Modern equations of state and spectroscopy in neutron-star matter

Sep 21, 2022, 9:00 AM → Sep 23, 2022, 6:00 PM Europe/Madrid

Universidad de Alcalá

Jose Manuel Alarcón (chair at Univ. Alcalá) (Univ. Alcalá de Henares), Felipe J. Llanes-Estrada (cochair at Univ. Complutense) (Universidad Complutense de Madrid)

 

   

 

Jointly organized by the Universidad Complutense de Madrid and the Universidad de Alcalá, that will be physically hosting it.

 

Scientific Committee 

Jose Manuel Alarcón (Univ. Alcalá)
Mark Alford (Washington Univ. St. Louis)
Norbert Kaiser (Technische Univ. München)
Felipe J. Llanes-Estrada (Univ. Complutense Madrid)
Jose Antonio Oller (Univ. Murcia)
Laura Tolós (Instituto Ciencias del Espacio, Barcelona)

Wed, September 21

9:00 AM → 9:30 AM Official welcome (informal one on the evening of the 20th, please check your email)

Speaker: José Manuel Alarcón (Universidad de Alcalá)

Welcome.pdf

9:30 AM → 11:00 AM Conference presentations

Convener: Felipe J. Llanes-Estrada (Universidad Complutense de Madrid)

9:30 AM Contraints on the Lambda-neutron interaction from charge symmetry breaking of A=4 hypernuclei

One key quantity for better constraining the contributions of hyperons to the equation of state of neutron matter is the $\Lambda$-neutron interaction. In absence of $\Lambda$-neutron scattering data, isospin symmetry is usually assume and interactions are determined by fitting to $\Lambda$-proton data.
But charge symmetry breaking (CSB) of the $\Lambda$-nucleon interaction has been well established by the experimentally known difference of the $\Lambda$ separation energies of the mirror hypernuclei $^4_\Lambda$He and $^4_\Lambda$H [1].

In this contribution, we employ chiral hyperon-nucleon interactions including the leading CSB contributions to constrain the $\Lambda$-neutron interaction. To this aim, we determine the strength of the two arising CSB contact terms by a fit to the differences of the separation energies of these hypernuclei in the $0^+$ and $1^+$ states, respectively, and then predict $\Lambda$n scattering lengths[2]. Based on two version of the hyperon-nucleon interaction and next-to-leading order and using different momentum cutoffs, we also estimate uncertainties of these predictions. The impact of the possible changes of the experimental input is discussed in view of recently improved experimental results for the separation energies of $^4_\Lambda$He and $^4_\Lambda$H.

References

[1] A. Gal, E.V. Hungerford and D.J. Millener,
Rev. Mod. Phys. 88 (2016), 035004 [arXiv:1605.00557 [nucl-th]].

[2] J. Haidenbauer, U.-G. Meißner and A. Nogga, Few Body Syst. 62 (2021), 105
[arXiv:2107.01134 [nucl-th]].

Speaker: Andreas Nogga (Forschungszentrum Jülich)

nogga-nstareos-2022-09-21.pdf

10:00 AM Why perturbative QCD constrains the equation of state in neutron stars

Calculations of equation of state of QCD become reliable at the densities of around 40 saturation densities. These densities are well beyond those that are reached within the cores of even the most massive neutron stars. However, knowing the equation state at these extreme densities still gives us robust information at lower densities because of global requirements imposed by causality, stability and thermodynamical consistency. In my talk I will demonstrate that due to these general physics conditions, the current state-of-the-art perturbative calculations constrain the equation of state even down to 2.3 saturation densities.

Speaker: Aleksi Kurkela (University of Stavanger)

Madrid-kurkela.pdf

10:30 AM Thermal index of neutron-star matter in the virial approximation

In this talk, I will discuss the thermal index of low-density, high-temperature matter, motivated by gravitational wave observations of neutron-star binaries. We use the virial approximation to include nuclear interaction effects. In pure neutron matter, we find a relatively temperature-independent thermal index close to $\Gamma_\text{th} \approx 5/3$, with a negligible contribution from nuclear interactions. Including isospin asymmetry, as well as electrons and photons, the results change substantially. For $\beta-$equilibrated matter, we find a smooth transition between $\Gamma_\text{th} \approx 4/3$ at low densities and $\Gamma_\text{th} \approx 5/3$ at high densities.

Speaker: Arnau Rios (Universitat de Barcelona)

rios_Alcala.pdf

11:00 AM → 11:30 AM Coffee break

11:30 AM → 1:00 PM Conference presentations

Convener: José Antonio Oller (Universidad de Murcia)

11:30 AM Brussels-Montreal unified equations of state for neutron stars

Formed in the aftermath of gravitational core-collapse supernova explosions, neutron stars are the most compact observed stars. Their average density exceeds that found inside the heaviest atomic nuclei. Neutron stars are also endowed with the highest magnetic fields known, which can reach millions of billion times that of the Earth. According to our current understanding, a neutron star is stratified into distinct layers. The surface is probably covered by a metallic ocean. The solid layers beneath consist of a crystal lattice of pressure-ionized atoms embedded in a highly degenerate relativistic electron gas. With increasing density, nuclei become progressively more neutron rich until neutrons start to drip out of nuclei thus delimiting the boundary between the outer and inner regions of the crust, where neutron-proton clusters are immersed in a neutron liquid. At about half the density of heavy nuclei, the crust dissolves into a homogeneous liquid mixture of nucleons and leptons. Over the past years, we have developed a series of unified equations of state of dense matter in neutron stars, available on the European CompOSE database. Based on the nuclear energy-density functional theory, these equations of state provide a thermodynamically consistent treatment of all regions of the star and were calculated using functionals that were precision fitted to experimental and theoretical nuclear data. These equations of state were specifically developed to assess the role of nuclear uncertainties on neutron-star properties. Predictions will be compared to constraints inferred from the detection of the gravitational-wave signal GW170817 from a binary neutron-star merger and from observations of the electromagnetic counterparts. Constraints inferred from other observations will be also discussed.

Speaker: Prof. Nicolas Chamel (Univ. Libre de Bruxelles)

talk_chamel.pdf

12:00 PM Hybrid stars with sharp interfaces: conditions for their existence and observational identification.

Abstract: Hybrid stars containing a quark matter core and a hadronic mantle may contain a sharp interface if the surface tension of dense matter is sufficiently high. When such a star is perturbed, conversion reactions may occur around the quark-hadron splitting surface. We show that the reaction speed has strong effects on the quasinormal mode spectrum and on stellar stability. In particular, if the conversion timescale is much larger than the perturbation one (slow reactions), changes of stellar stability do occur at critical points of the M(R) curve. As a consequence, a new class of dynamically stable hybrid stars is possible. We show that densities tens of times larger than the nuclear saturation density could be attained at the center of these hypothetic objects. We discuss possible formation mechanisms for the new class of hybrid configurations and smoking guns for their observational identification.

Speaker: Germán Lugones (Universidade Federal do ABC)

LUGONES.pdf

12:30 PM Quantum Simulation of Nuclear Many Body Systems

In this presentation I will talk about the prospects of using quantum computing for the simulation of nuclear many-problems. Thanks to the rapid growth of quantum platforms it is already possible to test some simulation schemes on small scale and I will show some recent results obtained for a simple model of light nuclei. I will conclude with a perspective on what we could expect quantum simulations can bring to the study of the nuclear equation of state and the properties of neutron-star matter.

Speaker: Alessandro Roggero (University of Trento)

slides_madrid_roggero.pdf

1:00 PM → 2:30 PM Lunch

2:30 PM → 4:30 PM Conference presentations

Convener: José Antonio Oller (Universidad de Murcia)

2:30 PM Free discussion on STRONG 2020 results, facilities, new research lines...

3:00 PM Equations of state for hot neutron stars

Studies of explosive astrophysical systems as core-collapse supernovae and binary neutron star mergers require equations of state (EOS) covering wide domains of baryon number density 10^{-14} fm^{-3} ≤ n_B ≤ 1.5 fm^{-3} , temperature 0 ≤ T ≤ 100 MeV and electron fraction 0 ≤ Y_e=n_e /n_B ≤ 0.6. Advances in this field during the last decade make that about 100 such EOS are presently available on the CompOSE database (https://compose.obspm.fr/), out of which 35 account for exotic degrees of freedom.

In the present talk we shall investigate the thermal properties (thermal energy density and pressure; thermal and adiabatic index; specific heat at constant volume and at constant pressure; entropy per baryon; speed of sound) of some of these models. Comparison between predictions of these models allows to identify the model-dependence of the finite temperature behavior; consequences of nucleation of exotic species; artifacts connected to the way in which the hadron to quark phase transition was dealt with; the role of Landau/Dirac effective masses.

The so-called Gamma-law, commonly used to supplement cold EOS with a thermal component, is found not to provide a reliable solution of the thermal behavior.

Finally, we shall discuss properties of hot stars, where profiles of entropy per baryon and electron fraction are inspired from proto-neutron star evolution.

Speaker: Adriana R. Raduta (IFIN-HH, Bucharest)

Raduta_Alcala2022.pdf

3:30 PM Neutron star M-R measurements and their impact on the equation of state.

This talk is a compact up-to-date review of astrophysical neutron star mass-radius measurements and a discussion of their relevance for the nuclear equation of state physics.

Speaker: Kostas Glampedakis (Universidad de Murcia)

Glampedakis_Alcala_2022.pdf

4:00 PM Neutron star equations of state for modify gravity studies

We provide equations of state (EoS) for matter at attainable densities in physical neutron stars at zero and finite temperature. These EoS are derived from current knowledge of the uncertainty bands of chiral effective field theories and pQCD constraints. The results are independent of neutron star observations and can be used to test general relativity as well as theories beyond GR, such as modified gravity. We show some results and their application to calculate the specific latent heat in a first-order phase transition. In addition, we use the EoS band to solve the Tolman-Oppenheimer-Volkoff (TOV) equations in GR and Palatiny f(R) gravity.

Speaker: Eva Lope Oter (Universidad Complutense de Madrid)

Workshop_Alcala_Lope.pdf

4:30 PM → 5:00 PM Coffee Break

5:00 PM → 7:00 PM Tour of Alcalá de Henares

Thu, September 22

9:00 AM → 11:00 AM Conference presentations

Convener: Laura Tolos

9:00 AM The low temperature phase diagram of heavy QCD

Lattice QCD with heavy dynamical quarks reduces to a three-dimensional effective theory of Polyakov loops, after truncated character and strong coupling expansions. This effective theory has a substantially milder sign problem than full QCD, and can either be simulated or treated successfully by analytical methods. This allows for investigations of the heavy QCD phase diagram as a function of temperature and chemical potentials, both for baryon number and isospin. At low temperatures, the expected first-order transition to baryon matter (in $\mu_B$-direction) and the second-order transition to a pion condensate (in $\mu_I$-direction) can be clearly identified. A $(T,\mu_B,\mu_I)$ phase diagram up to nuclear density is presented, based entirely on lattice QCD, and the prospects to reach smaller quark masses are discussed.

Speaker: Owe Philipsen

1_Philipsen.pdf

9:30 AM Equations of State for Dense Matter

Due to the present large uncertainty in the composition and interactions of dense nuclear matter, there are many different equation of state (EoS) models that can fulfill nuclear and astrophysical constraints. EoS repositories allow for a fast exchange of EoS between providers and simulation users, accelerating our understanding of dense matter. I discuss different EoS repositories, focusing on the MUSES infrastructure, and different EoSs, focusing on the CMF model.

Speaker: Veronica Dexheimer (Kent State University)

Equations of State for Dense Matter

10:00 AM Clusters, heavy baryons and strong magnetic fields in neutron star matter

Light (e.g. deuterons, tritons, helions, $\alpha-$particles), and heavy (pasta phases) nuclei exist in nature in core-collapse supernova matter and neutron star (NS) mergers, where temperatures of the order of 50 to 100 MeV may be attained. The appearance of these clusters can modify the neutrino transport, and, therefore, consequences on the dynamical evolution of supernovae and on the cooling of proto-neutron stars are expected. However, a correct estimation of their abundance implies that an in-medium modification of their binding energies is precisely derived. At such high temperatures, other exotic degrees of freedom, such as hyperons and $\Delta-$isobars, may appear.
Magnetars, mainly Soft Gamma Repeaters (SGRs) and Anomalous X-ray Pulsars (AXPs), belong to a kind of neutron stars with very strong magnetic fields at the surface, up to $10^{14} \sim 10^{15}$ G, and quite long spin periods, of the order of $2 \sim 20$ s. Nowadays, about thirty of such objects have been observed. Moreover, magnetars are good candidates to be a source of continuous gravitational wave emission, and we expect that in the future it will be possible to detect this type of gravitational waves.

In this talk, we will address not only from the theoretical point of view how these clusters and heavy baryons are calculated for warm stellar matter in the framework of relativistic mean-field (RMF) models with in-medium effects, but also how these models are calibrated to experimental data from heavy-ion collisions, measured by the INDRA Collaboration. We show that this in-medium correction, which was not considered in previous analyses from heavy-ion collisions, is necessary, since the observables of the analyzed systems show strong deviations from the expected results for an ideal gas of free clusters. It turns out that the resulting light cluster abundances come out to be in reasonable agreement with constraints at higher density coming from heavy ion collision data.
We are also going to consider nuclear matter in the NS inner crust under the presence of strong magnetic fields within the same RMF framework, and we will show that these strong fields cause an extension of the NS inner crust, with the occurrence of a series of disconnected non-homogeneous matter regions above the one existing for a null magnetic field. The existence of these extra non-homogeneous matter geometries could have a direct effect on the explanation of the magnetic field evolution inside NS.

Speaker: Helena Pais (University of Coimbra)

3_Pais.pdf

10:30 AM Inhomogeneous phases in the QCD phase diagram

For a few decades now, the possibility of spatially inhomogeneous crystalline phases in the QCD phase diagram has been investigated. Studies based on models of QCD such as NJL or quark-meson models do show such phases, however, no unambiguous confirmation that they happen in QCD has been achieved yet. In this talk, I will review the current state of the search for inhomogeneities and discuss the first attempts to perform a QCD-based stability analysis of such phases.

Speaker: Theo Motta (Justus Leibig University Gießen)

4_Motta.pdf

11:00 AM → 11:30 AM Coffee break

11:30 AM → 1:00 PM Conference presentations

Convener: José Manuel Alarcón (Universidad de Alcalá)

11:30 AM Hyperons and neutron stars

We will review the present status of the role played by hyperons in determining the properties of neutron and proto-neutron stars. In particular, we review the so-called “hyperon puzzle”, i.e., the problem of strong softening of the equation of state of dense matter due to the presence of hyperons which leads to maximum masses of compact stars that are not compatible with the recent observations
of about 2 solar mass millisecond pulsars. We discuss some of the solutions that were proposed to tackle this problem. We also re-examine the influence of hyperons on the cooling of newly born neutron stars as well as on the development of the r-mode instability. We discuss also the effecy of hyperons on transport properties including the thermal conductivity, the shear viscosity and the momentum transfer rates.

Speaker: Isaac Vidana ( Istituto Nazionale di Fisica Nucleare )

5_Vidana.pdf

12:00 PM Effective-field-theory-inspired energy density functionals for an improved description of neutron star matter

Phenomenological models which make use of energy density functionals (EDFs) represent the reference choice nowadays for an unified treatment of the neutron star matter Equation of State. Nevertheless, the empirical character reduces the predictive power of these approaches, when applied beyond the domain on which they have been determined.

As a common drawback, for example, phenomenological EDFs usually adopted in astrophysical simulations do not reproduce the behavior of pure neutron matter in the very dilute regime, where the well-known Lee-Yang expansion, properly described by construction within effective-field-theory (EFT), is known to hold at zero temperature.

In the last years, several attempts have been made to bridge modern analyses performed through ab-initio methods with the nuclear EDF theory, with the goal of rendering EDF approaches less empirical and reducing uncertainties in their construction. In particular, a new class of EDFs, built on completely microscopic ingredients and benchmarked on ab-initio EFT-based predictions, have recently been formulated and applied to study both nuclear matter and finite nuclei.

The main goal of this contribution is to give an overview of the main features of the new class of EDFs. The possibility of using these EFT-inspired functionals for describing also finite-temperature properties of neutron matter is in particular opening new and promising horizons for computations and modeling in various scenarios of astrophysical interest.

Speaker: Stefano Burrello (Institut für Kernphysik, Technische Universität Darmstadt, Germany)

6_Burrello.pdf

1:00 PM → 2:30 PM Lunch

2:30 PM → 4:30 PM Conference presentations

Convener: Laura Tolos

2:30 PM Free discussion on STRONG 2020 results, facilities, new research lines...

3:00 PM STRONG 2020 talk: Negative-parity strange baryons

A quick overview of the spectroscopy of negative-parity Lambda resonances.

Speaker: Juan Nieves (IFIC Valencia)

7_Nieves.pdf

3:30 PM NSCool 2D Rot: cooling of rapidly rotating neutron stars in 2D

We present one of the first results obtained with NSCool 2D Rot, a major upgrade of 1D neutron stars thermal evolution code NSCool by D. Page. Our new code allows to model thermal evolution of axisymmetric rotating neutron stars with arbitrary rotation frequencies up to the mass shedding limit in full general relativity. As an application, we address the question of cooling of rapidly rotating isolated neutron stars. We study the impact of equation of state (EOS) on the cooling by considering different EOSs of the core and crust. Simulation results show complex time-dependent dynamics of temperature distribution in the crust of the star. Nevertheless, we demonstrate that most of that complexity can be explained by formation of a ``heat blob'' in the crust and by timescales of heat diffusion through the crust.

Speaker: Dr Mikhail Beznogov (National Institute for Physics and Nuclear Engineering (IFIN-HH))

8_Beznogov.pdf

4:00 PM Renormalized resummation of particle-particle and hole-hole ladder diagrams for the energy density of 1/2 fermion many-body systems

We resum the ladder diagrams for the calculation of the energy per particle E/A of a spin 1/2 fermion many-body system in terms of any given vacuum two-body scattering amplitudes. The partial-wave decomposition of the in-medium two-body scattering amplitudes is worked out, and the expression for calculating E/A in a partial-wave amplitude expansion is also given. The case of contact interactions is completely solved for any number of partial waves and it is shown to provide renormalized results, expressed directly in terms of scattering data parameters, within a generic cutoff regularization schemes. We first discuss the case of including S- and P-wave interactions characterized by the first three-terms in the effective-range expansion, paying special attention to the parametric region around the unitary limit. This scheme is applied to study the resulting equation of state for neutron and symmetric nuclear matter, specially suited for low density.

Speaker: Prof. José Antonio Oller (Universidad de Murcia)

9_Oller.pdf

4:30 PM → 5:00 PM Coffee break

5:00 PM → 6:30 PM Conference presentations

Convener: Felipe J. Llanes-Estrada (Universidad Complutense de Madrid)

5:00 PM Deconfined QCD matter in superdense stars

In recent years it has become clear that in order to correctly interpret the many observables obtained for neutron stars (NS) such as their masses, radii and tidal deformabilities, one needs a better understanding of its equation of state at baryon densities of around 5 times the nuclear saturation density where a phase transition between hadronic and quark matter is also possible having characteristic thermodynamic properties. From a first-principle viewpoint, this represents a difficult task since most of the required central stellar densities immediately probe the nonperturbative sector of quantum chromodynamics (QCD) for which even today lattice QCD calculations are forbidden. Nevertheless, one can still resort to use ab initio results for the quark phase, in particular, cold and dense perturbative QCD, and study the non-trivial effects of short-range QCD interactions on superdense stars. In this talk I will discuss this impact on the structure and stability of several compact stars where interacting deconfined QCD matter might be present such as protoneutron stars, strange/charm stars, and hybrid NS with crossovers and discontinuous transitions for which in the latter case twin stars are also briefly discussed. Finally, I will present results for which instead of using general relativity and the standard model of particle physics when modeling quark stars, we now consider modified theories of gravity as well as adding the dark matter possibility, respectively.

Speaker: José C. Jiménez (University of São Paulo)

10_Jiménez.pdf

5:30 PM Crystallization of isolated and acrreting Neutron Star crusts

We perform microscopic Molecular Dynamics simulations to study crystallization energetics in the outer crust of Neutron Stars (NSs). We consider the approximation of one component plasma (OCP) and multicomponent plasma (MCP) to take into account contamination for accreting objects. We include Ewald summation techniques for screened interactions to allow a more efficient energy calculation and go beyond previous point-like attemps by using a finite width gaussian ion charge distribution and finite temperature. Our results indicate the crust is less energetically stable under the more realistic picture.

Speaker: David Barba González (Univ. of Salamanca)

11_Barba.pptm

6:00 PM Discussion on written proceedings and recommendations

Fri, September 23

10:30 AM → 11:00 AM Free discussion

11:00 AM → 11:30 AM Coffee

11:30 AM → 1:00 PM Conference presentations

Convener: José Antonio Oller (Universidad de Murcia)

11:30 AM NICER view on holographic QCD

Holographic techniques are particularly fit to analyzing matter at extreme conditions where QCD matter is strongly coupled. Combining predictions of the holographic model with state-of-the-art effective field theory models of nuclear matter, I construct a family of feasible “hybrid” equations of state which cover both the quark matter and nuclear matter phases. The model predicts, among other things, that the NICER’s radius measurement is fully consistent with the absence of quark matter inside massive neutron stars. I also briefly overview some results that holography has achieved on general level as well as discuss how I foresee holography contributing to compact-star physics in the coming years.

Speaker: Niko Jokela (University of Helsinki)

Jokela_Alcala_2022.pdf

12:00 PM Holographic approach to transport in dense QCD matter

The transport properties of dense QCD matter play a crucial role in the physics of neutron stars and their mergers, but are notoriously difficult to study with traditional quantum field theory tools. Specializing to the case of unpaired quark matter in beta equilibrium, we approach the problem through the machinery of holography, and derive results for the electrical and thermal conductivities and the shear and bulk viscosities. Our results differ dramatically from earlier predictions of perturbative QCD, the root causes and implications of which we analyze in detail.

Speaker: Carlos Hoyos (Universidad de Oviedo)

TransportNS.pdf

12:30 PM Early quark deconfinement in compact star astrophysics, supernovae explosions and neutron star mergers

We outline the role that an early deconfinement phase transition from normal nuclear matter to a color superconducting quark-gluon plasma phase plays for the phenomenology of supernova explosions and binary neutron star mergers. To this end we extend the compact star equation of state (EoS) from vanishing to moderately high temperatures that become accessible in the CBM experiment at FAIR. We study the connection of such hybrid EoS with the mass-radius relation of cold compact stars, including the intriguing possibility of additional families, as a consequence of the presence of an early and strong phase transition. Special emphasis is devoted to the simultaneous fulfillment of the new NICER mass and radius constraint from PSR J0740+6620 and the tidal deformability constraint from GW170817 which require the EoS to be soft at about twice saturation density and then to stiffen. Such a pattern is provided by an early and strong deconfinement transition.
Dynamical scenarios are being considered, such as binary compact star mergers including the subsequent emission of gravitational waves and supernova explosions of massive supergiant stars where neutrinos play the role of messengers.

Speaker: Oleksii Ivanytskyi (University of Wroclaw)

3_Ivanytskyi.pdf

1:00 PM → 2:30 PM Lunch

2:30 PM → 4:00 PM Conference presentations

Convener: Felipe J. Llanes-Estrada (Universidad Complutense de Madrid)

2:30 PM The Einstein Telescope Project

I present the details of the Einstein Telescope Project (ET), its current design, its scientific goals and the first steps towards the definition of the ET Collaboration and its model for governance. Special emphasis is put in aspects related to the Spanish contributions and
the opportunities for scientific and industrial engagement.

Speaker: Mario Martinez (ICREA/IFAE-Barcelona)

Madrid_Alcala_3G_GW.pdf

3:00 PM How accumulated dark matter in compact stars may affect the constraints we put on strongly interacting matter at high densities

We study the impact of asymmetric fermionic and bosonic dark matter on neutron star properties, including tidal deformability, maximum masses, radii, etc. The conditions at which dark matter particles tend to condensate in the core of the star or create an extended halo are presented. We show that dark matter condensed in a core leads to a decrease of the total gravitational mass and tidal deformability compared to a pure baryonic star, which we will perceive as an effective softening of the equation of state. On the other hand, the presence of a dark matter halo increases those observable quantities. Thus, observational data on compact stars could be affected by accumulated dark matter and, consequently, constraints we put on strongly interacting matter at high densities. We will discuss how the ongoing and future X-ray, radio and GW observations could shed light on dark matter admixed compact stars and put multi-messenger constraints on its effect.

Speaker: Edoardo Giangrandi (CFisUC, University of Coimbra)

5_Giangrandi.pdf

4:00 PM → 4:30 PM Coffee Break

4:30 PM → 5:30 PM Conference presentations

Convener: Laura Tolos

4:30 PM Nearly model independent constraints on dense matter equation of state in a Bayesian approach

We apply Bayesian approach to construct a large number of minimally constrained equations of state (EoSs) and study their correlations with a few selected properties of a neutron star (NS). Our set of minimal constraints includes a few basic properties of saturated nuclear matter and low density pure neutron
matter EoS which is obtained from a precise next-to-next-to-next-to-leading order (N$^{3}$LO) calculation in
chiral effective field theory. The tidal deformability and radius of NS with mass $1-2 M_\odot$ are found to be strongly correlated with the pressure of $\beta$-equilibrated matter at densities higher than the saturation density ($\rho_0 = 0.16$ fm$^{-3}$) in a nearly model-independent manner. These correlations are employed to parameterize the pressure for $\beta$-equilibrated matter, around 2$\rho_0$, as a function of neutron star mass and the corresponding tidal deformability. The maximum mass of a neutron star is also found to be strongly correlated with the pressure of $\beta$-equilibrated matter at densities $\sim 4.5\rho_0$.

Speaker: Naresh Kumar Patra (BITS Pilani K K Birla Goa Campus, NH-B, South Goa, Goa, Pin-757040)

5:00 PM Bayesian constraints on the neutron-star equation of state with QCD input

At asymptotically high densities, the neutron-star-matter equation of state (EOS) must approach the EOS of beta-equilibrated QCD matter, as calculated directly within the fundamental QCD theory. This nontrivial constraint at high density, pressure, and chemical potential impacts the inference of the neutron-star-matter EOS at even lower densities. In this talk, I show within a Bayesian approach how this constraint drives the densest matter in the cores of massive neutron stars towards thermodynamic properties consistent with quark matter, even after current astrophysical observations are included in the analysis.

Speaker: Tyler Gorda (TU Darmstadt)

6_Gorda.pdf