arXiv subjects

D. Blaschke

Publications and source records attributed to D. Blaschke.

At least 73 records · Page 4Linked to original sources

arXiv2015

Excluded volume effects in the hybrid star EoS

In this contribution, we outline a new 2-phase description of the quark-nuclear matter hybrid equation of state that takes into account effects of phase space occupation (excluded volume) in both, the hadronic and the quark matter phases. For the nuclear matter phase, the reduction of the available volume at increasing density leads to a stiffening, while for the quark matter phase a reduction of the effective string tension in the confining density functional is obtained. The deconfinement phase transition in the resulting hybrid equation of state is sensitive to both excluded volume effects. As an application, we consider matter under compact star constraints of electric neutrality and $β$-equilibrium. We obtain mass-radius relations for hybrid stars that fulfill the $2M_\odot$ constraint and exhibit the high-mass twin phenomenon. Both features depend sensitively on the excluded volume.

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arXiv2015

Mass-radius constraints for the neutron star EoS - Bayesian analysis

We suggest a new Bayesian analysis (BA) using disjunct M-R constraints for extracting probability measures for cold, dense matter equations of state (EoS). One of the key issues of such an analysis is the question of a deconfinement transition in compact stars and whether it proceeds as a crossover or rather as a first order transition. We show by postulating results of not yet existing radius measurements for the known pulsars with a mass of $2M_\odot$ that a radius gap of about 3 km would clearly select an EoS with a strong first order phase transition as the most probably one. This would support the existence of a critical endpoint in the QCD phase diagram under scrutiny in present and upcoming heavy-ion collision experiments.

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arXiv2015

Towards a new quark-nuclear matter EoS for applications in astrophysics and heavy-ion collisions

The aim of our work is to develop a unified equation of state (EoS) for nuclear and quark matter for a wide range in temperature, density and isospin so that it becomes applicable for heavy-ion collisions as well as for the astrophysics of neutron stars, their mergers and supernova explosions. As a first step, we use improved EoS for the hadronic and quark matter phases and join them via Maxwell construction. We discuss the limitations of a 2-phase description and outline steps beyond it, towards the formulation of a unified quark-nuclear matter EoS on a more fundamental level by a cluster virial expansion.

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arXiv2015

Pion and kaon in the Beth-Uhlenbeck approach

In the present work the Mott effect for pions and kaons is described within a Beth- Uhlenbeck approach on the basis of the PNJL model. The contribution of these degrees of freedom to the thermodynamics is encoded in the temperature dependence of their phase shifts. A comparison with results from $N_f = 2 + 1$ lattice QCD thermodynamics is performed.

hep-ph↗

arXiv2015

Nonequilibrium meson production in strong fields

We develop a kinetic equation approach to nonequilibrium pion and sigma meson production in a time-dependent, chiral symmetry breaking field (inertial mechanism). We investigate the question to what extent the low-momentum pion enhancement observed in heavy-ion collisions at CERN - LHC can be addressed within this formalism. In a first step, we consider the inertial mechanism for nonequilibrium production of $σ-$mesons and their simultaneous decay into pion pairs for two cases of $σ$ mass evolution. The resulting pion distribution shows a strong low-momentum enhancement which can be approximated by a thermal Bose distribution with a chemical potential that appears as a trace of the nonequilibrium process of its production.

hep-ph↗

arXiv2015

Assisted dynamical Schwinger effect: pair production in a pulsed bifrequent field

Electron-positron pair production by the superposition of two laser pulses with different frequencies and amplitudes is analyzed as a particular realization of the assisted dynamic Schwinger effect. It is demonstrated that, within a non-perturbative kinetic equation framework, an amplification effect is conceivable for certain parameters. When both pulses have wavelengths longer than the Compton wavelength, the residual net density of produced pairs is determined by the resultant field strength. The number of pairs starts to grow rapidly if the wavelength of the high-frequency laser component gets close to the Compton wavelength.

quant-ph↗

arXiv2015

Debye mass at the QCD transition in the PNJL model

We consider colour-electric screening as expressed by the quark contribution to the Debye mass calculated in a PNJL model with emphasis on confining and chiral symmetry breaking effects. We observe that the screening mass is entirely determined by the nonperturbative quark distribution function and temperature dependent QCD running coupling. The role of the gluon background (Polyakov loop) is to provide strong suppression of the number of charge carriers below the transition temperature, as an effect of confinement, while the temperature dependent dynamical quark mass contributes additional suppression, as an effect of chiral symmetry breaking. An alternative derivation of this result from a modified kinetic theory is given, which allows for a slight generalization and explicit contact with perturbative QCD. This gives the possibility to gain insights into the colour screening mechanism in the region near the QCD pseudocritical temperature and to provide a guideline for the interpretation of lattice QCD data.

hep-ph↗

arXiv2015

Energy bursts from deconfinement in high-mass twin stars

We estimate the energy reservoir available in the deconfinement phase transition induced collapse of a neutron star to its hybrid star mass twin on the "third family" branch, using a recent equation of state of dense matter. The available energy corresponding to the mass-energy difference between configurations is comparable with energies of the most violent astrophysical burst processes. An observational outcome of such a dynamical transition might be fast radio bursts, specifically a recent example of a FRB with a double-peak structure in its light curve.

astro-ph.HE↗

arXiv2015

Polyakov-loop suppression of colored states in a quark-meson-diquark plasma

A quark-meson-diquark plasma is considered within the PNJL model for dynamical chiral symmetry breaking and restoration in quark matter. Based on a generalized Beth-Uhlenbeck approach to mesons and diquarks we present the thermodynamics of this system including the Mott dissociation of mesons and diquarks at finite temperature. A striking result is the suppression of the diquark abundance below the chiral restoration temperature by the coupling to the Polyakov loop, because of their color degree of freedom. This is understood in close analogy to the suppression of quark distributions by the same mechanism. Mesons as color singlets are unaffected by the Polyakov-loop suppression. At temperatures above the chiral restoration mesons and diquarks are both suppressed due to the Mott effect, whereby the positive resonance contribution to the pressure is largely compensated by the negative scattering contribution in accordance with the Levinson theorem.

hep-ph↗

arXiv2015

Robustness of the Baryon-Stopping Signal for the Onset of Deconfinement in Relativistic Heavy-Ion Collisions

The impact of the experimental acceptance, i.e. transverse-momentum ($p_T$) cut-off and limited rapidity region, on the earlier predicted irregularity in the excitation function of the baryon stopping is studied. This irregularity is a consequence of the onset of deconfinement occurring in the compression stage of a nuclear collision and manifests itself as a wiggle in the excitation function of the reduced curvature ($C_y$) of the net-proton rapidity distribution at midrapidity. It is demonstrated that the wiggle is a very robust signal of a first-order phase transition that survives even under conditions of a very limited acceptance. At the same time the $C_y$ for pure hadronic and crossover transition scenarios become hardly distinguishable, if the acceptance cuts off too much of the low-$p_T$ proton spectrum and/or puts too narrow rapidity window around midrapidity. It is found that the shape of the net-proton rapidity distribution near midrapidity depends on the $p_T$ cut-off. This implies that the measurements should be taken at the same acceptance for all collision energies in order to reliably conclude on the presence or absence of the irregularity.

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arXiv2015

Quark-Hadron Phase Transition with Finite-Size Effects in Neutron Stars

We study the quark-hadron phase transition with the finite-size effects in neutron stars. The finite-size effects should be, generally, taken into account in the phase transition of multi-component system. The behavior of the phase transition, however, strongly depends on the models for quark and hadron matter, surface tension, neutrino fraction, and temperature. We find that, if the surface tension is strong, the EOS becomes similar to the case of a Maxwell construction for any hadron and/or quark model, though we adopt the Gibbs conditions. We also find that the mass-radius relations for that EOS are consistent with the observations, and our model is then applicable to realistic astrophysical phenomena such as the thermal evolution of compact stars.

astro-ph.HE↗

arXiv2015

Cooling of neutron stars and hybrid stars with a stiff hadronic EoS

Within the "nuclear medium cooling" scenario of neutron stars all reliably known temperature - age data, including those of the central compact objects in the supernova remnants of Cassiopeia A and XMMU-J1732, can be comfortably explained by a set of cooling curves obtained by variation of the star mass within the range of typical observed masses. The recent measurements of the high masses of the pulsars PSR J1614-2230 and PSR J0348-0432 on the one hand, and of the low masses for PSR J0737-3039B and the companion of PSR J1756-2251 on the other, provide independent proof for the existence of neutron stars with masses in a broad range from $\sim 1.2$ to 2 $M_\odot$. The values $M>2 M_{\odot}$ call for sufficiently stiff equations of state for neutron star matter. We investigate the response of the set of neutron star cooling curves to a stiffening of the nuclear equation of state so that maximum masses of about $2.4 M_\odot$ would be accessible and to a deconfinement phase transition from such stiff nuclear matter in the outer core to color superconducting quark matter in the inner core. Without readjustment of cooling inputs the mass range required to cover all cooling data for the stiff DD2 equation of state should include masses of $2.426 M_\odot$ for describing the fast cooling of CasA while the existence of a quark matter core accelerates the cooling so that CasA cooling data are described with a hybrid star of mass $1.674 M_\odot$.

astro-ph.HE↗

arXiv2015

Quark matter in high-mass neutron stars?

The recent measurements of the masses of the pulsars PSR J1614-2230 and PSR J0348-0432 provide independent proof for the existence of neutron stars with masses in range of 2 $M_\odot$. This fact has significant implications for the physics of high density matter and it challenges the hypothesis that the cores of NS can be composed of deconfined quark matter. In this contribution we study a description of quark matter based on the Nambu--Jona-Lasinio effective model and construct the equation of state for matter in beta equilibrium. This equation of state together with the hadronic Dirac-Brueckner-Hartree-Fock equation of state is used here to describe neutron star and hybrid star configurations. We show that compact stars masses of 2 $M_\odot$ are compatible with the possible existence of deconfined quark matter in their core.

nucl-th↗

arXiv2015

Mott-hadron resonance gas and lattice QCD thermodynamics

We present an effective model for the generic behaviour of hadron masses and phase shifts at finite temperature which shares basic features with recent developments within the PNJL model for correlations in quark matter. On this basis we obtain the transition between a hadron resonance gas phase and the quark gluon plasma in the spirit of the generalized Beth-Uhlenbeck approach where the Mott dissociation of hadrons is encoded in the hadronic phase shifts. Here we restrict ourselves to low-lying hadronic channels and perform a discussion of recent lattice QCD thermodynamics results from this perspective. We find agreement in the asymptotic regions while for the description of the transition itself the inclusion of further hadronic channels as well as a selfconsistent determination of the continuum thresholds is required.

hep-ph↗

arXiv2015

New Bayesian analysis of hybrid EoS constraints with mass-radius data for compact stars

We suggest a new Bayesian analysis using disjunct mass and radius constraints for extracting probability measures for cold, dense nuclear matter equations of state. One of the key issues of such an analysis is the question of a deconfinement transition in compact stars and whether it proceeds as a crossover or rather as a first order transition. The latter question is relevant for the possible existence of a critical endpoint in the QCD phase diagram under scrutiny in present and upcoming heavy-ion collision experiments.

astro-ph.HE↗

arXiv2015

NJL model approach to diquarks and baryons in quark matter

We describe baryons as quark-diquark bound states at finite temperature and density within the NJL model for chiral symmetry breaking and restoration in quark matter. Based on a generalized Beth-Uhlenbeck approach to mesons and diquarks we present in a first step the thermodynamics of quark-diquark matter which includes the Mott dissociation of diquarks at finite temperature. In a second step we solve the Bethe-Salpeter equation for the baryon as a quark-diquark bound state in quark-diquark matter. We obtain a stable, bound baryon even beyond the Mott temperature for diquark dissociation since the phase space occupation effect (Pauli blocking for quarks and Bose enhancement for diquarks) in the Bethe-Salpeter kernel for the nucleon approximately cancel so that the nucleon mass follows the in-medium behaviour of the quark and diquark masses towards chiral restoration. In this situation the baryon is obtained as a "borromean" three-quark state in medium because the two-particle state (diquark) is unbound while the three-particle state (baryon) is bound.

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arXiv2015

Mott-Anderson freeze-out and the strange matter "horn"

We discuss the $\sqrt{s}$-dependence of the $K^+/π^+$ ratio in heavy-ion collisions (the "horn" effect) within a Mott-Anderson localization model for chemical freeze-out. The different response of pion and kaon radii to the hot and dense hadronic medium results in different freeze-out conditions. We demonstrate within a simple model that this circumstance enhances the "horn" effect relative to statistical models with universal chemical freeze-out.

hep-ph↗

arXiv2014

Composite Fermions in Medium: Extending the Lipkin Model

The role of phase space occupation effects for the formation of two- and three-particle bound states in a dense medium is investigated within an algebraic approach suitable for systems with short-range interactions. It is shown that for two-fermion bound states due to the account of the exchange symmetry (phase space occupation) effect (Pauli blocking) in a dense medium the binding energy is reduced and vanishes at a critical density (Mott effect). For three-fermion bound states, within a Faddeev equation approach, the intermediate formation of pair correlations leads to the representation as a suitably symmetrized fermion-boson bound state. It is shown that the Bose enhancement of fermion pairs can partially compensate the Pauli blocking between the fermions. This leads to the general result obtained by algebraic methods: three-fermion bound states in a medium with high phase space occupation appear necessarily as Borromean states beyond the Mott density of the two-fermion bound state.

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