# Nuclear Theory/RIKEN Seminar

## "Hydrodynamic Fluctuations in Heavy Ion Collisions"

#### Presented by Derek Teaney, Stony Brook

Friday, June 2, 2017, 2:00 pm — Small Seminar Room, Bldg. 510

We develop a set of kinetic equations for hydrodynamic fluctuations which are equivalent to nonlinear hydrodynamics with noise. The hydrokinetic equations can be coupled to existing second-order hydrodynamic codes to incorporate the physics of these fluctuations. We use the hydrokinetic equations to analyze thermal fluctuations for a Bjorken expansion, evaluating the contribution of thermal noise from the earliest moments and at late times. In the Bjorken case, the solution to the kinetic equations determines the coefficient of the first fractional power of the gradient expansion $ \sim 1/(\tau T)^{3/2}$ for the expanding system. Numerically, we find that the contribution to the longitudinal pressure from hydrodynamic fluctuations is larger than second-order hydrodynamics for typical medium parameters used to simulate heavy ion collisions.

Subsequently we analyze the behaviour of hydrodynamic fluctuations of near the QCD critical point, and dilineate the relevance Kiblle-Zurek scaling relative to other physics. If time permits we will also describe how thermal fluctuations place a lower bound on the bulk viscosity of QCD.

References:

Y.~Akamatsu, A.~Mazeliauskas and D.~Teaney, ``A kinetic regime of hydrodynamic fluctuations and long time tails for a Bjorken expansion,'' [arXiv:1606.07742 [nucl-th]].

Y.~Akamatsu, D. Teaney, F. Yan, Y. Yin, ``Transitting the critical point,'' in progress.

Hosted by: Heikki Mantysaari

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