Gamma rays and neutrinos from dark matter annihilation in galaxy clusters

The $\gamma$-ray and neutrino emissions from dark matter (DM) annihilation in galaxy clusters are studied. After about one year operation of Fermi-LAT, several nearby clusters are reported with stringent upper limits of GeV $\gamma$-ray emission. We use the Fermi-LAT upper limits of these clusters to constrain the DM model parameters. We find that the DM model distributed with substructures predicted in cold DM (CDM) scenario is strongly constrained by Fermi-LAT $\gamma$-ray data. Especially for the leptonic annihilation scenario which may account for the $e^{\pm}$ excesses discovered by PAMELA/Fermi-LAT/HESS, the constraint on the minimum mass of substructures is of the level $10^2-10^3$ M$_{\odot}$, which is much larger than that expected in CDM picture, but is consistent with a warm DM scenario. We further investigate the sensitivity of neutrino detections of the clusters by IceCube. It is found that neutrino detection is much more difficult than $\gamma$-rays. Only for very heavy DM ($\sim 10$ TeV) together with a considerable branching ratio to line neutrinos the neutrino sensitivity is comparable with that of $\gamma$-rays.Comment: 21 pages, 8 figures and 1 table; extended discussion about the uncertainties of concentration and subhalo models, figures replotted for better read; references updated; accepted for publication by Phys. Rev.

Constraints and tests of the OPERA superluminal neutrinos

The superluminal neutrinos detected by OPERA indicates Lorentz invariance violation (LIV) of the neutrino sector at the order of $10^{-5}$. We study the implications of the result in this work. We find that such a large LIV implied by OPERA data will make the neutrino production process $\pi \to \mu + \nu_\mu$ kinematically forbidden for neutrino energy greater than about 5 GeV. The OPERA detection of neutrinos at 40 GeV can constrain the LIV parameter to be smaller than $3\times 10^{-7}$. Furthermore the neutrino decay in the LIV framework will modify the neutrino spectrum greatly. The atmospheric neutrino spectrum measured by IceCube can constrain the LIV parameter to the level of $10^{-12}$. The future detection of astrophysical neutrinos of Galactic sources is expected to be able to give even stronger constraint on the LIV parameter of neutrinos.Comment: 5 pages (2 column), 4 figures; published in Phys. Rev. Let

Discriminating different scenarios to account for the cosmic e±e^\pm excess by synchrotron and inverse Compton radiation

The excesses of the cosmic positron fraction recently measured by PAMELA and the electron spectra by ATIC, PPB-BETS, Fermi and H.E.S.S. indicate the existence of primary electron and positron sources. The possible explanations include dark matter annihilation, decay, and astrophysical origin, like pulsars. In this work we show that these three scenarios can all explain the experimental results of the cosmic $e^\pm$ excess. However, it may be difficult to discriminate these different scenarios by the local measurements of electrons and positrons. We propose possible discriminations among these scenarios through the synchrotron and inverse Compton radiation of the primary electrons/positrons from the region close to the Galactic center. Taking typical configurations, we find the three scenarios predict quite different spectra and skymaps of the synchrotron and inverse Compton radiation, though there are relatively large uncertainties. The most prominent differences come from the energy band $10^4\sim 10^9$ MHz for synchrotron emission and $\gtrsim 10$ GeV for inverse Compton emission. It might be able to discriminate at least the annihilating dark matter scenario from the other two given the high precision synchrotron and diffuse $\gamma$-ray skymaps in the future.Comment: published in Pr

Breit-Wigner Enhancement Considering the Dark Matter Kinetic Decoupling

In the paper we study the Breit-Wigner enhancement of dark matter (DM) annihilation considering the kinetic decoupling in the evolution of DM freeze-out at the early universe. Since the DM temperature decreases much faster (as $1/R^2$) after kinetic decoupling than that in kinetic equilibrium (as 1/R) we find the Breit-Wigner enhancement of DM annihilation rate after the kinetic decoupling will affect the DM relic density significantly. Focusing on the model parameters that trying to explain the anomalous cosmic positron/electron excesses observed by PAMELA/Fermi/ATIC we find the elastic scattering $Xf\to Xf$ is not efficient to keep dark matter in kinetic equilibrium, and the kinetic decoupling temperature $T_{kd}$ is comparable to the chemical decoupling temperature $T_f\sim O(10) GeV$. The reduction of the relic density after $T_{kd}$ is significant and leads to a limited enhancement factor $\sim O(10^2)$. Therefore it is difficult to explain the anomalous positron/electron excesses in cosmic rays by DM annihilation and give the correct DM relic density simultaneously in the minimal Breit-Wigner enhancement model

Crop classification of multitemporal PolSAR based on 3-D attention module with ViT

Multitemporal polarimertic SAR is considered to be very effective in crop classification and cultivated land detection, which has received much attention from researchers. Currently, for most multitemporal polarimetric SAR data classification methods, the simultaneous temporal–polarimetric–spatial feature extraction capability has not been exploited sufficiently. Also, the diversity of different time and different polarimetric features has not been taken into account sufficiently. In this letter, we propose a classification model that combines a dual-stream network as a temporal–polarimetric–spatial feature extraction module with vision transformer (ViT) called temporal–polarimetric–spatial transformer (TPST) to address the above problems. Second, a 3-D convolutional attention module that enables the network to weight the temporal dimension, polarimetric feature dimension and spatial dimension is developed, according to their importance. Experimental results on both the UAVSAR and RADARSAT-2 datasets show that the proposed method outperforms ResNet.This work was supported by the National Natural Science Foundation of China under Grant 62201027 and Grant 62271034.Peer ReviewedPostprint (author's final draft