1,260 research outputs found
A possible signature of annihilating dark matter
In this article, we report a new signature of dark matter annihilation based
on the radio continuum data of NGC 1569 galaxy detected in the past few
decades. After eliminating the thermal contribution of the radio signal, an
abrupt change in the spectral index is shown in the radio spectrum. Previously,
this signature was interpreted as an evidence of convective outflow of cosmic
ray. However, we show that the cosmic ray contribution is not enough to account
for the observed radio flux. We then discover that if dark matter annihilates
via the 4-e channel with the thermal relic cross section, the electrons and
positrons produced would emit a strong radio flux which can provide an
excellent agreement with the observed signature. The best-fit dark matter mass
is 25 GeV.Comment: Accepted for publication in MNRA
Constraining annihilating dark matter by x-ray data
In the past decade, gamma-ray observations and radio observations put strong
constraints on the parameters of dark matter annihilation. In this article, we
suggest another robust way to constrain the parameters of dark matter
annihilation. We expect that the electrons and positrons produced from dark
matter annihilation would scatter with the cosmic microwave background photons
and boost the photon energy to keV order. Based on the x-ray data from
the Draco dwarf galaxy, the new constraints for some of the annihilation
channels are generally tighter than the constraints obtained from 6 years of
Fermi Large Area Telescope (Fermi-LAT) gamma-ray observations of the Milky Way
dwarf spheroidal satellite galaxies. The lower limits of dark matter mass
annihilating via , , , , and
channels are 40 GeV, 28 GeV, 30 GeV, 57 GeV, 58 GeV and 66 GeV
respectively with the canonical thermal relic cross section. This method is
particularly useful to constrain dark matter annihilating via ,
, , and channels.Comment: Accepted for publication in Astrophysics and Space Scienc
Indirect evidence of GeV Dark Matter
Recently, an excess of GeV gamma ray near the Galactic Centre has
beenvreported. The spectrum obtained can be best fitted with the
annihilationvof GeV dark matter particles through channel.
In this letter, I show that this annihilation model can also solve the
mysteries of heating source in x-ray plasma and the unexpected high gamma-ray
luminosity. The cross section constrained by these observations give excellent
agreements with both the predicted range by using Fermi-LAT data and the
canonical thermal relic abundance cross section.Comment: Accepted by MNRAS Letter
Sommerfeld enhancement of invisible dark matter annihilation in galaxies and galaxy clusters
Recent observations indicate that core-like dark matter structures exist in
many galaxies, while numerical simulations reveal a singular dark matter
density profile at the center. In this article, I show that if the annihilation
of dark matter particles gives invisible sterile neutrinos, the Sommerfeld
enhancement of the annihilation cross-section can give a sufficiently large
annihilation rate to solve the core-cusp problem. The resultant core density,
core radius, and their scaling relation generally agree with recent empirical
fits from observations. Also, this model predicts that the resultant core-like
structures in dwarf galaxies can be easily observed, but not for large normal
galaxies and galaxy clusters.Comment: To appear in Astroparticle Physic
Does the gamma-ray signal from the central Milky Way indicate Sommerfeld enhancement of dark matter annihilation?
Recently, Daylan et al. (2014) show that the GeV gamma-ray excess signal from
the central Milky Way can be explained by the annihilation of GeV
dark matter through channel. Based on the morphology of the
gamma-ray flux, the best-fit inner slope of the dark matter density profile is
. However, recent analyses of Milky Way dark matter profile favor
. In this article, we show that the GeV gamma-ray excess can
also be explained by the Sommerfeld-enhanced dark matter annihilation through
channel with . We constrain the parameters of the
Sommerfeld-enhanced annihilation by using the data from Fermi-LAT. We also show
that the predicted gamma-ray fluxes emitted from dwarf galaxies generally
satisfy the recent upper limits of gamma-ray fluxes detected by Fermi-LAT.Comment: Accepted for publication in Research in Astronomy and Astrophysic
Electron-positron pair production near the Galactic Centre and the 511 keV emission line
Recent observations indicate that a high production rate of positrons (strong
511 keV line) and a significant amount of excess GeV gamma-ray exist in our
Galactic bulge. The latter issue can be explained by GeV dark matter
annihilation through channel while the former one remains a
mystery. On the other hand, recent studies reveal that a large amount of high
density gas might exist near the Galactic Centre million years ago to account
for the young, massive stars extending from 0.04 pc - 7 pc. In this article, I
propose a new scenario and show that the 40 GeV dark matter annihilation model
can also explain the required positron production rate (511 keV line) in the
bulge due to the existence of the high density gas cloud near the supermassive
black hole long time ago.Comment: Accepted for publication in MNRAS Letter
Analytic expressions for the dark matter-baryon relations
Recently, some very strong correlations between the distribution of dark
matter and baryons (the dark matter-baryon relations) in galaxies with very
different morphologies, masses, sizes, and gas fractions have been obtained.
Some models have been suggested to explain why the dark matter contribution is
fully specified by that of the baryons. In this article, we derive two analytic
expressions to explain the observed dark matter-baryon relations based on the
cold dark matter (CDM) model. The resultant expressions give excellent
agreement with the observational data. The parameters involved in the analytic
expressions are closely related to the amount of the baryon content. This model
can provide a theoretical understanding of the strong correlations observed. We
suggest that the observed relation represents the end product of galaxy
formation.Comment: 9 pages, appear in International Journal of Modern Physics
Reconciliation of MOND and Dark Matter theory
I show that Modified Newtonian Dynamics (MOND) is equivalent to assuming an
isothermal dark matter density profile, with its density related to the
enclosed total baryonic mass. This density profile can be deduced by physical
laws if a dark matter core exists and if the baryonic component is
spherically-symmetric, isotropic and isothermal. All the usual predictions of
MOND, as well as the universal constant , can be derived in this model.
Since the effects of baryonic matter are larger in galaxies than in galaxy
clusters, this result may explain why MOND appears to work well for galaxies
but poorly for clusters. As a consequence of the results presented here, MOND
can be regarded as a misinterpretation of a particular dark matter density
profile.Comment: Accepted by Physical Review
A tight scaling relation of dark matter in galaxy clusters
Recent studies in different types of galaxies reveal that the product of the
central density and the core radius () is a constant. However, some
empirical studies involving galaxy clusters suggest that the product
depends weakly on the total dark halo mass. In this article, we
re-analyse the hot gas data from 106 clusters and obtain a surprisingly tight
scaling relation: . This result generally
agrees with the claims that is not a constant for all scales of
structure. Moreover, this relation does not support the velocity-dependent
cross section of dark matter if the core formation is due to the
self-interaction of dark matter.Comment: Accepted by MNRAS Letter
Can decaying sterile neutrinos account for all dark matter?
The recent discovery of unexplained X-ray line of keV emitted from
the Perseus cluster of galaxies and M31 and the excess X-ray line of keV
emitted from the Milky Way center may indicate that dark matter would decay. In
this article, I show that approximately 80 \% of dark matter being 7.1 keV
sterile neutrinos and 20 \% of dark matter being 17.4 keV sterile neutrinos can
satisfactorily explain the observed X-ray lines and account for all missing
mass. No free parameter is needed in this model. This scenario is also
compatible with current robust observational constraints from the matter power
spectrum in large-scale structures and would alleviate the challenges faced by
the existing dark matter models.Comment: Accepted in Astrophysics and Space Scienc
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