108 research outputs found
Cosmic positron and antiproton constraints on the gauge-Higgs Dark Matter
We calculate the cosmic ray positron and antiproton spectra of a gauge-Higgs
dark matter candidate in a warped five-dimensional
gauge-Higgs unification model. The stability of the gauge-Higgs boson is
guaranteed by the H parity under which only the Higgs boson is odd at low
energy. The 4-point vertices of HHW^+W^- and HHZZ, allowed by H parity
conservation, have the same magnitude as in the standard model, which yields
efficient annihilation rate for . The most dominant annihilation
channel is followed by the subsequent decays of the
bosons into positrons or quarks, which undergo fragmentation into antiproton.
Comparing with the observed positron and antiproton spectra with the PAMALA and
Fermi/LAT, we found that the Higgs boson mass cannot be larger than 90 GeV, in
order not to overrun the observations. Together with the constraint on not
overclosing the Universe, the valid range of the dark matter mass is restricted
to 70-90 GeV.Comment: 13 pages, 3 figure
Galactic-Centre Gamma Rays in CMSSM Dark Matter Scenarios
We study the production of gamma rays via LSP annihilations in the core of
the Galaxy as a possible experimental signature of the constrained minimal
supersymmetric extension of the Standard Model (CMSSM), in which
supersymmetry-breaking parameters are assumed to be universal at the GUT scale,
assuming also that the LSP is the lightest neutralino chi. The part of the
CMSSM parameter space that is compatible with the measured astrophysical
density of cold dark matter is known to include a stau_1 - chi coannihilation
strip, a focus-point strip where chi has an enhanced Higgsino component, and a
funnel at large tanb where the annihilation rate is enhanced by the poles of
nearby heavy MSSM Higgs bosons, A/H. We calculate the total annihilation rates,
the fractions of annihilations into different Standard Model final states and
the resulting fluxes of gamma rays for CMSSM scenarios along these strips. We
observe that typical annihilation rates are much smaller in the coannihilation
strip for tanb = 10 than along the focus-point strip or for tanb = 55, and that
the annihilation branching ratios differ greatly between the different dark
matter strips. Whereas the current Fermi-LAT data are not sensitive to any of
the CMSSM scenarios studied, and the calculated gamma-ray fluxes are probably
unobservably low along the coannihilation strip for tanb = 10, we find that
substantial portions of the focus-point strips and rapid-annihilation funnel
regions could be pressured by several more years of Fermi-LAT data, if
understanding of the astrophysical background and/or systematic uncertainties
can be improved in parallel.Comment: 33 pages, 12 figures, comments and references added, version to
appear in JCA
A New Approach to Searching for Dark Matter Signals in Fermi-LAT Gamma Rays
Several cosmic ray experiments have measured excesses in electrons and
positrons, relative to standard backgrounds, for energies from ~ 10 GeV - 1
TeV. These excesses could be due to new astrophysical sources, but an
explanation in which the electrons and positrons are dark matter annihilation
or decay products is also consistent. Fortunately, the Fermi-LAT diffuse gamma
ray measurements can further test these models, since the electrons and
positrons produce gamma rays in their interactions in the interstellar medium.
Although the dark matter gamma ray signal consistent with the local electron
and positron measurements should be quite large, as we review, there are
substantial uncertainties in the modeling of diffuse backgrounds and,
additionally, experimental uncertainties that make it difficult to claim a dark
matter discovery. In this paper, we introduce an alternative method for
understanding the diffuse gamma ray spectrum in which we take the intensity
ratio in each energy bin of two different regions of the sky, thereby canceling
common systematic uncertainties. For many spectra, this ratio fits well to a
power law with a single break in energy. The two measured exponent indices are
a robust discriminant between candidate models, and we demonstrate that dark
matter annihilation scenarios can predict index values that require "extreme"
parameters for background-only explanations.Comment: v1: 11 pages, 7 figures, 1 table, revtex4; v2: 13 pages, 8 figures, 1
table, revtex4, Figure 4 added, minor additions made to text, references
added, conclusions unchanged, published versio
Antimatter signals of singlet scalar dark matter
We consider the singlet scalar model of dark matter and study the expected
antiproton and positron signals from dark matter annihilations. The regions of
the viable parameter space of the model that are excluded by present data are
determined, as well as those regions that will be probed by the forthcoming
experiment AMS-02. In all cases, different propagation models are investigated,
and the possible enhancement due to dark matter substructures is analyzed. We
find that the antiproton signal is more easily detectable than the positron one
over the whole parameter space. For a typical propagation model and without any
boost factor, AMS-02 will be able to probe --via antiprotons-- the singlet
model of dark matter up to masses of 600 GeV. Antiprotons constitute,
therefore, a promising signal to constraint or detect the singlet scalar model.Comment: 24 pages, 8 figures. v2: minor improvements. Accepted for publication
in JCA
Astrophysical Uncertainties in the Cosmic Ray Electron and Positron Spectrum From Annihilating Dark Matter
In recent years, a number of experiments have been conducted with the goal of
studying cosmic rays at GeV to TeV energies. This is a particularly interesting
regime from the perspective of indirect dark matter detection. To draw reliable
conclusions regarding dark matter from cosmic ray measurements, however, it is
important to first understand the propagation of cosmic rays through the
magnetic and radiation fields of the Milky Way. In this paper, we constrain the
characteristics of the cosmic ray propagation model through comparison with
observational inputs, including recent data from the CREAM experiment, and use
these constraints to estimate the corresponding uncertainties in the spectrum
of cosmic ray electrons and positrons from dark matter particles annihilating
in the halo of the Milky Way.Comment: 21 pages, 9 figure
Implications of the Fermi-LAT diffuse gamma-ray measurements on annihilating or decaying Dark Matter
We analyze the recently published Fermi-LAT diffuse gamma-ray measurements in
the context of leptonically annihilating or decaying dark matter (DM) with the
aim to explain simultaneously the isotropic diffuse gamma-ray and the PAMELA,
Fermi and HESS (PFH) anomalous data. Five different DM
annihilation/decay channels , , , , or (the latter
two via an intermediate light particle ) are generated with PYTHIA. We
calculate both the Galactic and extragalactic prompt and inverse Compton (IC)
contributions to the resulting gamma-ray spectra. To find the Galactic IC
spectra we use the interstellar radiation field model from the latest release
of GALPROP. For the extragalactic signal we show that the amplitude of the
prompt gamma-emission is very sensitive to the assumed model for the
extragalactic background light. For our Galaxy we use the Einasto, NFW and
Isothermal DM density profiles and include the effects of DM substructure
assuming a simple subhalo model. Our calculations show that for the
annihilating DM the extragalactic gamma-ray signal can dominate only if rather
extreme power-law concentration-mass relation is used, while more
realistic relations make the extragalactic component comparable or
subdominant to the Galactic signal. For the decaying DM the Galactic signal
always exceeds the extragalactic one. In the case of annihilating DM the PFH
favored parameters can be ruled out only if power-law relation is
assumed. For DM decaying into or the PFH favored DM parameters
are not in conflict with the Fermi gamma-ray data. We find that, due to the
(almost) featureless Galactic IC spectrum and the DM halo substructure,
annihilating DM may give a good simultaneous fit to the isotropic diffuse
gamma-ray and to the PFH data without being in clear conflict with the
other Fermi-LAT gamma-ray measurements.Comment: Accepted for publication in JCAP, added missing references, new Figs.
9 \& 10, 35 page
On possible interpretations of the high energy electron-positron spectrum measured by the Fermi Large Area Telescope
The Fermi-LAT experiment recently reported high precision measurements of the
spectrum of cosmic-ray electrons-plus-positrons (CRE) between 20 GeV and 1 TeV.
The spectrum shows no prominent spectral features, and is significantly harder
than that inferred from several previous experiments. Here we discuss several
interpretations of the Fermi results based either on a single large scale
Galactic CRE component or by invoking additional electron-positron primary
sources, e.g. nearby pulsars or particle Dark Matter annihilation. We show that
while the reported Fermi-LAT data alone can be interpreted in terms of a single
component scenario, when combined with other complementary experimental
results, specifically the CRE spectrum measured by H.E.S.S. and especially the
positron fraction reported by PAMELA between 1 and 100 GeV, that class of
models fails to provide a consistent interpretation. Rather, we find that
several combinations of parameters, involving both the pulsar and dark matter
scenarios, allow a consistent description of those results. We also briefly
discuss the possibility of discriminating between the pulsar and dark matter
interpretations by looking for a possible anisotropy in the CRE flux.Comment: 29 pages, 12 figures. Final version accepted for publication in
Astroparticle Physic
Pulsars as the Source of the WMAP Haze
The WMAP haze is an excess in the 22 to 93 GHz frequency bands of WMAP
extending about 10 degrees from the galactic center. We show that synchrotron
emission from electron-positron pairs injected into the interstellar medium by
the galactic population of pulsars with energies in the 1 to 100 GeV range can
explain the frequency spectrum of the WMAP haze and the drop in the average
haze power with latitude. The same spectrum of high energy electron-positron
pairs from pulsars, which gives rise to the haze, may also generate the
observed excesses in AMS, HEAT and PAMELA. We discuss the spatial morphology of
the pulsar synchrotron signal and its deviation from spherical symmetry, which
may provide an avenue to determine the pulsar contribution to the haze.Comment: 18 pages, 4 figures. Corrected errors in fig 1-3 and added discussion
of the detailed spatial morphology of the haze signa
The PAMELA Positron Excess from Annihilations into a Light Boson
Recently published results from the PAMELA experiment have shown conclusive
evidence for an excess of positrons at high (~ 10 - 100 GeV) energies,
confirming earlier indications from HEAT and AMS-01. Such a signal is generally
expected from dark matter annihilations. However, the hard positron spectrum
and large amplitude are difficult to achieve in most conventional WIMP models.
The absence of any associated excess in anti-protons is highly constraining on
any model with hadronic annihilation modes. We revisit an earlier proposal,
whereby the dark matter annihilates into a new light (<~GeV) boson phi, which
is kinematically constrained to go to hard leptonic states, without
anti-protons or pi0's. We find this provides a very good fit to the data. The
light boson naturally provides a mechanism by which large cross sections can be
achieved through the Sommerfeld enhancement, as was recently proposed.
Depending on the mass of the WIMP, the rise may continue above 300 GeV, the
extent of PAMELA's ability to discriminate electrons and positrons.Comment: 4 pages, 2 figures; v3 separated pions plot, references adde
Fluoroquinolones and the Risk for Methicillin-resistant Staphylococcus aureus in Hospitalized Patients1
To determine whether fluoroquinolone exposure is a risk factor for the isolation of Staphylococcus aureus and whether the effect is different for methicillin-resistant S. aureus (MRSA) versus methicillin-susceptible S. aureus (MSSA), we studied two case groups. The first case group included 222 patients with nosocomially acquired MRSA. The second case group included 163 patients with nosocomially acquired MSSA. A total of 343 patients admitted concurrently served as controls. Outcome measures were the adjusted odds ratio (OR) for isolation of MRSA and MSSA after fluoroquinolone exposure. Exposure to both levofloxacin (OR 5.4; p < 0.0001) and ciprofloxacin (OR 2.2; p < 0.003) was associated with isolation of MRSA but not MSSA. After adjustment for multiple variables, both drugs remained risk factors for MRSA (levofloxacin OR 3.4; p < 0.0001; ciprofloxacin OR 2.5; p = 0.005) but not MSSA. Exposure to levofloxacin or ciprofloxacin is a significant risk factor for the isolation of MRSA, but not MSSA
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