139 research outputs found
Potential of LOFT telescope for the search of dark matter
Large Observatory For X-ray Timing (LOFT) is a next generation X-ray
telescope selected by European Space Agency as one of the space mission
concepts within the ``Cosmic Vision'' programme. The Large Area Detector on
board of LOFT will be a collimator-type telescope with an unprecedentedly large
collecting area of about 10 square meters in the energy band between 2 and 100
keV. We demonstrate that LOFT will be a powerful dark matter detector, suitable
for the search of the X-ray line emission expected from decays of light dark
matter particles in galactic halos. We show that LOFT will have sensitivity for
dark matter line search more than an order of magnitude higher than that of all
existing X-ray telescopes. In this way, LOFT will be able to provide a new
insight into the fundamental problem of the nature of dark matter.Comment: 9 pages, 8 figure
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
Realistic sterile neutrino dark matter with KeV mass does not contradict cosmological bounds
International audiencePrevious fits of sterile neutrino dark matter models to cosmological dataassumed a peculiar production mechanism, which is not representative of thebest-motivated particle physics models given current data on neutrinooscillations. These analyses ruled out sterile neutrino masses smaller than8-10 keV. Here we focus on sterile neutrinos produced resonantly. We show thattheir cosmological signature can be approximated by that of mixed Cold plusWarm Dark Matter (CWDM). We use recent results on LambdaCWDM models to showthat for each mass greater than or equal to 2 keV, there exists at least onemodel of sterile neutrino accounting for the totality of dark matter, andconsistent with Lyman-alpha and other cosmological data. Resonant productionoccurs in the framework of the nuMSM (the extension of the Standard Model withthree right-handed neutrinos). The models we checked to be allowed correspondto parameter values consistent with neutrino oscillation data, baryogenesis andall other dark matter bounds
Laminar and turbulent dynamos in chiral magnetohydrodynamics-I: Theory
The magnetohydrodynamic (MHD) description of plasmas with relativistic
particles necessarily includes an additional new field, the chiral chemical
potential associated with the axial charge (i.e., the number difference between
right- and left-handed relativistic fermions). This chiral chemical potential
gives rise to a contribution to the electric current density of the plasma
(\emph{chiral magnetic effect}). We present a self-consistent treatment of the
\emph{chiral MHD equations}, which include the back-reaction of the magnetic
field on a chiral chemical potential and its interaction with the plasma
velocity field. A number of novel phenomena are exhibited. First, we show that
the chiral magnetic effect decreases the frequency of the Alfv\'{e}n wave for
incompressible flows, increases the frequencies of the Alfv\'{e}n wave and of
the fast magnetosonic wave for compressible flows, and decreases the frequency
of the slow magnetosonic wave. Second, we show that, in addition to the
well-known laminar chiral dynamo effect, which is not related to fluid motions,
there is a dynamo caused by the joint action of velocity shear and chiral
magnetic effect. In the presence of turbulence with vanishing mean kinetic
helicity, the derived mean-field chiral MHD equations describe turbulent
large-scale dynamos caused by the chiral alpha effect, which is dominant for
large fluid and magnetic Reynolds numbers. The chiral alpha effect is due to an
interaction of the chiral magnetic effect and fluctuations of the small-scale
current produced by tangling magnetic fluctuations (which are generated by
tangling of the large-scale magnetic field by sheared velocity fluctuations).
These dynamo effects may have interesting consequences in the dynamics of the
early universe, neutron stars, and the quark--gluon plasma.Comment: 23 pages, 4 figure
Anomalous Maxwell equations for inhomogeneous chiral plasma
Using the chiral kinetic theory we derive the electric and chiral current
densities in inhomogeneous relativistic plasma. We also derive equations for
the electric and chiral charge chemical potentials that close the Maxwell
equations in such a plasma. The analysis is done in the regimes with and
without a drift of the plasma as a whole. In addition to the currents present
in the homogeneous plasma (Hall current, chiral magnetic, chiral separation,
and chiral electric separation effects, as well as Ohm's current) we derive
several new terms associated with inhomogeneities of the plasma. Apart from
various diffusion-like terms, we find also new dissipation-less terms that are
independent of relaxation time. Their origin can be traced to the Berry
curvature modifications of the kinetic theory.Comment: 16 pages; published versio
How to constrain warm dark matter with the Lyman forest
The flux power spectrum of the high resolution Lyman- forest data
exhibits suppression at small scales. The origin of this suppression can be due
to long-sought warm dark matter (WDM) or to thermal effects, related to the
largely unknown reionization history of the Universe. Previous works explored a
specific class of reionization histories that exhibit sufficiently strong
thermal supression and leave little room for warm dark matter interpretation.
In this work we choose a different class of reionization histories, fully
compatible with available data on evolution of reionization, but much colder
then the reionization histories used by previous authors in determining the
nature of dark matter, thus leaving the broadest room for the WDM
interpretation of the suppression in the flux power spectrum. We find that WDM
thermal relics with masses below 1.9 keV (95% CL) would produce a suppression
at scales that are larger than observed maximum of the flux power spectrum,
independently of assumptions about thermal effects. This WDM mass is
significantly lower than previously claimed bounds, demonstrating the level of
systematic uncertainty of the Lyman- forest method, due to the previous
modelling. We also discuss how this uncertainty may affect also data at large
scales measured by eBOSS.Comment: 8 pages, 6 figure
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