52,068 research outputs found
Analysis of Leptogenesis in Supersymmetric Triplet Seesaw Model
We analyze leptogenesis in a supersymmetric triplet seesaw scenario that
explains the observed neutrino masses, adopting a phenomenological approach
where the decay branching ratios of the triplets and the amount of
CP--violation in its different decay channels are assumed as free parameters.
We find that the solutions of the relevant Boltzmann equations lead to a rich
phenomenology, in particular much more complex compared to the
non--supersymmetric case, mainly due to the presence of an additional Higgs
doublet. Several unexpected and counter--intuitive behaviors emerge from our
analysis: the amount of CP violation in one of the decay channels can prove to
be be irrelevant to the final lepton asymmetry, leading to successful
leptogenesis even in scenarios with a vanishing CP violation in the leptonic
sector; gauge annihilations can be the dominant effect in the determination of
the evolution of the triplet density up to very high values of its mass,
leading anyway to a sizeable final lepton asymmetry, which is also a growing
function of the wash--out parameter K=Gamma_d/H, defined as usual as the ratio
between the triplet decay amplitude Gamma_d and the Hubble constant H; on the
other hand, cancellations in the Boltzmann equations may lead to a vanishing
lepton asymmetry if in one of the decay channels both the branching ratio and
the amount of CP violation are suppressed, but not vanishing. The present
analysis suggests that in the supersymmetric triplet see-saw model successful
leptogenesis can be attained in a wide range of scenarios, provided that an
asymmetry in the decaying triplets can act as a lepton--number reservoir.Comment: 14 pages, 6 figure
Leptogenesis origin of Dirac gaugino dark matter
The Dirac nature of the gauginos (and also the Higgsinos) can be realized in
-symmetric supersymmetry models. In this class of models, the Dirac bino (or
wino) with a small mixture of the Dirac Higgsinos is a good dark matter
candidate. When the seesaw mechanism with Higgs triplet superfields is
implemented to account for the neutrino masses and mixing, the leptogenesis
driven by the heavy triplet decay is shown to produce not only the
matter-antimatter asymmetry but also the asymmetric relic density of the Dirac
gaugino dark matter. The dark matter mass turns out to be controlled by the
Yukawa couplings of the heavy Higgs triplets, and it can be naturally at the
weak scale for a mild hierarchy of the Yukawa couplings.Comment: 9 pages. Restructured for clear presentation, corrected some errors
and typos. No change in conclusio
Experimental constraints on nMSSM and implications on its phenomenology
We examine various direct and indirect experimental constraints on the nearly
minimal supersymmetric standard model (nMSSM) and obtain the following
observations: (i) Current experiments stringently constrain the parameter
space, setting a range of 1-37 GeV for the lightest neutralino (LSP), 30-140
GeV (1-250 GeV) for the lightest CP-even (CP-odd) Higgs boson, and 1.5-10 for
\tan\beta; (ii) To account for the dark matter relic density, besides the
s-channel exchange of a Z-boson, the s-channel exchange of a light A_1 (the
lightest CP-odd Higgs boson) can also play an important role in LSP
annihilation. Compared with the Z-exchange annihilation channel, the A_1
exchange channel is more favored by muon g-2 data and allows much broader
regions for the parameters; (iii) In a large part of the allowed parameter
space the SM-like Higgs boson may dominantly decay to LSP pair or A_1 pair and
the conventional visible decays (e.g. into bottom quarks) are severely
suppressed.Comment: version in PRD (Rapid Communication
Heavy Supersymmetric Particle Effects in Higgs Boson Production Associated with a Bottom Quark Pair at LHC and Tevatron
If all the supersymmetry particles (sparticles) except a light Higgs boson
are too heavy to be directly produced at the Large Hadron Collider (LHC) and
Tevatron, a possible way to reveal evidence for supersymmetry is through their
virtual effects in other processes. We examine such supersymmetric QCD effects
in bottom pair production associated with a light Higgs boson at the LHC and
Tevatron. We find that if the relevant sparticles (gluinos and squarks) are
well above the TeV scale, too heavy to be directly produced, they can still
have sizable virtual effects in this process. For large , such
residual effects can alter the production rate by as much as 40 percent, which
should be observable in future measurements of this process.Comment: results for Tevatron added, version in PR
Amorphous metallizations for high-temperature semiconductor device applications
The initial results of work on a class of semiconductor metallizations which appear to hold promise as primary metallizations and diffusion barriers for high temperature device applications are presented. These metallizations consist of sputter-deposited films of high T sub g amorphous-metal alloys which (primarily because of the absence of grain boundaries) exhibit exceptionally good corrosion-resistance and low diffusion coefficients. Amorphous films of the alloys Ni-Nb, Ni-Mo, W-Si, and Mo-Si were deposited on Si, GaAs, GaP, and various insulating substrates. The films adhere extremely well to the substrates and remain amorphous during thermal cycling to at least 500 C. Rutherford backscattering and Auger electron spectroscopy measurements indicate atomic diffussivities in the 10 to the -19th power sq cm/S range at 450 C
N_pN_n dependence of empirical formula for the lowest excitation energy of the 2^+ states in even-even nuclei
We examine the effects of the additional term of the type on the recently proposed empirical formula for the lowest excitation
energy of the states in even-even nuclei. This study is motivated by the
fact that this term carries the favorable dependence of the valence nucleon
numbers dictated by the scheme. We show explicitly that there is not
any improvement in reproducing by including the extra
term. However, our study also reveals that the excitation energies
, when calculated by the term alone (with the mass number
dependent term), are quite comparable to those calculated by the original
empirical formula.Comment: 14 pages, 5 figure
Photo-emission rate of sQGP at finite density
We calculate the thermal spectral function of SYM plasma with finite density
using holographic technique. We take the RN-AdS black hole as the dual gravity
theory. In the presence of charge, vector modes of gravitational and
electromagnetic perturbation are coupled with each other. By introducing master
variables for these modes, we solve the coupled system and calculate spectral
function. We also calculated photoemission rate of SYM plasma from spectral
function for light like momentum, AC conductivity and their density dependence.
The suppression of the conductivity in high density is noticed, which might be
yet another mechanism for the Jet quenching phenomena in RHIC experiment.Comment: 27 pages, 10 figure
Production of , , and in hadronic decays
A coherent study of the production of (, 2, 3 corresponding to
, , and ) in is
reported based on a previously proposed glueball and nonet mixing
scheme, and a factorization for the decay of , where
denotes the isoscalar vector mesons and , and denotes
pseudoscalar mesons. The results show that the decays are very
sensitive to the structure of those scalar mesons, and suggest a glueball in
the GeV region, in line with Lattice QCD. The presence of significant
glueball mixings in the scalar wavefunctions produces peculiar patterns in the
branching ratios for , which are in good agreement
with the recently published experimental data from the BES collaboration.Comment: Version accepted by PRD; Numerical results in Tab IV and VI changed
due to correction of an error in quoting an experimental datum; Conclusion is
not change
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