118 research outputs found
Restrictions on sterile neutrino parameters from astrophysical observations
Adding 3 right-handed (sterile) neutrino to the Standard Model (SM) can solve
several "beyond the Standard Model" problems within one consistent framework:
explain neutrino oscillations and baryon asymmetry of the Universe and provide
a dark matter (DM) candidate. In this talk I will present current status of
astrophysical searches for the DM sterile neutrino.Comment: 3 pages. Contribution to the Proceedings of 11 Marcel Grossmann
meetin
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
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
A Toy Model of the M5-brane: Anomalies of Monopole Strings in Five Dimensions
We study a five-dimensional field theory which contains a monopole (string)
solution with chiral fermion zero modes. This monostring solution is a close
analog of the fivebrane solution of M-theory. The cancellation of normal bundle
anomalies parallels that for the M-theory fivebrane, in particular, the
presence of a Chern-Simons term in the low-energy effective U(1) gauge theory
plays a central role. We comment on the relationship between the the
microscopic analysis of the world-volume theory and the low-energy analysis and
draw some cautionary lessons for M-theory.Comment: 32 pages, LaTe
Magnetohydrodynamics of Chiral Relativistic Fluids
We study the dynamics of a plasma of charged relativistic fermions at very
high temperature , where is the fermion mass, coupled to the
electromagnetic field. In particular, we derive a magneto-hydrodynamical
description of the evolution of such a plasma. We show that, as compared to
conventional MHD for a plasma of non-relativistic particles, the hydrodynamical
description of the relativistic plasma involves new degrees of freedom
described by a pseudo-scalar field originating in a local asymmetry in the
densities of left-handed and right-handed fermions. This field can be
interpreted as an effective axion field. Taking into account the chiral anomaly
we present dynamical equations for the evolution of this field, as well as of
other fields appearing in the MHD description of the plasma. Due to its
non-linear coupling to helical magnetic fields, the axion field significantly
affects the dynamics of a magnetized plasma and can give rise to a novel type
of inverse cascade
Observational manifestations of anomaly inflow
In theories with chiral couplings, one of the important consistency
requirements is that of the cancellation of a gauge anomaly. In particular,
this is one of the conditions imposed on the hypercharges in the Standard
Model. However, anomaly cancellation condition of the Standard Model looks
unnatural from the perspective of a theory with extra dimensions. Indeed, if
our world were embedded into an odd-dimensional space, then the full theory
would be automatically anomaly free. In this paper we discuss the physical
consequences of anomaly non-cancellation for effective 4-dimensional field
theory. We demonstrate that in such a theory parallel electric and magnetic
fields get modified. In particular, this happens for any particle possessing
both electric charge and magnetic moment. This effect, if observed, can serve
as a low energy signature of extra dimensions. On the other hand, if such an
effect is absent or is very small, then from the point of view of any theory
with extra dimensions it is just another fine-tuning and should acquire
theoretical explanation.Comment: 23 pages plus appendices, 3 figures. v2: final journal version.
References added; corrections to Appendix
Checking the dark matter origin of 3.53 keV line with the Milky Way center
We detect a line at 3.539 +/- 0.011 keV in the deep exposure dataset of the
Galactic Center region, observed with the XMM-Newton. The dark matter
interpretation of the signal observed in the Perseus galaxy cluster, the
Andromeda galaxy [1402.4119] and in the stacked spectra of galaxy clusters
[1402.2301], together with non-observation of the line in blank sky data, put
both lower and upper limits on the possible intensity of the line in the
Galactic Center data. Our result is consistent with these constraints for a
class of Milky Way mass models, presented previously by observers, and would
correspond to radiative decay dark matter lifetime tau_dm ~ (6-8) x 10^{27}
sec. Although it is hard to exclude an astrophysical origin of this line based
the Galactic Center data alone, this is an important consistency check of the
hypothesis that encourages to check it with more observational data that are
expected by the end of 2015.Comment: 12 pages, 3 figures. Accepted by Phys. Rev. Let
Universal properties of Dark Matter halos
We discuss the universal relation between density and size of observed Dark
Matter halos that was recently shown to hold on a wide range of scales, from
dwarf galaxies to galaxy clusters. Predictions of LambdaCDM N-body simulations
are consistent with this relation. We demonstrate that this property of
LambdaCDM can be understood analytically in the secondary infall model.
Qualitative understanding given by this model provides a new way to predict
which deviations from LambdaCDM or large-scale modifications of gravity can
affect universal behavior and, therefore, to constrain them observationally.Comment: 4 pages, 1 figure, revtex. Final version to appear in Phys. Rev. Let
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