One pion events by atmospheric neutrinos: A three flavor analysis

We study the one-pion events produced via neutral current (NC) and charged current (CC) interactions by the atmospheric neutrinos. We analyze the ratios of these events in the framework of oscillations between three neutrino flavors. The ratios of the CC events induced by $\nu_e$ to that of the NC events and a similar ratio defined with $\nu_\mu$ help us in distinguishing the different regions of the neutrino parameter space.Comment: 14 pages, 4 figures (separate postscript files

An analytic relation for the thickness of accretion flows

We take the vertical distribution of the radial and azimuthal velocity into account in spherical coordinates, and find that the analytic relation c_{s0}/(v_K \Theta) = [(\gamma -1)/(2\gamma)]^{1/2} is valid for both geometrically thin and thick accretion flows, where c_{s0} is the sound speed on the equatorial plane, v_K is the Keplerian velocity, \Theta is the half-opening angle of the flow, and \gamma is the adiabatic index.Comment: 4 pages, 2 figures, accepted by Science in China Series

Multi-Temperature Blackbody Spectra of Thin Accretion Disks With and Without a Zero-Torque Inner Boundary Condition

The standard spectral model for analyzing the soft component of thermal emission from a thin accretion disk around a black hole is the multi-temperature blackbody (MTB) model. The widely used implementation of this model, which is known as ``diskbb,'' assumes nonzero torque at the inner edge of the accretion disk. This assumption is contrary to the classic and current literature on thin-disk accretion, which advocates the use of a zero-torque boundary condition. Consequently, we have written code for a zero-torque model, ``ezdiskbb,'' which we compare to the nonzero-torque model diskbb by fitting RXTE spectra of three well-known black hole binaries: 4U 1543-47, XTE J1550-564, and GRO J1655-40. The chief difference we find is that the zero-torque model gives a value for the inner disk radius that is about 2.2 times smaller than the value given by diskbb. This result has important implications, especially for the determination of black-hole angular momentum and mass accretion rate.Comment: 27 pages, 9 figures, submitted to Ap

Phenomenology of Neutrino Oscillations

The phenomenology of solar, atmospheric, supernova and laboratory neutrino oscillations is described. Analytical formulae for matter effects are reviewed. The results from oscillations are confronted with neutrinoless double beta decay.Comment: 11 pages, 2 figures, latex, Plenary talk given at Workshop in High Energy Particle Physics-6, Chennai, Indi

Canonical Quantization Inside the Schwarzschild Black Hole

We propose a scheme for quantizing a scalar field over the Schwarzschild manifold including the interior of the horizon. On the exterior, the timelike Killing vector and on the horizon the isometry corresponding to restricted Lorentz boosts can be used to enforce the spectral condition. For the interior we appeal to the need for CPT invariance to construct an explicitly positive definite operator which allows identification of positive and negative frequencies. This operator is the translation operator corresponding to the inexorable propagation to smaller radii as expected from the classical metric. We also propose an expression for the propagator in the interior and express it as a mode sum.Comment: 8 pages, LaTex. Title altered. One reference added. A few typos esp. eq.(7),(38) corrected. To appear in Class.Q.Gra

Soft X-Ray Sources at the Centers of the Elliptical Galaxies NGC 4472 and NGC 4649

Analysis of recent Chandra observations of the elliptical galaxies NGC 4472 and NGC 4649 has revealed faint soft X-ray sources at their centers. The sources are located to within 1'' of the optical centers of the galaxies. They are most likely associated with the central supermassive black holes. Interest in these and several other similar objects stems from the unusually low luminosity of the supermassive black holes embedded in dense interstellar medium. Our Chandra sources have very soft spectra. They are detectable only below ~0.6 keV and have luminosities in the 0.2-2.5 keV energy band of ~ 6 * 10^{37} erg/s and ~1.7 * 10^{38} erg/s in NGC 4649 and NGC 4472, respectively.Comment: Shortened version of the paper published in Astronomy Letter

Gravitational Lens Statistics and The Density Profile of Dark Halos

We investigate the influence of the inner profile of lens objects on gravitational lens statistics taking into account of the effect of magnification bias and both the evolution and the scatter of halo profiles. We take the dark halos as the lens objects and consider the following three models for the density profile of dark halos; SIS (singular isothermal sphere), the NFW (Navarro Frenk White) profile, and the generalized NFW profile which has a different slope at smaller radii. The mass function of dark halos is assumed to be given by the Press-Schechter function. We find that magnification bias for the NFW profile is order of magnitude larger than that for SIS. We estimate the sensitivity of the lensing probability of distant sources to the inner profile of lenses and to the cosmological parameters. It turns out that the lensing probability is strongly dependent on the inner density profile as well as on the cosmological constant. We compare the predictions with the largest observational sample, the Cosmic Lens All-Sky Survey. The absence or presence of large splitting events in larger surveys currently underway such as the 2dF and SDSS could set constraints on the inner density profile of dark halos.Comment: 22 pages, minor changes and references added, accepted for publication in Ap

Self-similar solutions of viscous and resistive ADAFs with thermal conduction

We have studied the effects of thermal conduction on the structure of viscous and resistive advection-dominated accretion flows (ADAFs). The importance of thermal conduction on hot accretion flow is confirmed by observations of hot gas that surrounds Sgr A$^*$ and a few other nearby galactic nuclei. In this research, thermal conduction is studied by a saturated form of it, as is appropriated for weakly-collisional systems. It is assumed the viscosity and the magnetic diffusivity are due to turbulence and dissipation in the flow. The viscosity also is due to angular momentum transport. Here, the magnetic diffusivity and the kinematic viscosity are not constant and vary by position and $\alpha$-prescription is used for them. The govern equations on system have been solved by the steady self-similar method. The solutions show the radial velocity is highly subsonic and the rotational velocity behaves sub-Keplerian. The rotational velocity for a specific value of the thermal conduction coefficient becomes zero. This amount of conductivity strongly depends on magnetic pressure fraction, magnetic Prandtl number, and viscosity parameter. Comparison of energy transport by thermal conduction with the other energy mechanisms implies that thermal conduction can be a significant energy mechanism in resistive and magnetized ADAFs. This property is confirmed by non-ideal magnetohydrodynamics (MHD) simulations.Comment: 8 pages, 5 figures, accepted by Ap&S

Solar Neutrinos and the Eclipse Effect

The solar neutrino counting rate in a real time detector like Super--Kamiokanda, SNO, or Borexino is enhanced due to neutrino oscillations in the Moon during a partial or total solar eclipse. The enhancement is calculated as a function of the neutrino parameters in the case of three flavor mixing. This enhancement, if seen, can further help to determine the neutrino parameters.Comment: 24 Pages Revtex, 8 figures as one ps file. To appear in Phys. Rev. D; Some typos corrected and a reference adde

Constraining Alternate Models of Black Holes: Type I X-ray Bursts on Accreting Fermion-Fermion and Boson-Fermion Stars

The existence of black holes remains open to doubt until other conceivable options are excluded. With this motivation, we consider a model of a compact star in which most of the mass consists of dark particles of some kind, and a small fraction of the mass is in the form of ordinary nucleonic gas. The gas does not interact with the dark matter other than via gravity, but collects at the center as a separate fermionic fluid component. Depending on whether the dark mass is made of fermions or bosons, the objects may be called fermion-fermion stars or boson-fermion stars, respectively. For appropriate choices of the mass of the dark matter particles, these objects are viable models of black hole candidates in X-ray binaries. We consider models with a dark mass of 10 solar masses and a range of gas mass from 10^{-6} to nearly one solar mass, and analyse the bursting properties of the models when they accrete gas. We show that all the models would experience thermonuclear Type I X-ray bursts at appropriate mass accretion rates. Since no Type I bursts have been reported from black hole candidates, the models are ruled out. The case for identifying black hole candidates in X-ray binaries as true black holes is thus strengthened.Comment: 29 pages, 7 figures, to appear in The Astrophysical Journa