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At least 55 records · Page 3Linked to original sources
arXiv2007

The comparison of theoretical predictions with measuring data of stellar parameters

The Euler equation has been accepted as the basic postulate of stellar physics long before the plasma physics was developed. The existence of electrical interaction between particles of interstellar plasma poses the question, how this interaction must be accounted for. We argue that the right way is in formulation of a new postulate. On the base of the new postulate, the theory of a hot star interior is developed. Using this theory we obtain the distribution of stars over their masses and mass-radius, mass-temperature and mass-luminosity dependencies. The theory of the apsidal rotation of binary stars and the spectrum of solar oscillation is considered. All these theoretical predictions are in a good agreement with the known measurement data, which confirms the validity of this consideration.

astro-ph↗
arXiv2007

Current status of the CATS database

We describe the current status of CATS, a publicly accessible database (web-server http://cats.sao.ru) allowing one to search in hundreds of catalogs of astronomical objects discovered all along the electromagnetic spectrum. Our emphasis is mainly laid on catalogs of radio continuum sources observed from 30 to 15000 MHz, secondly on catalogs of objects such as radio and active stars, planetary nebulae, HII regions, supernova remnants (SNR), pulsars, nearby galaxies, AGN and quasars. CATS also includes the catalogs from the largest extragalactic surveys, like NVSS, FIRST, WENSS, VLSS, TXS, GB6, SUMSS, IRAS, 2MASS, SDSS, ROSAT, PGC, MCG, etc. In 2004 CATS comprised a total of $\sim10^9$ records from over 400 catalogs in the radio, IR, optical and X-ray windows, including most of RATAN--600 catalogs. CATS is being expanded and updated, both with newly published catalogs as well as older ones which we have created in electronic form for the first time. We describe the principles of organization of the database of astrophysical catalogs and the main functions of CATS.

astro-ph↗
arXiv2007

Fine-Tuning in Brane-antibrane Inflation

I give a brief overview of brane-antibrane inflation, with emphasis on the problems of tuning to get a flat potential in the KKLMMT framework, and recent work on the nature of superpotential corrections in that model.

hep-th↗
arXiv2011

Helium abundance in galaxy clusters and Sunyaev-Zeldovich effect

It has long been suggested that helium nuclei in the intracluster plasma can sediment in the cluster gravitational potential well. Some theoretical estimates for the cores of relaxed clusters predict an excess of helium abundance by up to a factor of a few over its primordial value. The intracluster helium abundance cannot be measured directly. This presents a significant source of uncertainty for cosmological tests based on the X-ray derived cluster quantities, such as the gas mass, total mass, and gas mass fraction, all of which depend on the assumed helium abundance. We point out that cluster distances derived by combining the Sunyaev-Zeldovich (SZ) and X-ray data also depend on the helium abundance. This dependence can be used to measure the abundance, provided the distance is known independently. For example, if one adopts the WMAP H_0 value, then the recent H_0 measurement by Bonamente and collaborators, derived from SZ data on 38 clusters assuming a primordial helium abundance, corresponds to an abundance excess by a factor of 1.9+-0.8 within r~1 Mpc (using only their statistical errors). This shows that interesting accuracy is within reach. We also briefly discuss how the SZ and X-ray cluster data can be combined to resolve the helium abundance dependence for the d_a(z) cosmological test.

astro-ph↗
arXiv2007

Hadronic Gamma Rays from Supernova Remnants

A gas cloud near a supernova remnant (SNR) provides a target for pp-collisions leading to subsequent gamma-ray emission through neutral pion decay. The assumption of a power-law ambient spectrum of accelerated particles with index near -2 is usually built into models predicting the spectra of very-high energy (VHE) gamma-ray emission from SNRs. However, if the gas cloud is located at some distance from the SNR shock, this assumption is not necessarily correct. In this case, the particles which interact with the cloud are those leaking from the shock and their spectrum is approximately monoenergetic with the injection energy gradually decreasing as the SNR ages. In the GLAST energy range the gamma-ray spectrum resulting from particle interactions with the gas cloud will be flatter than expected, with the cutoff defined by the pion momentum distribution in the laboratory frame. We evaluate the flux of particles escaping from a SNR shock and apply the results to the VHE diffuse emission detected by the HESS at the Galactic centre.

astro-ph↗
arXiv2007

Gamma-ray albedo of the moon

We use the GEANT4 Monte Carlo framework to calculate the gamma-ray albedo of the Moon due to interactions of cosmic ray (CR) nuclei with moon rock. Our calculation of the albedo spectrum agrees with the EGRET data. We show that the spectrum of gamma rays from the Moon is very steep with an effective cutoff around 4 GeV (600 MeV for the inner part of the Moon disc). Apart from other astrophysical sources, the albedo spectrum of the Moon is well understood, including its absolute normalisation; this makes it a useful "standard candle" for gamma-ray telescopes, such as the forthcoming Gamma Ray Large Area Space Telescope (GLAST). The albedo flux depends on the incident CR spectrum which changes over the solar cycle. Therefore, it is possible to monitor the CR spectrum using the albedo gamma-ray flux. Simultaneous measurements of CR proton and helium spectra by the Payload for Antimatter Matter Exploration and Light-nuclei Astrophysics (PAMELA), and observations of the albedo gamma rays by the GLAST Large Area Telescope (LAT), can be used to test the model predictions and will enable the GLAST LAT to monitor the CR spectrum near the Earth beyond the lifetime of PAMELA.

astro-ph↗
arXiv2008

Circumventing Astrophysical Bounds Upon PVLAS Experiment

We study the possibility of evading astrophysical bound on light pseudoscalars. We argue that the solar bounds can be evaded if we have a sufficiently strong self-coupling of the pseudoscalars. The required coupling does not conflict with any known experimental bounds. We also show that it is possible to find a coupling range such that the recent PVLAS experiment is not in conflict with any astrophysical bounds.

astro-ph↗
arXiv2007

An Experiment to Search for Light Dark Matter in Low-Energy ep Scattering

Anomalous production of low-energy photons from the galactic center have fueled speculations on the nature and properties of dark matter particles. In particular, it has been proposed that light scalars may be responsible for the bulk of the matter density of the universe, and that they couple to ordinary matter through a light spin-1 boson. If this is the case, then such particles may be produced in the quasi-elastic low-energy scattering of electrons off protons. We present a proposal for an experiment to search for this process and assess its viability.

hep-ex↗
arXiv2007

GHaFaS: Galaxy Halpha Fabry-Perot Spectrometer for the WHT

A new scanning Fabry-Perot system will soon be available at the Nasmyth focus of the 4,2m William Hershell Telescope (WHT). It has been designed by the Laboratoire d'Astrophysique Experimentale (LAE) in Montreal and is being built in collaboration with astronomers at the Instituto de Astrofisica de Canarias (IAC). The instrument will see first light at the beginning of July 2007.

astro-ph↗
arXiv2007

Characteristic length of dynamical reduction models and decay of cosmological vacuum

Characteristic length of mass density resolution in dynamical reduction models is calculated utilizing energy conservation law and viable cosmological model with decreasing energy density of vacuum (dark energy density). The value found, $ \sim 10^{-5}$ cm, numerically coincides with phenomenological spatial short-length cutoff parameter introduced in the Ghirardi-Rimini-Weber model. It seems that our results support the gravity induced mechanism of dynamical reduction.

quant-ph↗
arXiv2007

Solution of the Dirac equation in presence of an uniform magnetic field

In this work we discuss the properties of the solutions of the Dirac equation in presence of an uniform background magnetic field. In particular we focus on the nature of the solutions, their ortho-normality properties and how these solutions depend on the choice of the vector potential giving rise to the magnetic field. We explicitly calculate the spin-sum of the solutions and using it we calculate the propagator of the electron in presence of an uniform background magnetic field.

hep-th↗
arXiv2007

Accretion onto black holes and relativistic jets

Relativistic jets from Active Galactic Nuclei are known since decades, but the study of the connection between accretion and ejection in these systems is hampered by the long time scales associated to these events. The past decade has seen a rapid advancement due to the observation of similar radio jets in galactic X-ray binaries, where the time scales are much shorter. A clear connection between accretion and ejection has been found for these systems, together with a solid characterization of the phenomenological properties of their outbursts. This wealth of new results has led to a detailed comparison between X-ray binaries and AGN, from which a number of correlations and scaling laws has been established. Here I briefly review the current observational status.

astro-ph↗
arXiv2008

Higgs Particle Mass in Cosmology

A version of the Standard Model is considered, where the electroweak symmetry breaking is provided by cosmological initial data given for the zeroth Fourier harmonic of the Higgs field $<ϕ>$. The initial data symmetry breaking mechanism removes the Higgs field contribution to the vacuum energy density, possible creation of monopoles, and tachion behavior at high energies, if one imposes an ``inertial'' condition on the Higgs potential $\textsf{V}_{\rm Higgs}(<ϕ>)=0$. The requirement of zero radiative corrections to this {\em inertial} condition coincides with the limiting point of the vacuum stability in the Standard Model. The latter together with the direct experimental limit gives the prediction for the mass of the Higgs boson to be in the range $114 < m_h \lsim 134$ GeV.

hep-ph↗
arXiv2007

The radio properties of type II quasars

Quasars (of type I) are the luminous analogs of type I Seyfert galaxies. Within the framework of unified models of active galaxies, the population of quasars of type II recently discovered with the Sloan Digital Sky Survey are the luminous analogs of type II Seyfert galaxies. Since our knowledge and understanding of the radio properties of these type II quasars are very limited, we have performed Very Large Array observations for a sub-sample of such sources. Our detection rate of 61% is consistent with the detection rate for other AGN samples. We do not find a correlation between radio and [O III] $λ$5007 luminosities for these sources. Although the distribution of spectral indices is similar to that of the 3C sources, the lack of dependence of radio luminosity on [O III] $λ$5007 luminosity suggests that not all sources in the sample are genuine AGNs.

astro-ph↗
arXiv2007

The Diffuse Galactic Gamma-Ray Emission Model for GLAST LAT

Diffuse emission from the Milky Way dominates the gamma-ray sky. About 80% of the high-energy luminosity of the Milky Way comes from processes in the interstellar medium. The Galactic diffuse emission traces interactions of energetic particles, primarily protons and electrons, with the interstellar gas and radiation field, thus delivering information about cosmic-ray spectra and interstellar mass in distant locations. Additionally, the Galactic diffuse emission is the celestial foreground for the study of gamma-ray point sources and the extragalactic diffuse gamma-ray emission. We report on the latest developments in the modelling of the Galactic diffuse emission, which will be used for the Gamma Ray Large Area Space Telescope (GLAST) investigations.

astro-ph↗
arXiv2007

Diffuse Gamma-Rays Produced in Cosmic-Ray Interactions and the TeV-band Spectrum of RX J1713.7-3946

We employ the Monte Carlo particle collision code DPMJET3.04 to determine the multiplicity spectra of various secondary particles (in addition to $π^0$'s) with $γ$'s as the final decay state, that are produced in cosmic-ray ($p$'s and $α$'s) interactions with the interstellar medium. We derive an easy-to-use $γ$-ray production matrix for cosmic rays with energies up to about 10 PeV. This $γ$-ray production matrix is applied to the GeV excess in diffuse Galactic $γ$-rays observed by EGRET, and we conclude the non-$π^0$ decay components are insufficient to explain the GeV excess, although they have contributed a different spectrum from the $π^0$-decay component. We also test the hypothesis that the TeV-band $γ$-ray emission of the shell-type SNR RX J1713.7-3946 observed with HESS is caused by hadronic cosmic rays which are accelerated by a cosmic-ray modified shock. By the $χ^2$ statistics, we find a continuously softening spectrum is strongly preferred, in contrast to expectations. A hardening spectrum has about 1% probability to explain the HESS data, but then only if a hard cutoff at 50-100 TeV is imposed on the particle spectrum.

astro-ph↗
arXiv2007

Interpretation of the atmospheric muon charge ratio in MINOS

MINOS is the first large magnetic detector deep underground and is the first to measure the muon charge ratio with high statistics in the region near 1 TeV.\cite{bib:adamson} An approximate formula for the muon charge ratio can be expressed in terms of $ε_π$ = 115 GeV, $ε_K$ = 850 GeV and $\ec$. The implications for K production in the atmosphere will be discussed.

hep-ex↗