Dimitri Kusnezov

Canonical ensembles from chaos

Abstract We present methods to compute thermodynamic properties of classical systems which involve extending the phase space by two degrees of freedom. These two additional degrees of freedom are used to replicate the coupling of the original system to the infinite degrees of freedom of a heat bath. In the extended phase space, the trajectories are ergodic. This feature enables one to replace phase space averages by time averages, which are extremely simple to compute. We examine phase space patterns, thermal distributions, correlations, ergodicity, Lyapunov exponents, mixing, and rate of convergence in an analysis of several simple systems.

SCALING PROPERTIES OF THE GIANT DIPOLE RESONANCE WIDTH IN HOT ROTATING NUCLEI

We study the systematics of the giant dipole resonance width {Gamma} in hot rotating nuclei as a function of temperature T , spin J , and mass A . We compare available experimental results with theoretical calculations that include thermal shape fluctuations in nuclei ranging from A=45 to A=208 . Using the appropriate scaled variables, we find a simple phenomenological function {Gamma}(A,T,J) which approximates the global behavior of the giant dipole resonance width in the liquid drop model. We reanalyze recent experimental and theoretical results for the resonance width in Sn isotopes and {sup 208}Pb . {copyright} {ital 1998} {ital The American Physical Society}

Study of 110Cd by the 108Pd(α, 2nγ) reaction

Abstract The gamma-ray transitions following the 108Pd(α, 2n) reaction have been observed using different semiconductor detector systems, including a Compton suppression spectrometer. Approximately 200 transitions assigned to 110Cd were identified in the energy range 120 to 1600 keV. About 2.5 × 107 γγ-coincidence events were recorded and the angular distributions of most transitions were analyzed. The 110Cd level scheme was extended by 28 new levels. With the angular distribution results and a systematic use of the excitation slopes and of the side-feeding intensities (ESSI-method), the spins and parities of nearly all observed levels were determined. The results regarding the ground-state, intruder and octupole bands are interpreted in the framework of the s-p-d-f interacting boson model in which intruder mixing is explicitly included. The predictions of strong configuration mixing are also examined in detail in the neutron-proton interacting boson model framework. We shortly discuss possible non-collective, broken-pair excitations in a qualitative way.

Phase Transitions in Finite Nuclei and the Integer Nucleon Number Problem

The study of spherical-deformed ground-state phase transitions in finite nuclei as a function of N and Z is hindered by the discrete values of the nucleon number. A resolution of the integer nucleon number problem and evidence relating to phase transitions in finite nuclei are discussed from the experimental point of view and interpreted within the framework of the interacting boson model. {copyright} {ital 1999} {ital The American Physical Society}

Bulk properties of anharmonic chains in strong thermal gradients: non-equilibrium φ4 theory

Abstract We study nonequilibrium properties of a one-dimensional lattice Hamiltonian with quartic interactions in strong thermal gradients. Nonequilibrium temperature profiles, T(x), are found to develop significant curvature and boundary jumps. From the determination of the bulk thermal conductivity, we develop a quantitative description of T(x) including the jumps.

Canonical ensembles from chaos. II : Constrained dynamical systems

Abstract We present dynamical equations of motion to compute thermodynamic properties of constrained dynamical systems. In particular, we examine systems that can be described by generators of Lie algebras. In this method, additional (noncompact) degrees of freedom are added to the compact phase space to mock the effects of a heat bath. The equations of motion in this extended space are ergodic, and canonical ensemble averages reduce to time averages over the classical trajactory. We compute explicitly the thermodynamic properties of several simple systems, in particular, Hamiltonians with SU(2) and SU(3) symmetry.

Two-body random ensembles: from nuclear spectra to random polynomials

The two-body random ensemble for a many-body bosonic theory is mapped to a problem of random polynomials on the unit interval. In this way one can understand the predominance of 0(+) ground states, and analytic expressions can be derived for distributions of lowest eigenvalues, energy gaps, density of states, and so forth. Recently studied nuclear spectroscopic properties are addressed.

The transverse momentum spectrum in ultrarelativistic heavy ion collisions is not statistical

Abstract We examine the role of decays of excited hadrons in shaping the transverse momentum spectrum of pions in ultrarelativistic heavy ion collisions. No reasonable statistical model can reproduce the experimentally observed peak in the spectrum at low transverse momentum.

Robust nuclear observables and constraints on random interactions

The predictions of the interacting boson model two-body random ensemble are compared to empirical results on nuclei from Z = 8-100. Heretofore unrecognized but robust empirical trends are identified and related both to the distribution of valence nucleon numbers and to the need for and applicability of specific, nonrandom interactions. Applications to expected trends in exotic nuclei are discussed.

Nonequilibrium Statistical Mechanics of Classical Lattice φ4 Field Theory

Abstract We study the nonequilibrium statistical mechanics of classical lattice φ 4 theory in thermal gradients of arbitrary strength. The steady-state physics of the theory in (1+1) dimensions is investigated from first principles and classified into dynamical regimes. The bulk properties associated with thermal transport are derived. Starting with thermal equilibrium, we examine the relation to the kinetic theory description of the behavior of the system. Green–Kubo transport coefficients are computed and compared to measured transport near and far from equilibrium, defining the scope of linear response and including an analysis of long-time tails. Local equilibrium is investigated and seen to explicitly break down under sufficiently strong gradients. Additional measures of the nonequilibrium steady state are also discussed as well as the connections to irreversible thermodynamics.