Speaker
Koichi Murase
(The University of Tokyo)
Description
To investigate the physics of the strongly interacting system of quarks
and gluons under extreme conditions, heavy-ion collision experiments are
performed at Large Hadron Collider (LHC) and Relativistic Heavy Ion
Collider (RHIC). One of the major discoveries was that elliptic flow v_2
was comparable with an ideal hydrodynamic prediction and, as a result,
that a new paradigm of strongly coupled quark-gluon plasma (QGP) was
established. Recently, the higher harmonics v_n (n > 2) are
systematically observed at RHIC and LHC and attract a lot of theoretical
and experimental interests. Initial state fluctuations turned out to be
important to explain these higher harmonics.
In addition to initial state fluctuations, thermal fluctuation during
the space-time evolution of the QGP also plays an important role in
event-by-event simulations. We first formulate the relativistic
fluctuating hydrodynamics in the context of the second order causal
theory. Finite relaxation time for dissipative current is required to
make hydrodynamic equation consistent with causality. Instead of
introducing the relaxation term itself, one can define a kernel function
(or a retarded Green function) such that constitutive equation becomes
convolution of the kernel function including relaxation as well as
dissipation and the corresponding thermodynamic force. One can also
introduce a noise field as thermal fluctuation of the dissipative
current like in the Langevin equation. Thus the constitutive equation
becomes no longer a deterministic equation, but a stochastic equation.
The power spectrum of the noise fields is intimately related to the
kernel function via the fluctuation-dissipation relation and,
consequently, noise becomes colored noise rather than white one due to
the finite relaxation time. We then implement the colored noise together
with viscous kernels in numerical simulations of relativistic
hydrodynamics and perform simulations on an event-by-event basis to see
effects of thermal fluctuation on the dynamics of heavy ion collisions.
This framework is beyond the conventional second order dissipative
hydrodynamics and, thus, will become important in the upcoming era of
the precision QGP physics by means of high-energy heavy ion collisions.
Primary author
Koichi Murase
(The University of Tokyo)
Co-author
Tetsufumi Hirano
(Sophia Univ)
