21 research outputs found
Shakhov-type extension of the relaxation time approximation in relativistic kinetic theory and second-order fluid dynamics
We present a relativistic Shakhov-type generalization of the Anderson-Witting
relaxation time model for the Boltzmann collision integral to modify the ratio
of momentum diffusivity to thermal diffusivity. This is achieved by modifying
the path on which the single particle distribution function f_{\bk}
approaches local equilibrium f_{0\bk} by constructing an intermediate
Shakhov-type distribution f_{{\rm S} \bk} similar to the 14-moment
approximation of Israel and Stewart. We illustrate the effectiveness of this
model in case of the Bjorken expansion of an ideal gas of massive particles and
the damping of longitudinal waves through an ultrarelativistic ideal gas.Comment: 7 pages + 3 pages SM; 2 figure
Rigidly-rotating scalar fields: between real divergence and imaginary fractalization
The thermodynamics of rigidly rotating systems experience divergences when
the system dimensions transverse to the rotation axis exceed the critical size
imposed by the causality constraint. The rotation with imaginary angular
frequency, suitable for numerical lattice simulations in Euclidean
imaginary-time formalism, experiences fractalization of thermodynamics in the
thermodynamic limit, when the system's pressure becomes a fractal function of
the rotation frequency. Our work connects two phenomena by studying how
thermodynamics fractalizes as the system size grows. We examine an
analytically-accessible system of rotating massless scalar matter on a
one-dimensional ring and the numerically treatable case of rotation in the
cylindrical geometry and show how the ninionic deformation of statistics
emerges in these systems. We discuss a no-go theorem on analytical continuation
between real- and imaginary-rotating theories. Finally, we compute the moment
of inertia and shape deformation coefficients caused by the rotation of the
relativistic bosonic gas.Comment: 40 pages, 22 figures; accepted for publication in PRD; fractalization
video is available at https://youtu.be/Pk-S_10BM-
Corner transport upwind lattice Boltzmann model for bubble cavitation
Aiming to study the bubble cavitation problem in quiescent and sheared
liquids, a third-order isothermal lattice Boltzmann (LB) model that describes a
two-dimensional () fluid obeying the van der Waals equation of state, is
introduced. The evolution equations for the distribution functions in this
off-lattice model with 16 velocities are solved using the corner transport
upwind (CTU) numerical scheme on large square lattices (up to nodes). The numerical viscosity and the regularization of the model are
discussed for first and second order CTU schemes finding that the latter choice
allows to obtain a very accurate phase diagram of a nonideal fluid. In a
quiescent liquid, the present model allows to recover the solution of the
Rayleigh-Plesset equation for a growing vapor bubble. In a sheared liquid, we
investigated the evolution of the total bubble area, the bubble deformation and
the bubble tilt angle, for various values of the shear rate. A linear relation
between the dimensionless deformation coefficient and the capillary number
is found at small but with a different factor than in equilibrium
liquids. A non-linear regime is observed for .Comment: Accepted for publication in Phys. Rev.
Rotating quantum states
We revisit the definition of rotating thermal states for scalar and fermion fields in unbounded Minkowski space–time. For scalar fields such states are ill-defined everywhere, but for fermion fields an appropriate definition of the vacuum gives thermal states regular inside the speed-of-light surface. For a massless fermion field, we derive analytic expressions for the thermal expectation values of the fermion current and stress–energy tensor. These expressions may provide qualitative insights into the behaviour of thermal rotating states on more complex space–time geometries
Helical Separation Effect and helical heat transport for Dirac fermions
International audienceAn ensemble of massless fermions can be characterized by its total helicity charge given by the sum of axial charges of particles minus the sum of axial charges of antiparticles. We show that charged massless fermions develop a dissipationless flow of helicity along the background magnetic field. We dub this transport phenomenon as the Helical Separation Effect (HSE). Contrary to its chiral cousin, the Chiral Separation Effect, the HSE produces the helical current in a neutral plasma in which all chemical potentials vanish. In addition, we uncover the Helical Magnetic Heat Effect which generates a heat flux of Dirac fermions along the magnetic field in the presence of non-vanishing helical charge density. We also discuss possible hydrodynamic modes associated with the HSE in neutral plasma
Shakhov-type extension of the relaxation time approximation in relativistic kinetic theory and second-order fluid dynamics
We present a relativistic Shakhov-type generalization of the Anderson-Witting relaxation time model for the Boltzmann collision integral to modify the ratio of momentum diffusivity to thermal diffusivity. This is achieved by modifying the path on which the single particle distribution function fk approaches local equilibrium f0k by constructing an intermediate Shakhov-type distribution fSk similar to the 14-moment approximation of Israel and Stewart. We illustrate the effectiveness of this model in case of the Bjorken expansion of an ideal gas of massive particles and the damping of longitudinal waves through an ultrarelativistic ideal gas