506 research outputs found
Relativistic transport equations with generalized mass shell constraints
We reexamine the derivation of relativistic transport equations for fermions
when conserving the most general spinor structure of the interaction and Green
function. Such an extension of the formalism is needed when dealing with {\it
e.g.} spin-polarized nuclear matter or non-parity conserving interactions. It
is shown that some earlier derivations can lead to an incomplete description of
the evolution of the system even in the case of parity-conserving,
spin-saturated systems. The concepts of kinetic equation and mass shell
condition have to be extended, in particular both of them acquire a non trivial
spinor structure which describe a rich polarization dynamics.Comment: 11 pages, submitted to Proceedings KB99 Workshop, September 20-24
1999, Rostock, German
Phase diagram for interacting Bose gases
We propose a new form of the inversion method in terms of a selfenergy
expansion to access the phase diagram of the Bose-Einstein transition. The
dependence of the critical temperature on the interaction parameter is
calculated. This is discussed with the help of a new condition for
Bose-Einstein condensation in interacting systems which follows from the pole
of the T-matrix in the same way as from the divergence of the medium-dependent
scattering length. A many-body approximation consisting of screened ladder
diagrams is proposed which describes the Monte Carlo data more appropriately.
The specific results are that a non-selfconsistent T-matrix leads to a linear
coefficient in leading order of 4.7, the screened ladder approximation to 2.3,
and the selfconsistent T-matrix due to the effective mass to a coefficient of
1.3 close to the Monte Carlo data
Nonlinear relaxation field in charged systems under high electric fields
The influence of an external electric field on the current in charged systems
is investigated. The results from the classical hierarchy of density matrices
are compared with the results from the quantum kinetic theory. The kinetic
theory yields a systematic treatment of the nonlinear current beyond linear
response. To this end the dynamically screened and field-dependent
Lenard-Balescu equation is integrated analytically and the nonlinear relaxation
field is calculated. The classical linear response result known as Debye -
Onsager relaxation effect is only obtained if asymmetric screening is assumed.
Considering the kinetic equation of one specie the other species have to be
screened dynamically while the screening with the same specie itself has to be
performed statically. Different other approximations are discussed and
compared.Comment: language correction
Theory of water and charged liquid bridges
The phenomena of liquid bridge formation due to an applied electric field is
investigated. A new solution for the charged catenary is presented which allows
to determine the static and dynamical stability conditions where charged liquid
bridges are possible. The creeping height, the bridge radius and length as well
as the shape of the bridge is calculated showing an asymmetric profile in
agreement with observations. The flow profile is calculated from the Navier
Stokes equation leading to a mean velocity which combines charge transport with
neutral mass flow and which describes recent experiments on water bridges.Comment: 10 pages 12 figures, misprints corrected, assumptions more
transparen
Correlated two-particle scattering on finite cavities
The correlated two-particle problem is solved analytically in the presence of
a finite cavity. The method is demonstrated here in terms of exactly solvable
models for both the cavity as well as the two-particle correlation where the
two-particle potential is chosen in separable form. The two-particle phase
shift is calculated and compared to the single-particle one. The two-particle
bound state behavior is discussed and the influence of the cavity on the
binding properties is calculated.Comment: Derivation shortened and corrected, 14 pages 10 figure
Conductivity in quasi two-dimensional systems
The conductivity in quasi two-dimensional systems is calculated using the
quantum kinetic equation. Linearizing the Lenard-Balescu collision integral
with the extension to include external field dependences allows one to
calculate the conductivity with diagrams beyond the GW approximation including
maximally crossed lines. Consequently the weak localization correction as an
interference effect appears here from the field dependence of the collision
integral (the latter dependence sometimes called intra-collisional field
effect). It is shown that this weak localization correction has the same origin
as the Debye-Onsager relaxation effect in plasma physics. The approximation is
applied to a system of quasi two-dimensional electrons in hetero-junctions
which interact with charged and neutral impurities and the low temperature
correction to the conductivity is calculated analytically. It turns out that
the dynamical screening due to charged impurities leads to a linear temperature
dependence, while the scattering from neutral impurities leads to the usual
Fermi-liquid behavior. By considering an appropriate mass action law to
determine the ratio of charged to neutral impurities we can describe the
experimental metal-insulator transition at low temperatures as a Mott-Hubbard
transition.Comment: 7 pages 7 pages appendix 11 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
The Nonlinear Debye-Onsager Relaxation Effect in Weakly Ionized Plasmas
A weakly ionized plasma under the influence of a strong electric field is
considered. Supposing a local Maxwellian distribution for the electron momenta
the plasma is described by hydrodynamic equations for the pair distribution
functions. These equations are solved and the relaxation field is calculated
for an arbitrary field strength. It is found that the relaxation effect becomes
lower with increasing strength of the electrical field.Comment: 4 pages, 1 figur
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
- …