Relativistic nuclear and neutron matter at finite temperatures

Nuclear matter as well as neutron matter is studied in the framework of a relativistic nuclear field theory at finite temperature. A spectral representation for the two-point Green's function at finite temperature and finite density is constructed. The bulk properties of the interacting system are calculated in the Hartree and Hartree-Fock approach. In additionσ ³- andσ ⁴-self-interactions have been taken into account. We present and discuss the results of hot and dense matter for temperaturesT≦ 50 MeV and densitiesθ≦6θ ₀ (ρ ₀≈0.17 fm^?3) using six different model parameter sets.     

Neutrino emissivity of quark matter at finite temperatures

We evaluate the emissivity rates for d-decay and s-decay by exactly solving the angular integrals involved and without assuming the degeneracy of electrons. We have also studied the effects of QCD coupling constant as well as the s-quark mass on the emissivity rates. We find that these parameters are important in determining the threshold and extinction densities for d- and s-decays.     

The properties of nuclear matter at zero and finite temperatures

The properties of nuclear matter are studied in the frame of the Brueckner theory. The Brueckner-Hartree-Fock approximation plus two-body density-dependent Skyrme potential which is equivalent to three-body interaction are used. Various modern nucleon-nucleon potentials are used in the framework of the Brueckner-Hartree-Fock approximation, e.g.: CD-Bonn potential, Nijm1 potential, and Reid 93 potential. These modern nucleon-nucleon potentials fit the deuteron properties and are phase shifts equivalent. The equation of state at T = 0, pressure at T = 0, 8, and 12 MeV, free energy at T = 8 and 12 MeV, nuclear matter incompressibility, and the symmetry energy calculation are presented. The hot properties of nuclear matter are calculated using T ²-approximation method at low temperatures. Good agreement is obtained in comparison with previous theoretical estimates and experimental data, especially at low densities.     

Quasi-particles at finite temperatures

We study the consequences of the KMS-condition on the properties of quasi-particles, assuming their existence. We establish

1. If the correlation functions decay sufficiently, we can create them by quasi-free field operators.
2. The outgoing and incoming quasi-free fields coincide, there is no scattering.
3. There are may age-operatorsT conjugate toH. For special forms of the dispersion law ε(k) of the quasi-particles there is aT commuting with the number of quasi-particles and its time-monotonicity describes how the quasi-particles travel to infinity.

     

Quark potentials at finite temperatures

We scan the quark-antiquark potential and the meson-meson potential for static quarks in aSU ₃ gluon field from strong coupling to weak coupling. The breakdown of the confinement between quark and antiquark at the phase transition is observed. There is no interaction between pointlike mesons in the whole coupling regime. It is pointed out that the interaction mechanism between two quark clusters can be classified by these two fundamental examples.     

Gross features of finite nuclei at finite temperatures

A simple expression is obtained for the low-temperature behaviour of the energy and entropy of finite nuclei for 20 ￡ leq A ￡ leq 250 . The dependence on A of these quantities is for the most part due to the presence of the asymmetry energy.     

Boson Mott insulators at finite temperatures

We discuss the finite temperature properties of ultracold bosons in optical lattices in the presence of an additional, smoothly varying potential, as in current experiments. Three regimes emerge in the phase diagram: a low-temperature Mott regime similar to the zero-temperature quantum phase, an intermediate regime where Mott insulator features persist, but where superfluidity is absent, and a thermal regime where features of the Mott insulator state have disappeared. We obtain the thermodynamic functions of the Mott phase in the latter cases. The results are used to estimate the temperatures achieved by adiabatic loading in current experiments. We point out the crucial role of the trapping potential in determining the final temperature, and suggest a scheme for further cooling by adiabatic decompression.     

Nuclear interface energy at finite temperatures

The thermodynamic properties at finite temperatures of the plane interface between two phases of nuclear matter in equilibrium are examined theoretically, and explored numerically. The microscopic hamiltonian, the Skyrme I′ interaction, is used in the Thomas-Fermi approximation to obtain the finite-temperature extensions of earlier zero-temperature results which used the Hartree-Fock and Thomas-Fermi methods. Approximate analytic fits are given to the χ_i (proton fraction on the dense-matter side) dependence of the critical temperature, and to the T and χ_i dependences of the surface thermodynamic potentials, the density of surface neutrons, the surface entropy and the neutron and proton chemical potentials at phase equilibrium. These fits are an ingredient in a compressible liquid-drop nuclear model, the basis of an equation of state for hot, dense matter needed in certain astrophysical applications.The liquid-drop model is used here to construct an isolated, low-T nucleus, whose properties are compared with the original zero-T Hartree-Fock calculations which lead to the Skyrme I interaction, and with other mass formulae. The low-temperature expansion of the surface energy is compared with that obtained in other calculations. The nuclear level density at the Fermi surface, related to the low-T expansion of the entropy of the whole nucleus, is also discussed.     

Comment on the supersymmetry at finite temperatures

We comment on some of the general thermostatistical properties of the global supersymmetry characterized by Grassmann parameters, which are shared by the ordinary supersymmetry as well as by the BRS supersymmetry associated with any gauge symmetry including local supersymmetry.     

Epitaxially strained SnTiO_3 at finite temperatures

By combining the effective Hamiltonian approach and direct ab initio computation, we obtain the phase diagram of SnTiO_3 with respect to epitaxial strain and temperature. This demonstrates the complex features of the phase diagram and provides an insight into this system, which is a presumably simple perovskite. Two triple points, as shown in the phase diagram, may be exploited to achieve high-performance piezoelectric effects. Despite the inclusion of the degree of freedom related to oxygen octahedron tilting, the ferroelectric displacements dominate the structural phases over the whole misfit strain range. Finally, we show that SnTiO_3 can change from hard to soft ferroelectrics with the epitaxial strain.     

Static potentials for quarkonia at finite temperatures

We review non-perturbative static potentials commonly used in potential models for quarkonia at finite T. Potentials derived from Polyakov loop correlators are shown to be inappropriate for this purpose. The free energy is physical but has the wrong spatial decay and perturbative limit. The so-called singlet free energy is gauge dependent and unphysical. An appropriate static real time potential can be defined through a generalisation of pNRQCD to finite T. In perturbation theory, its real part reproduces the Debye-screened potential, its imaginary part accounts for Landau damping. Possibilities for its non-perturbative evaluation are discussed.     

A nonideal Bose gas at finite temperatures

The present paper, based on an obvious generalization of the formalism of Belyaev [1,5], supplements the work of Belyaev [2] for the case T 0. The temperature dependence of the quasiparticle excitation and damping spectrum, the ground state energy, and the thermodynamic quantities is determined to second order in the gas-density parameter using the constant amplitude approximation. In the limiting case of free particles, the results are obtained for an ideal gas with T < T₀, where T₀ is the condensation temperature of the ideal Bose gas.In conclusion I wish to thank B. T. Geilikman, under whose supervision this work was performed.     

Infrared instability of QCD at finite temperatures

The infrared behaviour of the transversal gluon propagator in QCD at T≠0 is investigated within the ghost-free axial gauge. The singularities found in this propagator for the momentum p ～ g²T remain for any choice of the gauge and indicate the infrared instability of QCD at finite temperatures.     

Strange mesons in dense nuclear matter

Experimental data on the production of kaons and antikaons in heavy-ion collisions at relativistic energies are presented and discussed with respect to in-medium effects. The K ^?/K⁺ ratios measured in nucleus-nucleus collisions are 1–2 orders of magnitude larger than in proton-proton collisions. The azimuthal angle distributions of K ⁺ mesons indicate a repulsive kaon-nucleon potential. Microscopic transport calculations consistently explain both the yields and the emission patterns of kaons and antikaons when assuming that their properties are modified in dense nuclear matter. The K ⁺ production excitation functions measured in light and heavy collision systems provide evidence for a soft nuclear equation-of-state.