arXiv subjects

Klaus Morawetz

Publications and source records attributed to Klaus Morawetz.

At least 55 records · Page 3Linked to original sources

arXiv2002

Dynamical local field, compressibility and frequency sum rules for quasiparticles

The finite temperature dynamical response function including the dynamical local field is derived within a quasiparticle picture for interacting one-, two- and three dimensional Fermi systems. The correlations are assumed to be given by a density dependent effective mass, quasiparticle energy shift and relaxation time. The latter one describes disorder or collisional effects. This parameterization of correlations includes local density functionals as a special case and is therefore applicable for density functional theories. With a single static local field, the third order frequency sum rule can be fulfilled simultaneously with the compressibility sum rule by relating the effective mass and quasiparticle energy shift to the structure function or pair correlation function. Consequently, solely local density functionals without taking into account effective masses cannot fulfill both sum rules simultaneously with a static local field. The comparison to the Monte-Carlo data seems to support such quasiparticle picture.

cond-mat.str-el↗

arXiv2002

Consequences of coarse grained Vlasov equations

The Vlasov equation is analyzed for coarse grained distributions resembling a finite width of test-particles as used in numerical implementations. It is shown that this coarse grained distribution obeys a kinetic equation similar to the Vlasov equation, but with additional terms. These terms give rise to entropy production indicating dissipative features due to a nonlinear mode coupling The interchange of coarse graining and dynamical evolution is discussed with the help of an exactly solvable model for the selfconsistent Vlasov equation and practical consequences are worked out. By calculating analytically the stationary solution of a general Vlasov equation we can show that a sum of modified Boltzmann-like distributions is approached dependent on the initial distribution. This behavior is independent of degeneracy and only controlled by the width of test-particles. The condition for approaching a stationary solution is derived and it is found that the coarse graining energy given by the momentum width of test particles should be smaller than a quarter of the kinetic energy. Observable consequences of this coarse graining are: (i) spatial correlations in observables, (ii) too large radii of clusters or nuclei in self-consistent Thomas-Fermi treatments, (iii) a structure term in the response function resembling vertex correction correlations or internal structure effects and (iv) a modified centroid energy and higher damping width of collective modes.

nucl-th↗

arXiv2001

Critical Tsallis exponent in heavy ion reaction

The numerical solution of the nonlocal kinetic equation allows to simulate heavy ion reactions around Fermi energy. The expansion velocity and density profile show specific radial dependence which can be described with a Tsallis exponent of $q=5/3$. This might be considered as an indication of a phase transition.

nucl-th↗

arXiv2001

Electrostatic potential in a superconductor

The electrostatic potential in a superconductor is studied. To this end Bardeen's extension of the Ginzburg-Landau theory to low temperatures is used to derive three Ginzburg-Landau equations - the Maxwell equation for the vector potential, the Schroedinger equation for the wave function and the Poisson equation for the electrostatic potential. The electrostatic and the thermodynamic potential compensate each other to a great extent resulting into an effective potential acting on the superconducting condensate. For the Abrikosov vortex lattice in Niobium, numerical solutions are presented and the different contributions to the electrostatic potential and the related charge distribution are discussed.

cond-mat.supr-con↗

arXiv2001

Bernoulli potential at a superconductor surface

The electrostatic Bernoulli potential measured at the surface of a superconductor via Kelvin capacitive coupling is shown to be independent of the pairing mechanism. This contrasts with the Bernoulli potential in the bulk where contributions due to pairing dominate close to $T_c$.

cond-mat.supr-con↗

arXiv2001

On a correspondence between classical and quantum particle systems

An exact correspondence is established between a $N$-body classical interacting system and a $N-1$-body quantum system with respect to the partition function. The resulting quantum-potential is a $N-1$-body one. Inversely the Kelbg potential is reproduced which describes quantum systems at a quasi-classical level. The found correspondence between classical and quantum systems allows also to approximate dense classical many body systems by lower order quantum perturbation theory replacing Planck's constant properly by temperature and density dependent expressions. As an example the dynamical behaviour of an one - component plasma is well reproduced concerning the formation of correlation energy after a disturbance utilising solely the analytical quantum - Born result for dense degenerated Fermi systems. As a practical guide the quantum - Bruckner parameter $r_s$ has been replaced by the classical plasma parameter $Γ$ as $r_s\approx0.3 Γ^{3/2}$

physics.plasm-ph↗

arXiv2001

Retarded versus time-nonlocal quantum kinetic equations

The finite duration of the collisions in Fermionic systems as expressed by the retardation time in non-Markovian Levinson-type kinetic equations is discussed in the quasiclassical limit. We separate individual contributions included in the memory effect resulting in (i) off-shell tails of the Wigner distribution, (ii) renormalization of scattering rates and (iii) of the single-particle energy, (iv) collision delay and (v) related non-local corrections to the scattering integral. In this way we transform the Levinson equation into the Landau-Silin equation extended by the non-local corrections known from the theory of dense gases. The derived nonlocal kinetic equation unifies the Landau theory of quasiparticle transport with the classical kinetic theory of dense gases. The space-time symmetry is discussed versus particle-hole symmetry and a solution is proposed which transforms these two exclusive pictures into each other.

cond-mat.stat-mech↗

arXiv2001

Space-time versus particle-hole symmetry in quantum Enskog equations

The non-local scattering-in and -out integrals of the Enskog equation have reversed displacements of colliding particles reflecting that the -in and -out processes are conjugated by the space and time inversions. Generalisations of the Enskog equation to Fermi liquid systems are hindered by a request of the 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 only be fulfilled simultaneously 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.

nucl-th↗

arXiv2001

Squeezing mode in nuclear collisions

The time dependent Schroedinger equation is solved analytically for a simplified model of moving infinite walls. A new knock-out mode is described which might occur during heavy ion collisions. The outer shell-nucleons are ionised due to the increase of level energy when two nuclei are approaching fast enough. This is analogous to the Mott effect but in contrast occurs only if the reaction time is short enough that no common ionisation threshold in the compound system is established. To demonstrate this pure nonequilibrium effect a simulation of realistic heavy ion collision by a nonlocal Boltzmann equation is performed.

nucl-th↗

arXiv2001

Non-local kinetic simulation of heavy ion collisions

The numerical solutions of nonlocal and local Boltzmann kinetic equations for the simulation of peripheral and central heavy ion reactions are compared. The experimental finding of enhancement of mid-rapidity matter shows the necessity to include nonlocal corrections. While the in-medium cross section changes the number of collisions and not the transferred energy, the nonlocal scenario changes the energy transferred during collisions. The renormalisation of quasiparticle energies by using the Pauli-rejected collisions leads to a further enhancement of mid-rapidity matter distribution and is accompanied by a dynamical softening of the equation of state. The simulation results are parameterised in terms of time dependent thermodynamical variables in the Fermi liquid sense. This allows one to discuss dynamical trajectories in phase space. A combination of thermodynamical observables is constructed which locates instabilities and points of possible phase transition under iso-nothing conditions. Two different mechanisms of instability, a short time surface-dominated instability and later a spinodal-dominated volume instability is found. The latter one occurs only if the incident energies do not exceed significantly the Fermi energy and might be attributed to spinodal decomposition.

nucl-th↗

arXiv2001

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 leaves 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 can be included in nonlocal scenarios 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 renormalisation 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, because of missing cluster formations in the kinetic theory used.

nucl-th↗

arXiv2000

Transport with three-particle interaction

Starting from a point - like two - and three - particle interaction the kinetic equation is derived. While the drift term of the kinetic equation turns out to be determined by the known Skyrme mean field the collision integral appears in two - and three - particle parts. The cross section results from the same microscopic footing and is naturally density dependent due to the three - particle force. By this way no hybrid model for drift and cross section is needed for nuclear transport. Besides the mean field correlation energy the resulting equation of state has also a two - and three - particle correlation energy which are both calculated analytically for the ground state. These energies contribute to the equation of state and lead to an occurrence of a maximum at 3 times nuclear density in the total energy.

nucl-th↗

arXiv2000

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.

physics.plasm-ph↗

arXiv2000

Dynamical constraints on phase transitions

The numerical solutions of nonlocal and local Boltzmann kinetic equations for the simulation of central heavy ion reactions are parameterized in terms of time dependent thermodynamical variables in the Fermi liquid sense. This allows one to discuss dynamical trajectories in phase space. The nonequilibrium state is characterized by non-isobaric, non-isochoric etc. conditions, shortly called iso-nothing conditions. Therefore a combination of thermodynamical observables is constructed which allows one to locate instabilities and points of possible phase transition in a dynamical sense. We find two different mechanisms of instability, a short time surface - dominated instability and later a spinodal - dominated volume instability. The latter one occurs only if the incident energies do not exceed significantly the Fermi energy and might be attributed to spinodal decomposition. In contrast the fast surface explosion occurs far outside the spinodal region and pertains also in the cases where the system develops too fast to suffer a spinodal decomposition and where the system approaches equilibrium outside the spinodal region.

nucl-th↗

arXiv2000

Momentum conservation and local field corrections for the response of interacting Fermi gases

We reanalyze the recently derived response function for interacting systems in relaxation time approximation respecting density, momentum and energy conservation. We find that momentum conservation leads exactly to the local field corrections for both cases respecting only density conservation and respecting density and energy conservation. This rewriting simplifies the former formulae dramatically. We discuss the small wave vector expansion and find that the response function shows a high frequency dependence of $ω^{-5}$ which allows to fulfill higher order sum rules. The momentum conservation also resolves a puzzle about the conductivity which should only be finite in multicomponent systems.

nucl-th↗

arXiv2000

Collective modes in asymmetric nuclei

The collective motion of a finite nuclear system is investigated by numerical simulation and by linear response theory. Using a pseudo-particle simulation technique we analyze the giant resonances with a multipole decomposition scheme. We examine the energy and the damping of different giant collective modes and obtain the dependence of these quantities on the proton-neutron ratio. ...(abbreviated) Alternatively the giant collective modes in asymmetric nuclear matter are investigated within linear response theory including the collisional correlations via a dynamic relaxation time approximation. For a multicomponent system we derive a coupled dispersion relation and show that two sources of coupling appear: (i) a coupling of isoscalar and isovector modes due to the action of different mean-fields and (ii) an explicit new coupling in asymmetric matter due to collisional interaction. We show that the latter is responsible for a new mode arising besides isovector and isoscalar modes...(abbreviated) Collective motion beyond the linear regime is demonstrated for the example of large-amplitude isoscalar giant octupole excitations in finite nuclear systems. Depending on the initial conditions we observe either clear octupole modes or over-damped octupole modes which decay immediately into quadrupole ones. This dependence on initial correlations represents a behaviour beyond linear response.

nucl-th↗

arXiv1999

Nonlocal kinetic theory

The short time behavior of a disturbed system is influenced by off-shell motion and best characterized by the reduced density matrix possessing high energetic tails. We present analytically the formation of correlations due to collisions in an interacting Fermionic system with and without initial correlation. After this short time regime the time evolution is controlled by small gradients. This leads to a nonlocal Boltzmann equation for the quasiparticle distribution and a functional relating the latter one to the reduced density matrix. The nonlocalities are presented as time and space shifts arising from gradient expansion and are leading to virial corrections in the thermodynamical limit.

quant-ph↗

arXiv1999

General response function for interacting quantum liquids

Linearizing the appropriate kinetic equation we derive general response functions including selfconsistent mean fields or density functionals and collisional dissipative contributions. The latter ones are considered in relaxation time approximation conserving successively different balance equations. The effect of collisions is represented by correlation functions which are possible to calculate with the help of the finite temperature Lindhard RPA expression. The presented results are applicable to finite temperature response of interacting quantum systems if the quasiparticle or mean field energy is parameterized within Skyrme - type of functionals including density, current and energy dependencies which can be considered alternatively as density functionals. By this way we allow to share correlations between density functional and collisional dissipative contributions appropriate for the special treatment. We present results for collective modes like the plasmon in plasma systems and the giant resonance in nuclei. The collisions lead in general to an enhanced damping of collective modes. If the collision frequency is close to the frequency of the collective mode, resonance occurs and the collective mode is enhanced showing a collisional narrowing.

nucl-th↗