546 research outputs found
Effects of Squark Processes on the Axino CDM Abundance
We investigate the role of an effective dimension-4 axino-quark-squark
coupling in the thermal processes producing stable cold axino relics in the
early Universe. We find that, while the induced squark and quark scattering
processes are always negligible, squark decays become important in the case of
low reheat temperature and large gluino mass. The effect can tighten the bounds
on the scenario from the requirement that cold dark matter axinos do not
overclose the Universe.Comment: 20 pages, 9 figures, uses JHEP3.cl
SuperWIMP Gravitino Dark Matter from Slepton and Sneutrino Decays
Dark matter may be composed of superWIMPs, superweakly-interacting massive
particles produced in the late decays of other particles. We focus on the case
of gravitinos produced in the late decays of sleptons or sneutrinos and assume
they are produced in sufficient numbers to constitute all of non-baryonic dark
matter. At leading order, these late decays are two-body and the accompanying
energy is electromagnetic. For natural weak-scale parameters, these decays have
been shown to satisfy bounds from Big Bang nucleosynthesis and the cosmic
microwave background. However, sleptons and sneutrinos may also decay to
three-body final states, producing hadronic energy, which is subject to even
more stringent nucleosynthesis bounds. We determine the three-body branching
fractions and the resulting hadronic energy release. We find that superWIMP
gravitino dark matter is viable and determine the gravitino and
slepton/sneutrino masses preferred by this solution to the dark matter problem.
In passing, we note that hadronic constraints disfavor the possibility of
superWIMPs produced by neutralino decays unless the neutralino is photino-like.Comment: 22 pages, updated figures and minor changes, version to appear in
Phys. Rev.
Signatures of Axinos and Gravitinos at Colliders
The axino and the gravitino are well-motivated candidates for the lightest
supersymmetric particle (LSP) and also for cold dark matter in the Universe.
Assuming that a charged slepton is the next-to-lightest supersymmetric particle
(NLSP), we show how the NLSP decays can be used to probe the axino LSP scenario
in hadronic axion models as well as the gravitino LSP scenario at the Large
Hadron Collider and the International Linear Collider. We show how one can
identify experimentally the scenario realized in nature. In the case of the
axino LSP, the NLSP decays will allow one to estimate the value of the axino
mass and the Peccei-Quinn scale.Comment: 20 pages, 5 figures, revised version as published in Phys.Lett.B
(comments on the experimental feasibility added
Supergravity with a Gravitino LSP
We investigate supergravity models in which the lightest supersymmetric
particle (LSP) is a stable gravitino. We assume that the next-lightest
supersymmetric particle (NLSP) freezes out with its thermal relic density
before decaying to the gravitino at time t ~ 10^4 s - 10^8 s. In contrast to
studies that assume a fixed gravitino relic density, the thermal relic density
assumption implies upper, not lower, bounds on superpartner masses, with
important implications for particle colliders. We consider slepton, sneutrino,
and neutralino NLSPs, and determine what superpartner masses are viable in all
of these cases, applying CMB and electromagnetic and hadronic BBN constraints
to the leading two- and three-body NLSP decays. Hadronic constraints have been
neglected previously, but we find that they provide the most stringent
constraints in much of the natural parameter space. We then discuss the
collider phenomenology of supergravity with a gravitino LSP. We find that
colliders may provide important insights to clarify BBN and the thermal history
of the Universe below temperatures around 10 GeV and may even provide precise
measurements of the gravitino's mass and couplings.Comment: 24 pages, updated figures and minor changes, version to appear in
Phys.Rev.
Thermal production of axino Dark Matter
We reconsider thermal production of axinos in the early universe, adding: a)
missed terms in the axino interaction; b) production via gluon decays
kinematically allowed by thermal masses; c) a precise modeling of reheating. We
find an axino abunance a few times larger than previous computations.Comment: 6 pages, 2 figures. Final version, to appear on JHE
Observational constraints on the spectral index of the cosmological curvature perturbation
We evaluate the observational constraints on the spectral index , in the
context of the CDM hypothesis which represents the simplest viable
cosmology. We first take to be practically scale-independent. Ignoring
reionization, we find at a nominal 2- level . If
we make the more realisitic assumption that reionization occurs when a fraction
to 1 of the matter has collapsed, the 2- lower bound is
unchanged while the 1- bound rises slightly. These constraints are
compared with the prediction of various inflation models. Then we investigate
the two-parameter scale-dependent spectral index, predicted by running-mass
inflation models, and find that present data allow significant scale-dependence
of , which occurs in a physically reasonable regime of parameter space.Comment: ReVTeX, 15 pages, 5 figures and 3 tables, uses epsf.sty Improved
treatment of reionization and small bug fixed in the constant n case; more
convenient parameterization and better treatment of the n dependence in the
CMB anisotropy for the running mass case; conclusions basically unchanged;
references adde
Hybrid inflation with running inflaton mass
We realize and study a model of hybrid inflation in the context of softly
broken supersymmetry. The inflaton is taken to be a flat direction in the
superfield space and, due to unsuppressed couplings, its soft supersymmetry
breaking mass runs with scale. Both gauge and Yukawa couplings are taken into
account and different inflationary scenarios are investigated depending on the
relative strenght of the couplings and the mass spectrum.Comment: latex file, 14 pages with 3 eps figures, uses epsf.st
- …