Exotic Freezing of Response in Quantum Many-Body System

We show that when a quantum many-body system is subjected to coherent periodic driving, the response may exhibit exotic freezing behavior in high driving frequency ($\omega$) regime. In a periodically driven classical thermodynamic system, freezing at high $\omega$ occurs when $1/\omega$ is much smaller than the characteristic relaxation time of the system, and hence the freezing always increases there as $\omega$ is increased. Here, in the contrary, we see surprising non-monotonic freezing behavior of the response with $\omega$, showing curious peak-valley structure. Quite interestingly, the entire system tends to freeze almost absolutely (the freezing peaks) when driven with a certain combination of driving parameters values (amplitude and $\omega$) due to coherent suppression of dynamics of the quantum many-body modes, which has no classical analog. We demonstrate this new freezing phenomenon analytically (supported by large-scale numerics) for a general class of integrable quantum spin systems.Comment: Presentation modified; version accepted in Phys. Rev.

Quantum Discord in a spin-1/2 transverse XY Chain Following a Quench

We report a study on the zero-temperature quantum discord as a measure of two-spin correlation of a transverse XY spin chain following a quench across a quantum critical point and investigate the behavior of mutual information, classical correlations and hence of discord in the final state as a function of the rate of quenching. We show that though discord vanishes in the limit of very slow as well as very fast quenching, it exhibits a peak for an intermediate value of the quenching rate. We show that though discord and also the mutual information exhibit a similar behavior with respect to the quenching rate to that of concurrence or negativity following an identical quenching, there are quantitative differences. Our studies indicate that like concurrence, discord also exhibits a power law scaling with the rate of quenching in the limit of slow quenching though it may not be expressible in a closed power law form. We also explore the behavior of discord on quenching linearly across a quantum multicritical point (MCP) and observe a scaling similar to that of the defect density.Comment: 6 pages, 5 figure

Jet quenching

Jet quenching studies play a prominent role in our current understanding of ultra-relativistic heavy ion collisions. In this review I first present the available formalism to compute medium-induced gluon radiation. Then I discuss its effect on single particle spectra, with dedicated attention to the case of the radiating parton being a massive quark. Next I examine more differential observables like jet shapes and multiplicities, and the consequences of flow on radiative energy loss. I conclude with some remarks.Comment: LaTeX, 8 pages, 7 eps figures, uses enclosed cjpsuppl.cls; invited talk at Physics at LHC, Vienna, Austria, July 13th-17th 200

Dependence of Galaxy Quenching on Halo Mass and Distance from its Centre

We study the dependence of star-formation quenching on galaxy mass and environment, in the SDSS (z~0.1) and the AEGIS (z~1). It is crucial that we define quenching by low star-formation rate rather than by red colour, given that one third of the red galaxies are star forming. We address stellar mass M*, halo mass Mh, density over the nearest N neighbours deltaN, and distance to the halo centre D. The fraction of quenched galaxies appears more strongly correlated with Mh at fixed M* than with M* at fixed Mh, while for satellites quenching also depends on D. We present the M*-Mh relation for centrals at z~1. At z~1, the dependence of quenching on M* at fixed Mh is somewhat more pronounced than at z~0, but the quenched fraction is low (10%) and the haloes are less massive. For satellites, M*-dependent quenching is noticeable at high D, suggesting a quenching dependence on sub-halo mass for recently captured satellites. At small D, where satellites likely fell in more than a few Gyr ago, quenching strongly depends on Mh, and not on M*. The Mh-dependence of quenching is consistent with theoretical wisdom where virial shock heating in massive haloes shuts down accretion and triggers ram-pressure stripping, causing quenching. The interpretation of deltaN is complicated by the fact that it depends on the number of observed group members compared to N, motivating the use of D as a better measure of local environment.Comment: 23 pages, 13 figures, accepted by MNRA

Jet Quenching

A short summary of the physics underlying jet quenching is givenComment: 10 pages, LaTex, 11 postscript figures, Proceedings of Quark Matter 2002, Nantes, France, July 18-24, 200