« fall 2008 - spring 2009 - summer 2009 »

This week | Next week | This semester | All future | Print view

This week | Next week | This semester | All future | Print view

Thursday, January 22nd 2009

2:30 pm:

Thursday, January 29th 2009

2:30 pm:

Thursday, February 5th 2009

2:30 pm:

Thursday, February 19th 2009

2:30 pm:

Thursday, February 26th 2009

2:30 pm:

Hydrogen and helium accreted on a neutron star can undergo unstablethermonuclear burning, which is observable as a flash of X-rays. When fuel is accreted continuously, X-ray bursts occur with recurrence times of hours or days. We discuss what determines this timescale and show the puzzling observations of bursts with recurrence times of only minutes. Hydrogen and helium flashes build up a carbon-rich layer that extends down to the neutron star crust. When this layer burns in a flash, a so-called superburst can be observed. These are much rarer events than ordinary bursts. We place constraints on the superburst recurrence time of nine sources and show how they can be used to constrain models of the neutron star interior.

Thursday, March 5th 2009

2:30 pm:

Thursday, March 12th 2009

2:30 pm:

There is now a large database on high-resolution observations of elemental abundances in old stars that reside in the halo of our Galaxy. This represents an exquisite record of chemical evolution of the early universe and has important implications for the stellar sources producing the various elements. The observational data will be reviewed, as well as the current stellar models for nucleosynthesis. It will be shown that three different types of massive stellar sources are required to explain the data. In particular, hypernovae with large explosion energies and Fe yields are an important player.

Thursday, March 19th 2009

2:30 pm:

Thursday, April 2nd 2009

2:30 pm:

Thursday, April 9th 2009

2:30 pm:

Thursday, April 16th 2009

2:30 pm:

Thursday, April 23rd 2009

2:30 pm:

I discuss the use of gauge/gravity duality in computing hydrodynamic dispersion relations for strongly coupled plasmas. I present recent work which has extended the computation of the sound mode dispersion relation up to third order in the momentum of the perturbation. Resulting formulas for the speed of sound, bulk viscosity, as well as some second order transport coefficients are presented for a specific class of gravity duals.

Thursday, April 30th 2009

2:30 pm:

Thursday, May 7th 2009

2:30 pm:

Thursday, May 14th 2009

2:30 pm:

Wednesday, September 9th 2009

1:25 pm:

Thursday, September 17th 2009

2:30 pm:

Wednesday, September 23rd 2009

1:25 pm:

Wednesday, September 30th 2009

1:25 pm:

Wednesday, October 7th 2009

1:25 pm:

Wednesday, October 14th 2009

1:25 pm:

Wednesday, October 21st 2009

1:25 pm:

The thermodynamics and critical exponents and amplitudes of high temperature and dense matter near the chiral critical point is studied. The parameterized equation of state matches on to that calculated with lattice QCD at zero chemical potential and to the known properties of nuclear matter at zero temperature. The extent to which finite size effects wash out the phase separation near the critical point is determined. The degree to which the critical point acts as an attractor in high energy heavy ion collisions is also investigated.

Wednesday, October 28th 2009

1:25 pm:

The heavy ion collision experiments are in progress in order to

investigate how the Universe has evolved after the Big Bang. The recent

observations show that a nearly perfect fluid is produced after heavy

ion collisions. An appropriate incorporation of the relativistic

hydrodynamics and the field theory would help us to describe the

dynamics of QCD (Quantum Chromodynamics) matter under extreme

conditions, and to survey the expected phase transitions. Some efforts

to investigate the characteristics of the QCD plasma are devoted to an

ideal, non-dissipative one. To get the results which are highly in

accordance with the experiment, it is necessary to bring also in mind

the role of dissipation, particularly the second order dissipation,

because the first order dissipation will result in instabilities and

causality violation. We are to couple the field theory and the

hydrodynamics of the dissipative fluid in such a way that the effect of

second order dissipative coefficients in addition to the effect of the

fields will emerge in the properties of the quark-gluon plasma (QGP)

such as sound velocity. In this seminar, after deriving the

thermodynamical potential using the effective potential of the linear

sigma model, we will study the effect of second order dissipation on the

sound velocity in the QGP and its variation near the chiral phase

transition.

Wednesday, November 4th 2009

1:25 pm:

I use the AdS/CFT correspondence to explore the non-perturbative realms of a QCD-like theory at finite temperatures. One hopes the strongly-coupled Quark-Gluon Plasma (sQGP) could be succinctly described by such a model.

Wednesday, November 11th 2009

1:25 pm:

The spectral split is the most interesting feature of neutrino

flavor transformation from the neutrino-neutrino interaction, which is dominant in a supernovae environment. A simple model to explain this phenomenon will be discussed.

Wednesday, November 18th 2009

1:25 pm:

Wednesday, November 25th 2009

1:25 pm:

Wednesday, December 2nd 2009

1:25 pm:

The vacuum of QCD is infinitely degenerate, but perturbative processes such as scattering or particle annihilation/creation do not change the vacuum of the gluons. However, nonperturbative topological solutions of the gluon field such as sphalerons, which are not suppressed at finite temperature, bring about transitions between different vacua. The Chern-Simons winding number associated with those transitions controls the anomaly of the U(1) axial current of the quarks. As a result of nonconservation of the axial current, sphalerons produce more left handed quarks and antiquarks than right handed ones, or vice versa. Under the influence of the strong magnetic field produced by off-central heavy-ion collisions, quark matter with nonzero net chirality (or handedness) polarizes along the axis of the magnetic field so that positively and negatively charged quarks accumulate oppositely, i.e., an electric current is produced parallel to the magnetic field. All these relate to the electric dipole moment of quark gluon plasma, P and CP violation, and the E.B term which has no effect in classical electromagnetism. Modification of the hydrodynamic equations for incorporation of the axial anomaly is also considered along with the calculation of the new kinetic coefficient appearing with the additional term of vorticity added to the current.

Wednesday, December 9th 2009

1:25 pm:

The AdS/CFT correspondence establishes an effective dictionary between strongly coupled theories and higher-dimensional gravitational theories. This has led to five-dimensional phenomonological models to describe quantum chromodynamics, known as AdS/QCD. Because of the running coupling constant, these models must have a cutoff in the fifth conformal dimension. The specific model studied here is known as a soft wall model, and it uses a dilaton field as an effective cutoff. This results in a realistic mass spectrum for the radial excitations of the lowest-lying mesons.I will describe our model and its successful modeling of the scalar, vector, and axial meson masses. I will also discuss I will also discuss my ongoing work on the pions, and the unique challenges of this sector.

The weekly calendar is also available via subscription to the physics-announce mailing list, and by RSS feed.