44 research outputs found
Kinetic equation for strongly interacting dense Fermi systems
We review the non-relativistic Green's-function approach to the kinetic
equations for Fermi liquids far from equilibrium. The emphasis is on the
consistent treatment of the off-shell motion between collisions and on the
non-instant and non-local picture of binary collisions. The resulting kinetic
equation is of the Boltzmann type, and it represents an interpolation between
the theory of transport in metals and the theory of moderately dense gases. The
free motion of particles is renormalised by various mean field and mass
corrections in the spirit of Landau's quasiparticles in metals. The collisions
are non-local in the spirit of Enskog's theory of non-ideal gases. The
collisions are moreover non-instant, a feature which is absent in the theory of
gases, but which is shown to be important for dense Fermi systems. In spite of
its formal complexity, the presented theory has a simple implementation within
the Monte-Carlo simulation schemes. Applications in nuclear physics are given
for heavy-ion reactions and the results are compared with the former theory and
recent experimental data. The effect of the off-shell motion and the non-local
and non-instant collisions on the dynamics of the system can be characterised
in terms of thermodynamic functions such as the energy density or the pressure
tensor. Non-equilibrium counterparts of these functions and the corresponding
balance equations are derived and discussed from two points of view. Firstly,
they are used to prove the conservation laws. Secondly, the role of individual
microscopic mechanisms in fluxes of particles and momenta and in
transformations of the energy is clarified.Comment: Boo
Charge profile in vortices
The electric charge density in the vortex lattice of superconductors is
studied within the Ginzburg-Landau theory. We show that the electrostatic
potential is proportional to the GL function,
. Numerical results for the triangular
vortex lattice are presented.Comment: 4 pages with 2 figure
In-medium two-nucleon properties in high electric fields
The quantum mechanical two - particle problem is considered in hot dense
nuclear matter under the influence of a strong electric field such as the field
of the residual nucleus in heavy - ion reactions. A generalized
Galitskii-Bethe-Salpeter equation is derived and solved which includes
retardation and field effects. Compared with the in-medium properties in the
zero-field case, bound states are turned into resonances and the scattering
phase shifts are modified. Four effects are observed due to the applied field:
(i) A suppression of the Pauli-blocking below nuclear matter densities, (ii)
the onset of pairing occurs already at higher temperatures due to the field,
(iii) a field dependent finite lifetime of deuterons and (iv) the imaginary
part of the quasiparticle self-energy changes its sign for special values of
density and temperatures indicating a phase instability. The latter effect may
influence the fragmentation processes. The lifetime of deuterons in a strong
Coulomb field is given explicitly.Comment: ps file + 7 figures (eps
Virial corrections to simulations of heavy ion reactions
Within QMD simulations we demonstrate the effect of virial corrections on heavy ion reactions. Unlike in standard codes, the binary collisions are treated as non-local so that the contribution of the collision flux to the reaction dynamics is covered. A comparison with standard QMD simulations shows that the virial corrections lead to a broader proton distribution bringing theoretical spectra closer towards experimental values. Complementary BUU simulations reveal that the non-locality enhances the collision rate in the early stage of the reaction. It suggests that the broader distribution appears due to an enhanced pre-equilibrium emission of particles
Mid-rapidity charge distribution in peripheral heavy ion collisions
The charge density distribution with respect to the velocity of matter produced in peripheral heavy ion reactions around Fermi energy is investigated. The experimental finding of enhancement of mid-rapidity matter shows the necessity to include correlations beyond BUU which was performed in the framework of nonlocal kinetic theory. Different theoretical improvements are discussed. While the in-medium cross section changes the number of collisions, it leads the transferred energy almost unchanged. In contrast the nonlocal scenario changes the energy transferred during collisions and leads to an enhancement of mid-rapidity matter. The renormalisation of quasiparticle energies is shown to be possible to include in nonlocal scenarios and and leads to a further enhancement of mid-rapidity matter distribution. This renormalisation is accompanied by a dynamical softening of the equation of state seen in longer oscillation periods of the excited compressional collective mode. We propose to include quasiparticle renormalization by using the Pauli-rejected collisions which circumvent the problem of backflows in Landau theory. Using the maximum relative velocity of projectile and target like fragments we associate experimental events with impact parameters of the simulations. For peripheral collisions we find a reasonable agreement between experiment and theory. For more central collisions the velocity damping is higher in one - body simulations than observed experimentally which is due to missing cluster formations in the used kinetic theory
The concept of correlated density and its application
The correlated density appears in many physical systems ranging from dense
interacting gases up to Fermi liquids which develop a coherent state at low
temperatures, the superconductivity. One consequence of the correlated density
is the Bernoulli potential in superconductors which compensates forces from
dielectric currents. This Bernoulli potential allows to access material
parameters. Though within the surface potential these contributions are largely
canceled, the bulk measurements with NMR can access this potential. Recent
experiments are explained and new ones suggested. The underlying quantum
statistical theory in nonequilibrium is the nonlocal kinetic theory developed
earlier.Comment: 14 pages, CMT30 proceeding
Temperature dependence of Vortex Charges in High Temperature Superconductors
Using a model Hamiltonian with d-wave superconductivity and competing
antiferromagnetic (AF) interactions, the temperature (T) dependence of the
vortex charge in high T_c superconductors is investigated by numerically
solving the Bogoliubov-de Gennes equations. The strength of the induced AF
order inside the vortex core is T dependent. The vortex charge could be
negative when the AF order with sufficient strength is present at low
temperatures. At higher temperatures, the AF order may be completely suppressed
and the vortex charge becomes positive. A first order like transition in the T
dependent vortex charge is seen near the critical temperature T_{AF}. For
underdoped sample, the spatial profiles of the induced spin-density wave and
charge-density wave orders could have stripe like structures at T < T_s, and
change to two-dimensional isotropic ones at T > T_s. As a result, a vortex
charge discontinuity occurs at T_s.Comment: 5 pages, 5 figure
2PI nonequilibrium versus transport equations for an ultracold Bose gas
The far-from-equilibrium dynamics of an ultracold, one-dimensional Bose gas
is studied. The focus is set on the comparison between the solutions of fully
dynamical evolution equations derived from the 2PI effective action and their
corresponding kinetic approximation in the form of Boltzmann-type transport
equations. It is shown that during the time evolution of the gas a kinetic
description which includes non-Markovian memory effects in a gradient expansion
becomes valid. The time scale at which this occurs is shown to exceed
significantly the time scale at which the system's evolution enters a
near-equilibrium drift period where a fluctuation dissipation relation is found
to hold and which would seem to be predestined for the kinetic approximation.Comment: 24 pages, 7 figures. References adde