Devasthal Fast Optical Telescope observations of Wolf-Rayet dwarf galaxy Mrk 996

The Devasthal Fast Optical Telescope (DFOT) is a 1.3 meter aperture optical telescope, recently installed at Devasthal, Nainital. We present here the first results using an \Ha filter with this telescope on a Wolf-Rayet dwarf galaxy Mrk 996. The instrumental response and the \Ha sensitivity obtained with the telescope are $(3.3 \pm 0.3)\times 10^{-15} (erg s^{-1} cm^{-2})/(counts s^{-1})$ and $7.5\times10^{-17} erg s^{-1} cm^{-2} arcsec^{-2}$ respectively. The \Ha flux and the equivalent width for Mrk~996 are estimated as $(132 \pm 37)\times 10^{-14} erg s^{-1} cm^{-2}$ and $\sim$96 $\mathring{A}$ respectively. The star formation rate is estimated as $0.4\pm0.1 M_\odot$yr$^{-1}$. Mrk~996 deviates from the radio-FIR correlation known for normal star forming galaxies with a deficiency in its radio continuum. The ionized gas as traced by \Ha emission is found in a disk shape which is misaligned with respect to the old stellar disk. This misalignment is indicative of a recent tidal interaction in the galaxy. We believe that galaxy-galaxy tidal interaction is the main cause of the WR phase in Mrk~996.Comment: 13 pages, 2 figures Accepted for publication in "Journal of Astrophysics and Astronomy

Four Generations, Higgs Physics, and the MSSM

We consider the effects of a fourth generation of chiral fermions within the MSSM. Such a model offers the possibility of having the lightest neutral Higgs boson significantly heavier than in the three generation MSSM. The model is highly constrained by precision electroweak data, along with Higgs searches at the Tevatron. In addition, the requirements of perturbative unitarity and direct searches for heavy quarks imply that the four generation MSSM is only consistent for tan beta ~ 1 and highly tuned 4th generation fermion masses.Comment: References added and minor typographical errors correcte

Dusty Plasma Experimental (DPEx) device for complex plasma experiments with flow

A versatile table-top dusty plasma experimental (DPEx) device to study flow induced excitations of linear and nonlinear waves/structures in a complex plasma is presented. In this {$\Pi$}-shaped apparatus a DC glow discharge plasma is produced between a disc shaped anode and a grounded long cathode {tray} by applying a high voltage DC in the background of a neutral gas {(Argon)} and subsequently a dusty plasma is created by introducing micron sized dust particles that get charged and levitated in the sheath region. A flow of the dust particles is induced in a controlled manner by adjusting the pumping speed and the gas flow rate into the device. A full characterisation of the plasma, using Langmuir and emissive probe data, and that of the dusty plasma using particle tracking data with the help of an idl based (super) Particle Identification and Tracking (sPIT) code is reported. Experimental results on the variation of the dust flow velocity as a function of the neutral pressure and the gas flow rate are given. {The neutral drag force acting on the particles and the Epstein coefficient are estimated from the initial acceleration of the particles}. The potential experimental capabilities of the device for conducting fundamental studies of flow induced instabilities are discussed.Comment: 7 pages, 6 figure

Experimental investigation of flow induced dust acoustic shock waves in a complex plasma

We report on experimental observations of flow induced large amplitude dust-acoustic shock waves (DASW) in a complex plasma. The experiments have been carried out in a $\Pi$ shaped DC glow discharge experimental device using kaolin particles as the dust component in a background of Argon plasma. A strong supersonic flow of the dust fluid is induced by adjusting the pumping speed and neutral gas flow into the device. An isolated copper wire mounted on the cathode acts as a potential barrier to the flow of dust particles. A sudden change of gas flow rate is used to trigger the onset of high velocity dust acoustic shocks whose dynamics are captured by fast video pictures of the evolving structures. The physical characteristics of these shocks are delineated through a parametric scan of their dynamical properties over a range of flow speeds and potential hill heights. The observed evolution of the shock waves and their propagation characteristics are found to compare well with model numerical results based on a modified Korteweg-de-Vries-Burgers type equation

Flowing dusty plasma experiments: Generation of flow and measurement techniques

A variety of experimental techniques for the generation of subsonic/supersonic dust fluid flows and means of measuring such flow velocities are presented. The experiments have been carried out in a $\Pi-$shaped Dusty Plasma Experimental (DPEx) device with micron size kaolin/Melamine Formaldehyde (MF) particles embedded in a background of Argon plasma created by a direct current (DC) glow discharge. A stationary dust cloud is formed over the cathode region by precisely balancing the pumping speed and gas flow rate. A flow of dust particles/fluid is generated by additional gas injection from a single or dual locations or by altering the dust confining potential. The flow velocity is then estimated by three different techniques, namely, by super Particle Identification (sPIT) code, Particle Image Velocimetry (PIV) analysis and the excitation of Dust Acoustic Waves (DAWs). The results obtained from these three different techniques along with their merits and demerits are discussed. An estimation of the neutral drag force responsible for the generation as well as the attenuation of the dust fluid flow is made. These techniques can be usefully employed in laboratory devices to investigate linear and non-linear collective excitations in a flowing dusty plasma.Comment: 8 pages, 10 figure

Theoretical study of head-on collision of dust acoustic solitary waves in a strongly coupled complex plasma

We investigate the propagation characteristics of two counter propagating dust acoustic solitary waves (DASWs) undergoing a head-on collision, in the presence of strong coupling between micron sized charged dust particles in a complex plasma. A coupled set of nonlinear dynamical equations describing the evolution of the two DASWs using the extended Poincar\'e-Lighthill-Kuo perturbation technique is derived. The nature and extent of post collision phase-shifts of these solitary waves are studied over a wide range of dusty plasma parameters in a strongly and a weakly coupled medium. We find a significant change in the nature and amount of phase delay in the strongly coupled regime as compared to a weakly coupled regime. The phase shift is seen to change its sign beyond a threshold value of compressibility of the medium for a given set of dusty plasma parameters.Comment: 8 pages, 5 figure

Optical spectroscopy of star-forming regions in dwarf Wolf-Rayet galaxies

We present here spatially-resolved optical spectroscopic observations of four nearby dwarf Wolf-Rayet (WR) galaxies. The ages of the most recent starburst events in these galaxies are found between 3 and 10 Myr. The gas-phase metallicities [12+log(O/H)] for the spatially-resolved star-forming regions are derived using several indicators. The star-forming regions within the galaxies are found chemically homogeneous within the uncertainties in the estimates. Nitrogen-enrichment as expected in the WR regions is not detected. This implies that metal-enrichment due to supernovae explosions in the most recent star-forming episode is not being detected here. It is suggested that the newly synthesized metals still reside in hot gas-phase. The metals from the previous episodes, cooled by now and well mixed across the whole extent of galaxies, are making galaxies chemically homogeneous with normal N/O ratio. These galaxies are residing in dense environments with galaxy density in the range of $8-80$ Mpc$^{-3}$.Comment: 24 pages, 14 figures, Accepted for publication in MNRA

Boltzmann equation with a nonlocal collision term and the resultant dissipative fluid dynamics

Starting with the relativistic Boltzmann equation where the collision term was generalized to include gradients of the phase-space distribution function, we recently presented a new derivation of the equations for the relativistic dissipative fluid dynamics. We compared them with the corresponding equations obtained in the standard Israel-Stewart and related approaches. Our method generates all the second-order terms that are allowed by symmetry, some of which have been missed by the traditional approaches, and the coefficients of other terms are altered. The first-order or Navier-Stokes equation too receives a small correction. Here we outline this work for the general audience.Comment: Invited talk given by Rajeev Bhalerao at Rencontres du Vietnam, International Conference on 'Heavy Ion Collisions in the LHC Era', 15-21 July 2012, Quy Nhon, Vietna

Complete relativistic second-order dissipative hydrodynamics from the entropy principle

We present a new derivation of relativistic dissipative hydrodynamic equations, which invokes the second law of thermodynamics for the entropy four-current expressed in terms of the single-particle phase-space distribution function obtained from Grad's 14-moment approximation. This derivation is complete in the sense that all the second-order transport coefficients are uniquely determined within a single theoretical framework. In particular, this removes the long-standing ambiguity in the relaxation time for bulk viscosity thereby eliminating one of the uncertainties in the extraction of the shear viscosity to entropy density ratio from confrontation with the anisotropic flow data in relativistic heavy-ion collisions. We find that in the one-dimensional scaling expansion, these transport coefficients prevent the occurrence of cavitation even for rather large values of the bulk viscosity estimated in lattice QCD.Comment: 5 pages, 2 figures, version to appear in PRC (Rapid Comm

Associated b-Quark Higgs Boson Production at the LHC

The associated production of a Higgs boson with a b quark is a discovery mode for an MSSM Higgs boson at large tan beta. We present updates on the production rate at the LHC, along with a discussion of the importance of the SQCD corrections from squark and gluino loops. We also discuss the purely electroweak contributions.Comment: 35th International Conference of High Energy Physics - ICHEP2010, July 22-28, 2010, Paris Franc