Observational constraints of sterile neutrinos in galaxies

We study a model in which degenerate sterile neutrinos account for galactic dark matter. We fit the rotation curves of 5 dwarf galaxies with the degenerate sterile neutrinos in hydrostatic equilibrium. Also we estimate the range of sterile neutrino mass by calculating the upper and lower bounds of the mass densities of sterile neutrino halos in the outermost regions of 21 normal galaxies. The observed rotation curves of 5 dwarf galaxies and 21 normal galaxies are consistent with having sterile neutrinos with mass (26–30) eV, and the similarity of the rotation curves of different galaxies emerges naturally in our model.     

Constraining the window on sterile neutrinos as warm dark matter

Sterile neutrinos may be one of the best warm dark matter candidates we have today. Both lower and upper bounds on the mass of the sterile neutrino come from astronomical observations. We show that the proper inclusion of the neutrino momentum distribution reduces the allowed region to be  2.6 keV< m <5 keV  for the simplest models. A search for a spectral line with   E = m /2  is thus more interesting than ever before.     

Decaying sterile neutrinos as a heating source in the Milky Way centre

Recent Chandra and XMM–Newton observations indicate that there are two-temperature components ( T ∼ 8 keV, 0.8 keV) of the diffuse X-rays emitted from deep inside the centre of Milky Way. We show that this can be explained by the existence of sterile neutrinos, which decay to emit photons that can be bound-free absorbed by the isothermal hot-gas particles in the centre of Milky Way. The model can account for a stable configuration of the two-temperature components hot gas naturally as well as the energy needed to maintain the ∼8 keV temperature in the hot gas. The predicted sterile neutrino mass is between 16–18 keV.     

Neutrino fluxes from a core-collapse supernova in a model with three sterile neutrinos

The characteristics of the gravitational collapse of a supernova and the fluxes of active and sterile neutrinos produced during the formation of its protoneutron core have been calculated numerically. The relative yields of active and sterile neutrinos in corematter with different degrees of neutronization have been calculated for various input parameters and various initial conditions. A significant increase in the fraction of sterile neutrinos produced in superdense core matter at the resonant degree of neutronization has been confirmed. The contributions of sterile neutrinos to the collapse dynamics and the total flux of neutrinos produced during collapse have been shown to be relatively small. The total luminosity of sterile neutrinos is considerably lower than the luminosity of electron neutrinos, but their spectrum is considerably harder at high energies.     

One-photon and two-photon annihilation lines in gamma-bursts,I

This paper and subsequent Paper II are an investigation of the annihilation line formation in gamma-ray bursts based on the assumption of positron production in a strong magnetic field (because of one-photon absorption of hard gamma-quanta radiated in the neutron star hot polar spot). We discuss a two-photon annihilation line in this paper. It is shown that if the star magnetic field is greater than 3×10¹² G, the relative flux in the line depends solely on the hardness of the continuum and is, as a rule, less than or about 10–20% of the total flux. This is consistent with the spectral data recorded by ‘Venera-11’ and ‘Venera-12’ space probes. The annihilation region formation above the hot polar spot is discussed, and positron density and annihilation region dimensions are estimated.     

One-photon and two-photon annihilation lines in gamma-bursts,II

This paper, which is a continuation of Paper I (Zheleznyakov and Litvinchuk, 1985), studies the formation of a one-quantum annihilation line in the spectrum of gamma-ray bursts. The radiative transfer equation together with the positron density balance relation is solved, and the expected photon fluxes in the one- and two-quantum annihilation lines are calculated. The fractional luminosities of these lines versus source parameters are investigated. For a gamma-burst one-photon annihilation line, the luminosity is always much less than that for the two-photon line-i.e., the positron source power transforms almost entirely into radiation in the two-quantum annihilation line and the positron density depends solely on the specific source power and two-quantum annihilation probability. The flux of one-quantum annihilation quanta 1 MeV is estimated to be less than what modern detectors can resolve. This explains failure to detect the one-photon annihilation lines in gamma-bursts so far.     

On the theory of annihilation lines in gamma-ray bursts

The mechanism of formation of an annihilation line 0.5 MeV in gamma-ray bursts due to electron-positron pair production in strong magnetic fields of neutron stars is discussed. Bremsstrahlung from a hot polar spot is supposed to be a source of gamma-quanta which produce the pairs. It is shown that a great part of radiation with the energyE>2mc ² per quantum (except for directions along or close to the magnetic field) is consumed by pair production and does not excape from the gamma-burster. This indicates a possible strong gap in continuum radiation at energies higher than 1 MeV. At the same time effective creation of pairs enables one to give a simple estimate of the expected annihilation line intensity in gamma-ray burst spectra. This estimate coincides with the available observational data.     

Red-shifted annihilation lines in thermal synchrotron model of gamma-ray bursts

The origins of the gravitationally-red-shifted annihilation lines of gamma-ray bursts in thermal synchrotron-radiation model are discussed in this paper. It is shown that the positrons produced by high-energy photons which are obtained by extrapolation from the continua through strong magnetic field could not be the main source of the annihilation lines, while that escaping from the hot thin region might account the emission features.     

Non-extensive statistics and slarr neutrinos

In this paper we will show that, assuming the existence of a long-range microscopic memory of the random force, acting in the solar core, mainly on the electrons and the protons rather than on the light and heavy ions (or, equally, assuming the existence of an anomalous diffusion of solar core constituents of light mass and of normal diffusion of heavy ions), the equilibrium statistical distribution that these particles must obey, is that of the Tsallis non-extensive statistics, the distribution differing very slightly from the usual Maxwellian distribution. Due to the high-energy depleted tail of the distribution, the nuclear rates are reduced and, using earlier results on the standard solar model neutrino fluxes, calculated by Clayton and collaborators, we can evaluate fluxes in good agreement with the experimental data. While the proton distribution is only very slightly different from the Maxwell one there is a slightly larger difference with the electron distribution. This revised version was published online in July 2006 with corrections to the Cover Date.     

TeV neutrinos and gamma-rays from pulsars

Recent studies suggest that pulsars could be strong sources of TeV muon neutrinos provided positive ions are accelerated by pulsar polar caps to PeV energies. In such a situation, muon neutrinos are produced through the Δ-resonance in interactions of pulsar-accelerated ions with its thermal radiation field. High-energy gamma-rays should also be produced simultaneously in pulsar environment as both charged and neutral pions are generated in the interactions of energetic hadrons with the ambient photon fields. Here, we estimate TeV gamma-ray flux at the Earth from a few nearby young pulsars. When compared with the observations, we find that proper consideration of the effect of polar cap geometry in flux calculation is important. Incorporating such an effect, we obtain the (revised) event rates at the Earth due to a few potential nearby pulsars. The results suggest that pulsars are unlikely to be detected by the upcoming neutrino telescopes. We also estimate TeV gamma-ray and neutrino fluxes from pulsar nebulae for the adopted model of particle acceleration.     

High-energy cosmic-ray neutrinos and tau particles

We propose a possible scheme that will accommodate the newly discovered tau particle in the generic relation between cosmic-ray particles at high energy. The scheme imposes a new lower mass limit on the tau-neutrino, 139 < < 250 MeV. A possible contribution of the tau-neutrino to high-energy neutrino flux is discussed. We then analyse the possible astrophysical situations suitable for the production of the tau particle and its neutrino.     

Electron-positron and photon wind from the surface of a strange star

We consider the problem of strange-star (SS) radiation. The bare quark SS surface and electrons on the stellar surface generate an electric field that is strong enough for electron-positron pairs to be produced from a vacuum at a nonzero temperature. The luminosity in pairs is assumed to be within ?10⁴⁹ erg s^?1 from a surface with a characteristic radius of 10 km. We consider the energy transfer from pairs to photons by taking into account the well-studied reactions between e, e ⁺, γ and obtain a change in the photon spectrum with luminosity. Our analysis is restricted to the spherically symmetric case. The magnetic field is disregarded. To solve the problem, we developed a new numerical method of integrating the Boltzmann kinetic equations for pairs and photons. This method is used to calculate the problem up to a luminosity of 10⁴² erg s^?1 This region is difficult to investigate when the optical path for pairs or photons is considerably larger than unity but the two optical depths are not simultaneously much larger than unity (when hydrodynamics with heat conduction is applicable). It turns out that the mean photon energy is approximately equal to $\bar \in _\gamma \approx m_e c^2$ (the annihilation line for pairs) at a modest luminosity, L?1×10³⁷ erg s^?1, and decreases to ≈210 keV at L?10³⁸ erg s^?1. Hydrodynamic estimates point to an increase in the mean energy $\bar \in _\gamma$ to 1 MeV as the luminosity further increases to L?10⁴⁹ erg s^?1. Our calculations may prove to be useful in interpreting soft gamma repeaters (SGRs) and are of methodological interest.     

Supernovae and positron annihilation radiation

Radioactive nuclei, especially those created in SN explosion, have long been suggested to be important contributors of galactic positrons. In this paper we describe the findings of three independent OSSE/SMM/TGRS studies of positron annihilation radiation, demonstrating that the three studies are largely in agreement as to the distribution of galactic annihilation radiation. We then assess the predicted yields and distributions of SN-synthesized radionuclei, determining that they are marginally compatible with the findings of the annihilation radiation studies.     

Pionic photons and neutrinos from cosmic ray accelerators

Identifying the accelerators that produce the Galactic and extragalactic cosmic rays has been a priority mission of several generations of high energy gamma ray and neutrino telescopes; success has been elusive so far. Detecting the gamma-ray and neutrino fluxes associated with cosmic rays reaches a new watershed with the completion of IceCube, the first neutrino detector with sensitivity to the anticipated fluxes, and the construction of CTA, a ground-based gamma ray detector that will map and study candidate sources with unprecedented precision. In this paper, we revisit the prospects for revealing the sources of the cosmic rays by a multiwavelength approach; after reviewing the methods, we discuss supernova remnants, gamma ray bursts, active galaxies and GZK neutrinos in some detail.     

Non-zero rest mass neutrinos and the cosmological constant

Recently it was pointed out that a non-zero cosmological constant can play a role in the formation of neutrino halos only in the case of neutrinos of very low rest mass (m _v <-0.1eV). However, phase-space considerations would requirem _v >50 eV if neutrinos dominate the missing mass in halos of large spiral galaxies and moreoverm _v >200 eV is implied in the case of dwarf spheroidals. These larger neutrino masses would be in conflict with observed constraints on the age of the Universe unless a cosmological constant is invoked.     

Cosmic neutrinos of ultra-high energies and detection possibility

The fluxes and spectra of galactic and extragalactic neutrinos at energy 10¹¹–10¹⁹ eV are calculated. In particular, the neutrino flux from the normal galaxies is calculated taking into account the spectral index distribution. The only assumption that seriously affects the calculated neutrino flux atE _v 10¹⁷ eV is the power-like generation spectrum of protons in the entire considered energy region.The normal galaxies with the accepted parameters generate the metagalactic equivalent electron component (electrons+their radiation) with energy density _e8.5×10^–7 eV cm^–3, while the density of the observed diffuse X-ray radiation alone is 100 times higher. This requires the existence of other neutrino sources and we found the minimized neutrino flux under two limitations: (1) the power-law generation spectrum of protons and (2) production of the observed energy density of the diffuse X-an -radiation. These requirements are met in the evolutionary model of origin of the metagalactic cosmic rays with modern energy density _M83.6×10^–7 eV cm^–3.The possibility of experiments with cosmic neutrinos of energyE _v 3×10¹⁷ eV is discussed. The upper bound on neutrino-nucleon cross-section <2.2×10^–29 cm² is obtained in evolutionary model from the observed zenith angular distribution of extensive air showers.In Appendix 2 the diffuse X-and -ray flux arising together with neutrino flux is calculated. It agrees with observed flux in the entire energy range from 1 keV up to 100 MeV.     

Interactions between solar neutrinos and solar magnetic fields

We attempt to correlate all of the available solar-neutrino data with the strong magnetic fields these neutrinos encounter in the solar interior along their Earth-bound path. We approximate these fields using the photospheric, magnetograph-measured flux from central latitude bands, time delayed to proxy the magnetic fields in the solar interior. Our strongest evidence for anticorrelation is for magnetic fields within the central ±5° solar-latitude band that have been delayed by 0.85 ± 0.55 yr. Assuming a neutrino-magnetic interaction, this might indicate that interior fields travel to the solar surface in this period of time. As more solar-neutrino flux information is gathered, the question of whether this result arises from a physical process or is merely a statistical fluke should be resolved, providing that new data are obtained spanning additional solar cycles and that correlation studies focus on these same regions of the solar magnetic field.     

Galactic halos,globular clusters and massive neutrinos

Within the framework of a Gamow cosmology with massive neutrinos a scenario is proposed in which both galactic halos and globular clusters are formed due to the existence of a critical injection mass. Galactic halos are formed at red shift z10–100 by self-gravitating neutrinos, and globular clusters atz10³ by a critical injection mass of primordial plasma (Gamow's Ylem).     

Spin-statistics connexion, neutrinos, and big bang nucleosynthesis

We show how the ⁴He-abundance in the early Universe can be used to demonstrate that macroscopic samples of neutrinos in thermal equilibrium are indeed distributed according to Fermi-Dirac statistics.