577 research outputs found
Top-Down Approach to Unified Supergravity Models
We introduce a new approach for studying unified supergravity models. In this
approach all the parameters of the grand unified theory (GUT) are fixed by
imposing the corresponding number of low energy observables. This determines
the remaining particle spectrum whose dependence on the low energy observables
can now be investigated. We also include some SUSY threshold corrections that
have previously been neglected. In particular the SUSY threshold corrections to
the fermion masses can have a significant impact on the Yukawa coupling
unification.Comment: 19 pages, uuencoded compressed ps file, DESY 94-057 (paper format
corrected
Supersymmetric effects in top quark decay into polarized W-boson
We investigate the one-loop supersymmetric QCD (SUSY-QCD) and electroweak
(SUSY-EW) corrections to the top quark decay into a b-quark and a longitudinal
or transverse W-boson. The corrections are presented in terms of the
longitudinal ratio \Gamma(t-->W_L b)/\Gamma(t--> W b) and the transverse ratio
\Gamma(t-->W_- b)/\Gamma(t--> W b). In most of the parameter space, both
SUSY-QCD and SUSY-EW corrections to these ratios are found to be less than 1%
in magnitude and they tend to have opposite signs. The corrections to the total
width \Gamma(t-->W b) are also presented for comparison with the existing
results in the literature. We find that our SUSY-EW corrections to the total
width differ significantly from previous studies: the previous studies give a
large correction of more than 10% in magnitude for a large part of the
parameter space while our results reach only few percent at most.Comment: Version in PRD (explanation and refs added
Interpreting Helioseismic Structure Inversion Results of Solar Active Regions
Helioseismic techniques such as ring-diagram analysis have often been used to
determine the subsurface structural differences between solar active and quiet
regions. Results obtained by inverting the frequency differences between the
regions are usually interpreted as the sound-speed differences between them.
These in turn are used as a measure of temperature and magnetic-field strength
differences between the two regions. In this paper we first show that the
"sound-speed" difference obtained from inversions is actually a combination of
sound-speed difference and a magnetic component. Hence, the inversion result is
not directly related to the thermal structure. Next, using solar models that
include magnetic fields, we develop a formulation to use the inversion results
to infer the differences in the magnetic and thermal structures between active
and quiet regions. We then apply our technique to existing structure inversion
results for different pairs of active and quiet regions. We find that the
effect of magnetic fields is strongest in a shallow region above 0.985R_sun and
that the strengths of magnetic-field effects at the surface and in the deeper
(r < 0.98R_sun) layers are inversely related, i.e., the stronger the surface
magnetic field the smaller the magnetic effects in the deeper layers, and vice
versa. We also find that the magnetic effects in the deeper layers are the
strongest in the quiet regions, consistent with the fact that these are
basically regions with weakest magnetic fields at the surface. Because the
quiet regions were selected to precede or follow their companion active
regions, the results could have implications about the evolution of magnetic
fields under active regions.Comment: Accepted for publication in Solar Physic
A New Relativistic High Temperature Bose-Einstein Condensation
We discuss the properties of an ideal relativistic gas of events possessing
Bose-Einstein statistics. We find that the mass spectrum of such a system is
bounded by where is the usual chemical
potential, is an intrinsic dimensional scale parameter for the motion of an
event in space-time, and is an additional mass potential of the
ensemble. For the system including both particles and antiparticles, with
nonzero chemical potential the mass spectrum is shown to be bounded by
and a special type of high-temperature
Bose-Einstein condensation can occur. We study this Bose-Einstein condensation,
and show that it corresponds to a phase transition from the sector of
continuous relativistic mass distributions to a sector in which the boson mass
distribution becomes sharp at a definite mass This phenomenon
provides a mechanism for the mass distribution of the particles to be sharp at
some definite value.Comment: Latex, 22 page
Probing the MSSM Higgs Boson Sector with Explicit CP Violation through Third Generation Fermion Pair Production at Muon Colliders
We perform a systematic study of the production of a third-generation
fermion-pair, for , and t in the minimal
supersymmetric standard model (MSSM) with explicit CP violation, which is
induced radiatively by soft trilinear interactions related to squarks of the
third generation. We classify all the observables for probing the CP property
of the Higgs bosons constructed by the initial muon beam polarization along
with the unpolarized final fermions and with the final-fermion polarization
configuration of equal helicity, respectively. The observables allow for
complete determination of CP property of the neutral Higgs bosons. The
interference between the Higgs boson and gauge boson contributions also could
provide a powerful method for the determination of the CP property of two heavy
Higgs bosons in the top-quark pair production near the energy region of the
Higgs-boson resonances. For the lightest Higgs-boson mass there is no sizable
interference between scalar and vector contributions for the determination of
the CP property of the lightest Higgs boson. We give a detailed numerical
analysis to show how the radiatively-induced CP violation in the Higgs sector
of the MSSM can be measured.Comment: 30 pages, 7 figures including 5 eps ones. Typos corrected and
references added. To appear in Phys. Rev.
PARP regulates nonhomologous end joining through retention of Ku at double-strand breaks
Poly ADP-ribosylation polymerases are necessary for recruitment and/or retention of Ku at double-strand breaks during nonhomologous end-joining DNA repair
Lepton flavour violation in e^{\pm}e^{-}\to \ell^{\pm}e^{-} (\ell = \mu,\tau) induced by R-conserving supersymmetry
The lepton flavour violating signals and
are studied in the context of low
energy R-parity conserving supersymmetry at center of mass energies of interest
for the next generation of linear colliders. Loop level amplitudes receive
contributions from electroweak penguin and box diagrams involving sleptons and
gauginos. Lepton flavour violation is due to off diagonal elements in
doublet slepton mass matrix. These masses are treated as model independent free
phenomenological parameters in order to discover regions in parameter space
where the signal cross section may be observable. The results are compared with
(a) the experimental bounds from the non-observation of rare radiative lepton
decays and (b) the general mSUGRA theoretical scenario
with seesaw mechanism where off diagonal slepton matrix entries are generated
by renormalization group evolution of neutrino Yukawa couplings induced by the
presence of new energy scales set by the heavy singlet neutrino
masses. It is found that in collisions the () signal can be
observable with a total integrated luminosity of 100 fb and the that the
background can be easily suppressed. In collisions the cross section
is smaller and higher luminosities are needed. The experimental bound on the
decay prevents the () signal from being observable.Comment: 14 pages, 12 figures, Revtex
Probing exotic phenomena at the interface of nuclear and particle physics with the electric dipole moments of diamagnetic atoms: A unique window to hadronic and semi-leptonic CP violation
The current status of electric dipole moments of diamagnetic atoms which
involves the synergy between atomic experiments and three different theoretical
areas -- particle, nuclear and atomic is reviewed. Various models of particle
physics that predict CP violation, which is necessary for the existence of such
electric dipole moments, are presented. These include the standard model of
particle physics and various extensions of it. Effective hadron level combined
charge conjugation (C) and parity (P) symmetry violating interactions are
derived taking into consideration different ways in which a nucleon interacts
with other nucleons as well as with electrons. Nuclear structure calculations
of the CP-odd nuclear Schiff moment are discussed using the shell model and
other theoretical approaches. Results of the calculations of atomic electric
dipole moments due to the interaction of the nuclear Schiff moment with the
electrons and the P and time-reversal (T) symmetry violating
tensor-pseudotensor electron-nucleus are elucidated using different
relativistic many-body theories. The principles of the measurement of the
electric dipole moments of diamagnetic atoms are outlined. Upper limits for the
nuclear Schiff moment and tensor-pseudotensor coupling constant are obtained
combining the results of atomic experiments and relativistic many-body
theories. The coefficients for the different sources of CP violation have been
estimated at the elementary particle level for all the diamagnetic atoms of
current experimental interest and their implications for physics beyond the
standard model is discussed. Possible improvements of the current results of
the measurements as well as quantum chromodynamics, nuclear and atomic
calculations are suggested.Comment: 46 pages, 19 tables and 16 figures. A review article accepted for
EPJ
Scalar Potential Without Cubic Term in 3-3-1 Models Without Exotic Electric Charges
A detailed study of the criteria for stability of the scalar potential, and
the proper electroweak symmetry breaking pattern in some 3-3-1 models without
exotic electric charges is presented. In this paper we concentrate in a scalar
sector with three Higgs scalar triplets, with a potential that does not include
the cubic term, due to the presence of a discrete symmetry. For the analysis we
use, and improve, a method previously developed to study the scalar potential
in the two-Higgs-doublet extension of the standard model. Our main result is to
show the consistency of those 3-3-1 models without exotic electric charges.Comment: 19 page
Search for direct production of charginos and neutralinos in events with three leptons and missing transverse momentum in √s = 7 TeV pp collisions with the ATLAS detector
A search for the direct production of charginos and neutralinos in final states with three electrons or muons and missing transverse momentum is presented. The analysis is based on 4.7 fb−1 of proton–proton collision data delivered by the Large Hadron Collider and recorded with the ATLAS detector. Observations are consistent with Standard Model expectations in three signal regions that are either depleted or enriched in Z-boson decays. Upper limits at 95% confidence level are set in R-parity conserving phenomenological minimal supersymmetric models and in simplified models, significantly extending previous results
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