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.

The Late-Time Radio Emission from SN 1993J at Meter Wavelengths

Abstract: This paper presents the investigations of SN 1993J using low-frequency observations with the Giant Metrewave Radio Telescope (GMRT). We analyze the light curves of SN 1993J at 1420, 610, 325, and 243 MHz during 7.5 10 yr after the explosion. The supernova has become optically thin early on in the 1420 and 610 MHz bands, while it has only recently entered the optically thin phase in the 325 MHz band. The radio light curve in the 235 MHz band is more or less flat. This indicates that the supernova is undergoing a transition from an optically thick to optically thin limit in this frequency band. In addition, we analyze the supernova radio spectra at five epochs on days 3000, 3200, 3266, 3460, and 3730 after the explosion. The spectral break in the day 3200 composite spectrum from the GMRT and Very Large Array implies that the plasma is dominated by a magnetic field, and the latter is far from being in equipartition with relativistic particles. SN 1993J is the only young supernova for which the magnetic field and the size of the radio-emitting region are determined through unrelated methods. Thus, the mechanism that controls the evolution of the radio spectra can be identified. We suggest that at all epochs, the synchrotron self-absorption mechanism is primarily responsible for the turnover in the spectra. Light-curve models based on free-free absorption in homogeneous or inhomogeneous media at high frequencies overpredict the flux densities at low frequencies. The discrepancy is increasingly larger at lower and lower frequencies. We suggest that an extra opacity, sensitively dependent on frequency, is likely to account for the difference at lower frequencies. The evolution of the magnetic field (determined from synchrotron self-absorption turnover) is roughly consistent with $B \propto t^{-1}$. The radio spectral index in the optically thin part evolves from \alpha \sim 0.8 1.0 at a few tens of days to 0.6 in about 10 yr.

Study of double parton scattering using W + 2-jet events in proton-proton collisions at √s = 7 TeV

Abstract: Double parton scattering is investigated in proton-proton collisions at sqrt(s) = 7 TeV where the final state includes a W boson, which decays into a muon and a neutrino, and two jets. The data sample corresponds to an integrated luminosity of 5 inverse femtobarns, collected with the CMS detector at the LHC. Observables sensitive to double parton scattering are investigated after being corrected for detector effects and selection efficiencies. The fraction of W + 2-jet events due to double parton scattering is measured to be 0.055 +/- 0.002 (stat.) +/- 0.014 (syst.). The effective cross section, sigma[eff], characterizing the effective transverse area of hard partonic interactions in collisions between protons is measured to be 20.7 +/- 0.8 (stat.) +/- 6.6 (syst.) mb.

Renormalized Polyakov loops in many representations

Abstract: We present a renormalization procedure for Polyakov loops which explicitly implements the fact that the renormalization constant depends only on the ultraviolet cutoff. Using this we study the renormalized Polyakov loops in all representations up to the 27 of the gauge group SU(3). We find good evidence for Casimir scaling of the Polyakov loops and for approximate large-N factorization. By studying many loops together, we are able to show that there is a matrix model with a single coupling which can describe the high temperature phase of QCD, although it is hard to construct explicitly. We present the first results for the nonvanishing renormalized octet loop in the thermodynamic limit below the SU(3) phase transition, and estimate the associated string breaking distance and the gluelump binding energy. By studying the connection of the direct renormalization procedure with a generalization of an earlier suggestion which goes by the name of the QQ renormalization procedure, we find that they are functionally equivalent.