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.
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.
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.
118532372
Constraints on ultracompact minihalos from extragalactic {\gamma}-ray background
It has been proposed that ultracompact minihalos (UCMHs) might be formed in earlier epoch. If dark matter consists of Weakly Interacting Massive Particles (WIMPs), UCMHs can be treated as the γ-ray sources due to dark matter annihilation within them. In this paper, we investigate the contributions of UCMHs formed during three phase transitions (i.e., electroweak symmetry breaking, QCD confinement and e+e− annihilation) to the extragalactic γ-ray background. Moreover, we use the Fermi-LAT observation data of the extragalactic γ-ray background to get the constraints on the current abundance of UCMHs produced during these phase transitions. We also compare these results with those obtained from Cosmic Microwave Background (CMB) observations and find that the constraints from the Fermi-LAT are more stringent than those from CMB.
91177988
AMS-02 positron excess: New bounds on dark matter models and hint for primary electron spectrum hardening ✩
The data collected by ATIC, CREAM and PAMELA all display remarkable cosmic ray nuclei spectrum hardening above the magnetic rigidity similar to 240 GV. One natural speculation is that the primary electron spectrum also gets hardened (possibly at similar to 80 CV) and the hardening partly accounts for the electron/positron total spectrum excess discovered by ATIC, HESS and Fermi-LAT. If it is the case, the increasing behavior of the subsequent positron-to-electron ratio will get flattened and the spectrum hardening should be taken into account in the joint fit of the electron/positron data otherwise the inferred parameters will be biased. Our joint fits of the latest AMS-02 positron fraction data together with the PAMELA/Fermi-LAT electron/positron spectrum data suggest that the primary electron spectrum hardening is needed in most though not all modelings. The bounds on dark matter models have also been investigated. In the presence of spectrum hardening of primary electrons, the amount of dark-matter-originated electron/positron pairs needed in the modeling is smaller. Even with such a modification, the annihilation channel chi chi -> mu(+) mu(-) has been tightly constrained by the Fermi-EAT Galactic diffuse emission data. The decay channel chi -> mu(+) mu(-) is found to be viable. (C) 2013 The Authors. Published by Elsevier B.V. All rights reserved.
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.
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.
117036857
On Refinement of Quark-Gluon Plasma Signal in Ultra-Relativistic Heavy Ion Collisions
The relation between the formation of a unique system and the upward-bending parameter a of 2-D(η, )lnFq vs lnM in relativistic heavy-ion collisions is discussed. It is argued that the correlation between the value of upward-bending parameter a for individual events and the value for the same events of some other quantity, e.g., K/π ratio, commonly used as quark-gluon plasma signal can be utilized to increase the reliability of this signal.
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.
121116255
EMC effect and the distortion of the vacuum in nuclei
Based on the argument that the bag radius of a bounded nucleon is larger than that of a free one due to the change of vacuum property in nucleus, a good fit is obtained for the EMC effect.
120439954
Effects of elliptic flow and resonance decay process on the Kurtosis of net baryon distributions
Kurtosis is regarded as a meaningful and promising observable in searching for the possible critical point predicted by QCD. In this paper, the effects of elliptic flow and resonance decay process on the Kurtosis have been studied with Monte Carlo event generators in Au + Au collisions at GeV. The results show that the Kurtosis is not sensitive to elliptic flow and resonance decay process.