725 research outputs found
Light mixed sneutrinos as thermal dark matter
In supersymmetric models with Dirac neutrino masses, a left-right mixed
sneutrino can be a viable dark matter candidate. We examine the
MSSM+ parameter space where this is the case with particular
emphasis on light sneutrinos with masses below 10 GeV. We discuss implications
for direct and indirect dark matter searches, including the relevant
uncertainties, as well as consequences for collider phenomenology.Comment: 33 pages, 14 figures; one figure and references adde
Abundance of Cosmological Relics in Low-Temperature Scenarios
We investigate the relic density n_\chi of non-relativistic long-lived or
stable particles \chi in cosmological scenarios in which the temperature T is
too low for \chi to achieve full chemical equilibrium. The case with a heavier
particle decaying into \chi is also investigated. We derive approximate
solutions for n_\chi(T) which accurately reproduce numerical results when full
thermal equilibrium is not achieved. If full equilibrium is reached, our ansatz
no longer reproduces the correct temperature dependence of the \chi number
density. However, it does give the correct final relic density, to an accuracy
of about 3% or better, for all cross sections and initial temperatures.Comment: 26 pages, 8 figures, comments added, to appear in Phys. Rev.
Update on Fermion Mass Models with an Anomalous Horizontal U(1) Symmetry
We reconsider models of fermion masses and mixings based on a gauge anomalous
horizontal U(1) symmetry. In the simplest model with a single flavon field and
horizontal charges of the same sign for all Standard Model fields, only very
few charge assignements are allowed when all experimental data, including
neutrino oscillation data, is taken into account. We show that a precise
description of the observed fermion masses and mixing angles can easily be
obtained by generating sets of the order one parameters left unconstrained by
the U(1) symmetry. The corresponding Yukawa matrices show several interesting
features which may be important for flavour changing neutral currents and CP
violation effects in supersymmetric models.Comment: 23 pages, 8 figure
Search for Higgs bosons of the Universal Extra Dimensions at the Large Hadron Collider
The Higgs sector of the Universal Extra Dimensions (UED) has a rather
involved setup. With one extra space dimension, the main ingredients to the
construct are the higher Kaluza-Klein (KK) excitations of the Standard Model
Higgs boson and the fifth components of the gauge fields which on
compactification appear as scalar degrees of freedom and can mix with the
former thus leading to physical KK-Higgs states of the scenario. In this work,
we explore in detail the phenomenology of such a Higgs sector of the UED with
the Large Hadron Collider (LHC) in focus. We work out relevant decay branching
fractions involving the KK-Higgs excitations. Possible production modes of the
KK-Higgs bosons are then discussed with an emphasis on their associated
production with the third generation KK-quarks and that under the cascade
decays of strongly interacting UED excitations which turn out to be the only
phenomenologically significant modes. It is pointed out that the collider
searches of such Higgs bosons face generic hardship due to soft end-products
which result from severe degeneracies in the masses of the involved excitations
in the minimal version of the UED (MUED). Generic implications of either
observing some or all of the KK-Higgs bosons at the LHC are discussed.Comment: 25 pages, 9 figures and 1 tabl
Precise Calculation of the Relic Density of Kaluza-Klein Dark Matter in Universal Extra Dimensions
We revisit the calculation of the relic density of the lightest Kaluza-Klein
particle (LKP) in the model of Universal Extra Dimensions. The Kaluza-Klein
(KK) particle spectrum at level one is rather degenerate, and various
coannihilation processes may be relevant. We extend the calculation of
hep-ph/0206071 to include coannihilation processes with all level one KK
particles. In our computation we consider a most general KK particle spectrum,
without any simplifying assumptions. In particular, we do not assume a
completely degenerate KK spectrum and instead retain the dependence on each
individual KK mass. As an application of our results, we calculate the
Kaluza-Klein relic density in the Minimal UED model, turning on coannihilations
with all level one KK particles. We then go beyond the minimal model and
discuss the size of the coannihilation effects separately for each class of
level 1 KK particles. Our results provide the basis for consistent relic
density computations in arbitrarily general models with Universal Extra
Dimenions.Comment: 44 pages, 19 figures, typeset in JHEP styl
Minimal Universal Extra Dimensions in CalcHEP/CompHEP
We present an implementation of the model of minimal universal extra
dimensions (MUED) in CalcHEP/CompHEP. We include all level-1 and level-2
Kaluza-Klein (KK) particles outside the Higgs sector. The mass spectrum is
automatically calculated at one loop in terms of the two input parameters in
MUED: the radius of the extra dimension and the cut-off scale of the model. We
implement both the KK number conserving and the KK number violating
interactions of the KK particles. We also account for the proper running of the
gauge coupling constants above the electroweak scale. The implementation has
been extensively cross-checked against known analytical results in the
literature and numerical results from other programs. Our files are publicly
available and can be used to perform various automated calculations within the
MUED model.Comment: 32 pages, 4 figures, 6 tables, invited contribution for New Journal
of Physics Focus Issue on 'Extra Space Dimensions', the model file can be
downloaded from http://home.fnal.gov/~kckong/mued
- âŠ