arXiv subjects

T. Gaitanos

Publications and source records attributed to T. Gaitanos.

At least 19 recordsLinked to original sources

arXiv2024

A novel solution to the hyperon-puzzle in neutron stars

Neutron stars offer a great opportunity to study highly compressed hadronic matter experimentally and theoretically. However, the so-called hyperon-puzzle arises at neutron star densities. The hyperon coexistence with other particles in compressed matter softens the equation of state and many widely-accepted models fail to reproduce precise observations of large neutron star masses. Here, we propose a novel mechanism to retain the stiffness of the high density state with hyperons by considering the explicit momentum dependence of their in-medium potentials. Our approach modifies conventional strangeness threshold conditions and generates new threshold effects on hyperons in high-density matter. We demonstrate these effects within the Non-Linear Derivative model, which incorporates baryon momentum-dependent fields based on empirical and microscopic studies. It turns out that even soft momentum-dependent strangeness fields do prohibit their populations in neutron star matter. The generic momentum dependence of strangeness potentials, as modeled by the non-linear derivative approach, is crucial for resolving the long-standing hyperon-puzzle in neutron stars.

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arXiv2021

Momentum dependent mean-fields of (anti)hyperons

We investigate the in-medium properties of hyperons and anti-hyperons in the framework of the Non-Linear Derivative (NLD) model. We focus on the momentum dependence of in-medium strangeness optical potentials. The NLD model is based on the simplicity of the well-established Relativistic Mean-Field (RMF) approximation, but it incorporates an explicit momentum dependence on a field-theoretical level. The extension of the NLD model to the (anti)baryon-octet is formulated in the spirit of SU(6) and G-parity arguments. It is shown that with an appropriate choice of momentum cut-offs the $Λ$, $Σ$ and $Ξ$ optical potentials are consistent with recent studies of the chiral effective field theory and Lattice-QCD calculations over a wide momentum region. In addition, we present NLD predictions for the in-medium momentum dependence of $\overlineΛ$-, $\overlineΣ$- and $\overlineΞ$-hyperons. This work is important for future experimental studies such as CBM, PANDA at the Facility for Antiproton and Ion Research (FAIR). It is relevant for nuclear astrophysics too.

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arXiv2017

Bounds on the speed of sound in dense matter, and neutron star structure

The accurate determination of the maximum mass of the neutron stars is one of the most important tasks in astrophysics. It is directly related to the identification of the black holes in the universe, the production of neutron stars from the supernovae explosion, and the equation of state (EoS) of dense matter. However, not only the EoS is directly connected with neutron star masses, but also the speed of sound in dense matter is a crucial quantity which characterizes the stiffness of the EoS. The upper bound of the speed of sound imposes strong constraints on the maximum mass of neutron stars. However, this upper bound remains still an open issue. Recent observations, of binary neutron star systems, offer the possibility of measuring with high accuracy both the mass and the tidal polarizability of the stars. We study possible effects of the upper bound of the speed of sound on the upper bound of the mass and the tidal polarizability. We conclude that these kinds of measurements, combined with recent observations of neutron stars with masses close to $2 M_{\odot}$, will provide robust constraints on the equation of state of hadronic matter at high densities.

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arXiv2016

Recent progress on superstrange dynamics

We review the present activities related to hypernuclear production in hadronic in-medium reactions at intermediate energies. The status of theoretical predictions and experimental evidences for the in-medium formation of bound superstrange matter is discussed. Heavy-ion collisions and antiproton-induced reactions at energies close to strangeness production thresholds create the conditions of hypermatter formation. This allows to understand better in-medium hyperon interactions and sets constraints on the strangeness sector of the nuclear equation of state.

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arXiv2016

Multi-Strangeness Production in Hadron Induced Reactions

We discuss in detail the formation and propagation of multi-strangeness particles in reactions induced by hadron beams relevant for the forthcoming experiments at FAIR. We focus the discussion on the production of the decuplet-particle $Ω$ and study for the first time the production and propagation mechanism of this heavy hyperon inside hadronic environments. The transport calculations show the possibility of $Ω$-production in the forthcoming \panda-experiment, which can be achieved with measurable probabilities using high-energy secondary $Ξ$-beams. We predict cross sections for $Ω$-production. The theoretical results are important in understanding the hyperon-nucleon and, in particular, the hyperon-hyperon interactions also in the high-strangeness sector. We emphasize the importance of our studies for the research plans at FAIR.

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arXiv2016

SU(3) Approach to Hypernuclear Interactions and Spectroscopy

The $SU(3)$ meson exchange approach to interactions within the baryon octet and nuclear density functional theory are used to derive an \emph{ab initio} description of hypernuclear interactions. The density dependence of interactions is recast into a DFT with density dependent interaction vertices. The field-theoretical structure is retained by expressing the vertices as functionals of the matter field operators. Applications to infinite hypermatter and neutron star matter are discussed. A new approach is presented allowing to determine in-medium coupling constants out of the $NN$-vertex functionals, obtained e.g. by DBHF theory, for the full baryon octet by exploiting $SU(3)$ relations.

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arXiv2015

Toward relativistic mean-field description of $\bar{\text{N}}$-nucleus reactions

In this work we study the antinucleon-nucleus optical potential in the framework of the non-linear derivative (NLD) model with momentum dependent mean-fields. We apply the NLD model to interaction of antinucleons ($\bar{\text{N}}$) in nuclear matter and, in particular, to antiproton scattering on nuclei. In nuclear matter a strong suppression of the $\bar{\text{N}}$-optical potential at rest and at high kinetic energies is found and caused by the momentum dependence of relativistic mean-fields. The NLD results are consistent with known empirical $\bar{\text{N}}$-nucleus observations and agree well with antiproton-nucleus scattering data. This makes the NLD approach compatible with both, nucleon and antinucleon Dirac phenomenologies. Furthermore, in nuclear matter an effective mass splitting between nucleons and antinucleons is predicted.

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arXiv2014

Production of multi-strangeness hypernuclei and the YN-interaction

We investigate for the first time the influence of hyperon-nucleon (YN) interaction models on the strangeness dynamics of antiproton- and $Ξ$-nucleus interactions. Of particular interest is the formation of bound multi-strangeness hypermatter in reactions relevant for \panda. The main features of two well-established microscopic approaches for YN-scattering are first discussed and their results are then analysed such that they can be applied in transport-theoretical simulations. The transport calculations for reactions induced by antiproton beams on a primary target including also the secondary cascade beams on a secondary target show a strong sensitivity on the underlying YN-interaction. In particular, we predict the formation of $Ξ$-hypernuclei with an observable sensitivity on the underlying $Ξ$N-interaction. We conclude the importance of our studies for the forthcoming research plans at FAIR.

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arXiv2013

In-medium effects on hypernuclear formation

We study strangeness dynamics in reactions relevant for the formation of multi-strange hypernuclei. In particular, we discuss the in-medium effects on elementary hyperon-nucleon ($YN$) channels, which are relevant for the production of hypernuclei at PANDA. The results indicate strong in-medium effects on $YN$-scattering, which might be important for hypernuclear studies at PANDA.

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arXiv2012

Strangeness production in antiproton-nucleus annihilation

The results of the microscopic transport calculations of $\bar p$-nucleus interactions within a GiBUU model are presented. The dominating mechanism of hyperon production is the strangeness exchange processes $\bar K N \to Y π$ and $\bar K N \to ΞK$. The calculated rapidity spectra of $Ξ$ hyperons are significantly shifted to forward rapidities with respect to the spectra of $S=-1$ hyperons. We argue that this shift should be a sensitive test for the possible exotic mechanisms of $\bar p$-nucleus annihilation. The production of the double $Λ$-hypernuclei by $Ξ^-$ interaction with a secondary target is calculated.

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arXiv2012

Strangeness production in antiproton-nucleus collisions

Antiproton annihilations on nuclei provide a very interesting way to study the behaviour of strange particles in the nuclear medium. In low energy $\bar p$ annihilations, the hyperons are produced mostly by strangeness exchange mechanisms. Thus, hyperon production in $\bar p A$ interactions is very sensitive to the properties of the antikaon-nucleon interaction in nuclear medium. Within the Giessen Boltzmann-Uehling-Uhlenbeck transport model (GiBUU), we analyse the experimental data on $Λ$ and $K^0_S$ production in $\bar p A$ collisions at $p_{\rm lab}=0.2-4$ GeV/c. A satisfactory overall agreement is reached, except for the $K^0_S$ production in $\bar p+^{20}$Ne collisions at $p_{\rm lab}=608$ MeV/c, where we obtain substantially larger $K^0_S$ production rate. We also study the $Ξ$ hyperon production, important in view of the forthcoming experiments at FAIR and J-PARC.

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arXiv2012

Kaon and hyperon production in antiproton-induced reactions on nuclei

We study the strangeness production in antiproton-nucleus collisions at the beam momenta from 200 MeV/c to 15 GeV/c within the Giessen Botzmann-Uehling-Uhlenbeck (GiBUU) transport model. The GiBUU model contains a very detailed description of the underlying antinucleon-nucleon cross sections, in-particular, of the strangeness production channels. We compare our calculations with the bubble chamber data on Λ- and K^0_S-production in antiproton-nucleus collisions and with the earlier intranuclear cascade calculations. The contributions of the various partial channels to the hyperon production are reported and systematic differences with experiment are discussed. The possible formation of the bound Λ- and ΛΛ-nucleus systems is also considered. Finally, the results on the Ξ-hyperon production are presented in view of the forthcoming experiments with antiproton beams at FAIR.

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arXiv2012

Transport-theoretical Description of Nuclear Reactions

In this review we first outline the basics of transport theory and its recent generalization to off-shell transport. We then present in some detail the main ingredients of any transport method using in particular the Giessen Boltzmann-Uehling-Uhlenbeck (GiBUU) implementation of this theory as an example. We discuss the potentials used, the ground state initialization and the collision term, including the in-medium modifications of the latter. The central part of this review covers applications of GiBUU to a wide class of reactions, starting from pion-induced reactions over proton and antiproton reactions on nuclei to heavy-ion collisions (up to about 30 AGeV). A major part concerns also the description of photon-, electron- and neutrino-induced reactions (in the energy range from a few 100 MeV to a few 100 GeV). For this wide class of reactions GiBUU gives an excellent description with the same physics input and the same code being used. We argue that GiBUU is an indispensable tool for any investigation of nuclear reactions in which final-state interactions play a role. Studies of pion-nucleus interactions, nuclear fragmentation, heavy ion reactions, hyper nucleus formation, hadronization, color transparency, electron-nucleus collisions and neutrino-nucleus interactions are all possible applications of GiBUU and are discussed in this article.

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arXiv2012

Energy Dependent Isospin Asymmetry in Mean-Field Dynamics

The Lagrangian density of relativistic mean-field (RMF) theory with non-linear derivative (NLD) interactions is applied to isospin asymmetric nuclear matter. We study the symmetry energy and the density and energy dependences of nucleon selfenergies. At high baryon densities a soft symmetry energy is obtained. The energy dependence of the isovector selfenergy suppresses the Lane-type optical potential with increasing energy and predicts a $ρ$-meson induced mass splitting between protons and neutrons in isospin asymmetric matter.

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arXiv2012

Formation of double-$Λ$ hypernuclei at PANDA

We study the formation of single- and double-$Λ$ hypernuclei in antiproton-induced reactions relevant for the forthcoming PANDA experiment at FAIR. We use the Giessen Boltzmann-Uehling-Uhlenbeck (GiBUU) transport model with relativistic mean-fields for the description of non-equilibrium dynamics and the statistical multifragmentation model (SMM) for fragment formation. This combined approach describes the dynamical properties of strangeness and fragments in low energy $\bar{p}$-induced reactions fairly well. We then focus on the formation of double-$Λ$ hypernuclei in high energy $\bar{p}$-nucleus collisions on a primary target including the complementary $Ξ$-induced reactions to a secondary one, as proposed by the PANDA collaboration. Our results show that a copious production of double-$Λ$ hyperfragments is possible at PANDA. In particular, we provide first theoretical estimations on the double-$Λ$ production cross section, which strongly rises with decreasing energy of the secondary $Ξ$-beam.

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arXiv2011

How Deep is the Antinucleon Optical Potential at FAIR energies

The key question in the interaction of antinucleons in the nuclear medium concerns the deepness of the antinucleon-nucleus optical potential. In this work we study this task in the framework of the non-linear derivative (NLD) model which describes consistently bulk properties of nuclear matter and Dirac phenomenology of nucleon-nucleus interactions. We apply the NLD model to antinucleon interactions in nuclear matter and find a strong decrease of the vector and scalar self-energies in energy and density and thus a strong suppression of the optical potential at zero momentum and, in particular, at FAIR energies. This is in agreement with available empirical information and, therefore, resolves the issue concerning the incompatibility of G-parity arguments in relativistic mean-field (RMF) models. We conclude the relevance of our results for the future activities at FAIR.

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arXiv2010

Breathing mode in an improved transport approach

The nuclear breathing-mode giant monopole resonance is studied within an improved relativistic Boltzmann-Uehling-Uhlenbeck (BUU) transport approach. As a new feature, the numerical treatment of ground state nuclei and their phase-space evolution is realized with the same semiclassical energy density functional. With this new method a very good stability of ground state nuclei in BUU simulations is achieved. This is important in extracting clear breathing-mode signals for the excitation energy and, in particular, for the lifetime from transport theoretical studies including mean-field and collisional effects.

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arXiv2009

Isospin Effects on Strangeness in Heavy-Ion Collisions

Kaon properties are studied within the framework of a fully covariant transport approach. The kaon-nucleon potential is evaluated in two schemes, a chiral perturbative approach and an effective One-Boson-Exchange model. Isospin effects are explicitly accounted for in both models. The transport calculations indicate a significant sensitivity of momentum distributions and total yields of $K^{0,+}$ isospin states on the choice of the kaon-nucleon interaction. Furthermore, isospin effects are rather moderate on absolute kaon yields, but appear on strangeness ratios. This is an important issue in determining the high density symmetry energy from studies of strangeness production in heavy-ion collisions.

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