900 research outputs found
Constraining the primordial spectrum of metric perturbations from gravitino and moduli production
We consider the production of gravitinos and moduli fields from quantum
vacuum fluctuations induced by the presence of scalar metric perturbations at
the end of inflation. We obtain the corresponding occupation numbers, up to
first order in perturbation theory, in terms of the power spectrum of the
metric perturbations. We compute the limits imposed by nucleosynthesis on the
spectral index for different models with constant . The results show
that, in certain cases, such limits can be as strong as , which is
more stringent than those coming from primordial black hole production.Comment: 16 pages, LaTeX, 5 figures. Corrected figures, new references
included. Final version to appear in Phys. Rev.
Numerical simulation of nonunitary gravity-induced localization
The localization of a quantum state is numerically exhibited in a nonunitary
Newtonian model for gravity. It is shown that an unlocalized state of a ball of
mass just above the expected threshold of 10^11 proton masses evolves into a
mixed state with vanishing coherences above some localization lengths.Comment: RevTex, 6 figures available on request from the authors To appear in
Physica
Possible astrophysical signatures of heavy stable neutral relics in supergravity models
We consider heavy stable neutral particles in the context of supergravity and
show that a gravitationally suppressed inflaton decay can produce such
particles in cosmologically interesting abundances within a wide mass range
. In gravity-mediated
supersymmetry breaking models, a heavy particle can decay into its superpartner
and a photon-photino pair or a gravitino. Such decays only change the identity
of a possible dark matter candidate. However, for , astrophysical bounds from gamma-ray background and
photodissociation of light elements can be more stringent than the overclosure
bound, thus ruling out the particle as a dark matter candidate.Comment: 12 page
Is nonperturbative inflatino production during preheating a real threat to cosmology?
We discuss toy models where supersymmetry is broken due to non-vanishing
time-varying vacuum expectation value of the inflaton field during preheating.
We discuss the production of inflatino the superpartner of inflaton due to
vacuum fluctuations and then we argue that they do not survive until
nucleosynthesis and decay along with the inflaton to produce a thermal bath
after preheating. Thus the only relevant remnant is the helicity \pm 3/2
gravitinos which can genuinely cause problem to nucleosynthesis.Comment: 10 pages, Updates to match the accepted version in Phys. Rev.
On Yukawa quasi-unification with mu<0
Although recent data on the muon anomalous magnetic moment strongly disfavor
the constrained minimal supersymmetric standard model with mu<0, they cannot
exclude it because of theoretical ambiguities. We consider this model
supplemented by a Yukawa quasi-unification condition which allows an acceptable
b-quark mass. We find that the cosmological upper bound on the lightest
sparticle relic abundance is incompatible with the data on the branching ratio
of b-->s gamma, which is evaluated by including all the next-to-leading order
corrections. Thus, this scheme is not viable.Comment: 4 pages including 3 figures, Revte
Production and decay of the Standard Model Higgs Bososn at LEP200
We collect and update theoretical predictions for the production rate and
decay branching fractions of the Standard Model Higgs boson that will be
relevant for the Higgs search at LEP200. We make full use of the present
knowledge of radiative corrections. We estimate the systematics arising from
theoretical and experimental uncertainties.Comment: 27 page
Measurement of the gluon PDF at small x with neutrino telescopes
We analyze the possibility that neutrino telescopes may provide an
experimental determination of the slope lambda of the gluon distribution in the
proton at momentum fractions x smaller than the accelerator reach. The method
is based on a linear relation between lambda and the spectral index (slope) of
the down-going atmospheric muon flux above 100 TeV, for which there is no
background. Considering the uncertainties in the charm production cross section
and in the cosmic ray composition, we estimate the error on the measurement of
lambda through this method, excluding the experimental error of the telescopes,
to be ~ +/- 0.2Comment: 16 pages with 16 figures - new version, comments added, same results
and figure
Higher twists and extractions from the NNLO QCD analysis of the CCFR data for structure function
A detailed next-to-next-to-leading order (NNLO) QCD analysis is performed for
the experimental data of the CCFR collaboration for the structure
function. Theoretical ambiguities of the results of our NNLO fits are estimated
by application of the Pad\'e resummation technique and variation of the
factorization and renormalization scales. The NNLO and NLO
-matching conditions are used. In the process of the fits we are
taking into account of twist-4 -terms. We found that the amplitude of
the -shape of the twist-4 factor is decreasing in NLO and NNLO, though some
remaining twist-4 structure seems to retain in NNLO in the case when
statistical uncertainties are taken into account. The question of the stability
of these results to the application of the [0/2] Pad\'e resummation technique
is considered. Our NNLO results for values, extracted from the
CCFR data, are provided the twist-4 contributions are fixed through the
infrared renormalon model and provided the twist-4 terms are considered as
free parameters.Comment: 33 pages LaTeX, 3 ps figures; minor misprints are eliminated, 2 new
referencies are added; accepted for publication in Nucl. Phys.
Reconstructing Sparticle Mass Spectra using Hadronic Decays
Most sparticle decay cascades envisaged at the Large Hadron Collider (LHC)
involve hadronic decays of intermediate particles. We use state-of-the art
techniques based on the \kt jet algorithm to reconstruct the resulting hadronic
final states for simulated LHC events in a number of benchmark supersymmetric
scenarios. In particular, we show that a general method of selecting
preferentially boosted massive particles such as W, Z or Higgs bosons decaying
to jets, using sub-jets found by the \kt algorithm, suppresses QCD backgrounds
and thereby enhances the observability of signals that would otherwise be
indistinct. Consequently, measurements of the supersymmetric mass spectrum at
the per-cent level can be obtained from cascades including the hadronic decays
of such massive intermediate bosons.Comment: 1+29 pages, 12 figure
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