arXiv subjects

Irina Sagert

Publications and source records attributed to Irina Sagert.

27 records · Page 2Linked to original sources

arXiv2010

Detecting the QCD phase transition in the next Galactic supernova neutrino burst

Predictions of the thermodynamic conditions for phase transitions at high baryon densities and large chemical potentials are currently uncertain and largely phenomenological. Neutrino observations of core-collapse supernovae can be used to constrain the situation. Recent simulations of stellar core collapse that include a description of quark matter predict a sharp burst of anti ν_e several hundred milliseconds after the prompt ν_e neutronization burst. We study the observational signatures of that anti ν_e burst at current neutrino detectors - IceCube and Super-Kamiokande. For a Galactic core-collapse supernova, we find that signatures of the QCD phase transition can be detected, regardless of the neutrino oscillation scenario. The detection would constitute strong evidence of a phase transition in the stellar core, with implications for the equation of state at high matter density and the supernova explosion mechanism.

astro-ph.HE↗

arXiv2010

Strangeness in Astrophysics and Cosmology

Some recent developments concerning the role of strange quark matter for astrophysical systems and the QCD phase transition in the early universe are addressed. Causality constraints of the soft nuclear equation of state as extracted from subthreshold kaon production in heavy-ion collisions are used to derive an upper mass limit for compact stars. The interplay between the viscosity of strange quark matter and the gravitational wave emission from rotation-powered pulsars are outlined. The flux of strange quark matter nuggets in cosmic rays is put in perspective with a detailed numerical investigation of the merger of two strange stars. Finally, we discuss a novel scenario for the QCD phase transition in the early universe, which allows for a small inflationary period due to a pronounced first order phase transition at large baryochemical potential.

astro-ph.CO↗

arXiv2009

The Strange Prospects for Astrophysics

The implications of the formation of strange quark matter in neutron stars and in core-collapse supernovae is discussed with special emphasis on the possibility of having a strong first order QCD phase transition at high baryon densities. If strange quark matter is formed in core-collapse supernovae shortly after the bounce, it causes the launch of a second outgoing shock which is energetic enough to lead to a explosion. A signal for the formation of strange quark matter can be read off from the neutrino spectrum, as a second peak in antineutrinos is released when the second shock runs over the neutrinosphere.

astro-ph.HE↗

arXiv2009

Astrophysical Implications of the QCD phase transition

The possible role of a first order QCD phase transition at nonvanishing quark chemical potential and temperature for cold neutron stars and for supernovae is delineated. For cold neutron stars, we use the NJL model with nonvanishing color superconducting pairing gaps, which describes the phase transition to the 2SC and the CFL quark matter phases at high baryon densities. We demonstrate that these two phase transitions can both be present in the core of neutron stars and that they lead to the appearance of a third family of solution for compact stars. In particular, a core of CFL quark matter can be present in stable compact star configurations when slightly adjusting the vacuum pressure to the onset of the chiral phase transition from the hadronic model to the NJL model. We show that a strong first order phase transition can have strong impact on the dynamics of core collapse supernovae. If the QCD phase transition sets in shortly after the first bounce, a second outgoing shock wave can be generated which leads to an explosion. The presence of the QCD phase transition can be read off from the neutrino and antineutrino signal of the supernova.

astro-ph.SR↗

arXiv2008

Is there Quark Matter in (Low-Mass) Pulsars?

The effect of the QCD phase transition is studied for the mass-radius relation of compact stars and for hot and dense matter at a given proton fraction used as input in core-collapse supernova simulations. The phase transitions to the 2SC and CFL color superconducting phases lead to stable hybrid star configurations with a pure quark matter core. In supernova explosions quark matter could be easily produced due to $β$-equilibrium, small proton fractions and nonvanishing temperatures. A low critical density for the phase transition to quark matter is compatible with present pulsar mass measurements.

astro-ph↗

arXiv2007

Neutron star versus heavy-ion data: is the nuclear equation of state hard or soft?

Recent astrophysical observations of neutron stars and heavy-ion data are confronted with our present understanding of the equation of state of dense hadronic matter. Emphasis is put on the possible role of the presence of hyperons in the interior of compact stars. We argue that data from low-mass pulsars provide an important cross-check between high-density astrophysics and heavy-ion physics.

astro-ph↗

arXiv2007

Is a soft nuclear equation of state extracted from heavy-ion data incompatible with pulsar data?

We discuss the recent constraints on the nuclear equation of state from pulsar mass measurements and from subthreshold production of kaons in heavy-ion collisions. While recent pulsar data points towards a hard equation of state, the analysis of the heavy-ion data allows only for soft equations of state. We resolve the apparent contradiction by considering the different density regimes probed. We argue that future measurements of global properties of low-mass pulsars can serve as an excellent cross-check to heavy-ion data.

astro-ph↗

arXiv2006

Strange Exotic States and Compact Stars

We discuss the possible appearance of strange exotic multi-quark states in the interior of neutron stars and signals for the existence of strange quark matter in the core of compact stars. We show how the in-medium properties of possible pentaquark states are constrained by pulsar mass measurements. The possibility of generating the observed large pulsar kick velocities by asymmetric emission of neutrinos from strange quark matter in magnetic fields is outlined.

astro-ph↗

arXiv2005

Compact Stars for Undergraduates

We report on an undergraduate student project initiated in the summer semester of 2004 with the aim to establish equations of state for white dwarfs and neutron stars for computing mass-radius relations as well as corresponding maximum masses. First, white dwarfs are described by a Fermi gas model of degenerate electrons and neutrons and effects from general relativity are examined. For neutron star matter, the influence of a finite fraction of protons and electrons and of strong nucleon-nucleon interactions are studied. The nucleon--nucleon interactions are introduced within a Hartree-Fock scheme using a Skyrme-type interaction. Finally, masses and radii of neutron stars are computed for given central pressure.

astro-ph↗