190 research outputs found
Complexified Starobinsky Inflation in Supergravity in the Light of Recent BICEP2 Result
Motivated by the recent observation of the B-mode signal in the cosmic
microwave background by BICEP2, we stuty the Starobinsky-type inflation model
in the framework of old-minimal supergravity, where the inflaton field in the
original (non-supersymmetric) Starobinsky inflation model becomes a complex
field. We study how the inflaton evolves on the two-dimensional field space,
varying the initial condition. We show that (i) one of the scalar fields has a
very steep potential once the trajectory is off from that of the original
Starobinsky inflation, and that (ii) the B-mode signal observed by BICEP2 is
too large to be consistent with the prediction of the model irrespective of the
initial condition. Thus, the BICEP2 result strongly disfavors the complexified
Starobinsky inflation in supergravity.Comment: 8 pages, 2 figures, the published versio
Gravitino/Axino as Decaying Dark Matter and Cosmological Tensions
In supersymmetric axion models, if the gravitino or axino is the lightest
SUSY particle (LSP), the other is often the next-to-LSP (NLSP). We investigate
the cosmology of such a scenario and point out that the lifetime of the NLSP
naturally becomes comparable to the present age of the universe in a viable
parameter region. This is a well-motivated example of the so-called decaying
dark matter model, which is recently considered as an extension of the
CDM model to relax some cosmological tensions.Comment: 16 pages, 2 figures, Journal versio
AMS-02 Antiprotons from Annihilating or Decaying Dark Matter
Recently the AMS-02 experiment reported an excess of cosmic ray antiprotons
over the expected astrophysical background. We interpret the excess as a signal
from annihilating or decaying dark matter and find that the observed spectrum
is well fitted by adding contributions from the annihilation or decay of dark
matter with mass of O(TeV) or larger. Interestingly, Wino dark matter with mass
of around 3 TeV, whose thermal relic abundance is consistent with present dark
matter abundance, can explain the antiproton excess. We also discuss the
implications for the decaying gravitino dark matter with R-parity violation.Comment: 12 pages, 3 figure
Predictions for the neutrino parameters in the minimal gauged U(1) model
We study the structure of the neutrino mass matrix in the minimal gauged
U(1) model, where three right-handed neutrinos are added to
the Standard Model in order to obtain non-zero masses for active neutrinos.
Because of the U(1) gauge symmetry, the structure of both
Dirac and Majorana mass terms of neutrinos is tightly restricted. In
particular, the inverse of the neutrino mass matrix has zeros in the
and components, namely, this model offers a symmetric
realization of the so-called two-zero-minor structure in the neutrino mass
matrix. Due to these constraints, all the CP phases-the Dirac CP phase
and the Majorana CP phases and -as well as the mass
eigenvalues of the light neutrinos are uniquely determined as functions
of the neutrino mixing angles , , and ,
and the squared mass differences and . We
find that this model predicts the Dirac CP phase to be - (-), the sum of the neutrino masses to be
-0.22 eV (-0.40 eV), and the effective mass for
the neutrinoless double beta decay to be -0.055 eV (-0.12 eV) at () level, which
are totally consistent with the current experimental limits. These predictions
can soon be tested in future neutrino experiments. Implications for
leptogenesis are also discussed.Comment: v1: 23 pages, 6 figures. v2: 24 pages, 8 figures, Discussion on
leptogenesis adde
Higgs mass, muon g-2, and LHC prospects in gauge mediation models with vector-like matters
Recently the ATLAS and CMS collaborations presented preliminary results of
Standard Model Higgs searches and reported excesses of events for a Higgs boson
at 124-126 GeV. Such a Higgs mass can be naturally realized, simultaneously
explaining the muon g-2 anomaly, in gauge-mediated SUSY breaking models with
extra vector-like matters. Upper bounds are obtained on the gluino mass,
m_{\tilde g}\lesssim 1.2 (1.8) TeV, and on the extra vector-like quark mass,
M_{Q'} \lesssim 1.0 (1.8) GeV, in the parameter region where the Higgs boson
mass is 124-126 GeV and the muon g-2 is consistent with the experimental value
at the 1 sigma (2 sigma) level. The LHC prospects are explored in the parameter
region. It is found that some of the regions are already excluded by the LHC,
and most of the parameter space is expected to be covered at \sqrt{s} = 14 TeV.
A study on the extra vector-like quarks, especially current bounds on their
masses and prospects for future searches, is also included.Comment: 28 pages, 10 figure
- …