11202067
FERMI LARGE AREA TELESCOPE DETECTION OF SUPERNOVA REMNANT RCW 86
Using 5.4 yr Fermi Large Area Telescope data, we report the detection of GeV. gamma- ray emission from the shell-type supernova remnant RCW 86 (G315.4-2.3) with a significance of similar to 5.1 sigma. The data slightly favors an extended emission of this supernova remnant. The spectral index of RCW 86 is found to be very hard, Gamma similar to 1.4, in the 0.4-300 GeV range. A one-zone leptonic model can well fit the multi-wavelength data from radio to very high energy gamma-rays. The very hard GeV gamma-ray spectrum and the inferred low gas density seem to disfavor a hadronic origin for the gamma-rays. The. - ray behavior of RCW 86 is very similar to several other TeV shell-type supernova remnants, e. g., RX J1713.7- 3946, RX J0852.0-4622, SN 1006, and HESS J1731-347.
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.
383345
Probing dark matter decay and annihilation with Fermi LAT observations of nearby galaxy clusters
Galaxy clusters are promising targets for indirect dark matter searches. Gamma-ray signatures from the decay or annihilation of dark matter particles inside these clusters could be observable with the Fermi Large Area Telescope (LAT). Based on three years of Fermi LAT gamma-ray data, we analyze the flux coming from eight nearby clusters individually as well as in a combined likelihood analysis. Concentrating mostly on signals from dark matter decay, we take into account uncertainties of the cluster masses as determined by X-ray observations and model the cluster emission as extended sources. Searching for different hadronic and leptonic decay and annihilation spectra, we do not find significant emission from any of the considered clusters and present limits on the dark matter lifetime and annihilation cross-section. We compare our lifetime limits derived from cluster observations with the limits that can be obtained from the extragalactic gamma-ray background (EGBG), and find that in case of hadronic decay the cluster limits become competitive at dark matter masses below a few hundred GeV. In case of leptonic decay, however, galaxy cluster limits are stronger than the limits from the EGBG over the full considered mass range. Finally, we show that in presence of dark matter substructures down to 10?6 solar masses the limits on the dark matter annihilation cross-section could improve by a factor of a few hundred, possibly going down to the thermal cross-section of 3 ? 10?26cm3s?1 for dark matter masses 150GeV and annihilation into b. As a direct application of our results, we derive limits on the lifetime of gravitino dark matter in scenarios with R-parity violation. Implications of these limits for the possible observation of long-lived superparticles at the LHC are discussed.
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
118505894
Contribution of ultracompact dark matter minihalos to the isotropic radio background
The ultracompact minihalos could be formed during the earlier epoch of the Universe. The dark matter annihilation within them is very strong due to the steep density profile, rho similar to r(-2.25). The high-energy electrons and positrons from the dark matter annihilation can inverse Compton scatter with the background photons, such as cosmic microwave background photons, to acquire higher energy. On the other hand, the synchrotron radiation can also be produced when they meet the magnetic field. In this paper, we study the signals from the ultracompact minihalos (UCMHs) due to the dark matter annihilation for the radio, x-ray and gamma-ray band. We found that for the radio emission, the UCMHs can provide one kind of source for the radio excess observed by ARCADE 2. But the x-ray signals due to the inverse Compton scatter effect or the gamma-ray signals mainly due to the prompt emission from dark matter would exceed the present observations, such as Fermi, COMPTEL, and CHANDRA. We found that the strongest limits on the fraction of UCMHs come from the x-ray observations, and the constraints from the radio data are the weakest. DOI: 10.1103/PhysRevD.87.083519
119290233
Fermi LAT search for internal bremsstrahlung signatures from dark matter annihilation
A commonly encountered obstacle in indirect searches for galactic dark matter is how to disentangle possible signals from astrophysical backgrounds. Given that such signals are most likely subdominant, the search for pronounced spectral features plays a key role for indirect detection experiments; monochromatic gamma-ray lines or similar features related to internal bremsstrahlung, in particular, provide smoking gun signatures. We perform a dedicated search for the latter in the data taken by the Fermi gamma-ray space telescope during its first 43 months. To this end, we use a new adaptive procedure to select optimal target regions that takes into account both standard and contracted dark matter profiles. The behaviour of our statistical method is tested by a subsampling analysis of the full sky data and found to reproduce the theoretical expectations very well. The limits on the dark matter annihilation cross-section that we derive are stronger than what can be obtained from the observation of dwarf galaxies and, at least for the model considered here, collider searches. While these limits are still not quite strong enough to probe annihilation rates expected for thermally produced dark matter, future prospects to do so are very good. In fact, we already find a weak indication, with a significance of 3.1σ (4.3σ) when (not) taking into account the look-elsewhere effect, for an internal bremsstrahlung-like signal that would correspond to a dark matter mass of ~150 GeV; the same signal is also well fitted by a gamma-ray line at around 130 GeV. Although this would be a fascinating possibility, we caution that a much more dedicated analysis and additional data will be necessary to rule out or confirm this option.
11909349
Simulation of ultra-short pulses in a storage ring
Simulation study was performed with the tracking code Elegant [M. Borland, APS Report LS-287] to show beam quality evolution for a short, intense electron bunch after being injected to the SPEAR3 storage ring. The electron bunch with an intensity of 1 mA (0.78 nC) and a length of nearly 1 ps (FWHM) is found to degrade rapidly due to coherent synchrotron radiation (CSR) which causes large uneven longitudinal phase space distortion. The bunch length remains short and the longitudinal line density remains smooth for about 10 turns. For such a beam to circulate in the ring, a total of 10 MV rf power is needed to compensate for the energy loss.
119271491
Searching for string resonances in $e^+e^-$ and $\gamma \gamma$ collisions
If the fundamental mass scale of superstring theory is as low as few TeVs, the massive modes of vibrating strings, Regge excitations, will be copiously produced at the Large Hadron Collider (LHC). We discuss the complementary signals of low mass superstrings at the proposed electron-positron facility (CLIC), in e^+e^- and \gamma \gamma collisions. We examine all relevant four-particle amplitudes evaluated at the center of mass energies near the mass of lightest Regge excitations and extract the corresponding pole terms. The Regge poles of all four-point amplitudes, in particular the spin content of the resonances, are completely model independent, universal properties of the entire landscape of string compactifications. We show that \gamma \gamma \to e^+ e^- scattering proceeds only through a spin-2 Regge state. We estimate that for this particular channel, string scales as high as 4 TeV can be discovered at the 11\sigma level with the first fb^{-1} of data collected at a center-of-mass energy \approx 5 TeV. We also show that for e^+e^- annihilation into fermion-antifermion pairs, string theory predicts the precise value, equal 1/3, of the relative weight of spin 2 and spin 1 contributions. This yields a dimuon angular distribution with a pronounced forward-backward asymmetry, which will help distinguishing between low mass strings and other beyond the standard model scenarios.
16264551
Neutrino Emission From Inhomogeneous Pion Condensed Quark Matter
It is believed that quark matter can exist in neutron star interior if the baryon density is high enough. When there is a large isospin density, quark matter could be in a pion condensed phase. We compute neutrino emission from direct Urca processes in such a phase, particularly in the inhomogeneous Larkin-Ovchinnikov-Fulde-Ferrell (LOFF) states. The neutrino emissivity and specific heat are obtained, from which the cooling rate is estimated.
125972493
Phase Diagram of Asymmetric Fermion Superfluid Including Single-Species Pairing
119193640
Clarifying some remaining questions in the anomaly puzzle
We discuss several points that may help to clarify some questions that remain about the anomaly puzzle in supersymmetric theories. In particular, we consider a general $\mathcal{N}=1$ supersymmetric Yang–Mills theory. The anomaly puzzle concerns the question of whether there is a consistent way in the quantized theory to put the R-current and the stress tensor in a single supermultiplet called the supercurrent, even though in the classical theory they are in the same supermultiplet. It was proposed that the classically conserved supercurrent bifurcates into two supercurrents having different anomalies in the quantum regime. The most interesting result we obtain is an explicit expression for the lowest component of one of the two supercurrents in 4-dimensional spacetime, namely the supercurrent that has the energy-momentum tensor as one of its components. This expression for the lowest component is an energy-dependent linear combination of two chiral currents, which itself does not correspond to a classically conserved chiral current. The lowest component of the other supercurrent, namely, the R-current, satisfies the Adler–Bardeen theorem. The lowest component of the first supercurrent has an anomaly, which we show is consistent with the anomaly of the trace of the energy-momentum tensor. Therefore, we conclude that there is no consistent way to construct a single supercurrent multiplet that contains the R-current and the stress tensor in the straightforward way originally proposed. We also discuss and try to clarify some technical points in the derivations of the two supercurrents in the literature. These latter points concern the significance of infrared contributions to the NSVZ β-function and the role of the equations of motion in deriving the two supercurrents.