7,353 research outputs found
Revising Limits on Neutrino-Majoron Couplings
Any theory that have a global spontaneously broken symmetry will imply the
existence of very light neutral bosons or massless bosons (sometimes called
Majorons). For most of these models we have neutrino-Majoron couplings, that
appear as additional branching ratios in decays of mesons and leptons. Here we
present an updated limits on the couplings between the electron, muon and tau
neutrinos and Majorons. For such we analyze the possible effects of Majoron
emission in both meson and lepton decays. In the latter we also include an
analysis of the muon decay spectrum. Our results are
, and
at 90 % C. L., where .Comment: 12 pages, 5 figure
Reconciling thermal leptogenesis with the gravitino problem in SUSY models with mixed axion/axino dark matter
Successful implementation of thermal leptogenesis requires re-heat
temperatures T_R\agt 2\times 10^9 GeV, in apparent conflict with SUSY models
with TeV-scale gravitinos, which require much lower T_R in order to avoid Big
Bang Nucleosynthesis (BBN) constraints. We show that mixed axion/axino dark
matter can reconcile thermal leptogenesis with the gravitino problem in models
with m_{\tG}\agt 30 TeV, a rather high Peccei-Quinn breaking scale and an
initial mis-alignment angle \theta_i < 1. We calculate axion and axino dark
matter production from four sources, and impose BBN constraints on long-lived
gravitinos and neutralinos. Moreover, we discuss several SUSY models which
naturally have gravitino masses of the order of tens of TeV. We find a
reconciliation difficult in Yukawa-unified SUSY and in AMSB with a wino-like
lightest neutralino. However, T_R\sim 10^{10}-10^{12} GeV can easily be
achieved in effective SUSY and in models based on mixed moduli-anomaly
mediation. Consequences of this scenario include: 1. an LHC SUSY discovery
should be consistent with SUSY models with a large gravitino mass, 2. an
apparent neutralino relic abundance \Omega_{\tz_1}h^2\alt 1, 3. no WIMP direct
or indirect detection signals should be found, and 4. the axion mass should be
less than \sim 10^{-6} eV, somewhat below the conventional range which is
explored by microwave cavity axion detection experiments.Comment: 25 pages including 15 .eps figures; updated version to coincide with
published versio
Thermal leptogenesis and the gravitino problem in the Asaka-Yanagida axion/axino dark matter scenario
A successful implementation of thermal leptogenesis requires the re-heat
temperature after inflation T_R to exceed ~2\times 10^9 GeV. Such a high T_R
value typically leads to an overproduction of gravitinos in the early universe,
which will cause conflicts, mainly with BBN constraints. Asaka and Yanagida
(AY) have proposed that these two issues can be reconciled in the context of
the Peccei-Quinn augmented MSSM (PQMSSM) if one adopts a mass hierarchy
m(sparticle)>m(gravitino)>m(axino), with m(axino) keV. We calculate the relic
abundance of mixed axion/axino dark matter in the AY scenario, and investigate
under what conditions a value of T_R sufficient for thermal leptogenesis can be
generated. A high value of PQ breaking scale f_a is needed to suppress
overproduction of axinos, while a small vacuum misalignment angle \theta_i is
needed to suppress overproduction of axions. The large value of f_a results in
late decaying neutralinos. To avoid BBN constraints, the AY scenario requires a
low thermal abundance of neutralinos and high values of neutralino mass. We
include entropy production from late decaying saxions, and find the saxion
needs to be typically at least several times heavier than the gravitino. A
viable AY scenario suggests that LHC should discover a spectrum of SUSY
particles consistent with weak scale supergravity; that the apparent neutralino
abundance is low; that a possible axion detection signal (probably with m_axion
in the sub-micro-eV range) should occur, but no direct or indirect signals for
WIMP dark matter should be observed.Comment: 28 pages including 21 .eps figures; high resolution pdf version
available at http://www.nhn.ou.edu/~bae
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