Viscosity: From air to hot nuclei/ The Luminosity-time correlation (Lx-Ta) in GRB afterglows as a cosmological tool/ Supernova Remnants --- Active Retirement Life of Stars

Wednesday 27 Nov 2013, 11:00 → 12:30 Asia/Tokyo

RIBF Bldg. Room 203 (RIKEN Wako)

Date: Wednesday, November 27th, 11:00- Place: Room 203, RIBF building Title: Viscosity: From air to hot nuclei Speaker: Dr. Nguyen Dinh Dang (TNP Lab) Abstract: The recent observations of the charged particle elliptic flow and jet quenching in ultrarelativistic Au-Au and Pb-Pb collisions performed at the Relativistic Heavy Ion Collider (RHIC) at Brookhaven National Laboratory and Large Hadron Collider (LHC) at CERN have been the key experimental discoveries in the creation and study of quark-gluon plasma (QGP). The analysis of the data obtained from the hot and dense system produced in these experiments revealed that the strongly interacting matter formed in these collisions is a nearly perfect fluid with extremely low viscosity. In the verification of the condition for applying hydrodynamics to nuclear system, it turned out that the quantum mechanical uncertainty principle requires a finite viscosity for any thermal fluid. In this respect, one of the most fascinating theoretical findings has been the conjecture by Kovtun, Son and Starinets (KSS) that the ratio eta/s of shear viscosity eta to the entropy volume density s is bound below for all fluids, namely the value eta/s=/(4 x pi x k_B) (k_B is the Boltzmann constant) is the universal lower bound (the KSS bound or KSS unit) [1]. The QGP fluid produced at RHIC has eta/s ~ (2 - 3) KSS units. Given this conjectured universality, there has been an increasing interest in calculating the ratio eta/s in different systems. After a brief account on the history of the viscosity from classical to quantum fluids, the present lecture discusses how the shear viscosity eta of a finite hot nucleus is calculated from the giant dipole resonance (GDR) of this nucleus. The ratio eta/s is extracted from the experimental systematic of GDR in copper, tin and lead isotopes at finite temperature T. These empirical results are then compared with the predictions by several independent models, as well as with almost model-independent estimations. Based on these results, it is concluded that the ratio eta/s in medium and heavy nuclei decreases with increasing T to reach (1.3 - 4) KSS units at T= 5 MeV, i.e. almost the same value as that obtained for QGP at T > 170 MeV [2]. References: [1] P.K. Kovtun, D.T. Son, and A.O. Starinets, Phys. Rev. Lett. 94 (2005) 111601. [2] N. Dinh Dang, Phys. Rev. C 84 (2011) 034309. Title: The Luminosity-time correlation (Lx-Ta) in GRB afterglows as a cosmological tool Speaker: Dr. Maria Dainotti (ABB Lab) Abstract: We introduce how GRBs have been used for cosmological tools so far, in particular with the Lx-Ta correlation. We show how changes of the observed slope, bobs, of the LX-TX correlation in GRB afterglows affect the determination of the cosmological parameters. With 101 GRBs simulated with a central value of bobs that differs on the intrinsic one by a 5σ factor, we find an overestimated value of the matter density parameter, ΩM compared to the value obtained with SNe Ia, while the Hubble constant, H0, best fit value is still compatible in 1 σ. Instead, for a subsample of high luminous GRBs (HighL), H0 and ΩM are not more compatible in 1 σ and ΩM is underestimated by the 13%. However, the HighL sample choice reduces dramatically the intrinsic scatter of the correlation, thus possibly identifying this sample as the standard canonical `GRBs'. We conclude that any approach that involves cosmology should take into consideration only intrinsic correlations not the observed ones. Title: Supernova Remnants --- Active Retirement Life of Stars Speaker: Dr. Herman Lee (ABB Lab) Abstract: Stars spend millions and millions of years working hard and shining bright, and eventually they get exhausted and retire. However, some retired stars are so fanatic that they do not go to elderly homes, but rather they would explode themselves as supernovae. Their bodies (ejecta) expand into the surrounding material at supersonic speed, creating fast shock waves which heats up the shocked plasma to hundreds of millions of degree. Not only does these stellar ‘remnants’ shines bright across the whole electromagnetic spectrum with interesting nebular-like morphologies, they are also known to be powerful particle accelerators, probably responsible for generating most of the cosmic-rays in our Galaxy. I will give a very general overview on these fascinating objects and where we stand now in our understanding of their high-energy phenomena. Other TNP seminars