1201.6408 (Yuki Minami)

Critical dynamics near QCD critical point    [PDF]

Yuki Minami

In this thesis, we study the critical dynamics near the QCD critical point.
Near the critical point, the relevant modes for the critical dynamics are
identified as the hydrodynamic modes. Thus, we first study the linear dynamics
of them by the relativistic hydrodynamics.
We show that the thermal diffusion mode is the most relevant mode, whereas
the sound mode is suppressed around the critical point. We also find that the
Landau equation, which is believed to be an acausal hydrodynamic equation, has
no problem to describe slowly varying fluctuations. Moreover, we find that the
Israel-Stewart equation, which is a causal one, gives the same result as the
Landau equation gives in the long-wavelength region.
Next, we study the nonlinear dynamics of the hydrodynamic modes by the
nonlinear Langevin equation and the dynamic renormalization group (RG). In the
vicinity of the critical point, the usual hydrodynamics breaks down by large
fluctuations. Thus, we must consider the nonlinear Langevin equation. We
construct the nonlinear Langevin equation based on the generalized Langevin
theory. After the construction, we apply the dynamic RG to the Langevin
equation and derive the RG equation for the transport coefficients.
We find that the resulting RG equation turns out to be the same as that for
the liquid-gas critical point except for an insignificant constant.
Consequently, the bulk viscosity and the thermal conductivity strongly diverge
at the critical point. Then, a system near the critical point can not be
described as a perfect fluid by their strong divergences.
We also show that the thermal and viscous diffusion modes exhibit
critical-slowing down with the dynamic critical exponents z_{thermal} \sim 3
and z_{viscous} \sim 2, respectively.
In contrast, the sound mode shows critical-speeding up with the negative
exponent z_{sound} \sim -0.8.

View original: http://arxiv.org/abs/1201.6408