclei if stable neutral SIMPs exist. We also consider the
prospects and problems of detecting such particles at the Tevatron. We estimate
optimistically that such detection might be possible for SIMPs with
SIMP-nucleon cross sections larger than 0.1 millibarn and masses between 25 and
50 GeV.Comment: RevTeX, 10 pages, 3 figures; Minor updates to match published versio
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