12 research outputs found
Low-Energy Thermal Leptogenesis in an Extended NMSSM Model
Thermal leptogenesis in the canonical seesaw model in supersymmetry suffers
from the incompatibility of a generic lower bound on the mass scale of the
lightest right-handed neutrino and the upper bound on the reheating temperature
of the Universe after inflation. This is resolved by adding an extra singlet
superfield, with a discrete symmetry, to the NMSSM (Next to Minimal
Supersymmetric Standard Model). This generic mechanism is applicable to any
supersymmetric model for lowering the scale of leptogenesis.Comment: 16 pages, revtex, 9 eps figure
The Gravitino-Stau Scenario after Catalyzed BBN
We consider the impact of Catalyzed Big Bang Nucleosynthesis on theories with
a gravitino LSP and a charged slepton NLSP. In models where the gravitino to
gaugino mass ratio is bounded from below, such as gaugino-mediated SUSY
breaking, we derive a lower bound on the gaugino mass parameter m_1/2. As a
concrete example, we determine the parameter space of gaugino mediation that is
compatible with all cosmological constraints.Comment: 1+14 pages, 6 figures; v2: minor clarifications, 1 reference added,
matches version to appear in JCA
Bounds on long-lived charged massive particles from Big Bang nucleosynthesis
The Big Bang nucleosynthesis (BBN) in the presence of charged massive
particles (CHAMPs) is studied in detail. All currently known effects due to the
existence of bound states between CHAMPs and nuclei, including possible
late-time destruction of Li6 and Li7 are included. The study sets conservative
bounds on CHAMP abundances in the decay time range 3x10^2 sec - 10^12 sec. It
is stressed that the production of Li6 at early times T ~ 10keV is
overestimated by a factor ~ 10 when the approximation of the Saha equation for
the He4 bound state fraction is utilised. To obtain conservative limits on the
abundance of CHAMPs, a Monte-Carlo analysis with ~ 3x10^6 independent BBN runs,
varying reaction rates of nineteen different reactions, is performed (see
attached erratum, however). The analysis yields the surprising result that
except for small areas in the particle parameter space conservative constraints
on the abundance of decaying charged particles are currently very close to
those of neutral particles. It is shown that, in case a number of heretofore
unconsidered reactions may be determined reliably in future, it is conceivable
that the limit on CHAMPs in the early Universe could be tightened by orders of
magnitude. An ERRATUM gives limits on primordial CHAMP densities when the by
Ref. Kamimura et al. recently more accurately determined CHAMP reaction rates
are employed.Comment: includes Erratum showing most up to date limits after determination
of the most important reaction rate
A note on the primordial abundance of stau NLSPs
In scenarios with a gravitino LSP, there exist strong BBN constraints on the
abundance of a possible stau NLSP. We find that in settings with substantial
left-right mixing of the stau mass eigenstates these constraints can be evaded
even for very long-lived staus.Comment: 17 pages, 5 figures, discussion on vacuum stability adde
Flaxino dark matter and stau decay
If the spontaneous breaking of Peccei-Quinn symmetry comes from soft
supersymmetry breaking, the fermionic partners of the symmetry-breaking fields
have mass of order the gravitino mass, and are called flatinos. The lightest
flatino, called here the flaxino, is a CDM candidate if it is the lightest
supersymmetric particle. We here explore flaxino dark matter assuming that the
lightest ordinary supersymmetric particle is the stau, with gravity-mediated
supersymmetry breaking. The decay of the stau to the flaxino is fast enough not
to spoil the standard predictions of Big Bang Nucleosynthesis, and its track
and decay can be seen in future colliders.Comment: 9 pages, 4 figures, to appear in JHE
A Bitter Pill: The Primordial Lithium Problem Worsens
The lithium problem arises from the significant discrepancy between the
primordial 7Li abundance as predicted by BBN theory and the WMAP baryon
density, and the pre-Galactic lithium abundance inferred from observations of
metal-poor (Population II) stars. This problem has loomed for the past decade,
with a persistent discrepancy of a factor of 2--3 in 7Li/H. Recent developments
have sharpened all aspects of the Li problem. Namely: (1) BBN theory
predictions have sharpened due to new nuclear data, particularly the
uncertainty on 3He(alpha,gamma)7Be, has reduced to 7.4%, and with a central
value shift of ~ +0.04 keV barn. (2) The WMAP 5-year data now yields a cosmic
baryon density with an uncertainty reduced to 2.7%. (3) Observations of
metal-poor stars have tested for systematic effects, and have reaped new
lithium isotopic data. With these, we now find that the BBN+WMAP predicts 7Li/H
= (5.24+0.71-0.67) 10^{-10}. The Li problem remains and indeed is exacerbated;
the discrepancy is now a factor 2.4--4.3 or 4.2sigma (from globular cluster
stars) to 5.3sigma (from halo field stars). Possible resolutions to the lithium
problem are briefly reviewed, and key nuclear, particle, and astronomical
measurements highlighted.Comment: 21 pages, 4 figures. Comments welcom
Nucleosynthesis Constraints on a Massive Gravitino in Neutralino Dark Matter Scenarios
The decays of massive gravitinos into neutralino dark matter particles and
Standard Model secondaries during or after Big-Bang nucleosynthesis (BBN) may
alter the primordial light-element abundances. We present here details of a new
suite of codes for evaluating such effects, including a new treatment based on
PYTHIA of the evolution of showers induced by hadronic decays of massive,
unstable particles such as a gravitino. We also develop an analytical treatment
of non-thermal hadron propagation in the early universe, and use this to derive
analytical estimates for light-element production and in turn on decaying
particle lifetimes and abundances. We then consider specifically the case of an
unstable massive gravitino within the constrained minimal supersymmetric
extension of the Standard Model (CMSSM). We present upper limits on its
possible primordial abundance before decay for different possible gravitino
masses, with CMSSM parameters along strips where the lightest neutralino
provides all the astrophysical cold dark matter density. We do not find any
CMSSM solution to the cosmological Li7 problem for small m_{3/2}. Discounting
this, for m_{1/2} ~ 500 GeV and tan beta = 10 the other light-element
abundances impose an upper limit m_{3/2} n_{3/2}/n_\gamma < 3 \times 10^{-12}
GeV to < 2 \times 10^{-13} GeV for m_{3/2} = 250 GeV to 1 TeV, which is similar
in both the coannihilation and focus-point strips and somewhat weaker for tan
beta = 50, particularly for larger m_{1/2}. The constraints also weaken in
general for larger m_{3/2}, and for m_{3/2} > 3 TeV we find a narrow range of
m_{3/2} n_{3/2}/n_\gamma, at values which increase with m_{3/2}, where the Li7
abundance is marginally compatible with the other light-element abundances.Comment: 74 pages, 40 Figure
The Number Density of a Charged Relic.
We investigate scenarios in which a charged, long-lived scalar particle
decouples from the primordial plasma in the Early Universe. We compute the
number density at time of freeze-out considering both the cases of abelian and
non-abelian interactions and including the effect of Sommerfeld enhancement at
low initial velocity. We also discuss as extreme case the maximal cross section
that fulfils the unitarity bound. We then compare these number densities to the
exotic nuclei searches for stable relics and to the BBN bounds on unstable
relics and draw conclusions for the cases of a stau or stop NLSP in
supersymmetric models with a gravitino or axino LSP.Comment: 45 page
Dark Matter from Gaugino Mediation.
We study dark matter for gaugino-mediated supersymmetry breaking and compact
dimensions of order the grand unification scale. Higgs fields are bulk fields,
and in general their masses differ from those of squarks and sleptons at the
unification scale. As a consequence, at different points in parameter space,
the gravitino, a neutralino or a scalar lepton can be the lightest (LSP) or
next-to-lightest (NLSP) superparticle. We investigate the constraints from
primordial nucleosynthesis on the different scenarios. While neutralino and
gravitino dark matter with a sneutrino NLSP are consistent for a wide range of
parameters, gravitino dark matter with a stau NLSP is strongly constrained.Comment: 18 pages, updated to published version (minor modifications,
reference added