17 research outputs found
Gravitino dark matter in brane-world cosmology
The gravitino dark matter hypothesis in the brane cosmology is studied. The
theoretical framework is the CMSSM for particle physics and RS II brane model
for gravity. It is found that the gravitino can play the role of dark matter in
the universe and we determine what the gravitino mass should be for different
values of the five-dimensional Planck mass. An upper bound is obtained for the
latter.Comment: Improved version with minor corrections, to appear in JCA
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
Towards constraints on the SUSY seesaw from flavour-dependent leptogenesis
We systematically investigate constraints on the parameters of the
supersymmetric type-I seesaw mechanism from the requirement of successful
thermal leptogenesis in the presence of upper bounds on the reheat temperature
of the early Universe. To this end, we solve the
flavour-dependent Boltzmann equations in the MSSM, extended to include
reheating. With conservative bounds on , leading to mildly
constrained scenarios for thermal leptogenesis, compatibility with observation
can be obtained for extensive new regions of the parameter space, due to
flavour-dependent effects. On the other hand, focusing on (normal) hierarchical
light and heavy neutrinos, the hypothesis that there is no CP violation
associated with the right-handed neutrino sector, and that leptogenesis
exclusively arises from the CP-violating phases of the matrix,
is only marginally consistent. Taking into account stricter bounds on
further suggests that (additional) sources of CP violation must
arise from the right-handed neutrino sector, further implying stronger
constraints for the right-handed neutrino parameters.Comment: 42 pages, 12 figures; final version published in JCAP; numerical
results for the efficiency factor can be downloaded from
http://www.newphysics.eu/leptogenesis
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
Constraints on Supersymmetric Models from Catalytic Primordial Nucleosynthesis of Beryllium
The catalysis of nuclear reactions by negatively charged relics leads to
increased outputs of primordial ^6Li and ^9Be. In combination with
observational constraints on the primordial fractions of ^6Li and ^9Be, this
imposes strong restrictions on the primordial abundance and the lifetime of
charged relics. We analyze the constraints from the catalysis of ^9Be on
supersymmetric models in which the gravitino is the lightest supersymmetric
particle and a charged slepton--such as the lighter stau--the next-to-lightest
supersymmetric particle (NLSP). Barring the special cases in which the
primordial fraction of the slepton NLSP is significantly depleted, we find that
the ^9Be data require a slepton NLSP lifetime of less than 6x10^3 seconds. We
also address the issue of the catalytic destruction of ^6Li and ^9Be by late
forming bound states of protons with negatively charged relics finding that it
does not lead to any significant modification of the limit on the slepton
lifetime.Comment: 31 pages, 8 figures; minor additions, matches published versio
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
Direct stau production at hadron colliders in cosmologically motivated scenarios
We calculate dominant cross section contributions for stau pair production at
hadron colliders within the MSSM, taking into account left-right mixing of the
stau eigenstates. We find that b-quark annihilation and gluon fusion can
enhance the cross sections by more than one order of magnitude with respect to
the Drell-Yan predictions. These additional production channels are not yet
included in the common Monte Carlo analysis programs and have been neglected in
experimental analyses so far. For long-lived staus, we investigate differential
distributions and prospects for their stopping in the collider detectors. New
possible strategies are outlined to determine the mass and width of the heavy
CP-even Higgs boson H0. Scans of the relevant regions in the CMSSM are
performed and predictions are given for the current experiments at the LHC and
the Tevatron. The obtained insights allow us to propose collider tests of
cosmologically motivated scenarios with long-lived staus that have an
exceptionally small thermal relic abundance.Comment: 49 pages, 13 figures; v2: references added, typos corrected, text
streamlined, results unchange