ABSTRACT
In the context of an ultracold Fermi gas, we derive conservation laws for mass, energy and momentum based on a generalized nonlocal Boltzmann equation with gradient corrections in the collision integral. The corrections are expressed in terms of effective collision duration, particle displacement and changes of total momentum and energy. Their origin is in the in-medium T matrix. Using variations of the optical theorem, we show that in the collision integral the particle-hole symmetry can be recast into a form of collision symmetry amenable to semiclassical simulation. Pauli-blocked collisions are distinguished from Bose-stimulated nondissipative ones; the latter are not present in the absence of gradient corrections. Consolidating with the microscopic theory, we extract local conservation laws for a general time-dependent interaction potential, and demonstrate how both types of collisions affect densities and flows of conserving quantities. Comparison is made with the approach of Nozières and Schmitt-Rink in the limit of thermal equilibrium. Under approximations used for normal-state ultracold Fermi gases interacting via Feshbach resonances we demonstrate the effect of the collision delay on the shear viscosity.
ABSTRACT
The article [Phys. Rev. E 96, 032106 (2017)10.1103/PhysRevE.96.032106] recovers conservation laws and derives the H-theorem for the kinetic equation with gradient corrections. Here we show that this approach is not valid, leading to missing terms in the balance of energy and momentum and to disagreement with correlation entropy known from the Enskog equation.
ABSTRACT
The nonlocal scattering-in and scattering-out integrals of the Enskog equation have reversed displacements of colliding particles reflecting that the scattering-in and -out processes are conjugated by the space and time inversions. Generalizations of the Enskog equation to Fermi liquid systems are hindered by the need for particle-hole symmetry which contradicts the reversed displacements. We resolve this problem with the help of the optical theorem. It is found that space-time and particle-hole symmetry can be fulfilled simultaneously only for the Bruckner type of internal Pauli blocking while the Feynman-Galitskii form allows only for particle-hole symmetry but not for space-time symmetry due to a stimulated emission of bosons.
ABSTRACT
The electric charge density in the vortex lattice of superconductors is studied within the Ginzburg-Landau (GL) theory. We show that the electrostatic potential varphi is proportional to the GL function, varphi /psi/2-/psi(infinity)/2. Numerical results for the triangular vortex lattice are presented.
