7 research outputs found
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
Bound-State Effects on Light-Element Abundances in Gravitino Dark Matter Scenarios
If the gravitino is the lightest supersymmetric particle and the long-lived
next-to-lightest sparticle (NSP) is the stau, the charged partner of the tau
lepton, it may be metastable and form bound states with several nuclei. These
bound states may affect the cosmological abundances of Li6 and Li7 by enhancing
nuclear rates that would otherwise be strongly suppressed. We consider the
effects of these enhanced rates on the final abundances produced in Big-Bang
nucleosynthesis (BBN), including injections of both electromagnetic and
hadronic energy during and after BBN. We calculate the dominant two- and
three-body decays of both neutralino and stau NSPs, and model the
electromagnetic and hadronic decay products using the PYTHIA event generator
and a cascade equation. Generically, the introduction of bound states drives
light element abundances further from their observed values; however, for small
regions of parameter space bound state effects can bring lithium abundances in
particular in better accord with observations. We show that in regions where
the stau is the NSP with a lifetime longer than 10^3-10^4 s, the abundances of
Li6 and Li7 are far in excess of those allowed by observations. For shorter
lifetimes of order 1000 s, we comment on the possibility in minimal
supersymmetric and supergravity models that stau decays could reduce the Li7
abundance from standard BBN values while at the same time enhancing the Li6
abundance.Comment: 22 pages 6 figure
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
Graviton Cosmology in Universal Extra Dimensions
In models of universal extra dimensions, gravity and all standard model
fields propagate in the extra dimensions. Previous studies of such models have
concentrated on the Kaluza-Klein (KK) partners of standard model particles.
Here we determine the properties of the KK gravitons and explore their
cosmological implications. We find the lifetimes of decays to KK gravitons, of
relevance for the viability of KK gravitons as dark matter. We then discuss the
primordial production of KK gravitons after reheating. The existence of a tower
of KK graviton states makes such production extremely efficient: for reheat
temperature T_RH and d extra dimensions, the energy density stored in gravitons
scales as T_RH^{2+3d/2}. Overclosure and Big Bang nucleosynthesis therefore
stringently constrain T_RH in all universal extra dimension scenarios. At the
same time, there is a window of reheat temperatures low enough to avoid these
constraints and high enough to generate the desired thermal relic density for
KK WIMP and superWIMP dark matter.Comment: 19 pages, 1 figur
Dark matter with invisible light from heavy double charged leptons of almost-commutative geometry?
A new candidate of cold dark matter arises by a novel elementary particle
model: the almostcommutative AC-geometrical framework. Two heavy leptons are
added to the Standard Model, each one sharing a double opposite electric charge
and an own lepton flavor number The novel mathematical theory of
almost-commutative geometry [1] wishes to unify gauge models with gravity. In
this scenario two new heavy (m_L>100GeV), oppositely double charged leptons
(A,C),(A with charge -2 and C with charge +2), are born with no twin quark
companions. The model naturally involves a new U(1) gauge interaction,
possessed only by the AC-leptons and providing a Coulomblike attraction between
them. AC-leptons posses electro-magnetic as well as Z-boson interaction and,
according to the charge chosen for the new U(1) gauge interaction, a new
"invisible light" interaction. Their final cosmic relics are bounded into
"neutral" stable atoms (AC) forming the mysterious cold dark matter, in the
spirit of the Glashow's Sinister model. An (AC) state is reached in the early
Universe along a tail of a few secondary frozen exotic components. They should
be now here somehow hidden in the surrounding matter. The two main secondary
manifest relics are C (mostly hidden in a neutral (Cee) "anomalous helium"
atom, at a 10-8 ratio) and a corresponding "ion" A bounded with an ordinary
helium ion (4He); indeed the positive helium ions are able to attract and
capture the free A fixing them into a neutral relic cage that has nuclear
interaction (4HeA).Comment: This paper has been merged with [astro-ph/0603187] for publication in
Classical and Quantum Gravit
Single-field inflation, anomalous enhancement of superhorizon fluctuations, and non-Gaussianity in primordial black hole formation
We show a text-book potential for single-field inflation, namely, the
Coleman-Weinberg model can induce double inflation and formation of primordial
black holes (PBHs), because fluctuations that leave the horizon near the end of
first inflation are anomalously enhanced at the onset of second inflation when
the time-dependent mode turns to a growing mode rather than a decaying mode.
The mass of PBHs produced in this mechanism lies in several discrete ranges
depending on the model parameters. We also calculate the effects of
non-Gaussian statistics due to higher-order interactions on the abundance of
PBHs, which turns out to be small.Comment: 22pages, 8figure
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