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Stefan Typel

Publications and source records attributed to Stefan Typel.

At least 19 recordsLinked to original sources
arXiv2026

Strongly interacting matter with criticality induced by modified excluded volume in core-collapse supernova simulations

This article reviews critically the core-collapse supernova explosion mechanism associated with a sufficiently strong first-order phase transition from normal nuclear, in general hadronic matter to deconfined quark matter, which commonly assumes Gibbs conditions for the coexistence of phases and a phase transition construction accordingly. To this end, a novel class of multi-purpose equation of state (EOS) is developed, based on the modified excluded volume (MEV) approach employing a medium-dependent excluded-volume functional within the relativistic mean field framework with density-dependent meson-nucleon couplings. The chosen MEV parametrisation features the change in the number of degrees of freedom, mimicking the EOS softening in excess of nuclear saturation density, featuring a first-order phase transition with van der Waals like behaviour and the presence of a critical point at high temperatures. Simulations of core-collapse supernovae are performed, based on general relativistic neutrino radiation hydrodynamics in spherical symmetry, in order to explore the previously reported supernova explosion scenario within this class of phenomenological modified microscopic hadronic EOS. A burst-like neutrino signature is released, substantially longer than previously reported based on common hadron-quark hybrid model EOS with two-phase approach and Gibbs phase-transition construction, as observable signal, which is complemented by a gravitational wave mode analysis.

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arXiv2026

Establishing the $^{40}$Ca$(p,p \alpha)$ reaction at 392 MeV under quasi-free scattering conditions

The $(p,p \alpha)$ reaction offers a direct means to probe preformed $\alpha$-cluster structures in nuclei under quasi-free scattering conditions. Previous studies around 100 MeV provided valuable insights into $\alpha$ clustering, but quantitative comparison with microscopic cluster wave functions remained limited due to strong distortion effects. At higher energies, the reaction mechanism becomes simpler and the distorted-wave impulse approximation (DWIA) provides a more reliable framework for quantitative analysis. In the present work, the $^{40}$Ca$(p,p\alpha)$ reaction was measured at an incident energy of 392 MeV using the high-resolution Grand Raiden and LAS spectrometers at RCNP. Despite the small cross section in this energy region, the achieved resolution allowed clear separation of the ground and excited states of the residual $^{36}$Ar nucleus, and corresponding momentum distributions were extracted. DWIA calculations using a Woods-Saxon $\alpha + ^{36}$Ar bound-state wave function yielded an experimental spectroscopic factor of $ S_{\mathrm{FAC}}^{\mathrm{WS}} = 0.51 \pm 0.05 $, consistent with the previous result at 101.5 MeV $(0.52 \pm 0.23 )$. This agreement demonstrates that the reaction mechanism is well described across a wide energy range. The present study establishes the feasibility of high-precision $(p,p\alpha)$ measurements at several hundred MeV and highlights their potential as a quantitative probe of $\alpha$ clustering in medium-mass nuclei, forming the basis for systematic studies in both stable and unstable systems.

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arXiv2024

Improving relativistic energy density functionals with tensor couplings

Energy density functionals (EDFs) have been used extensively with great success to calculate properties of nuclei and to predict the equation of state (EOS) of dense nuclear matter. Besides non-relativistic EDFs, mostly of the Skyrme or Gogny type, relativistic EDFs of different types are in widespread use. In these latter approaches, the effective in-medium interaction is described by an exchange of mesons between nucleons. In most cases, only minimal meson-nucleon couplings are considered. The effects of additional tensor couplings were rarely investigated. In this work, a new relativistic EDF with tensor couplings and density dependent minimal meson-nucleon couplings will be presented. The parameters of the model are determined using a carefully selected set of experimental data with realistic uncertainties that are determined self-consistently. Predictions for various nuclear observables, the nuclear matter equation of state, and properties of neutron stars are discussed.

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arXiv2024

Observational Probes of the Neutron Star Equation of State with Hyperons, Bosonic Dark Matter, and Quark Matter

Context. The presence of dark matter in neutron stars is of growing interest due to its potential impact on the structure and observable properties of these objects. Among the various candidates, the hypothetical sexaquark has emerged as a promising bosonic dark matter particle, potentially forming under extreme conditions in neutron star cores. Aims. We investigate whether a hybrid neutron star model that includes hyperons, bosonic dark matter (in the form of sexaquarks), and deconfined quark matter can satisfy all current observational constraints. We particularly focus on identifying the range of sexaquark masses consistent with mass-radius measurements and the tidal deformability limit. Methods. We used the DD2Y-T model for the hadronic phase, which includes hyperons, and a nonlocal Nambu-Jona-Lasinio model for the deconfined quark phase. The phase transition was modeled as a smooth crossover using the replacement interpolation construction method. Sexaquark-baryon interactions were introduced via an effective mass shift representing repulsion. We incorporated the full set of current observational data, including NICER measurements of PSRs J0437-4715 and newly published J0614-3329 data, and performed a Bayesian analysis to constrain the sexaquark mass. Results. Our results show that the presence of the sexaquark softens the equation of state, enabling the hybrid model to satisfy both the radius and tidal deformability constraints around the canonical 1.4 M_\odot neutron stars. We find that hybrid EOSs with a sexaquark mass around 1900 MeV are in agreement with all available constraints, including those from HESS J1731-347 and PSR J0952-0607, which represent the lowest and highest mass neutron stars observed to date. The Bayesian analysis favors a sexaquark mass range of 1885-1935 MeV, supporting the potential relevance of this exotic particle in neutron star interiors.

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arXiv2024

Exploring the distribution and impact of bosonic dark matter in neutron stars

The presence of dark matter (DM) within neutron stars (NSs) can be introduced by different accumulation scenarios in which DM and baryonic matter (BM) may interact only through the gravitational force. In this work, we consider asymmetric self-interacting bosonic DM which can reside as a dense core inside the NS or form an extended halo around it. It is seen that depending on the boson mass ($m_{\chi}$), self-coupling constant ($\lambda$) and DM fraction ($F_{\chi}$), the maximum mass, radius and tidal deformability of NSs with DM admixture will be altered significantly. The impact of DM causes some modifications in the observable features induced solely by the BM component. Here, we focus on the widely used nuclear matter equation of state (EoS) called DD2 for describing NS matter. We show that by involving DM in NSs, the corresponding observational parameters will be changed to be consistent with the latest multi-messenger observations of NSs. It is seen that for $m_{\chi}\gtrsim200$ MeV and $\lambda\lesssim2\pi$, DM admixed NSs with $4\%\lesssim F_{\chi}\lesssim20\%$ are consistent with the maximum mass and tidal deformability constraints.

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arXiv2023

Quick Guides for Use of the CompOSE Data Base

We present a combination of two quick guides aimed at summarizing relevant information about the CompOSE nuclear equation of state repository. The first is aimed at nuclear physicists and describes how to provide standard equation of state tables. The second quick guide is meant for users and describes the basic procedures to obtain customized tables with equation of state data. Several examples are included to help providers and users to understand and benefit from the CompOSE database.

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arXiv2023

Exploring thermal effects of the hadron-quark matter transition in neutron star mergers

We study the importance of the thermal behavior of the hadron-quark phase transition in neutron star (NS) mergers. To this end, we devise a new scheme approximating thermal effects to supplement any cold, barotropic hybrid equation of state (EoS) model, i.e. two-phase EoS constructions with a hadronic regime and a phase of deconfined quark matter. The consideration of temperature-dependent phase boundaries turns out to be critical for a quantitative description of quark matter effects in NS mergers, since the coexistence phase can introduce a strong softening of the EoS at finite temperature, which is even more significant than the change of the EoS by the phase transition at T=0. We validate our approach by comparing to existing fully temperature-dependent EoS models and find a very good quantitative agreement of postmerger gravitational-wave (GW) features. Simulations with the commonly-used thermal ideal-gas approach exhibit sizable differences compared to full hybrid models implying that its use in NS merger simulations with quark matter is problematic. Our new scheme provides the means to isolate thermal effects of quark matter from the properties of the cold hybrid EoS and thus allows an assessment of the thermal behavior alone. We show that different shapes of the phase boundaries at finite temperature can have a large impact on the postmerger dynamics and GW signal for the same cold hybrid model. This finding demonstrates that postmerger GW emission contains important complementary information compared to properties extracted from cold stars. We also show by concrete examples that it is even possible for quark matter to only occur and thus be detectable in finite-temperature systems like merger remnants but not in cold NSs (abbreviated).

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arXiv2020

Constraining the onset density of the hadron-quark phase transition with gravitational-wave observations

We study the possible occurrence of the hadron-quark phase transition (PT) during the merging of neutron star binaries by hydrodynamical simulations employing a set of temperature dependent hybrid equations of state (EoSs). Following previous work we describe an unambiguous and measurable signature of deconfined quark matter in the gravitational-wave (GW) signal of neutron star binary mergers including equal-mass and unequal-mass systems of different total binary mass. The softening of the EoS by the PT at higher densities, i.e. after merging, leads to a characteristic increase of the dominant postmerger GW frequency f_peak relative to the tidal deformability Lambda inferred during the premerger inspiral phase. Hence, measuring such an increase of the postmerger frequency provides evidence for the presence of a strong PT. If the postmerger frequency and the tidal deformability are compatible with results from purely baryonic EoS models yielding very tight relations between f_peak and Lambda, a strong PT can be excluded up to a certain density. We find tight correlations of f_peak and Lambda with the maximum density during the early postmerger remnant evolution. These GW observables thus inform about the density regime which is probed by the remnant and its GW emission. Exploiting such relations we devise a directly applicable, concrete procedure to constrain the onset density of the QCD PT from future GW measurements. We point out two interesting scenarios: if no indications for a PT are inferred from a GW detection, our procedure yields a lower limit on the onset density of the hadron quark PT. On the contrary, if a merger event reveals evidence for the occurrence of deconfined quark matter, the inferred GW parameters set an upper limit on the PT onset density. (abridged)

astro-ph.HE↗
arXiv2020

Medium modifications for light and heavy nuclear clusters in simulations of core collapse supernovae -- Impact on equation of state and weak interactions

The present article investigates the role of heavy nuclear clusters and weakly bound light nuclear clusters based on a newly developed equation of state for core collapse supernova studies. A novel approach is brought forward for the description of nuclear clusters, taking into account the quasiparticle approach and continuum correlations. It demonstrates that the commonly employed nuclear statistical equilibrium approach, based on non-interacting particles, for the description of light and heavy clusters becomes invalid for warm nuclear matter near the saturation density. This has important consequences for studies of core collapse supernovae. To this end, we implement this nuclear equation of state provided for arbitrary temperature, baryon density and isospin asymmetry, to spherically symmetric core collapse supernova simulations in order to study the impact on the dynamics as well as on the neutrino emission. For the inclusion of a set of weak processes involving light clusters the rate expressions are derived, including medium modifications at the mean field level. A substantial impact from the inclusion of a variety of weak reactions involving light clusters on the post bounce dynamics nor on the neutrino emission could not be found.

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arXiv2020

Parametrisations of relativistic energy density functionals with tensor couplings

The relativistic density functional with minimal density dependent nucleon-meson couplings for nuclei and nuclear matter is extended to include tensor couplings of the nucleons to the vector mesons. The dependence of the minimal couplings on either vector or scalar densities is explored. New parametrisations are obtained by a fit to nuclear observables with uncertainties that are determined self-consistently. The corresponding nuclear matter parameters at saturation are determined including their uncertainties. An improvement in the description of nuclear observables, in particular for binding energies and diffraction radii, is found when tensor couplings are considered, accompanied by an increase of the Dirac effective mass. The equations of state for symmetric nuclear matter and pure neutron matter are studied for all models. The density dependence of the nuclear symmetry energy, the Dirac effective masses and scalar densities is explored. Problems at high densities for parametrisations using a scalar density dependence of the couplings are identified due to the rearrangement contributions in the scalar self-energies that lead to vanishing Dirac effective masses.

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arXiv2019

Post-formation in alpha emission from nuclei

We propose a novel mechanism to explain nuclear decay by emission of an alpha particle. We show that the famous Geiger-Nuttall law can be explained by post-forming an alpha particle outside the range of the nuclear interaction with the daughter nucleus. This contrasts with the commonly accepted mechanism of first alpha particle pre-formation followed by emission through barrier penetration. We predict that the post-formation mechanism is more likely to occur for alpha-particles with higher energy.

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arXiv2018

Quark deconfinement as supernova explosion engine for massive blue-supergiant stars

Blue-supergiant stars develop into core-collapse supernovae --- one of the most energetic outbursts in the universe --- when all nuclear burning fuel is exhausted in the stellar core. Previous attempts failed to explain observed explosions of such stars which have a zero-age main sequence mass of 50~M$_\odot$ or more. Here we exploit the largely uncertain state of matter at high density, and connect the modeling of such stellar explosions with a first-order phase transition from nuclear matter to the quark-gluon plasma. The resulting energetic supernova explosions can account for a large variety of lightcurves, from peculiar type II to super-luminous events. The remnants are neutron stars with quark matter core, known as hybrid stars, of about 2~M$_\odot$ at birth. A galactic event of this kind could be observable due to the release of a second neutrino burst. Its observation would confirm such a first-order phase transition at densities relevant for astrophysics.

astro-ph.HE↗
arXiv2018

Phenomenological Equation of State of Strongly Interacting Matter with First-Order Phase Transitions and Critical Points

An extension of the relativistic density functional approach to the equation of state for strongly interacting matter is suggested which generalizes a recently developed modified excluded-volume mechanism to the case of temperature and density dependent available-volume fractions. A parametrisation of this dependence is presented for which at low temperatures and suprasaturation densities a first-order phase transition is obtained. It changes for increasing temperatures to a crossover transition via a critical endpoint. This provides a benchmark case for studies of the role of such a point in hydrodynamic simulations of ultrarelativistic heavy-ion collisions. The approach is thermodynamically consistent and extendable to finite isospin asymmetries that are relevant for simulations of neutron stars, their mergers and core-collapse supernova explosions.

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arXiv2018

The state of matter in simulations of core-collapse supernovae -- Reflections and recent developments

In this review article we discuss selected developments regarding the role of the equation of state (EOS) in simulations of core-collapse supernovae. There are no first-principle calculations of the state of matter under supernova conditions since a wide range of conditions is covered, in terms of density, temperature and isospin asymmetry. Instead, model EOS are commonly employed in supernova studies. These can be divided into regimes with intrinsically different degrees of freedom: heavy nuclei at low temperatures, inhomogeneous nuclear matter where light and heavy nuclei coexist together with unbound nucleons, and the transition to homogeneous matter at high densities and temperatures. In this article we discuss each of these phases with particular view on their role in supernova simulations.

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arXiv2017

Mixed Phase within the Multi-polytrope Approach to High Mass Twins

We present a multi-polytrope approach to describe high-mass twins fulfilling chiral effective field theory estimations of the neutron star equation state and test it against the appearance of mixed phases at the hadron-quark interface. In addition, we discuss astrophysical applications of this method and expected future measurements that shall further constrain neutron star matter and the understanding of the QCD phase diagram.

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arXiv2017

How Well Do We Know The Supernova Equation of State?

We give an overview about equations of state (EOS) which are currently available for simulations of core-collapse supernovae and neutron star mergers. A few selected important aspects of the EOS, such as the symmetry energy, the maximum mass of neutron stars, and cluster formation, are confronted with constraints from experiments and astrophysical observations. There are just very few models which are compatible even with this very restricted set of constraints. These remaining models illustrate the uncertainty of the uniform nuclear matter EOS at high densities. In addition, at finite temperatures the medium modifications of nuclear clusters represent a conceptual challenge. In conclusion, there has been significant development in the recent years, but there is still need for further improved general purpose EOS tables.

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arXiv2016

Comparison of equation of state models with different cluster dissolution mechanisms

The appearance of nuclear clusters in stellar matter at densities below nuclear saturation is an important feature in the modeling of the equation of state for astrophysical applications. There are different theoretical concepts to describe the dissolution of nuclei with increasing density and temperature. In this contribution, the predictions of two approaches are compared: the medium dependent change of the nuclear masses in a generalized relativistic density functional approach and the excluded-volume mechanism in a statistical model. Both approaches use the same description for the interaction between the nucleons. The composition of neutron star matter, in particular the occurrence of light and heavy nuclei, and its thermodynamic properties are studied.

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