Abstract

Abstract

Centaurus A is the nearest radio-loud AGN and is detected from radioto very high energy gamma-rays. Its nuclear spectral energydistribution shows two peaks, one in the far-infrared band and anotherat about 170 keV. Although, the flux from this nuclear region iswell explained by leptonic models, it fails to account for highenergy tail region above few GeV. We show that, within the jet, thecollision of Fermi accelerated high energy protons with the IC photonsaround the second peak region can produce multi-GeV to TeV gamma-raysand GeV neutrinos through delta-resonance which can explainsimultaneously, the observed GeV-TeV tail in the photon flux and theobserved cosmic ray events by Pierre Auger Observatory. We also estimatethe GeV neutrino flux from it.

Abstract

In this talk we propose a novel method to characterize first order phasetransitions using the scalar curvature of the equilibrium thermodynamicstate space. Furthermore, our construction naturally characterizes theWidom line through the maxima of the correlation length. As anillustration, we use it in conjunction with the mean field Van der Waalsequation of state to predict the coexistence curve and the Widom line.Where closely applicable, it provides good agreement with experimentaldata. It generalizes to diverse systems like anti de Sitter black holes,which also exhibit first-order phase transitions.

Abstract

Two-particle momentum correlations between pairs of identical particles produced in relativistic heavyion reactions can be analyzed to extract the information on the spatial and temporal structure of the source as well as the dynamics of fireball in Relativistic Heavy Ion collision.We have calculated twobody correlation function of lepton pairs produced from decay of virtual photon in central Au+Au collisions at the Relativistic Heavy Ion Collider. Our calculation includes contributions from the radiation of lepton pairs from a thermalized QuarkGluonPlasma (QGP) and the subsequent expanding hadron gas. The lepton pair interferometry provides a faithful probe of the details of the spacetime evolution and of the early stages of the system produced in Heavy Ion Collision. We have demonstrated that the study of mass dependence of various HBT radii extracted from the correlation functions of lepton pairs can be used as a powerful tool to characterize and distinguish the hadronic and the partonic phases and also focus on the collective expansion of the system. This study is carried out for Au+Au collisions at √ sNN = 200 GeV by solving relativistic hydrodynamical equations with boost invariance along the longitudinal direction. The equation of state is taken from lattice QCD calculations. The initial conditions for the solution of hydrodynamic equation is constrained by the measured single photon at RHIC. We obtain very different values for the HBT radii (Rside and Rout ) in the mass region around rhomeson and those beyond 1.2 GeV. The physical implications of these results and how these can be used to characterize the hadronic and partonic phases produced in high energy heavyion collisions will be discussed in the presentation

Abstract

Cross-linked microgel particles constitute an interesting class of softcolloidal systems which possess a variable degree of softness and atuneable interaction potential that can be varied between hard spherecolloid and polymeric systems. These microgel colloids have a wide rangeof potential applications in drug delivery, sensing, fabrication ofphotonic crystals, template-based synthesis of inorganic nanoparticles,micro lenses, etc. Basically, these applications arise from theirstimulus-responsive nature, that is, their ability to undergo reversiblevolume phasetransitions in response to external stimuli such as a change intemperature, pH, and ionic strength of the surrounding medium. Moreover,it is also this responsiveness of the microgel particles which make theminteresting to use them as a model system for the investigation of manyfundamental thermodynamical phenomena.Here we study the phase behaviour of a particular class of soft-repulsivecolloids such as poly(N-isopropylacrylamide) ( PNIPAM ) microgel. Due to their soft- repulsivenature, microgels can interpenetrate or compress to a certain degree inorder to create states with densities far above the close packing (volumefraction=0.74) of hard sphere colloids. We look at the influence of theintrinsic softness of these particles on dynamical arrest, and investigatethe nature of the dense phases that exist at ultra-highdensities far beyond close packing. We use confocal laser scanningmicroscopy (CLSM) that allows us to track the particles in real time anddetermine quantities such the pair correlation function orthe mean square displacement of the particles as a function of effectivevolume fraction. We combine these experiments with static (SLS) anddynamic (DLS) light scattering, small-angle neutron (SANS) and small-anglex-ray scattering (SAXS) to obtain a full characterization of thestructural and dynamic properties of these suspensions at all relevantlength and time scales. In particular, a special variant of small-angleneutron scattering (SANS), experiments under so-called zero averagecontrast conditions, we also extract size and shape of the microgelparticles at all densities which allows us to completely decoupleinteractions and particle size and shape experimentally for the first time.