Gamma-ray bursts (GRBs) have been suggested as possible sources of the high-energy neutrino flux recently detected by the IceCube telescope. We revisit the fireball emission model and elaborate an analytical prescription to estimate the high-energy n
eutrino prompt emission from pion and kaon decays, assuming that the leading mechanism for the neutrino production is lepto-hadronic. To this purpose, we include hadronic, radiative and adiabatic cooling effects and discuss their relevance for long- (including high- and low-luminosity) and short-duration GRBs. The expected diffuse neutrino background is derived, by requiring that the GRB high-energy neutrino counterparts follow up-to-date gamma-ray luminosity functions and redshift evolutions of the long and short GRBs. Although dedicated stacking searches have been unsuccessful up to now, we find that GRBs could contribute up to a few % to the observed IceCube high-energy neutrino flux for sub-PeV energies, assuming that the latter has a diffuse origin. Gamma-ray bursts, especially low-luminosity ones, could however be the main sources of the IceCube high-energy neutrino flux in the PeV range. While high-luminosity and low-luminosity GRBs have comparable intensities, the contribution from the short-duration component is significantly smaller. Our findings confirm the most-recent IceCube results on the GRB searches and suggest that larger exposure is mandatory to detect high-energy neutrinos from high-luminosity GRBs in the near future.
The intra-cluster medium of several galaxy clusters hosts large-scale regions of diffuse synchrotron radio emission, known as radio halos and relics, which demonstrate the presence of magnetic fields and relativistic electrons in clusters. These rela
tivistic electrons should also emit X-rays through inverse-Compton scattering off of cosmic microwave background photons. The detection of such a non-thermal X-ray component, together with the radio measurement, would permit to clearly separate the magnetic field from the relativistic electron distribution as the inverse-Compton emission is independent from the magnetic field in the cluster. However, non-thermal X-rays have not been conclusively detected from any cluster of galaxies so far. In this paper, for the first time, we model the synchrotron and inverse-Compton emission of all clusters hosting radio halos and relics for which the spectral index can be determined. We provide constraints on the volume-average magnetic field by comparing with current X-ray measurements. We then estimate the maximum volume-average magnetic field that will allow the detection of inverse-Compton hard X-rays by the ASTRO-H satellite. We found that several clusters are good targets for ASTRO-H to detect their inverse-Compton emission, in particular that corresponding to radio relics, and propose a list of promising targets for which ASTRO-H can test $ge1$~$mu$G magnetic fields. We conclude that future hard X-ray observations by the already-operating NuSTAR and the soon-to-be-launched ASTRO-H definitely have the potential to shed light on the long-sought non-thermal hard-X-ray emission in clusters of galaxies.
Cross-correlating the gamma-ray background with local galaxy catalogs potentially gives stringent constraints on dark matter annihilation. We provide updated theoretical estimates of sensitivities to the annihilation cross section from gamma-ray data
with Fermi telescope and 2MASS galaxy catalogs, by elaborating the galaxy power spectrum and astrophysical backgrounds, and adopting the Markov-Chain Monte Carlo simulations. In particular, we show that taking tomographic approach by dividing the galaxy catalogs into more than one redshift slice will improve the sensitivity by a factor of a few to several. If dark matter halos contain lots of bright substructures, yielding a large annihilation boost (e.g., a factor of $sim$100 for galaxy-size halos), then one may be able to probe the canonical annihilation cross section for thermal production mechanism up to masses of $sim$700 GeV. Even with modest substructure boost (e.g., a factor of $sim$10 for galaxy-size halos), on the other hand, the sensitivities could still reach a factor of three larger than the canonical cross section for dark matter masses of tens to a few hundreds of GeV.
Cross-correlating gamma-ray maps with locations of galaxies in the low-redshift Universe vastly increases sensitivity to signatures of annihilation of dark matter particles. Low-redshift galaxies are ideal targets, as the largest contribution to anis
otropy in the gamma-ray sky from annihilation comes from $zlesssim 0.1$, where we expect minimal contributions from astrophysical sources such as blazars. Cross-correlating the five-year data of Fermi-LAT with the redshift catalog of the 2MASS survey can detect gamma rays from annihilation if dark matter has the canonical annihilation cross section and its mass is smaller than $sim$100 GeV.
Annihilation of dark matter particles in cosmological halos (including a halo of the Milky Way) contributes to the diffuse gamma-ray background (DGRB). As this contribution will appear anisotropic in the sky, one can use the angular power spectrum of
anisotropies in DGRB to constrain properties of dark matter particles. By comparing the updated analytic model of the angular power spectrum of DGRB from dark matter annihilation with the power spectrum recently measured from the 22-month data of Fermi Large Area Telescope (LAT), we place upper limits on the annihilation cross section of dark matter particles as a function of dark matter masses. We find that the current data exclude <sigma v> >~ 10^{-25} cm^3 s^{-1} for annihilation into bbar{b} at the dark matter mass of 10 GeV, which is a factor of three times larger than the canonical cross section. The limits are weaker for larger dark matter masses. The limits can be improved further with more Fermi-LAT data as well as by using the power spectrum at lower multipoles (l <~ 150), which are currently not used due to a potential Galactic foreground contamination.
We analyze 2.8-yr data of 1-100 GeV photons for clusters of galaxies, collected with the Large Area Telescope onboard the Fermi satellite. By analyzing 49 nearby massive clusters located at high Galactic latitudes, we find no excess gamma-ray emissio
n towards directions of the galaxy clusters. Using flux upper limits, we show that the Fornax cluster provides the most stringent constraints on the dark matter annihilation cross section. Stacking a large sample of nearby clusters does not help improve the limit for most dark matter models. This suggests that a detailed modeling of the Fornax cluster is important for setting robust limits on the dark matter annihilation cross section based on clusters. We therefore perform the detailed mass modeling and predict the expected dark matter annihilation signals from the Fornax cluster, by taking into account effects of dark matter contraction and substructures. By modeling the mass distribution of baryons (stars and gas) around a central bright elliptical galaxy, NGC 1399, and using a modified contraction model motivated by numerical simulations, we show that the dark matter contraction boosts the annihilation signatures by a factor of 4. For dark matter masses around 10 GeV, the upper limit obtained on the annihilation cross section times relative velocity is <sigma v> <~ (2-3)x10^{-25} cm^3 s^{-1}, which is within a factor of 10 from the value required to explain the dark matter relic density. This effect is more robust than the annihilation boost due to substructure, and it is more important unless the mass of the smallest subhalos is much smaller than that of the Sun.
Intergalactic magnetic fields (IGMF) can cause the appearance of halos around the gamma-ray images of distant objects because an electromagnetic cascade initiated by a high-energy gamma-ray interaction with the photon background is broadened by magne
tic deflections. We report evidence of such gamma-ray halos in the stacked images of the 170 brightest active galactic nuclei (AGN) in the 11-month source catalog of the Fermi Gamma-Ray Space Telescope. Excess over point spread function in the surface brightness profile is statistically significant at 3.5sigma (99.95% confidence level), for the nearby, hard population of AGN. The halo size and brightness are consistent with IGMF, B_{IGMF} ~ 10^{-15} G. The knowledge of IGMF will facilitate the future gamma-ray and charged-particle astronomy. Furthermore, since IGMF are likely to originate from the primordial seed fields created shortly after the Big Bang, this potentially opens a new window on the origin of cosmological magnetic fields, inflation, and the phase transitions in the early Universe.
If dark energy (DE) couples to neutrinos, then there may be apparent violations of Lorentz/CPT invariance in neutrino oscillations. The DE-induced Lorentz/CPT violation takes a specific form that introduces neutrino oscillations that are energy indep
endent, differ for particles and antiparticles, and can lead to novel effects for neutrinos propagating through matter. We show that ultra-high-energy neutrinos may provide one avenue to seek this type of Lorentz/CPT violation in u_mu- u_tau oscillations, improving the current sensitivity to such effects by seven orders of magnitude. Lorentz/CPT violation in electron-neutrino oscillations may be probed with the zenith-angle dependence for high-energy atmospheric neutrinos. The ``smoking gun, for DE-neutrino coupling would, however, be a dependence of neutrino oscillations on the direction of the neutrino momentum relative to our peculiar velocity with respect to the CMB rest frame. While the amplitude of this directional dependence is expected to be small, it may nevertheless be worth seeking in current data and may be a target for future neutrino experiments.
As suggested by some extensions of the Standard Model of particle physics, dark matter may be a super-weakly interacting lightest stable particle, while the next-to-lightest particle (NLP) is charged and meta-stable. One could test such a possibility
with neutrino telescopes, by detecting the charged NLPs produced in high-energy neutrino collisions with Earth matter. We study the production of charged NLPs by both atmospheric and astrophysical neutrinos; only the latter, which is largely uncertain and has not been detected yet, was the focus of previous studies. We compute the resulting fluxes of the charged NLPs, compare those of different origins, and analyze the dependence on the underlying particle physics setup. We point out that even if the astrophysical neutrino flux is very small, atmospheric neutrinos, especially those from the prompt decay of charmed mesons, may provide a detectable flux of NLP pairs at neutrino telescopes such as IceCube. We also comment on the flux of charged NLPs expected from proton-nucleon collisions, and show that, for theoretically motivated and phenomenologically viable models, it is typically sub-dominant and below detectable rates.
