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.
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.
119270902
A new equation of state for dark energy model
A new parameterization for the dark energy equation of state(EoS) is proposed and some of its cosmological consequences are also investigated. This new parameterization is the modification of Efstathiou' dark energy EoS parameterization. w(z) is a well behaved function for z >> 1 and has same behavior in z at low redshifts with Efstathiou' parameterization. In this parameterization there are two free parameter w(0) and w(a). We discuss the constraints on this model's parameters from current observational data. The best fit values of the cosmological parameters with la confidence-level regions are: Omega(m) = 0.2735(-0.0163)(+0.0171) w(0) = -1.0537(-0.1511)(+0.1432) and w(a) = 0.2738(-0.8288)(+0.8018).
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.
123132096
Observational constraints on the early dark energy model
Dark energy can be studied by its influence on the expansion of the Universe. We investigate current constraints on early dark energy (EDE) achievable by the combined observational data from type Ia supernovae (557), baryon acoustic oscillations, the current cosmic microwave background and the observed Hubble parameter. We find that combining these data sets provides powerful constraints on early dark energy and the best fit values of the parameters in 68% and 95% confidence-level regions are: Omega(m0) = 0.2897(-0.0138-0.0194)(+0.0149+0.0207) Omega(e) = 0.0125(-0.0129-0.0129)(+0.0272+0.0381), omega(0) = -1.0415(-0.109-0.1604)(+0.0891+0.1182), and h = 0.6988(-0.0058-0.0081)(+0.0059+0.0083).
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.
18220605
Thermal Equilibration and Ellipsoidal Expansion of Rotationally-Symmetrical Longitudinal Flow in Relativistc Heavy Ion Collisions
A rotationally-symmetrical ellipsoidal flow model is proposed for the relativistic heavy-ion collisions and compared with the 14.6 A GeV/c Si-Al and 10.8 A GeV/c Au-Au collision data. The large stopping in the heavier collision system and heavier produced particles is accounted for by using the ellipsoidal flow picture. The central dip in the proton and deuteron rapidity distributions for Si-Al collision are reproduced.
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.
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.
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.