The MUSES Seminar Series is a great opportunity to learn about the physics and computer science involved in the MUSES project and to meet the people driving the research. To receive email notifications with information about upcoming seminars, please complete the seminar registration form here đ .

# Spring 2024

## Inhomogeneous Phases in QCD

### Theo Motta

2024/04/15 — 4 p.m. CT

**Abstract**: At high chemical potentials and low temperatures, a plethora of different phases have been speculated to exist in the QCD phase diagram. Naturally, due to the sign problem, first-principle lattice calculations are not feasible. However, several QCD-inspired models point to the possibility of a crystalline phase in this region. In this talk, I will briefly summarise some of such model results and discuss our efforts to verify whether or not these phases exist in QCD via Dyson-Schwinger Equations.

## Needle in a Bayes Stack: a Hierarchical Bayesian Model for Equation of State Constraints from Subthreshold Post-merger Gravitational Waves

### Alexander Criswell

2024/04/01 — 4 p.m. CT

**Abstract**: Binary neutron star (BNS) post-merger gravitational-wave emission is expected to be produced by the unstable hypermassive remnants of most BNS mergers. The post-merger gravitational-wave spectrum possesses a characteristic peak frequency that has been shown to be dependent on both the binary chirp mass and the neutron star equation of state (EoS), rendering post-merger gravitational waves a powerful tool for constraining neutron star composition. Unfortunately, individual BNS post-merger signals are unlikely to be confidently detected until the advent of next-generation detectors. However, it may be possible to infer collective information about the EoS from an ensemble of subthreshold post-merger signals by leveraging the connections between them and their respective inspiral detections. I present a hierarchical Bayesian method for deriving EoS constraints through an ensemble analysis of subthreshold BNS post-merger signals and discuss the prospects of this analysis as applied to simulations of BNS observations with current-generation gravitational wave detectors.

## Constraining Nuclear Parameters Using Gravitational Waves from f-mode Oscillations in Neutron Stars

### Debarati Chatterjee

2024/03/18 — 4 p.m. CT

**Abstract**: Unstable oscillation modes in Neutron Stars can be important sources of Gravitational waves. In particular, the fundamental f-modes could be detectable with the improved sensitivity band of the current generation of GW detectors or with the future generation detectors. These mode characteristics are sensitive to the neutron star internal composition. In a series of recently published works, we performed systematic investigations of gravitational wave emission via f-modes within the relativistic mean field model framework. We identified the important nuclear empirical parameters that are strongly correlated with the mode characteristics, both in Cowling approximation and full general relativistic formalism. We then constructed improved universal relations and demonstrated how they can be applied in neutron star asteroseismology to constrain the equation of state from f-mode observations. We also investigated the effect of the equation of state on dynamical tides in f-modes, and the bias that would result from ignoring their effect in inferring nuclear properties from f-modes in binary neutron stars. We also showed how tidal heating from high bulk viscous dissipation of the dynamical fâmode excitations during binary inspirals can indicate the presence of strangeness in the interior of neutron stars.

## Thermodynamic properties and phase diagram of quark matter within Polyakov chiral SU (3) quark mean field model

### Arvind Kumar

2024/03/04 — 4 p.m. CT

**Abstract**: In this talk, I will present our work on the thermodynamic properties and phase diagram of quark matter using Polyakov chiral SU(3) quark mean field (PCQMF) model. In the PCQMF model, the properties of the quark matter are modified through the scalar fields $\sigma, \zeta, \delta, \chi$, the vector fields $\omega, \rho$, $\phi$, and the Polyakov fields $\Phi$ and $\bar{\Phi}$ at finite temperature and chemical potential. I will discuss the impact of (i) finite volume (ii) finite magnetic field (iii) and consideration of non-extensive statistics on various thermodynamic properties such as pressure, energy, and entropy density as well as the trace anomaly. The impact of these different scenarios on the deconfinement phase transition as well as the chiral phase transition of $u, d,$ and $s$ quarks will also be discussed.

## Assessing equation of state-independent relations for neutron stars with non-parametric models

### Isaac Legred

2024/02/19 — 4 p.m. CT

**Abstract**: Despite the large sensitivity of neutron star structure to the dense-matter equation of state, relations between certain neutron-star properties appear to be nearly equation-of-state independent. These equation-of-state independent relations (sometimes called universal relations) can substantially simplify the analysis of neutron stars, if they are reliable. In this talk I will discuss a strategy for quantifying equation-of-state independence for relations with respect to measurability of neutron-star observables. Using this strategy, we evaluate the EoS-independence of several relations under an array of distributions on the equation of state, including a flexible, model-agnostic distribution based on Gaussian processes. We find that while certain relations, such as the so-called âI-Love-Qâ relations, are robust and will likely be useful even for analyzing next generation neutron-star observations, others may introduce systematic errors even with current sensitivities.

## Searching for the QCD critical point using Lee-Yang edge singularities

### David A. Clarke

2024/02/05 — 4 p.m. CT

**Abstract**: Using 2+1 flavors QCD calculations at physical quark mass and purely imaginary baryon chemical potential, we locate Lee-Yang edge singularities in the complex chemical potential plane. These singularities have been obtained by the multi-point PadĂ© approach applied to the net baryon number density. We recently showed that singularities extracted with this approach are consistent with the correct universal scaling near the Roberge-Weiss transition. Here we study the universal scaling of these singularities in the vicinity of the QCD critical endpoint. Making use of an appropriate scaling ansatz, we extrapolate these singularities on 6 and 8 lattices towards the real axis to estimate the position of a possible QCD critical point. We find an apparent approach toward the real axis with decreasing temperature.

## Nonequilibrium effects on stability of compact stars with first-order phase transitions

### Peter Rau

2024/01/22 — 4 p.m. CT

**Abstract**: Constraining the dense matter equation of state (EOS), including the nature of its phase transitions, is a fundamental goal of nuclear physics and neutron star astrophysics. To this end, we consider the effects of out-of-chemical-equilibrium physics at first-order phase transitions on the radial modes and hence stability of compact stars. For barotropic EOS, this is done by allowing the adiabatic sound speed to differ from the equilibrium sound speed. We show that doing so extends the stable branches of stellar models, allowing stars with rapid phase transitions to support stable higher-order stellar multiplets similarly to stars with multiple slow phase transitions. For non-barotropic EOS, we derive a new junction condition to impose on the oscillation modes at the phase transitions. This âreactiveâ condition is consistent with the generalized junction conditions between two phases and has the common rapid and slow conditions as limiting cases. We apply this junction condition to hybrid stellar models and show that like in the slow limiting case, stars that are unstable according to the standard Bardeen-Thorne-Meltzer criterion are stabilized by a finite chemical reaction speed.

# Fall 2023

## The neutron star non-homogenous EoS: description and effects

### Constanca Providencia

2023/12/04 — 9 a.m. CT

**Abstract**: The determination of the crust-core transition is discussed within different approaches. The inner crust is calculated and some properties are discussed. The effect of not considering a unified equation of state on the determination of the radius and tidal deformability of low-mass stars is discussed. The effect of temperature and magnetic field on the inhomogeneous EoS is referred. The inclusion of light clusters in the finite temperature EoS will be presented. I will use the relativistic mean field description of nuclear matter throughout the talk.

## Fluid-dynamic approach to heavy quarks in the QGP

### Federica Capellino

2023/11/20 — 9 a.m. CT

**Abstract**: Heavy-ion collision experiments allow us to study nuclear matter under extreme conditions. At these high temperatures, quarks and gluons exist in a deconfined phase, which we call quark-gluon plasma (QGP). Among all particles produced in the collision, heavy quarks (i.e. charm and beauty) play a special role: they experience all the stages of the expanding system and thus are powerful tools to study the transport properties of the plasma. Although they are initially produced out of kinetic equilibrium via hard partonic scattering processes, recent measurements of anisotropic flow of charmed hadrons pose the question regarding the possible thermalization of heavy quarks in the medium. In this talk I will give an overview of experimental and theoretical results of heavy flavors that motivate a fluid-dynamic description of heavy quarks in the QGP.

## Dense QCD with effective models: a Bayesian approach

### Antoine Pfaff

2023/11/06 — 9 a.m. CT

**Abstract**: Our understanding of matter inside neutron stars relies on our ability to describe QCD at finite density and (close to) zero temperature, which remains both an experimental and theoretical challenge to this day. One possibility to tackle this problem is to rely on effective approaches that try to extrapolate from known properties of QCD (asymptotic freedom, flavor symmetries, lQCD, âŠ) and low-energy nuclear physics (chiral perturbation theory, mass and phase shift measurements, âŠ) to build a viable and credible equation of state. These types of models are crucial to investigate on the occurrence of a deconfinement phase transition in neutron star cores. In the past decade, multi-messenger astronomy has also become a major asset to constrain the equation of state, and will become more decisive in the coming years as the sensitivities of the detectors are improved. In this talk, I will present two different approaches that have been suggested to model a possible deconfinement in the context of dense matter, based respectively on the NambuâJona-Lasinio model and the quarkyonic hypothesis. I will then discuss how we can use the Bayesian method to take into account consistently measurements of compact star observables and help to decide whether or not quark matter can appear in neutron star cores.

## QCD in the core of neutron stars

### Oleg Komoltsev

2023/10/23 — 9 a.m. CT

**Abstract**: Rapid advancement in neutron-star observations allows unprecedented empirical access to cold, ultra-dense QCD matter. The combination of these observations with theoretical calculations reveals previously inaccessible features of the equation of state (EOS) and the phase diagram of QCD. In this talk, I demonstrate how perturbative-QCD calculations at asymptotically high densities based solely on causality and stability provides robust constraints on the EOS of QCD at neutron-star densities. By comparing the calculations to neutron-star observations using a Bayesian framework, I show that perturbative-QCD calculations offer significant information beyond current observations. QCD input softens the equation of state at high densities. The results support the hypothesis of quark matter cores in the most massive neutron stars.

## Nuclear pasta in Neutron Stars

### Mateus Reinke Pelicer

2023/09/25 — 4 p.m. CT

**Abstract**: In the inner crust of neutron stars, we expect that anisotropic nuclei appear due to the competition between nuclear and electric forces. These are called pasta phase due to its resemblance to spaghetti and lasagna. The existence of this phase of nuclear matter can directly impact several macroscopic properties of the star, such as its cooling, magnetic field evolution and gravitational wave emission. In this colloquium, I will discuss some basic properties of the pasta and how we calculate them in a relativistic mean field model. Then, I will talk about how the presence of charge impurities may be important for some macroscopic properties of the star, and about its electric conductivity.

## Simulations of baryon and electric charge stopping in isobar collisions

### Gregoire Pihan

2023/09/11 — 4 p.m. CT

**Abstract**: It is a fundamental question to understand what is the effective carrier of conserved quantum charges inside a proton at high energy. The net baryon and electric charge rapidity distributions in relativistic heavy-ion collisions can elucidate how different conserved charges are transported along the longitudinal direction during the collision. Recent preliminary measurements in isobar collisions at the Relativistic Heavy Ion Collider (RHIC) show that the scaled net-baryon to net-electric charge number ratio at midrapidity ($ B/\Delta_Q * \Delta Z /A$) is between 1.2 and 2, in line with predictions from the string junction model. This measurement is compatible with the picture where the baryon number is carried by gluon junctions. In this work, we develop a comprehensive (3+1)D relativistic hydrodynamic framework with multiple conserved charge currents. We employ the 3D MC-Glauber model for the initial conditions, which allows for modeling baryon stopping separately from electric charge stopping within the string junction picture. Simulating the coupled propagation of net baryon and electric charge currents including the charge-dependent lattice-QCD-based equation of state, we study how net baryon and electric charges are evolved during different stages of heavy-ion collisions. We make predictions of net baryon and net electric charge rapidity distributions for Ru+Ru and Zr+Zr collisions at $ \sqrt{s_{NN} = 200}$ GeV, which can be compared with STAR measurements.

# Spring 2023

## Dynamical properties of the QGP matter at finite temperatures and chemical potentials

### Olga Soloveva

2023/05/08 — 9 a.m. CT

**Abstract**: In this seminar we will discuss latest results on the dynamical properties of QGP matter at finite temperature and chemical potential obtained within the framework of kinetic theory and various effective models. Moreover, Machine Learning techniques, in particular Deep Neural Networks, have been applied to improve phenomenological model description of the QGP matter and gain insights on the possible parametrisation of strong coupling constant at finite temperature and baryon chemical potential. Finally we will discuss possible influence of the order of phase transition on the transport coefficients at finite temperature and chemical potential.

## The far from equilibrium search for the QCD critical point

### Travis Dore

2023/04/24 — 9 a.m. CT

**Abstract**: The conjectured QCD critical point in the nuclear matter phase diagram would be the point which separates the known crossover confinement transition at vanishing baryonic chemical potential from a first-order phase transition at higher chemical potential. Heavy-ion collisions at relatively low center of mass energies offer a way for us to search for signals of such a critical end point by exploiting the hydrodynamic description of the evolution of the nuclear matter and comparing directly with data. However, in order to unambiguously determine its existence, it is necessary to disentangle many different effects such as those driven by event-by-event fluctuations or more systematic uncertainties stemming from our incomplete knowledge of relevant physics. In particular, event-by-event fluctuations lead to a highly non-equilibrium initial state for the hot and dense nuclear matter and we also lack precise knowledge about the details of the critical point such as the precise size and shape of the critical region in the phase diagram. In this work we use a simple model to study the effects that different critical regions have on hydrodynamic trajectories both with and without non-equilibrium hydrodynamic effects. We argue that equilibrium hydrodynamic trajectories are a poor guide for studying more realistic evolution evidenced by large changes in thermal entropy within the system. Although initial viscous effects may push or pull trajectories towards or away from the critical point, there exists a dynamic lensing effect that may be able to focus many of these trajectories towards the critical region.

## The Nuclear Equation of State from Experiments and Astronomical Observations

### Rohit Kumar

2023/04/03 — 4 p.m. CT

**Abstract**: With recent advances in astronomical observations, major progress has been made in determining the pressure of neutron star matter at high density. This pressure is constrained by the neutron star deformability, determined from gravitational waves emitted in a neutron-star merger, and the mass-radius relation of two neutron stars, determined from a new X-ray observatory on the International Space Station. Previous studies have relied on nuclear theory calculations to constrain the equation of state at low density. In this work, we combined constraints composed of three astronomical observations and twelve nuclear experimental constraints that extend over a wide range of densities to obtain the nuclear equation of state. This data-centric result obtained using the Bayesian framework provides benchmarks for theoretical calculations and modeling of nuclear matter and neutron stars. Furthermore, it provides insights into the microscopic degrees of freedom of the nuclear matter equation of state and on the composition of neutron stars and their cooling via neutrino radiation.

## Rapid stiffening and conformality in neutron star matter

### Yuki Fujimoto

2023/03/20 — 4 p.m. CT

**Abstract**: I shed a light on the nature of neutron star matter at high baryon density by using the trace anomaly as a measure of conformality. I discuss an interpretation that a peak in the sound velocity, as suggested by the neutron-star observational data, signifies strongly-correlated conformal matter. The normalized trace anomaly is a dimensionless measure of conformality leading to the derivative and the non-derivative contributions to the sound velocity. We find that the peak in the sound velocity is attributed to the derivative contribution from the trace anomaly that steeply approaches the conformal limit. Smooth continuity to the behavior of high-density QCD implies that the matter part of the trace anomaly may be positive definite. I discuss a possible implication of the positivity condition of the trace anomaly on the neutron star observation. Possible underlying mechanism of the rapid stiffening of the equation of state is also mentioned.

## Relativistic mean-field models with couplings and masses depending on the scalar field

### Konstantin Maslov

2023/03/06 — 9 am CT

**Abstract**:In this talk, I will discuss the relativistic mean-field (RMF) models with hadron masses and couplings dependent on the scalar field and the solution of the hyperon and Delta-isobar puzzles within this framework. I will introduce the “sigma-cut” method of making any RMF equation of state (EoS) stiffer at large densities without changing it at low density, which relies on introducing a non-linear increase into the potential of the scalar field. This limits the maximum possible value of the scalar mean field responsible for the attraction and stiffens the EoS as a result. A similar mechanism is incorporated into a model with the field dependence of meson couplings and hadron masses to build two families of realistic EoSs, different mainly by the density dependence of the symmetry energy. One of them, KVOR-based, relies on the sharp field dependence of the vector meson coupling to baryons, and the second class, MKVOR-based, employs a rapid field dependence of the isovector-meson coupling constants. Both of these families of EoSs are stiff enough at high densities to satisfy the NS maximum mass constraint with the inclusion of hyperons and Delta-isobars, and at the same time, they satisfy available constraints, including the flow constraint in the isospin-symmetric matter.

## Magnetic-Field Induced Deformation in Neutron Stars with Exotic Phases

### Ishfaq Ahmad Rather

2023/02/20 — 4pm CT

**Abstract**: In this talk, I will discuss the effects of strong magnetic fields on the hyperon matter and deconfinement phase transition expected to take place in the interior of massive neutron stars (NS). For hadronic matter, the very general density-dependent relativistic mean field model is employed, while the simple, but effective vector-enhanced bag model is used to study quark matter. Magnetic-field effects are incorporated into the matter equation of state and in the general-relativity solutions, which also satisfy Maxwellâs equations. Its observed that the magnetic fields stiffen the hyperonic equations of state and generate more massive neutron stars, which can satisfy the possible GW 190814 mass constraint but present a large deformation with respect to spherical symmetry. With the phase transition to the quark matter, for large values of magnetic dipole moment, the NS properties obtained for stars using spherically symmetric TolmanâOppenheimerâVolkoff (TOV) equations and axisymmetric solutions attained through the LORENE library differ considerably. The deviations depend on the stiffness of the equation of state and on the star mass being analyzed. This points to the fact that the magnetic field thresholds for the approximation of isotropic stars and the acceptable use of TOV equations depend on the matter composition and interactions.

## Semi-analytical trajectories of relativistic heavy ion collisions in the QCD phase diagram.

### Todd Mendenhall – East Carolina University

2023/02/06 — 4pm CT

**Abstract**: Discovering the hypothesized critical endpoint (CEP) of the first-order phase transition in the QCD phase diagram would be a significant step forward in our understanding of the behavior of sub-nuclear matter. Theoretical and computational studies aim to refine our understanding of the the QCD equation of state (EoS) which relates thermodynamic properties such as the temperature, baryon chemical potential, energy density, and net-baryon density. Recently, the estimates of the initial energy and net conserved-charge densities produced in relativistic nuclear collisions were improved by including the finite nuclear thickness in a semi-analytical model. In this talk, I will first discuss our semi-analytical model that includes the finite nuclear thickness to calculate the initial densities produced in central, relativistic Au+Au collisions. Next, I will compare several EoS and highlight our method of extracting the time evolution of the thermodynamic quantities. Then, I will present the trajectories extracted using various conditions, especially those which are relevant to heavy ion collisions. Finally, I will review the usefulness of our semi-analytical model for the ongoing search for the CEP and consider several directions for future work.

# Fall 2022

## Extending AMY viscosity calculations to finite baryon chemical potentials

### Isabella Danhoni

2022/12/05 — 4pm CT

**Abstract**: Transport coefficients, such as viscosity, can be calculated theoretically in weakly coupled quantum field theory, and present interesting information about hydrodynamic models of heavy-ion collisions. We present the results for shear viscosity calculations at leading-log in QCD in a regime of high baryon density, where the chemical potentials are greater than the temperature, which is a very unknown region of the QCD phase diagram. For that, we extend the results obtained by Arnold, Moore, and Yaffe. Such conditions of temperature and baryon density are found in medium-energy heavy-ion collisions and in the nuclei of neutron star mergers.

## Nuclear equation of state constrained by nuclear physics, microscopic and macroscopic collisions

### Sabrina Huth – Technische UniversitĂ€t Darmstadt

2022/11/22 — 9am CT

**Abstract**: Interpreting high-energy, astrophysical phenomena, such as supernova explosions or neutron-star collisions, requires a robust understanding of matter at supranuclear densities. We present new equations of state where the parameter range of the energy-density functional underlying the equation of state is constrained by chiral effective field theory as well as by functional renormalization group computations based on QCD. We implement observational constraints from measurements of heavy neutron stars, the gravitational wave signal of GW170817, and NICER results. Thermal effects are captured by a novel effective mass parametrization. This has been shown to determine the proto-neutron star contraction in supernova simulations. Additionally, we use Bayesian inference to combine data from astrophysical multi-messenger observations of neutron stars and from heavy-ion collisions with microscopic nuclear theory calculations to improve our understanding of dense matter. Our findings show that constraints from heavy-ion collision experiments show a remarkable consistency with multi-messenger observations and provide complementary information on nuclear matter at intermediate densities.

## The Bayesian Analysis of Nuclear Dynamics (BAND) Cyberinfrastructre Framework

### Daniel Phillips – Ohio University

2022/11/07

**Abstract**: Nuclear physicists seek an accurate description of the properties of atomic nuclei, collisions between nuclei, and extreme environments such as the first few seconds of our universe or the interior of a neutron star. These situations involve many particles interacting through complex forces. Theyâre each described by a number of different models: these typically do a good job of explaining the results of experiments that have already occurred. The models donât do as well predicting what will happen in future experiments or in environments that are inaccessible here on Earth.

## Finite density equation of state from lattice QCD: recent results from an alternative expansion

### Paolo Parotto – Pennsylvania State University and the University of Wuppertal

2022/10/24

**Abstract**: The determination of the equation of state of QCD at finite chemical potential from direct lattice simulations is hindered by the fermion sign problem. Extrapolations of different nature, from zero or imaginary chemical potentials, have been widely exploited to circumvent this issue. With a new resummation of the Taylor series, and the aid of simulations at imaginary chemical potential, we are now able to extrapolate the equation of state to chemical potentials up to \(\mu_B/T=3.5\). We do so both with and without enforcing the strangeness neutrality condition typical of heavy-ion collisions. In addition, we perform a first extrapolation beyond exact strangeness neutrality, constructing an expansion in the strangeness-to-baryon density ratio.

## Constraining the QCD critical point using active learning

### DĂ©bora Mroczek – University of Illinois at Urbana-Champaign

2022/09/26

**Abstract**: The Beam Energy Scan Theory (BEST) collaborationâs equation of state (EoS) incorporates a 3D Ising model critical point into the Quantum Chromodynamics (QCD) equation of state from lattice simulations [1]. However, it contains 4 free parameters related to the size and location of the critical region in the QCD phase diagram. Certain combinations of the free parameters lead to acausal or unstable realizations of the EoS that should not be considered. I will discuss how to use an active learning framework to rule out pathological EoS efficiently. We find that checking stability and causality for a small portion of the parametersâ range is sufficient to construct algorithms that perform with >96% accuracy across the entire parameter space. These findings support a preference for critical regions that allow for strong critical lensing effects in and out-of-equilibrium.

[1] Paolo Parotto, Marcus Bluhm, Debora Mroczek, Marlene Nahrgang, Jacquelyn Noronha-Hostler, Krishna Rajagopal, Claudia Ratti, Thomas Schaefer, and Mikhail Stephanov. QCD equation of state matched to lattice data and exhibiting a critical point singularity. Phys. Rev. C, 101(3):034901, 2020.

## Finding Structure in the Speed of Sound of Supranuclear Matter from Binary Love Relations

### Hung Tan – University of Illinois at Urbana-Champaign

2022/09/12

**Abstract**: Gravitational wave observation is a promising way of probing a neutron star core, which is an environment cannot be created through terrestrial experiments. However, the observables from current gravitational wave observations are degenerate. To break this degeneracy, one can rely on an equation of state insensitive relation called the binary Love relation. One might expect that the binary Love relation does not tell us much about equation of state because the relation is insensitive to it. We found that the relation actually contains information about equation of state, and future gravitational wave detectors are capable of extracting those information.

# Spring 2022

## Binary neutron star mergers likely contributed more to heavy elements production than neutron star-black hole mergers

### Hsin-Yu Chen – Massachusetts Institute of Technology

2022/05/16

**Abstract**: The origin of the heavy elements in the Universe is not fully determined. Neutron star-black hole and binary neutron star mergers may both produce heavy elements via rapid neutron-capture. In this talk, I will present how we used the detections of gravitational waves from mergers, improved measurements of the neutron star equation-of-state, and the numerical simulations of ejected material from binary collisions to measure the relative contribution of neutron star-black hole and binary neutron star mergers to the production of heavy elements. We found that in most scenarios, binary neutron star mergers have produced more heavy elements than neutron star-black hole mergers over the past 2.5 billion years.

## Temperature and Magnetic Field Effects in Astrophysical Equations of State

### Jeffrey Peterson – Kent State University

2022/05/02

**Abstract**: This talk will discuss the effects of simultaneously including temperature and magnetic field effects in the Equation of State (EOS) for compact stars, both for neutron stars and the simpler case of white dwarfs. Neutron star results are calculated using the Chiral Mean Field (CMF) model, while the white dwarf results are a simple Relativistic Free Fermi Gas (RFFG). We will discuss the QCD Lagrangian and the CMF approximation which results in the CMF Lagrangian, briefly state the thermodynamic quantities that come from the CMF and RFFG Lagrangians, and look at preliminary EOS results from the CMF code.

## Chiral effective field theory and the nuclear equation of state

### Christian Drischler – Michigan State University

2022/04/18

**Abstract**: Statistically robust comparisons between observational, experimental, and theoretical constraints on the nuclear equation of state (EOS) are crucial for obtaining a fundamental understanding of the structure and formation of neutron stars, heavy neutron-rich nuclei, and the underlying microscopic dynamics of strongly interacting nuclear matter. In this seminar, I will discuss recent advances in many-body perturbation theory calculations of the nuclear EOS using chiral two- and three-nucleon interactions. Furthermore, I will show how chiral effective field theory combined with Bayesian machine learning allows us to quantify theoretical uncertainties rigorously and guide the construction of the nuclear EOS across the wide range of densities, proton fractions, and temperatures relevant to nuclear (astro)physics.

## Transport in Neutron Star Mergers

### Alexander Haber – Washington University, St. Louis

2022/03/21

**Abstract**:
Transport properties of compact stars have been computed in the past mostly for the conditions in old, isolated, and therefore cold neutron stars. Gravitational wave observations of binary neutron star mergers allow us to examine dense matter in even denser, but more importantly significantly hotter matter. This requires a careful reexamination of transport properties of dense matter. In this talk I will present our work on nuclear bulk viscosity and Urca like processes in these environments.

## Lee-Yang Singularities, Series Expansions, and the Critical Point

### GĂ¶kĂ§e Basar – University of North Carolina, Chapel Hill

2022/02/21

**Abstract**: Determining the existence and the location of the QCD critical point remains a major open problem, both theoretically and experimentally. In this talk, I present a new way of reconstructing the equation of state in the vicinity of the nearest singularity (the Lee-Yang edge singularity in the crossover region) from a truncated Taylor series expansion for small \(\mu\). This is done by using a combination of Padâe resummation and conformal/uniformization maps. Then, I show that this information can be used to (i) determine the location of the critical point and (ii) constrain the non-universal mapping parameters between the Ising and QCD equations of state. I explicitly demonstrate these ideas in the 2d Gross-Neveu model whose phase diagram shares the key aspects of the conjectured QCD phase diagram including the existence of a critical point.

## Insights on the Peak in the Speed of Sound of Ultradense Matter

### Mauricio Hippert – University of Illinois at Urbana-Champaign

2022/02/07

**Abstract**:

Recent neutron-star observations indicate that ultradense matter must be stiffer than previously thought, with the speed of sound potentially rising well above its asymptotic conformal limit of \(\sqrt{1/3}\). In this work, we address the general physics requirements needed for generating a speed of sound that surpasses its asymptotic conformal limit, and propose a generic mechanism to explain this feature. We build a minimal model realization of this mechanism, based on the spontaneous breakdown of an approximate particle-antiparticle symmetry, and determine its thermodynamic properties.

## Quark-Hadron Continuity equations of state

### Toru Kojo – Key Laboratory of Quark and Lepton Physics (MOE) and Institute of Particle Physics, Central China Normal University, Wuhan

2022/01/24

**Abstract**:

I discuss equations of state with quark-hadron continuity which give us useful baselines to delineate neutron star observations. Following the continuity idea, we choose the effective interactions motivated by the physics inside of hadrons. The peak in sound velocity is derived by treating hadrons as composites of quarks. The baryon density at the peak is sensitive to the tails in quark wavefunctions, while the peak should appear at a density lower than estimated from the overlap of baryon hard cores. The relation to quarkyonic matter models is also discussed.

# Fall 2021

## Equations of state for hot neutron stars

### Adriana R. Raduta – IFIN-HH Bucharest

2021/12/13

**Abstract**: In the last decades the EoS of cold NS has been intensively studied and constrained by experimental nuclear physics data, astrophysical data from radio/X-ray pulsars, gravitational wave events, and ab initio calculations of (neutron) matter. The different data are complementary in the sense that the conditions of each measurement imply that constraints on the EoS can be obtained within a particular density and isospin asymmetry domain. Dynamics of core-collapse supernovae, evolution of proto-neutron stars, formation of stellar black holes, and the post-merger phase of binary neutron star mergers require an EoS depending on three thermodynamic parameters, typically chosen as temperature, baryon number density, and electron fraction. Contrary to the case of NS EoS no firm constraint exists so far for finite temperature EoS. In my talk I shall review thermal properties of a series of finite temperature nucleonic EoS available on Compose. These include thermal pressure and energy, heat capacities at constant volume and constant pressure, thermal and adiabatic index and speed of sound. I shall then show that all these quantities are strongly influenced by the density dependence of the nucleon effective mass. A bunch of models will be used to investigate the EoS dependence of hot star properties, where entropy per baryon and electron fraction profiles are inspired from proto-NS evolution. The performances of the Gamma-law analytical thermal EoS used in many simulation will be discussed at different instances in the evolution of a proto-NS.

## Quarkyonic Effective Field Theory

### Dyana C. Duarte – Instituto TecnolĂłgico de AeronĂĄutica

2021/11/29

**Abstract**: A field theoretical description of quarkyonic matter is presented. In such a theory, the quark-nucleon duality is accomplished by the inclusion of ghost fields in a way that the nucleon extra degrees of freedom are compensated by the ghosts.

This theory is a nucleon effective field theory at low density and allows for the study of the dynamic generation of a shell of nucleons at the Fermi surface with the increase of the baryon density. It is also valid ad finite temperature and opens the possibility of the study of the relation between the chiral symmetry restoration and quarkyonic matter. Finally, some questions that might be addressed with this formulation are indicated.

## Lattice simulations of the QCD chiral transition at real baryon density

### Attila Pasztor – Institute of Theoretical Physics at EĂ¶tvĂ¶s LorĂĄnd University

2021/11/15

**Abstract**: In order to circumvent the infamous sign problem, state-of-the-art lattice QCD studies of hot and dense strongly interacting matter currently rely on extrapolation from zero or imaginary chemical potentials. The ill-posedness of numerical analytic continuation puts severe limitations on the reliability of such methods. I will talk about a more direct approach: sign reweighting. This allows one to obtain results at a finite baryon density without the uncontrolled systematic uncertainties associated with analytic continuation methods. The main bottleneck of the method is the sign problem itself. However, as I will demonstrate with direct simulation results, the sign problem for this reweighting scheme can be kept under numerical control for the entire RHIC Beam Energy Scan range in the chemical potential, opening up a new window to study the thermodynamics of hot and dense QCD matter from first principles.

## Quarkyonic Matter

### Srimoyee Sen – Iowa State University

2021/11/01

**Abstract**: The observed mass and radius relations of neutron stars can be explained remarkably well using a model of dense matter known as quarkyonic matter. I describe how the quarkyonic matter can arise dynamically from an excluded volume model for nuclear interactions and how thermal effects can be incorporated in such a model. I also discuss how one can improve the excluded volume model to correctly reproduce low energy nuclear interactions and recover mass radius relations of neutron stars.

## The Chiral Mean Field model

### Nikolas Cruz Camacho – the University of Illinois at Urbana-Champaign

2021/09/27

**Abstract:** A very successful model for the equation of state at large baryon densities that has been used to describe neutron stars, neutron star mergers, and heavy-ion collisions is the Chiral Mean Field model. In this seminar, I will describe the main key points of the CMF model from a physical and computational viewpoint, and how it fits within the MUSES infrastructure. In addition, I will talk about the numerical optimizations made to reduce the runtime from months to hours for either stellar mater or isospin symmetric matter. Finally, the plans to rewrite the CMF engine in a modern C++ framework will be sketched.

## MUSES Cyberinfrastructure

### T. Andrew Manning – National Center for Supercomputing Applications, University of Illinois at Urbana-Champaign

2021/09/27

**Abstract:** The MUSES project is funded by a Framework Implementations class award from the NSF Cyberinfrastructure for Sustained Scientific Innovation (CSSI) program. I will explain what cyberinfrastructure means in the context of the MUSES collaboration and describe how its various aspects â including collaborative tools, web services, computing environment, deployment system, and software architecture â will provide a powerful platform to drive scientific discovery.

## The MUSES Collaboration

### Claudia Ratti – University of Houston

2021/09/13

**Abstract**: MUSES (Modular Unified Solver of the Equation of State (EoS)) is a new NSF-funded collaboration that develops a cyberinfrastructure to provide to the scientific community novel tools to answer critical interdisciplinary questions in nuclear physics, gravitational wave astrophysics, and heavy-ion physics. I will review the scientific goals of the collaboration and the tools that will be used and developed to achieve them.