Nonperturbative calculation of the shear viscosity in hot phi**4 theory in real time

Starting from the Kubo formula we calculate the shear viscosity in hot phi**4 theory nonperturbatively by resumming ladders with a real-time version of the Bethe-Salpeter equation at finite temperature. In the weak coupling limit, the generalized Fluctuation-Dissipation Theorem is shown to decouple the Bethe-Salpeter equations for the different real-time components of the 4-point function. The resulting scalar integral equation is identical with the one obtained by Jeon using diagrammatic ``cutting rules'' in the Imaginary Time Formalism.Comment: 4 pages LateX. The 2 postscript figures are now incorporated into the text, facilitating download. No other changes. Accepted by Physics Letters

Interplay of soft and hard processes and hadron pTp_T spectra in pApA and AAAA collisions

Motivated by a schematic model of multiple parton scattering within the Glauber formalism, the transverse momentum spectra in $pA$ and $AA$ collisions are analyzed in terms of a nuclear modification factor with respect to $pp$ collisions. The existing data at the CERN Super Proton Synchrotron (SPS) energies are shown to be consistent with the picture of Glauber multiple scattering in which the interplay between soft and hard processes and the effect of absorptive processes lead to nontrivial nuclear modification of the particle spectra. Relative to the additive model of incoherent hard scattering, the spectra are enhanced at large $p_T$ (hard) by multiple scattering while suppressed at low $p_T$ (soft) by absorptive correction with the transition occurring at around a scale $p_0\sim 1-2$ GeV/$c$ that separates soft and hard processes. Around the same scale, the $p_T$ spectra in $pp$ collisions also change from an exponential form at low $p_T$ to a power-law behavior at high $p_T$. At very large $p_T\gg p_0$, the nuclear enhancement is shown to decrease like $1/p_T^2$. Implications of these nuclear effects on the study of jet quenching, parton thermalization and collective radial flow in high-energy $AA$ collisions are discussed.Comment: 9 pages in Revtex, 7 eps figure

Spin Hydrodynamic Generation in the Charged Subatomic Swirl

Recently there have been significant interests in the spin hydrodynamic generation phenomenon from multiple disciplines of physics. Such phenomenon arises from global polarization effect of microscopic spin by macroscopic fluid rotation and is expected to occur in the hot quark-gluon fluid (the ``subatomic swirl'') created in relativistic nuclear collisions. This was indeed discovered in experiments which however revealed an intriguing puzzle: a polarization difference between particles and anti-particles. We suggest a novel application of a general connection between rotation and magnetic field: a magnetic field naturally arises along the fluid vorticity in the charged subatomic swirl. We establish this mechanism as a new way for generating long-lived in-medium magnetic field in heavy ion collisions. Due to its novel feature, this new magnetic field provides a nontrivial explanation to the puzzling observation of a difference in spin hydrodynamic generation for particles and anti-particles in heavy ion collisions.Comment: 10 pages, 3 figures, title changed according to published versio