118116548
GeV excess in the Milky Way: Depending on Diffuse Galactic gamma ray Emission template?
University of Chinese Academy of Sciences, Yuquan Road 19, Beijing, 100049, China.(Dated: June 27, 2014)Several groups have analyzed the publicly-available Fermi-LAT data and reported a spatiallyextended gamma rays excess of around 1−3 GeV from the region surrounding the Galactic Centerthat might originate from annihilation of dark matter particles with a rest mass m
118397778
Search for dark matter signals with Fermi-LAT observation of globular clusters NGC 6388 and M15
The globular clusters are probably good targets for dark matter (DM) searches in gamma-rays due to the possible adiabatic contraction of DM by baryons. In this work we analyse the three-year data collected by Fermi Large Area Telescope of globular clusters NGC 6388 and M 15 to search for possible DM signals. For NGC 6388 the detection of gamma-ray emission was reported by Fermi collaboration, which is consistent with the emission of a population of millisecond pulsars. The spectral shape of NGC 6388 is also shown to be consistent with a DM contribution if assuming the annihilation final state is b (b) over bar. No significant gamma-ray emission from M 15 is observed. We give the upper limits of DM contribution to gamma-ray emission in both NGC 6388 and M 15, for annihilation final states b (b) over bar, W+W-, mu(+)mu(-), tau(+)tau(-) and monochromatic line. The constraints are stronger than that derived from observation of dwarf galaxies by Fermi.
44050071
Closing in on singlet scalar dark matter: LUX, invisible Higgs decays and gamma-ray lines
A bstractWe study the implications of the Higgs discovery and of recent results from dark matter searches on real singlet scalar dark matter. The phenomenology of the model is defined by only two parameters, the singlet scalar mass mS and the quartic coupling a2 between the SU(2) Higgs and the singlet scalar. We concentrate on the window 5 < mS/GeV < 300. The most dramatic impact on the viable parameter space of the model comes from direct dark matter searches with LUX, and, for very low masses in the few GeV range, from constraints from the invisible decay width of the Higgs. In the resonant region the best constraints come from gamma-ray line searches. We show that they leave only a small region of viable parameter space, for dark matter masses within a few percent of half the mass of the Higgs. We demonstrate that direct and indirect dark matter searches (especially the search for monochromatic gamma-ray lines) will play a key role in closing the residual parameter space in the near future.
119187156
Decaying asymmetric dark matter relaxes the AMS-Fermi tension
The first result of AMS-02 confirms the positron fraction excess observed by PAMELA, but the spectrum is somewhat softer than that of PAMELA. In the dark matter (DM) interpretation it brings a tension between AMS-02 and Fermi-LAT, which reported an excess of the electron plus positron flux. In this work we point out that the asymmetric cosmic ray from asymmetric dark matter (ADM) decay relaxes the tension. It is found that in the case of two-body decay a bosonic ADM around 2.4 TeV and decaying into mu(-)tau(+) can significantly improve the fits. Based on the R-parity-violating supersymmetry with operators LLEe, we propose a minimal model to realize that ADM. The model introduces only a pair of singlets (X, (X) over bar) with a tiny coupling LHuX, which makes the ADM share the lepton asymmetry and decay into mu(-)tau(+) along the operator LLEe.
85553258
CONSTRAINING THE DISTRIBUTION OF DARK MATTER IN THE INNER GALAXY WITH AN INDIRECT DETECTION SIGNAL: THE CASE OF A TENTATIVE 130 GeV {gamma}-RAY LINE
Dark matter distribution in the very inner region of our Galaxy is still debated. In N-body simulations, a cuspy dark matter halo density profile is favored. Several dissipative baryonic processes, however, are found to be able to significantly flatten dark matter distribution, and a cored dark matter halo density profile is possible. Baryons dominate the gravitational potential in the inner Galaxy, hence a direct constraint on the abundance of dark matter particles is rather challenging. Recently, a few groups have identified a tentative 130 GeV line signal in the Galactic center, which could be interpreted as the signal of dark matter annihilation. Using current 130 GeV line data and adopting the generalized Navarro-Frenk-White profile of the dark matter halo-local dark matter density rho(0) = 0.4 GeV cm(-3) and r(s) = 20 kpc-we obtain a 95% confidence level lower (upper) limit on the inner slope of dark matter density distribution, alpha = 1.06 (the cross section of dark matter annihilation into gamma-rays (xx -> gamma gamma) = 1.3 x 10(-27) cm(3) s(-1)). Such a slope is consistent with the results of some N-body simulations and, if the signal is due to dark matter, suggests that baryonic processes may be unimportant.
119110786
Statistical interpretation of the spatial distribution of current 130 GeV gamma-ray line signal within the dark matter annihilation scenario
Recently, several groups identified a tentative gamma-ray line signal with energy similar to 130 GeV in the central Galaxy from the Fermi-EAT data. Such a gamma-ray line can be interpreted as the signal of dark matter annihilation. However, the offset similar to 220 pc (1.5 degrees) of the center of the most prominent signal region from the Galactic center Sgr A* has been thought to challenge the dark matter annihilation interpretation. Considering the fact that such a 130 GeV gamma-ray line signal consists of only similar to 14 photons, we suggest that the "imperfect" consistency of these photons with the expected dark matter distribution is due to the limited statistics. The offset will be smaller as more signal photons have been collected in the near future. Our Monte Carlo simulation supports the above speculation. (c) 2012 Elsevier B.V. All rights reserved.
14417574
A WENO algorithm of the temperature and ionization profiles around a point source
Abstract We develop a numerical solver for radiative transfer problems based on the weighted essentially nonoscillatory (WENO) scheme modified with anti-diffusive flux corrections, in order to solve the temperature and ionization profiles around a point source of photons in the reionization epoch. Algorithms for such simulation must be able to handle the following two features: (1) the sharp profiles of ionization and temperature at the ionizing front (I-front) and the heating front (T-front), and (2) the fraction of neutral hydrogen within the ionized sphere is extremely small due to the stiffness of the rate equations of atom processes. The WENO scheme can properly handle these two features, as it has been shown to have high order of accuracy and good convergence in capturing discontinuities and complicated structures in fluid as well as to be significantly superior over piecewise smooth solutions containing discontinuities. With this algorithm, we show the time-dependence of the preheated shell around a UV photon source. In the first stage the I-front and T-front are coincident, and propagate with almost the speed of light. In later stage, when the frequency spectrum of UV photons is hardened, the speeds of propagation of the ionizing and heating fronts are both significantly less than the speed of light, and the heating front is always beyond the ionizing front. In the spherical shell between the I- and T-fronts, the IGM is heated, while atoms keep almost neutral. The time scale of the preheated shell evolution is dependent on the intensity of the photon source. We also find that the details of the pre-heated shell and the distribution of neutral hydrogen remained in the ionized sphere are actually sensitive to the parameters used. The WENO algorithm can provide stable and robust solutions to study these details.
2019917
The Beylkin-Cramer Summation Rule and a New Fast Algorithm of Cosmic Statistics for Large Data Sets
Based on the Beylkin-Cramer summation rule, we introduce a new fast algorithm that enables us to explore the high-order statistics efficiently in large data sets. Central to this technique is to make decompositions both of fields and operators within the framework of multiresolution analysis and to realize their discrete representations. Accordingly, a homogeneous point process could be equivalently described by the operation of a Toeplitz matrix on a vector, which is accomplished by making use of the fast Fourier transformation. The algorithm could be applied widely in cosmic statistics to tackle large data sets. We demonstrate this novel technique using the spherical, cubic, and cylindrical counts in cells. The numerical test shows that the algorithm produces an excellent agreement with the expected results. Moreover, the algorithm naturally introduces a sharp filter, which is capable of suppressing shot noise in weak signals. In the numerical procedures, the algorithm is somewhat similar to particle-mesh methods in N-body simulations. Since it is scaled with O(N log N), it is significantly faster than the current particle-based methods, and its computational cost does not rely on the shape or size of the sampling cells. In addition, based on this technique, we further propose a simple fast scheme to compute the second statistics for cosmic density fields and justify it using simulation samples. Hopefully, the technique developed here allows us to make a comprehensive study of non-Gaussianity of the cosmic fields in high-precision cosmology. A specific implementation of the algorithm is publicly available on request to the author.
14666852
Thermal Freeze-out and Longitudinally Non-uniform Collective Expansion Flow in Relativistic Heavy Ion Collisions
The non-uniform longitudinal flow model (NUFM) propsed recently is extended to include also transverse flow. The resulting longitudinally non-uniform collective expansion model (NUCEM) is applied to the calculation of rapidity distribution of kaons, lambdas and protons in relativistic heavy ion collisions at CERN-SPS energies. The model results are compared with the 200 A GeV/$c$ S-S and 158 A GeV/$c$ Pb-Pb collision data. The central dips observed in experiments are reproduced in a natural way.