Alpha matter on a lattice

We obtain the equation of state of interacting alpha matter and the critical temperature of Bose-Einstein condensation of alpha particles within an effective scalar field theory. We start from a non-relativistic model of uniform alpha matter interacting with attractive two-body and repulsive three-body potentials and reformulate this model as a O(2) symmetric scalar \phi^6 field theory with negative quartic and positive sextic interactions. Upon restricting the Matsubara sums, near the temperature of Bose-Einstein condensation, to the zeroth order modes we further obtain an effective classical theory in three spatial dimensions. The phase diagram of the alpha matter is obtained from simulations of this effective field theory on a lattice using local Monte-Carlo algorithms.Comment: 14 pages, 2 figures; v2: improved presentation, results unchanged; to appear in Nucl. Phys.

Relativistic Effects in Nuclear Matter and Nuclei

The status of relativistic nuclear many-body calculations of nuclear systems to be built up in terms of protons and neutrons is reviewed. In detail, relativistic effects on several aspects of nuclear matter such as the effective mass, saturation mechanism, and the symmetry energy are considered. This review will especially focus on isospin asymmetric issues, since these aspects are of high interest in astrophysical and nuclear structure studies. Furthermore, from the experimental side these aspects are experiencing an additional boost from a new generation of radioactive beam facilities, e.g. the future GSI facility FAIR in Germany or SPIRAL2 at GANIL/France. Finally, the prospects of studying finite nuclei in microscopic calculations which are based on realistic $NN$ interactions by including relativistic effects in calculations of low momentum interactions are discussed.Comment: 57 pages, 16 figure

Anomalous specific heat jump in a two-component ultracold Fermi gas

The thermodynamic functions of a Fermi gas with spin population imbalance are studied in the temperature-asymmetry plane in the BCS limit. The low temperature domain is characterized by anomalous enhancement of the entropy and the specific heat above their values in the unpaired state, decrease of the gap and eventual unpairing phase transition as the temperature is lowered. The unpairing phase transition induces a second jump in the specific heat, which can be measured in calorimetric experiments. While the superfluid is unstable against a supercurrent carrying state, it may sustain a metastable state if cooled adiabatically down from the stable high-temperature domain. In the latter domain the temperature dependence of the gap and related functions is analogous to the predictions of the BCS theory.Comment: 4 pages, 3 figures. v2 includes a discussion of instabilities; v3: final version to appear in PR

The 0nbb-decay nuclear matrix elements with self-consistent short-range correlations

A self-consistent calculation of nuclear matrix elements of the neutrinoless double beta decays (0nbb) of 76Ge, 82Se, 96Zr, 100Mo, 116Cd, 128Te, 130Te and 130Xe is presented in the framework of the renormalized quasiparticle random phase approximation (RQRPA) and the standard QRPA. The pairing and residual interactions as well as the two-nucleon short-range correlations are for the first time derived from the same modern realistic nucleon-nucleon potentials, namely from charge-dependent Bonn potential (CD-Bonn) and the Argonne V18 potential. In a comparison with the traditional approach of using the Miller-Spencer Jastrow correlations matrix elements for the 0nbb-decay are obtained, which are larger in magnitude. We analyze the differences among various two-nucleon correlations including those of the unitary correlation operator method (UCOM) and quantify the uncertainties in the calculated 0nbb-decay matrix elements.Comment: 11 pages, 5 figure

Anomalous Specific-Heat Jump in a Two-Component Ultracold Fermi Gas

The thermodynamic functions of a Fermi gas with spin population imbalance are studied in the temperature-asymmetry plane in the BCS limit. The low-temperature domain is characterized by an anomalous enhancement of the entropy and the specific heat above their values in the unpaired state, decrease of the gap and eventual unpairing phase transition as the temperature is lowered. The unpairing phase transition induces a second jump in the specific heat, which can be measured in calorimetric experiments. While the superfluid is unstable against a supercurrent carrying state, it may sustain a metastable state if cooled adiabatically down from the stable high-temperature domain. In the latter domain the temperature dependence of the gap and related functions is analogous to the predictions of the BCS theory. DOI: 10.1103/PhysRevLett.97.140404 PACS numbers: 05.30.Fk, 03.75.Hh, 03.75.Ss, 74.20.Fg Recent experiments [1,2] on ultracold dilute gases of fermionic atoms trapped an unequal number of fermions in two different hyperfine states. These experiments started addressing some of the long-standing problems in the theory of asymmetric superconductors (ASCs) that are of interest in a variety of fields including metallic superconductors The population asymmetry in ASC can be characterized either in terms of the difference (mismatch) in the chemical potentials or the difference in the densities of the species. The first case arises when the ''chemical'' equilibrium between populations admits transmutation between the different spin states, as, e.g., under the equilibrium with respect to the weak interactions in cold dense hadronic or quark matter. We shall specify our discussion from the outset to the second case and assume that the total number of fermions is fixed and the asymmetry is maintained with respect to the number densities of different species, as is the case in the experiments on ultracold fermions. The aim of this Letter is the study of the temperatureasymmetry phase diagram of an ultracold Fermi gas with pairing between two unequally populated hyperfine states in the BCS regime. We propose that calorimetric experiments, which are within the current experimental capabilitie