18 research outputs found
Leptogenesis, Gravitino Dark Matter and Entropy Production
Many extensions of the Standard Model predict super-weakly interacting
particles, which typically have to decay before Big Bang Nucleosynthesis (BBN).
The entropy produced in the decays may help to reconcile thermal leptogenesis
and BBN in scenarios with gravitino dark matter, which is usually difficult due
to late decays of the next-to-lightest supersymmetric particle (NLSP) spoiling
the predictions of BBN. We study this possibility for a general neutralino
NLSP. We elaborate general properties of the scenario and strong constraints on
the entropy-producing particle. As an example, we consider the saxion from the
axion multiplet and show that, while enabling a solution of the strong CP
problem, it can also produce a suitable amount of entropy.Comment: 28 pages, 3 figures; v2: references updated, changes in presentation
including some generalization, results and conclusions unchanged; v3: 1
reference added, matches published versio
A new life for sterile neutrinos: resolving inconsistencies using hot dark matter
Within the standard LCDM model of cosmology, the recent Planck measurements
have shown discrepancies with other observations, e.g., measurements of the
current expansion rate H_0, the galaxy shear power spectrum and counts of
galaxy clusters. We show that if LCDM is extended by a hot dark matter
component, which could be interpreted as a sterile neutrino, the data sets can
be combined consistently. A combination of Planck data, WMAP-9 polarisation
data, measurements of the BAO scale, the HST measurement of H_0, Planck galaxy
cluster counts and galaxy shear data from the CFHTLens survey yields Delta
N_eff = 0.61 pm 0.30 and m_s^eff = (0.41 pm 0.13) eV at 1 sigma. The former is
driven mainly by the large H_0 of the HST measurement, while the latter is
driven by cluster data. CFHTLens galaxy shear data prefer Delta N_eff >0 and a
non-zero mass. Taken together, we find hints for the presence of a hot dark
matter component at 3 sigma. A sterile neutrino motivated by the reactor and
gallium anomalies appears rejected at even higher significance and an
accelerator anomaly sterile neutrino is found in tension at 2 sigma.Comment: 11 pages, 2 figures; v2: 12 pages, 3 figures, references added and
discussion slightly expanded, matches version published in JCA
Testing Superstring Theories with Gravitational Waves
We provide a simple transfer function that determines the effect of an early
matter dominated era on the gravitational wave background and show that a large
class of compactifications of superstring theory might be tested by
observations of the gravitational wave background from inflation. For large
enough reheating temperatures > 10^9 \GeV the test applies to all models
containing at least one scalar with mass < 10^{12}\GeV that acquires a large
initial oscillation amplitude after inflation and has only gravitational
interaction strength, i.e., a field with the typical properties of a modulus.Comment: 5 pages 2 figures, v2: changes in presentation, refs revised, matches
version in print in PR
Dark and visible matter with broken R-parity and the axion multiplet
A small breaking of R-parity reconciles thermal leptogenesis, gravitino dark
matter and primordial nucleosynthesis. We find that the same breaking relaxes
cosmological bounds on the axion multiplet. Naturally expected spectra become
allowed and bounds from late particle decays become so weak that they are
superseded by bounds from non-thermal axion production. In this sense, the
strong CP problem serves as an additional motivation for broken R-parity.Comment: 13 pages + refs, 1 table, v2: refs added, minor changes in
presentation, v3: refs added, added discussion of decays into Higgs and
Higgsino, matches published versio
NMSSM with Gravitino Dark Matter to be tested at LHC
We present a solution to the gravitino problem, which arises in the NMSSM, allowing for sparticle spectra from ordinary gravity-mediated supersymmetry breaking with weak-scale gravitino dark matter. The coupling, which links the singlet to the MSSM sector, enhances the tree-level Higgs mass, providing an attractive explanation why the observed Higgs boson is so heavy. The same coupling induces very efficient pair-annihilation processes of the neutralino NLSP. Its relic abundance can be sufficiently suppressed to satisfy the strong constraints on late decaying relics from primordial nucleosynthesis -- even for very long neutralino lifetimes. The striking prediction of this scenario is the detection of a pseudoscalar Higgs boson in the search for top-top resonances at LHC-14, rendering it completely testable