1,776 research outputs found
Constraints on parameters of radiatively decaying dark matter from the galaxy cluster 1E0657-56
We derived constraints on parameters of a radiatively decaying warm dark
matter particle, e.g., the mass and mixing angle for a sterile neutrino, using
Chandra X-ray spectra of a galaxy cluster 1E0657-56 (the ``bullet'' cluster).
The constraints are based on nondetection of the sterile neutrino decay
emission line. This cluster exhibits spatial separation between the hot
intergalactic gas and the dark matter, helping to disentangle their X-ray
signals. It also has a very long X-ray observation and a total mass measured
via gravitational lensing. This makes the resulting constraints on sterile
neutrino complementary to earlier results that used different cluster mass
estimates. Our limits are comparable to the best existing constraints.Comment: 6p
Bounds on Light Dark Matter
In this talk we review existing cosmological and astrophysical bounds on
light (with the mass in keV - MeV range) and super-weakly interacting dark
matter candidates. A particular attention is paid to the sterile neutrino DM
candidate.Comment: 5 pages, 3 figures. Contribution to the proceedings of 4th Patras
Workshop on Axions, WIMPs and WISPs, DESY, Hamburg, Germany, 18-21 June 200
Axion alternatives
If recent results of the PVLAS collaboration proved to be correct, some
alternative to the traditional axion models are needed. We present one of the
simplest possible modifications of axion paradigm, which explains the results
of PVLAS experiment, while avoiding all the astrophysical and cosmological
restrictions. We also mention other possible models that possess similar
effects.Comment: 12 pages, 3 figure
Spectral and spatial variations of the diffuse gamma-ray background in the vicinity of the Galactic plane and possible nature of the feature at 130 GeV
We study the properties of the diffuse gamma-ray background around the
Galactic plane at energies 20 -- 200 GeV. We find that the spectrum of this
emission possesses significant spacial variations with respect to the average
smooth component. The positions and shapes of these spectral features change
with the direction on the sky. We therefore argue, that the spectral feature
around 130 GeV, found in several regions around the Galactic Center and in the
Galactic plane in [1203.1312, 1204.2797, 1205.1045, 1206.1616], can not be
interpreted with confidence as a gamma-ray line, but may be a component of the
diffuse background and can be of instrumental or astrophysical origin.
Therefore, the dark matter origin of this spectral feature becomes dubious.Comment: Extended analysis that further confirms the existence of several "hot
spots" around the Galactic plane and discussion of their possible origi
Quantum cosmology of the brane universe
We canonically quantize the dynamics of the brane universe embedded into the
five-dimensional Schwarzschild-anti-deSitter bulk space-time. We show that in
the brane-world settings the formulation of the quantum cosmology, including
the problem of initial conditions, is conceptually more simple than in the
3+1-dimensional case. The Wheeler-deWitt equation is a finite-difference
equation. It is exactly solvable in the case of a flat universe and we find the
ground state of the system. The closed brane universe can be created as a
result of decay of the bulk black hole.Comment: 4 pages, revte
Next decade of sterile neutrino studies
We review the status of sterile neutrino dark matter and discuss
astrophysical and cosmological bounds on its properties as well as future
prospects for its experimental searches. We argue that if sterile neutrinos are
the dominant fraction of dark matter, detecting an astrophysical signal from
their decay (the so-called 'indirect detection') may be the only way to
identify these particles experimentally. However, it may be possible to check
the dark matter origin of the observed signal unambiguously using its
characteristic properties and/or using synergy with accelerator experiments,
searching for other sterile neutrinos, responsible for neutrino flavor
oscillations. We argue that to fully explore this possibility a dedicated
cosmic mission - an X-ray spectrometer - is needed.Comment: 23 pages, 6 figure
Searching for dark matter in X-rays: how to check the dark matter origin of a spectral feature
A signal from decaying dark matter (DM) can be unambiguously distinguished
from spectral features of astrophysical or instrumental origin by studying its
spatial distribution. We demonstrate this approach by examining the recent
claim of 0912.0552 regarding the possible DM origin of the 2.5 keV line in
Chandra observations of the Milky Way satellite known as Willman 1. Our
conservative strategy is to adopt a relatively large dark mass for Willman 1
and relatively small dark masses for the comparison objects. We analyze
archival observations by XMM-Newton of M31 and Fornax dwarf spheroidal galaxy
(dSph) and Chandra observations of Sculptor dSph. By performing a conservative
analysis of X-ray spectra, we show the absence of a DM decay line with
parameters consistent with those of 0912.0552. For M31, the observations of the
regions between 10 and 20 kpc from the center, where the uncertainties in the
DM distribution are minimal, make a strong exclusion at the level above
10sigma. The minimal estimate for the amount of DM in the central 40 kpc of M31
is provided by the model of 0912.4133, assuming the stellar disk's mass to
light ratio ~8 and almost constant DM density within a core of 28 kpc. Even in
this case one gets an exclusion at 5.7sigma from central region of M31 whereas
modeling all processed data from M31 and Fornax produces more than 14sigma
exclusion. Therefore, despite possible systematic uncertainties, we exclude the
possibility that the spectral feature at ~2.5 keV found in 0912.0552 is a DM
decay line. We conclude, however, that the search for DM decay line, although
demanding prolonged observations of well-studied dSphs, M31 outskirts and other
similar objects, is rather promising, as the nature of a possible signal can be
checked. An (expected) non-observation of a DM decay signal in the planned
observations of Willman 1 should not discourage further dedicated observations.Comment: 16 pages, 8 figures; journal version; analysis of additional data
from M31 outskirts and comments on arXiv:1001.4055 are adde
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