541 research outputs found
Modern compact star observations and the quark matter EoS
A hybrid equation of state for dense matter is presented that satisfies
phenomenological constraints from modern compact star observations which
indicate high maximum masses of about 2 M_sun and large radii of R> 12 km. The
corresponding isospin symmetric equation of state is consistent with flow data
analyses of heavy-ion collisions. The transition from nuclear to two-flavor
color superconducting quark matter at n approximately 0.55 fm^{-3} is almost a
crossover.Comment: 2 pages, 2 figures; Proceedings of the Erice School on 'Radioactive
Beams, Nuclear Dynamics and Astrophysics' to be published in 'Prog. Part.
Nucl. Phys.
Consequences of simultaneous chiral symmetry breaking and deconfinement for the isospin symmetric phase diagram
The thermodynamic bag model (tdBag) has been applied widely to model quark
matter properties in both heavy-ion and astrophysics communities. Several
fundamental physics aspects are missing in tdBag, e.g., dynamical chiral
symmetry breaking (DSB) and repulsions due to the vector interaction are
both included explicitly in the novel vBag quark matter model of Kl\"ahn and
Fischer (2015) (Astrophys. J. 810, 134 (2015)). An important feature of vBag is
the simultaneous DSB and deconfinement, where the latter links vBag to a
given hadronic model for the construction of the phase transition. In this
article we discuss the extension to finite temperatures and the resulting phase
diagram for the isospin symmetric medium.Comment: 6 pages, 2 figures, Contribution to the Topical Issue Exploring
strongly interacting matter at high densities - NICA White Paper edited by
David Blaschke et a
Composition and thermodynamics of nuclear matter with light clusters
We investigate nuclear matter at finite temperature and density, including
the formation of light clusters up to the alpha particle The novel feature of
this work is to include the formation of clusters as well as their dissolution
due to medium effects in a systematic way using two many-body theories: a
microscopic quantum statistical (QS) approach and a generalized relativistic
mean field (RMF) model. Nucleons and clusters are modified by medium effects.
Both approaches reproduce the limiting cases of nuclear statistical equilibrium
(NSE) at low densities and cluster-free nuclear matter at high densities. The
treatment of the cluster dissociation is based on the Mott effect due to Pauli
blocking, implemented in slightly different ways in the QS and the generalized
RMF approaches. We compare the numerical results of these models for cluster
abundances and thermodynamics in the region of medium excitation energies with
temperatures T <= 20 MeV and baryon number densities from zero to a few times
saturation density. The effect of cluster formation on the liquid-gas phase
transition and on the density dependence of the symmetry energy is studied.
Comparison is made with other theoretical approaches, in particular those,
which are commonly used in astrophysical calculations. The results are relevant
for heavy-ion collisions and astrophysical applications.Comment: 32 pages, 15 figures, minor corrections, accepted for publication in
Physical Review
Equation of state at high densities and modern compact star observations
Recently, observations of compact stars have provided new data of high
accuracy which put strong constraints on the high-density behaviour of the
equation of state of strongly interacting matter otherwise not accessible in
terrestrial laboratories. The evidence for neutron stars with high mass (M =2.1
+/- 0.2 M_sun for PSR J0751+1807) and large radii (R > 12 km for RX J1856-3754)
rules out soft equations of state and has provoked a debate whether the
occurence of quark matter in compact stars can be excluded as well. In this
contribution it is shown that modern quantum field theoretical approaches to
quark matter including color superconductivity and a vector meanfield allow a
microscopic description of hybrid stars which fulfill the new, strong
constraints. The deconfinement transition in the resulting stiff hybrid
equation of state is weakly first order so that signals of it have to be
expected due to specific changes in transport properties governing the
rotational and cooling evolution caused by the color superconductivity of quark
matter. A similar conclusion holds for the investigation of quark deconfinement
in future generations of nucleus-nucleus collision experiments at low
temperatures and high baryon densities such as CBM @ FAIR.Comment: 6 pages, 2 figures, accepted for publication in J. Phys. G. (Special
Issue
The Distinctive Regulation of Cyanobacterial Glutamine Synthetase
Glutamine synthetase (GS) features prominently in bacterial nitrogen assimilation as it catalyzes the entry of bioavailable nitrogen in form of ammonium into cellular metabolism. The classic example, the comprehensively characterized GS of enterobacteria, is subject to exquisite regulation at multiple levels, among them gene expression regulation to control GS abundance, as well as feedback inhibition and covalent modifications to control enzyme activity. Intriguingly, the GS of the ecologically important clade of cyanobacteria features fundamentally different regulatory systems to those of most prokaryotes. These include the interaction with small proteins, the so-called inactivating factors (IFs) that inhibit GS linearly with their abundance. In addition to this protein interaction-based regulation of GS activity, cyanobacteria use alternative elements to control the synthesis of GS and IFs at the transcriptional level. Moreover, cyanobacteria evolved unique RNA-based regulatory mechanisms such as glutamine riboswitches to tightly tune IF abundance. In this review, we aim to outline the current knowledge on the distinctive features of the cyanobacterial GS encompassing the overall control of its activity, sensing the nitrogen status, transcriptional and post-transcriptional regulation, as well as strain-specific differences.Deutsche Forschungsgemeinschaft KL 3114/2-1Ministerio de Economía y Competitividad BIO2016-75634-PFEDER BIO2016-75634-
Baryon chemical potential and in-medium properties of BPS skyrmions
We continue the investigation of thermodynamical properties of the BPS Skyrme
model. In particular, we analytically compute the baryon chemical potential
both in the full field theory and in a mean-field approximation. In the full
field theory case, we find that the baryon chemical potential is always exactly
proportional to the baryon density, for arbitrary solutions. We further find
that, in the mean-field approximation, the BPS Skyrme model approaches the
Walecka model in the limit of high density - their thermodynamical functions as
well as the equation of state agree in this limit. This fact allows to read off
some properties of the -meson from the BPS Skyrme action, even though
the latter model is entirely based on the (pionic) Skyrme field. On the
other hand, at low densities, at the order of the usual nuclear matter density,
the equations of state of the two models are no longer universal, such that a
comparison depends on some model details. Still, also the BPS Skyrme model
gives rise to nuclear saturation in this regime, leading, in fact, to an exact
balance between repulsive and attractive forces. The perfect fluid aspects of
the BPS Skyrme model, which, together with its BPS properties, form the base of
our results, are shown to be in close formal analogy with the Eulerian
formulation of relativistic fluid dynamics. Within this analogy, the BPS Skyrme
model, in general, corresponds to a non-barotropic perfect fluid.Comment: Latex, 28 pages, 3 figure
1-2-3-flavor color superconductivity in compact stars
We suggest a scenario where the three light quark flavors are sequentially
deconfined under increasing pressure in cold asymmetric nuclear matter, e.g.,
as in neutron stars. The basis for our analysis is a chiral quark matter model
of Nambu--Jona-Lasinio (NJL) type with diquark pairing in the spin-1 single
flavor (CSL) and spin-0 two/three flavor (2SC/CFL) channels, and a
Dirac-Brueckner Hartree-Fock (DBHF) approach in the nuclear matter sector. We
find that nucleon dissociation sets in at about the saturation density, n_0,
when the down-quark Fermi sea is populated (d-quark dripline) due to the flavor
asymmetry imposed by beta-equilibrium and charge neutrality. At about 3n_0
u-quarks appear forming a two-flavor color superconducting (2SC) phase, while
the s-quark Fermi sea is populated only at still higher baryon density. The
hybrid star sequence has a maximum mass of 2.1 M_sun. Two- and three-flavor
quark matter phases are found only in gravitationally unstable hybrid star
solutions.Comment: 4 pages, 2 figures, to appear in the proceedings of Quark Matter
2008: 20th International Conference on Ultra-Relativistic Nucleus Nucleus
Collisions (QM 2008), Jaipur, India, 4-10 Feb 200
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