130 research outputs found
Small steps towards Grand Unification and the electron/positron excesses in cosmic-ray experiments
We consider a small extension of the standard model by adding two Majorana
fermions; those are adjoint representations of the SU(2)_L and SU(3)_c gauge
groups of the standard model. In this extension, the gauge coupling unification
at an energy scale higher than 10^{15} GeV is realized when the masses of the
triplet and the octet fermions are smaller than 10^4 GeV and 10^{12} GeV,
respectively. We also show that an appropriate symmetry ensures a long lifetime
of the neutral component of the triplet fermion whose thermal relic density
naturally explains the observed dark matter density. The electron/positron
excesses observed in recent cosmic-ray experiments can be also explained by the
decay of the triplet fermion.Comment: 11 pages, 5 figure
Dirac gaugino as leptophilic dark matter
We investigate the leptophilic properties of Dirac gauginos in an
R--symmetric N=2 supersymmetric model with extended gauge and Higgs sectors.
The annihilation of Dirac gauginos to leptons requires no chirality flip in the
final states so that it is not suppressed as in the Majorana case. This implies
that it can be sizable enough to explain the positron excess observed by the
PAMELA experiment with moderate or no boost factors. When squark masses are
heavy, the annihilation of Dirac gauginos to hadrons is controlled by their
Higgsino fraction and is driven by the and final states.
Moreover, at variance with the Majorana case, Dirac gauginos with a
non-vanishing higgsino fraction can also have a vector coupling with the
gauge boson leading to a sizable spin--independent scattering cross section off
nuclei. Saturating the current antiproton limit, we show that Dirac gauginos
can leave a signal in direct detection experiments at the level of the
sensitivity of dark matter searches at present and in the near future.Comment: 24 pages, 10 figures, typos corrected, final version published on
JCA
Indirect Detection of Kaluza-Klein Dark Matter from Latticized Universal Dimensions
We consider Kaluza-Klein dark matter from latticized universal dimensions. We
motivate and investigate two different lattice models, where the models differ
in the choice of boundary conditions. The models reproduce relevant features of
the continuum model for Kaluza-Klein dark matter. For the model with simple
boundary conditions, this is the case even for a model with only a few lattice
sites. We study the effects of the latticization on the differential flux of
positrons from Kaluza-Klein dark matter annihilation in the galactic halo. We
find that for different choices of the compactification radius, the
differential positron flux rapidly converges to the continuum model results as
a function of the number of lattice sites. In addition, we consider the
prospects for upcoming space-based experiments such as PAMELA and AMS-02 to
probe the latticization effect.Comment: 25 pages, 9 figures, LaTeX. Final version published in JCA
Cosmic Ray Spectra in Nambu-Goldstone Dark Matter Models
We discuss the cosmic ray spectra in annihilating/decaying Nambu-Goldstone
dark matter models. The recent observed positron/electron excesses at PAMELA
and Fermi experiments are well fitted by the dark matter with a mass of 3TeV
for the annihilating model, while with a mass of 6 TeV for the decaying model.
We also show that the Nambu-Goldstone dark matter models predict a distinctive
gamma-ray spectrum in a certain parameter space.Comment: 16 pages, 4 figure
A Pyramid Scheme for Particle Physics
We introduce a new model, the Pyramid Scheme, of direct mediation of SUSY
breaking, which is compatible with the idea of Cosmological SUSY Breaking
(CSB). It uses the trinification scheme of grand unification and avoids
problems with Landau poles in standard model gauge couplings. It also avoids
problems, which have recently come to light, associated with rapid stellar
cooling due to emission of the pseudo Nambu-Goldstone Boson (PNGB) of
spontaneously broken hidden sector baryon number. With a certain pattern of
R-symmetry breaking masses, a pattern more or less required by CSB, the Pyramid
Scheme leads to a dark matter candidate that decays predominantly into leptons,
with cross sections compatible with a variety of recent observations. The dark
matter particle is not a thermal WIMP but a particle with new strong
interactions, produced in the late decay of some other scalar, perhaps the
superpartner of the QCD axion, with a reheat temperature in the TeV range. This
is compatible with a variety of scenarios for baryogenesis, including some
novel ones which exploit specific features of the Pyramid Scheme.Comment: JHEP Latex, 32 pages, 1 figur
Fundamental physics in space with the Fermi Gamma-ray Space Telescope
Successfully launched in June 2008, the Fermi Gamma-ray Space Telescope,
formerly named GLAST, has been observing the high-energy gamma-ray sky with
unprecedented sensitivity for more than two years, opening a new window on a
wide variety of exotic astrophysical objects. This paper is a short overview of
the main science highlights, aimed at non-specialists, with emphasis on those
which are more directly connected with the study of fundamental
physics---particularly the search for signals of new physics in the diffuse
gamma-ray emission and in the cosmic radiation and the study of Gamma-Ray Burst
as laboratories for testing possible violations of the Lorentz invariance.Comment: 12 pages, 7 figures, submitted for the proceedings of DICE 201
Gamma-ray and radio tests of the e+e- excess from DM annihilations
PAMELA and ATIC recently reported an excess in e+e- cosmic rays. We show that
if it is due to Dark Matter annihilations, the associated gamma-ray flux and
the synchrotron emission produced by e+e- in the galactic magnetic field
violate HESS and radio observations of the galactic center and HESS
observations of dwarf Spheroidals, unless the DM density profile is
significantly less steep than the benchmark NFW and Einasto profiles.Comment: 16 pages, 4 figures; v2: normalizations fixed in Table 2 and typos
corrected (no changes in the analysis nor the results), some references and
comments added; v3: minor additions, matches published versio
Dark matter and sub-GeV hidden U(1) in GMSB models
Motivated by the recent PAMELA and ATIC data, one is led to a scenario with
heavy vector-like dark matter in association with a hidden sector
below GeV scale. Realizing this idea in the context of gauge mediated
supersymmetry breaking (GMSB), a heavy scalar component charged under
is found to be a good dark matter candidate which can be searched for direct
scattering mediated by the Higgs boson and/or by the hidden gauge boson. The
latter turns out to put a stringent bound on the kinetic mixing parameter
between and : . For the typical range
of model parameters, we find that the decay rates of the ordinary lightest
neutralino into hidden gauge boson/gaugino and photon/gravitino are comparable,
and the former decay mode leaves displaced vertices of lepton pairs and missing
energy with distinctive length scale larger than 20 cm for invariant lepton
pair mass below 0.5 GeV. An unsatisfactory aspect of our model is that the
Sommerfeld effect cannot raise the galactic dark matter annihilation by more
than 60 times for the dark matter mass below TeV.Comment: 1+15 pages, 4 figures, version published in JCAP, references added,
minor change
Two component dark matter
We explain the PAMELA positron excess and the PPB-BETS/ATIC e+ + e- data
using a simple two component dark matter model (2DM). The two particle species
in the dark matter sector are assumed to be in thermal equilibrium in the early
universe. While one particle is stable and is the present day dark matter, the
second one is metastable and decays after the universe is 10^-8 s old. In this
model it is simple to accommodate the large boost factors required to explain
the PAMELA positron excess without the need for large spikes in the local dark
matter density. We provide the constraints on the parameters of the model and
comment on possible signals at future colliders.Comment: 6 pages, 2 figures, discussion clarified and extende
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