Dense baryonic matter: constraints from recent neutron star observations

Updated constraints from neutron star masses and radii impose stronger restrictions on the equation of state for baryonic matter at high densities and low temperatures. The existence of two-solar-mass neutron stars rules out many soft equations of state with prominent "exotic" compositions. The present work reviews the conditions required for the pressure as a function of baryon density in order to satisfy these new constraints. Several scenarios for sufficiently stiff equations of state are evaluated. The common starting point is a realistic description of both nuclear and neutron matter based on a chiral effective field theory approach to the nuclear many-body problem. Possible forms of hybrid matter featuring a quark core in the center of the star are discussed using a three-flavor Polyakov--Nambu--Jona-Lasinio (PNJL) model. It is found that a conventional equation of state based on nuclear chiral dynamics meets the astrophysical constraints. Hybrid matter generally turns out to be too soft unless additional strongly repulsive correlations, e.g. through vector current interactions between quarks, are introduced. The extent to which strangeness can accumulate in the equation of state is also discussed.Comment: v2; substantial revisions with respect to v1; 17 pages, 15 figure

Chiral Magnetism of the Nucleon

We study the quark mass expansion of the magnetic moments of the nucleon in a chiral effective field theory including nucleons, pions and delta resonances as explicit degrees of freedom. We point out that the usual powercounting applied so far to this problem misses important quark mass structures generated via an intermediate isovector M1 nucleon-delta transition. We propose a modified powercounting and compare the resulting chiral extrapolation function to available (quenched) lattice data. The extrapolation is found to work surprisingly well, given that the lattice data result from rather large quark masses. Our calculation raises the hope that extrapolations of lattice data utilizing chiral effective field theory might be applicable over a wider range in quark masses than previously thought, and we discuss some open questions in this context. Furthermore, we observe that within the current lattice data uncertainties the extrapolations presented here are consistent with the Pade fit ansatz introduced by the Adelaide group a few years ago.Comment: 30 pages, Latex, 7 figure

Limits to the private enforcement of antitrust law

Following Regulation No. 1/2003 EC which permits the substitution of decentralised and private enforcement for centralised and public enforcement of Articles 81 and 82 EC, the European Commission in December 2005 presented a Green Paper on "damages actions for breach of the EC antitrust rules". The purpose of this initiative is to foster private tort suits by victims of anti-competitive behaviour. However, there are limits to the private enforcement of antitrust law through actions for damages, since the harm is typically shifted to a large number of final victims who are badly informed or face a rational disincentive to sue for damages.Our paper focuses on a so far neglected aspect of loss diffusion which results from hardcore price cartels. Under reasonable conditions the owners of production factors are also affected by price cartels, whereas consumers are typically affected less than is commonly assumed.

Impact of vector-current interactions on the QCD phase diagram

Using a nonlocal version of the Polyakov-loop-extended Nambu--Jona-Lasinio model, we investi- gate effects of a nonderivative vector-current interaction (relating to the quark-number density) at both real and imaginary chemical potentials. This repulsive vector interaction between quarks has the following impact on the chiral first-order phase transition: at imaginary chemical potential it sharpens the transition at the Roberge-Weiss (RW) end point and moves this critical point toward lower temperatures; at real chemical potential, the critical end point moves on a trajectory towards larger chemical potentials and lower temperatures with increasing vector coupling strength. The conditions are discussed at which the first-order phase transition disappears and turns into a smooth crossover.Comment: 6 pages, 4 figure

How neutron stars constrain the nuclear equation of state

Recent neutron star observations set new constraints for the equation of state of baryonic matter. A chiral effective field theory approach is used for the description of neutron-dominated nuclear matter present in the outer core of neutron stars. Possible hybrid stars with quark matter in the inner core are discussed using a three-flavor Nambu--Jona-Lasinio model.Comment: Conference Proceedings for INPC 2013, Florence; 4 pages, 4 figure

Chiral extrapolations of nucleon properties from lattice QCD

We report on recent work about the study of quark mass dependence of nucleon magnetic moments and axial-vector coupling constant. We examine the feasibility of chiral effective field theory methods for the extrapolation of lattice QCD data obtained at relative large pion masses down to the physical values.Comment: 5pages, LaTeX, 3 figures, uses World Scientific style file; presented at PANIC 02, Osak

Thermodynamic phases and mesonic fluctuations in a chiral nucleon-meson model

Studies of the QCD phase diagram must properly include nucleonic degrees of freedom and their thermodynamics in the range of baryon chemical potentials characteristic of nuclear matter. A useful framework for incorporating relevant nuclear physics constraints in this context is a chiral nucleon-meson effective Lagrangian. In the present paper, such a chiral nucleon-meson model is extended with systematic inclusion of mesonic fluctuations using the functional renormalization group approach. The resulting description of the nuclear liquid-gas phase transition shows a remarkable agreement with three-loop calculations based on in-medium chiral effective field theory. No signs of a chiral first-order phase transition and its critical endpoint are found in the region of applicability of the model, at least up to twice the density of normal nuclear matter and at temperatures T<100 MeV. Fluctuations close to the critical point of the first-order liquid-gas transition are also examined with a detailed study of the chiral susceptibility.Comment: 10 pages, 11 figures; references added, discussions enlarge