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

Potential of the Large Observatory for X-ray Timing telescope for the search for dark matter

Theoretical Physic

On the validity of the 5-dimensional Birkhoff theorem: The tale of an exceptional case

The 5-dimensional (5d) Birkhoff theorem gives the class of 5d vacuum space-times containing spatial hypersurfaces with cosmological symmetries. This theorem is violated by the 5d vacuum Gergely-Maartens (GM) space-time, which is not a representant of the above class, but contains the static Einstein brane as embedded hypersurface. We prove that the 5d Birkhoff theorem is still satisfied in a weaker sense: the GM space-time is related to the degenerated horizon metric of certain black-hole space-times of the allowed class. This result resembles the connection between the Bertotti-Robinson space-time and the horizon region of the extremal Reissner-Nordstrom space-time in general relativity.Comment: 13 pages; v2: title amended, to be published in Classical and Quantum Gravit

RADIAL PROFILE OF THE 3.5 keV LINE OUT TO R 200 IN THE PERSEUS CLUSTER

The recent discovery of the unidentified emission line at 3.5 keV in galaxies and clusters has attracted great interest from the community. As the origin of the line remains uncertain, we study the surface brightness distribution of the line in the Perseus cluster since that information can be used to identify its origin. We examine the flux distribution of the 3.5 keV line in the deep Suzaku observations of the Perseus cluster in detail. The 3.5 keV line is observed in three concentric annuli in the central observations, although the observations of the outskirts of the cluster did not reveal such a signal. We establish that these detections and the upper limits from the non-detections are consistent with a dark matter decay origin. However, absence of positive detection in the outskirts is also consistent with some unknown astrophysical origin of the line in the dense gas of the Perseus core, as well as with a dark matter origin with a steeper dependence on mass than the dark matter decay. We also comment on several recently published analyses of the 3.5 keV line.United States. National Aeronautics and Space Administration (Contracts NNX14AF78G and NNX123AE77G

Diluted equilibrium sterile neutrino dark matter

We present a model where sterile neutrinos with rest masses in the range ~ keV to ~ MeV can be the dark matter and be consistent with all laboratory, cosmological, large-scale structure, as well as x-ray constraints. These sterile neutrinos are assumed to freeze out of thermal and chemical equilibrium with matter and radiation in the very early Universe, prior to an epoch of prodigious entropy generation ("dilution") from out-of-equilibrium decay of heavy particles. In this work, we consider heavy, entropy-producing particles in the ~ TeV to ~ EeV rest-mass range, possibly associated with new physics at high-energy scales. The process of dilution can give the sterile neutrinos the appropriate relic densities, but it also alters their energy spectra so that they could act like cold dark matter, despite relatively low rest masses as compared to conventional dark matter candidates. Moreover, since the model does not rely on active-sterile mixing for producing the relic density, the mixing angles can be small enough to evade current x-ray or lifetime constraints. Nevertheless, we discuss how future x-ray observations, future lepton number constraints, and future observations and sophisticated simulations of large-scale structure could, in conjunction, provide evidence for this model and/or constrain and probe its parameters.Comment: 15 pages, 6 figures. v2: changes in text and figures; matches published versio

Radial profile of the 3.5 keV line out to R_200 in the perseus cluster

GalaxiesTheoretical Physic

Sterile neutrino dark matter as a consequence of nuMSM-induced lepton asymmetry

It has been pointed out in ref.[1] that in the nuMSM (Standard Model extended by three right-handed neutrinos with masses smaller than the electroweak scale), there is a corner in the parameter space where CP-violating resonant oscillations among the two heaviest right-handed neutrinos continue to operate below the freeze-out temperature of sphaleron transitions, leading to a lepton asymmetry which is considerably larger than the baryon asymmetry. Consequently, the lightest right-handed (``sterile'') neutrinos, which may serve as dark matter, are generated through an efficient resonant mechanism proposed by Shi and Fuller [2]. We re-compute the dark matter relic density and non-equilibrium momentum distribution function in this situation with quantum field theoretic methods and, confronting the results with existing astrophysical data, derive bounds on the properties of the lightest right-handed neutrinos. Our spectra can be used as an input for structure formation simulations in warm dark matter cosmologies, for a Lyman-alpha analysis of the dark matter distribution on small scales, and for studying the properties of haloes of dwarf spheroidal galaxies.Comment: 25 pages. v2: many clarifications and references added; published versio