Effects of atmospheric electric fields on detection of ultrahigh-energy cosmic rays

We show that atmospheric electric fields may affect the cosmic ray observations in several ways and may lead to an overestimation of the cosmic ray energies. The electric field in thunderclouds can be as high as a few kV/cm. This field can accelerate the shower electrons and can feed some additional energy into the shower. Therefore, ground array observations in certain weather conditions may overestimate the energy of ultrahigh-energy cosmic rays if they don't take this effect into account. In addition, the electric field can bend the muon trajectories and affect the direction and energy reconstruction of inclined showers. Finally, there is a possibility of an avalanche multiplication of the shower electrons due to a runaway breakdown, which may lead to a significant miscalculation of the cosmic ray energy.Comment: 4 pages, 2 figures, notation clarifie

First measurement of cluster temperature using the thermal Sunyaev-Zeldovich effect

We discuss a new method of finding the cluster temperatures which is independent of distance and therefore very useful for distant clusters. The hot gas of electrons in clusters of galaxies scatters and distorts the cosmic microwave background radiation in a well determined way. This Sunyaev-Zel'dovich (SZ) effect is a useful tool for extracting information about clusters such as their peculiar radial velocity and optical depth. Here we show how the temperature of the cluster can be inferred from the SZ effect, in principle without use of X-ray data. We use recent millimetre observation of Abell 2163 to determine for the first time a cluster temperature using SZ observations only. The result T_e = 26^+34_-19 keV at 68% confidence level (at 95% c.l. we find T>1.5 keV) is in reasonable agreement with the X-ray results, T_e =12.4^+2.8_-1.9 keV.Comment: 7 pages, 2 figure

Ultra-High Energy Cosmic Rays and the GeV-TeV Diffuse Gamma-Ray Flux

Ultra-high energy cosmic ray protons accelerated in astrophysical objects produce secondary electromagnetic cascades during propagation in the cosmic microwave and infrared backgrounds. We show that such cascades can contribute between ~1% and ~50% of the GeV-TeV diffuse photon flux measured by the EGRET experiment. The GLAST satellite should have a good chance to discover this flux.Comment: 4 pages, 5 figure

Standard Model Neutrinos as Warm Dark Matter

Standard Model neutrinos are not usually considered plausible dark matter candidates because the usual treatment of their decoupling in the early universe implies that their mass must be sufficiently small to make them ``hot'' dark matter. In this paper we show that decoupling of Standard Model neutrinos in low reheat models may result in neutrino densities very much less than usually assumed, and thus their mass may be in the keV range. Standard Model neutrinos may therefore be warm dark matter candidates.Comment: 5 pages, 5 figures, LaTeX file uses revtex packag

Bounds on heavy sterile neutrinos revisited

We revise the bounds on heavy sterile neutrinos, especially in the case of their mixing with muon neutrinos in the charged current. We summarize the present experimental limits, and we reanalyze the existing data from the accelerator neutrino experiments and from Super-Kamiokande to set new bounds on a heavy sterile neutrino in the range of masses from 8 MeV to 390 MeV. We also discuss how the future accelerator neutrino experiments can improve the present limits.Comment: 14 pages, 6 figures; a detailed and expanded versio

GZK Photons in the Minimal Ultra High Energy Cosmic Rays Model

In a recently proposed model the cosmic rays spectrum at energies above 10^{18} eV can be fitted with a minimal number of unknown parameters assuming that the extragalactic cosmic rays are only protons with a power law source spectrum ~E^{-alpha} and alpha~2.6. Within this minimal model, after fitting the observed HiRes spectrum with four parameters (proton injection spectrum power law index and maximum energy, minimum distance to sources and evolution parameter) we compute the flux of ultra-high energy photons due to photon-pion production, the GZK photons, for several radio background models and average extragalactic magnetic fields with amplitude between 10^{-11} G and 10^{-9} G. We find the photon fraction to be between 10^{-4} and 10^{-3} in cosmic rays at energies above 10^{19} eV. These small fluxes could only be detected in future experiments like Auger North plus South and EUSO.Comment: 13 pages, 9 figure

Neutrinos from Extra-Large Hadron Collider in the Milky Way

Neutrino telescope IceCube has recently discovered astrophysical neutrinos with energies in the TeV-PeV range. We use the data of Fermi gamma-ray telescope to demonstrate that the neutrino signal has significant contribution from the Milky Way galaxy. Matching the gamma-ray and neutrino spectra we find that TeV-PeV Galactic cosmic rays form a powerlaw spectrum with the slope p~2.45. This spectral slope is consistent with the average cosmic ray spectrum in the disks of the Milky Way and Large Magellanic Cloud galaxies. It is also consistent with the theoretical model of cosmic ray injection by diffusive shock acceleration followed by escape through the Galactic magnetic field with Kolmogorov turbulence. The locally observed TeV-PeV cosmic ray proton spectrum is softer than the average Galactic cosmic ray spectrum. This could be readily explained by variability of injection of cosmic rays in the local interstellar medium over the past 1e7 yr and discreetness of the cosmic ray source distribution.Comment: 6 pages 3 figures, accepted to Astroparticle Physic

GZK Photons Above 10 EeV

We calculate the flux of "GZK-photons", namely the flux of photons produced by extragalactic nucleons through the resonant photoproduction of pions, the so called GZK effect. This flux depends on the UHECR spectrum on Earth, of the spectrum of nucleons emitted at the sources, which we characterize by its slope and maximum energy, on the distribution of sources and on the intervening cosmological backgrounds, in particular the magnetic field and radio backgrounds. For the first time we calculate the GZK photons produced by nuclei. We calculate the possible range of the GZK photon fraction of the total UHECR flux for the AGASA and the HiRes spectra. We find that for nucleons produced at the sources it could be as large as a few % and as low as 10^{-4} above 10 EeV. For nuclei produced at the sources the maximum photon fraction is a factor of 2 to 3 times smaller above 10 EeV but the minimum could be much smaller than for nucleons. We also comment on cosmogenic neutrino fluxes.Comment: 20 pages, 9 figures (21 panels), iopart.cls and iopart12.clo needed to typese