24 research outputs found
Phase diagram and nucleation in the Polyakov-loop-extended Quark-Meson truncation of QCD with the unquenched Polyakov-loop potential
Unquenching of the Polyakov-loop potential showed to be an important
improvement for the description of the phase structure and thermodynamics of
strongly-interacting matter at zero quark chemical potentials with
Polyakov-loop extended chiral models. This work constitutes the first
application of the quark backreaction on the Polyakov-loop potential at nonzero
density. The observation is that it links the chiral and deconfinement phase
transition also at small temperatures and large quark chemical potentials. The
build up of the surface tension in the Polyakov-loop extended Quark-Meson model
is explored by investigating the two and 2+1-flavour Quark-Meson model and
analysing the impact of the Polyakov-loop extension. In general, the order of
magnitude of the surface tension is given by the chiral phase transition. The
coupling of the chiral and deconfinement transition with the unquenched
Polyakov-loop potential leads to the fact that the Polyakov-loop contributes at
all temperatures.Comment: 28 pages, 13 figures; version published in Phys. Rev.
Thermodynamics of (2+1)-flavor strongly interacting matter at nonzero isospin
We investigate the phase structure of strongly interacting matter at
non-vanishing isospin before the onset of pion condensation in the framework of
the unquenched Polyakov-Quark-Meson model with 2+1 quark flavors. We show
results for the order parameters and all relevant thermodynamic quantities. In
particular, we obtain a moderate change of the pressure with isospin at
vanishing baryon chemical potential, whereas the chiral condensate decreases
more appreciably. We compare the effective model to recent lattice data for the
decrease of the pseudo-critical temperature with the isospin chemical
potential. We also demonstrate the major role played by the value of the pion
mass in the curvature of the transition line, and the need for lattice results
with a physical pion mass. Limitations of the model at nonzero chemical
potential are also discussed.Comment: 8 pages, 4 figures; version published in Phys. Lett.
On the Thermodynamics and Phase Structure of Strongly-Interacting Matter in a Polyakov-loop–extended Constituent-Quark Model
Polyakov-loop–extended constituent-quark models are useful to investigate the chiral and (de)confinement phase structure and the thermodynamics of strongly-interacting
matter. It is shown that taking into account the quark backreaction on the gauge-field
dynamics as well as quantum and thermal fluctuations of quarks and mesons is crucial
in such models to achieve results for order parameters and thermodynamics that
are in line with non-perturbative calculations at vanishing chemical potential. The dependence
of the results on remaining parameters is discussed. The investigations are
extended to nonzero quark density and isospin. The impact of unquenching effects in
the Polyakov-loop potential on the phase structure at non-vanishing quark densities
is discussed. Predictions for thermodynamics at nonzero isospin are shown. Furthermore,
the reliability of those models is tested by confronting its results with lattice data
on the isospin dependence of the transition temperature. The phase structure of the
three-dimensional temperature - isospin - quark density phase diagram is investigated.
Moreover, the process of nucleation at small temperatures and large densities is investigated
and the surface tension for the phase transition calculated. Some consequences
of the results for the early Universe, for heavy-ion collisions, and for proto-neutron stars
are discussed
Cosmological implications of a Dark Matter self-interaction energy density
We investigate cosmological constraints on an energy density contribution of
elastic dark matter self-interactions characterized by the mass of the exchange
particle and coupling constant. Because of the expansion behaviour in a
Robertson-Walker metric we investigate self-interacting dark matter that is
warm in the case of thermal relics. The scaling behaviour of dark matter
self-interaction energy density shows that it can be the dominant contribution
(only) in the very early universe. Thus its impact on primordial
nucleosynthesis is used to restrict the interaction strength, which we find to
be at least as strong as the strong interaction. Furthermore we explore dark
matter decoupling in a self-interaction dominated universe, which is done for
the self-interacting warm dark matter as well as for collisionless cold dark
matter in a two component scenario. We find that strong dark matter
self-interactions do not contradict super-weak inelastic interactions between
self-interacting dark matter and baryonic matter and that the natural scale of
collisionless cold dark matter decoupling exceeds the weak scale and depends
linearly on the particle mass. Finally structure formation analysis reveals a
linear growing solution during self-interaction domination; however, only
non-cosmological scales are enhanced.Comment: 14 pages, 14 figures; version published in Phys. Rev.
Phase diagram and surface tension in the three-flavor Polyakov-quark-meson model
We obtain the in-medium effective potential of the three-flavor
Polyakov-Quark-Meson model as a real function of real variables in the Polyakov
loop variable, to allow for the study of all possible minima of the model. At
finite quark chemical potential, the real and imaginary parts of the effective
potential, in terms of the Polyakov loop variables, are made apparent, showing
explicitly the fermion sign problem of the theory. The phase diagram and other
equilibrium observables, obtained from the real part of the effective
potential, are calculated in the mean-field approximation. The obtained results
are compared to those found with the so-called saddle-point approach. Our
procedure also allows the calculation of the surface tension between the
chirally broken and confined phase, and the chirally restored and deconfined
phase. The values of surface tension we find for low temperatures are very
close to the ones recently found for two-flavor chiral models. Some
consequences of our results for the early Universe, for heavy-ion collisions,
and for proto-neutron stars are briefly discussed.Comment: 17 pages, 6 figures. V2: typos fixed, references adde
Thermodynamics of QCD at vanishing density
We study the phase structure of QCD at finite temperature within a
Polyakov-loop enhanced quark-meson model. Such a model describes the chiral as
well as the confinement-deconfinement dynamics. In the present investigation,
based on the approach and results put forward in [1-4], both, matter as well as
glue fluctuations are included. We present results for the order parameters as
well as some thermodynamic observables and find very good agreement with recent
results from lattice QCD.Comment: 12 pages, 7 figures; published versio
Exploring the Phase Structure and Thermodynamics of QCD
We put forward a Polyakov-loop extended quark meson model, where matter as
well as glue fluctuations are taken into account, cf. [1]. The latter are
included via a Polyakov-loop potential. Usually such a glue potential is based
on Yang-Mills lattice data only. We show that a parametrisation of unquenching
effects as proposed in [2], together with the inclusion of fluctuations via the
functional renormalisation group [3,4], accounts for the relevant dynamics.
This is demonstrated by a comparison of order parameters and thermodynamic
observables to recent lattice results at vanishing chemical potential, where we
find very good agreement.Comment: 11 pages, 2 figures, contribution to "QCD-TNT-III: From quarks and
gluons to hadronic matter: A bridge too far?", ECT*, Trento (Italy),
September 2-6, 201
Improved Polyakov-loop potential for effective models from functional calculations
We investigate the quark backreaction on the Polyakov loop and its impact on
the thermodynamics of quantum chromodynamics. The dynamics of the gluons
generating the Polyakov-loop potential is altered by the presence of dynamical
quarks. However, this backreaction of the quarks has not yet been taken into
account in Polyakov-loop extended model studies. In the present work, we show
within a 2+1 flavour Polyakov-quark-meson model that a quark-improved
Polyakov-loop potential leads to a smoother transition between the
low-temperature hadronic phase and the high-temperature quark-gluon plasma
phase. In particular, we discuss the dependence of our results on the remaining
uncertainties that are the critical temperature and the parametrisation of the
Polyakov-loop potential as well as the mass of the sigma-meson.Comment: 19 pages, 25 figures; version published in Phys. Rev.