Tata Institute of Fundamental Research

About: Tata Institute of Fundamental Research is a education organization based out in Mumbai, Maharashtra, India. It is known for research contribution in the topics: Magnetization & Large Hadron Collider. The organization has 7786 authors who have published 21742 publications receiving 622368 citations. The organization is also known as: TIFR.

Collective three-flavor oscillations of supernova neutrinos

Abstract: Neutrinos and antineutrinos emitted from a core collapse supernova interact among themselves, giving rise to collective flavor conversion effects that are significant near the neutrinosphere. We develop a formalism to analyze these collective effects in the complete three-flavor framework. It naturally generalizes the spin-precession analogy to three flavors and is capable of analytically describing phenomena like vacuum/Mikheyev-Smirnov-Wolfenstein (MSW) oscillations, synchronized oscillations, bipolar oscillations, and spectral split. Using the formalism, we demonstrate that the flavor conversions may be ``factorized'' into two-flavor oscillations with hierarchical frequencies. We explicitly show how the three-flavor solution may be constructed by combining two-flavor solutions. For a typical supernova density profile, we identify an approximate separation of regions where distinctly different flavor conversion mechanisms operate, and demonstrate the interplay between collective and MSW effects. We pictorialize our results in terms of the ``${\mathbf{e}}_{3}\mathrm{\text{\ensuremath{-}}}{\mathbf{e}}_{8}$ triangle'' diagram, which is a tool that can be used to visualize three-neutrino flavor conversions in general, and offers insights into the analysis of the collective effects in particular.

OSSE and RXTE Observations of GRS 1915+105: Evidence for Nonthermal Comptonization

Abstract: GRS 1915+105 was observed by the Oriented Scintillation Spectroscopy Experiment (OSSE) aboard the Compton Gamma Ray Observatory nine times in 1995-2000, and eight of those observations were simultaneous with those by the Rossi X-Ray Timing Explorer (RXTE). We present an analysis of all of the OSSE data and of two RXTE-OSSE spectra with the lowest and highest X-ray fluxes. The OSSE data show a power-law-like spectrum extending up to 600 keV without any break. We interpret this emission as strong evidence for the presence of nonthermal electrons in the source. The broadband spectra cannot be described by either thermal or bulk-motion Comptonization, whereas they are well described by Comptonization in hybrid thermal/nonthermal plasmas.

The Solar Acoustic Spectrum and Eigenmode Parameters

Abstract: The Global Oscillation Network Group (GONG) project estimates the frequencies, amplitudes, and linewidths of more than 250,000 acoustic resonances of the sun from data sets lasting 36 days. The frequency resolution of a single data set is 0.321 microhertz. For frequencies averaged over the azimuthal order m , the median formal error is 0.044 microhertz, and the associated median fractional error is 1.6 × 10 −5 . For a 3-year data set, the fractional error is expected to be 3 × 10 −6 . The GONG m -averaged frequency measurements differ from other helioseismic data sets by 0.03 to 0.08 microhertz. The differences arise from a combination of systematic errors, random errors, and possible changes in solar structure.

Search for long-lived neutral particles decaying to quark-antiquark pairs in proton-proton collisions at √s =8TeV

Abstract: A search is performed for long-lived massive neutral particles decaying to quark-antiquark pairs. The experimental signature is a distinctive topology of a pair of jets, originating at a secondary vertex. Events were collected with the CMS detector at the CERN LHC in proton-proton collisions at a centre-of-mass energy of 8 TeV. The data analyzed correspond to an integrated luminosity of 18.5 inverse femtobarns. No significant excess is observed above standard model expectations. Upper limits at 95% confidence level are set on the production cross section of a heavy neutral scalar particle, H, in the mass range of 200 to 1000 GeV, decaying promptly into a pair of long-lived neutral X particles in the mass range of 50 to 350 GeV, each in turn decaying into a quark-antiquark pair. For X with mean proper decay lengths of 0.4 to 200 cm, the upper limits are typically 0.5-200 fb. The results are also interpreted in the context of an R-parity-violating supersymmetric model with long-lived neutralinos decaying into a quark-antiquark pair and a muon. For pair production of squarks that promptly decay to neutralinos with mean proper decay lengths of 2-40 cm, the upper limits on the cross section are typically 0.5-3 fb. The above limits are the most stringent on these channels to date.