arXiv subjects
Publications and source records attributed to Todor Stanev.
We discuss the relation between the acceleration spectra of extragalactic cosmic ray protons and the luminosity and cosmological evolution of their sources and the production of ultra high energy cosmogenic neutrinos in their propagation from the sources to us.
The muon flux at the South-Pole was measured for five zenith angles, $0^{\circ}$, $15^{\circ}$, $35^{\circ}$, $82.13^{\circ}$ and $85.15^{\circ}$ with a scintillator muon telescope incorporating ice Cherenkov tank detectors as the absorber. We compare the measurements with other data and with calculations.
We discuss the production of cosmogenic neutrinos on extragalactic infrared photons in a model of its cosmological evolution. The relative importance of these infrared photons as a target for proton interactions is significant, especially in the case of steep injection spectra of the ultrahigh energy cosmic rays. For an E$^{-2.5}$ cosmic ray injection spectrum, for example, the event rate of neutrinos of energy above 1 PeV is more than doubled.
We discuss briefly the potential sources of high energy astrophysical neutrinos and show estimates of the neutrino fluxes that they can produce. A special attention is paid to the connection between the highest energy cosmic rays and astrophysical neutrinos.
The spatial clustering of galaxies in galaxy clusters implies that the background of infrared (IR) light in the intracluster medium (ICM) may exceed the universal background. Cosmic rays injected within the ICM propagate diffusively and at low enough energies are trapped there for cosmological times. The photopion production interactions of cosmic rays with the IR photons are responsible for the generation of neutrinos whose detection may shed some light on the origin and propagation of high energy cosmic rays in the universe. Here we discuss our calculations of the flux of neutrinos from single clusters as well as the contribution of photopion production in clusters of galaxies to the diffuse neutrino background.
After a brief review of galactic cosmic rays in the GeV to TeV energy range, we describe some current problems of interest for particles of very high energy. Particularly interesting are two features of the spectrum, the `knee' above $10^{15}$ eV and the `ankle' above $10^{18}$ eV. An important question is whether the highest energy particles are of extra-galactic origin and, if so, at what energy the transition occurs. A theme common to all energy ranges is use of nuclear abundances as a tool for understanding the origin of the cosmic radiation.
We fit the ultra high energy cosmic ray spectra above 10$^{19}$ eV with different injection spectra at cosmic ray sources that are uniformly and homogeneously distributed in the Universe. We conclude that the current UHE spectra are consistent with power laws of index $α$ between 2.4 and 2.7. There is a slow dependence of these indices on the cosmological evolution of the cosmic ray sources, which in this model determines the end of the galactic cosmic rays spectrum.
The magnetic field in our Galaxy is not well known and is difficult to measure. A spiral regular field in the disk between the Galactic arms is favored by observations, however it is still controversial if the field reverses from arm to arm. The parity of the field across the Galactic plane is also not well established. In this letter we demonstrate that cosmic ray protons in the energy range 10^18 to 10^19 eV, if accelerated near the center of the Galaxy, can probe the large scale structure of the Galactic Magnetic Field. In particular if the field is of even parity, and the spiral field reverses direction from arm to arm, i.e. if it is bi-symmetric (BSS), ultra high energy protons will predominantly come from the Southern Galactic hemisphere, and predominantly from the Northern Galactic hemisphere if the field is of even parity and axi-symmetric (ASS). There is no sensitivity to the BSS or ASS configurations if the field is of odd parity.
We briefly review the high energy astrophysical processes that are related to the production of high energy $γ$-ray and neutrino signals and are likely to be important for the energy loss of high and ultrahigh energy cosmic rays. We also give examples for neutrino fluxes generated by different astrophysical objects and describe the cosmological link provided by cosmogenic neutrinos.
Observations of ultrahigh energy cosmic rays (UHECR) do not uniquely determine both the injection spectrum and the evolution model for UHECR sources - primarily because interactions during propagation obscure the early Universe from direct observation. Detection of neutrinos produced in those same interactions, coupled with UHECR results, would provide a full description of UHECR source properties.
IceTop is the surface component of IceCube neutrino telescope. Goals, plans and status of IceTop in 2004 are reported
In 2002, Ray Davis and Masatoshi Koshiba were awarded the Nobel Prize in Physics ``for pioneering contributions to astrophysics, in particular for the detection of cosmic neutrinos.'' However, while astronomy has undergone a revolution in understanding by synthesizing data taken at many wavelengths, the universe has only barely been glimpsed in neutrinos, just the Sun and the nearby SN 1987A. An entire universe awaits, and since neutrinos can probe astrophysical objects at densities, energies, and distances that are otherwise inaccessible, the results are expected to be particularly exciting. Similarly, the revolution in quantitative cosmology has heightened the need for very precise tests that depend on the effects of neutrinos, and prominent among them is the search for the effects of neutrino mass, since neutrinos are a small but known component of the dark matter. In this report, we highlight some of the key opportunties for progress in neutrino astrophysics and cosmology, and the implications for other areas of physics.
We briefly review the improvements in the predictions of atmospheric neutrino fluxes since the NOW2000 workshop. In spite of the great progress in calculational technique the predictions are still not exact because of the uncertainties in the two major sets of input - cosmic ray flux and hadronic interactions on light nuclei.
We discuss theoretical issues and experimental data that brought the ultra high energy cosmic rays in the list of Nature's greatest puzzles. After many years of research we still do not know how astrophysical acceleration processes can reach energies exceeding 10$^{11}$ GeV. The main alternative {\em top-down} mechanism postulates the existence of super massive $X$-particles that create a particle spectrum extending down to the observed energy through their decay channels. The propagation of nuclei and photons from their sources to us adds to the puzzle as all particles of these energies interact with the ambient photons, mostly of the microwave background. We also describe briefly the main observational results and give some information on the new experiments that are being built and designed now.
We discuss the contribution of proton photoproduction interactions on the isotropic infrared/optical background to the cosmic neutrino fluxes. This contribution has a strong dependence on the proton injection energy spectrum, and is essential at high redshifts. It is thus closely correlated with the cosmological evolution of the ultra high energy proton sources and of the inrared background itself. These interactions may also contribute to the source fluxes of neutrinos if the proton sources are located in regious of high infrared emission and magnetic fields.
We study the influence of shower fluctuations, and the possible presence of different nuclear species in the primary cosmic ray spectrum, on the experimental determination of both shower energy and the proton air inelastic cross section from studies of the longitudinal development of atmospheric showers in fluorescence experiments. We investigate the potential of track length integral and shower size at maximum as estimators of shower energy. We find that at very high energy (~10^19-10^20 eV) the error of the total energy assignment is dominated by the dependence on the hadronic interaction model, and is of the order of 5%. At lower energy (~10^17-10^18 eV), the uncertainty of the energy determination due to the limited knowledge of the primary cosmic ray composition is more important. The distribution of depth of shower maximum is discussed as a measure of the proton-air cross section. Uncertainties in a possible experimental measurement of this cross section introduced by intrinsic shower fluctuations, the model of hadronic interactions, and the unknown mixture of primary nuclei in the cosmic radiation are numerically evaluated.
We study the proton flux expected from sources of ultra high energy cosmic rays (UHECR) in the presence of regular extragalactic magnetic fields. It is assumed that a local source of ultra-high energy protons and the magnetic field are all in a wall of matter concentration with dimensions characteristic of the supergalactic plane. For a single source, the observed proton flux and the local cosmic ray energy spectrum depend strongly on the strength of the field, the position of the observer, and the orientation of the field relative to the observer's line of sight. Regular fields also affect protons emitted by sources outside the local magnetic fields structure. We discuss the possibility that such effects could contribute to an explanation of the excess of UHECR above $5.10^{19}$ eV, and the possibility that sources of such particles may be missed if such magnetic fields are not taken into account.
The energy density of the Ultra High Energy Cosmic Rays (UHECR) in the Universe is a very important parameter for the solution of the puzzle of their origin. It defines the luminosity of the UHECR sources and thus the type of objects they are. This is also of crucial importance for the design of high energy neutrino telescopes. The current attempts to derive the source luminosity are hindered by the small world experimental statistics. We show that the unknown strength and structure of the large scale cosmic magnetic fields affect strongly the UHECR propagation history. The identification of the UHECR sources will bring important information on the large scale magnetic fields.