728 research outputs found
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
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