144 research outputs found
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
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
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
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
Ground truth? Concept-based communities versus the external classification of physics manuscripts
Community detection techniques are widely used to infer hidden structures
within interconnected systems. Despite demonstrating high accuracy on
benchmarks, they reproduce the external classification for many real-world
systems with a significant level of discrepancy. A widely accepted reason
behind such outcome is the unavoidable loss of non-topological information
(such as node attributes) encountered when the original complex system is
represented as a network. In this article we emphasize that the observed
discrepancies may also be caused by a different reason: the external
classification itself. For this end we use scientific publication data which i)
exhibit a well defined modular structure and ii) hold an expert-made
classification of research articles. Having represented the articles and the
extracted scientific concepts both as a bipartite network and as its unipartite
projection, we applied modularity optimization to uncover the inner thematic
structure. The resulting clusters are shown to partly reflect the author-made
classification, although some significant discrepancies are observed. A
detailed analysis of these discrepancies shows that they carry essential
information about the system, mainly related to the use of similar techniques
and methods across different (sub)disciplines, that is otherwise omitted when
only the external classification is considered.Comment: 15 pages, 2 figure
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
Constraining self-interacting dark matter with scaling laws of observed halo surface densities
The observed surface densities of dark matter halos are known to follow a
simple scaling law, ranging from dwarf galaxies to galaxy clusters, with a weak
dependence on their virial mass. Here we point out that this can not only be
used to provide a method to determine the standard relation between halo mass
and concentration, but also to use large samples of objects in order to place
constraints on dark matter self-interactions that can be more robust than
constraints derived from individual objects. We demonstrate our method by
considering a sample of about 50 objects distributed across the whole halo mass
range, and by modelling the effect of self-interactions in a way similar to
what has been previously done in the literature. Using additional input from
simulations then results in a constraint on the self-interaction cross section
per unit dark matter mass of about cm/g. We
expect that these constraints can be significantly improved in the future, and
made more robust, by i) an improved modelling of the effect of
self-interactions, both theoretical and by comparison with simulations, ii)
taking into account a larger sample of objects and iii) by reducing the
currently still relatively large uncertainties that we conservatively assign to
the surface densities of individual objects. The latter can be achieved in
particular by using kinematic observations to directly constrain the average
halo mass inside a given radius, rather than fitting the data to a pre-selected
profile and then reconstruct the mass. For a velocity-independent
cross-section, our current result is formally already somewhat smaller than the
range cm/g that has been invoked to explain potential
inconsistencies between small-scale observations and expectations in the
standard collisionless cold dark matter paradigm.Comment: 29 pages with jcappub.sty, 10 figures. Significantly improved
discussion of method and limits. Version submitted to JCA
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