I will introduce recent astronomical observations and hot topics of neutron stars and magnetars.
In this talk I review our current understanding of the interior of neutron stars and modern constraints relevant for dense matter. This includes theoretical first-principle results from lattice and perturbative QCD, as well as chiral effective field theory results. From the experimental side, it includes heavy-ion collision and low-energy nuclear physics results, as well as observations from...
We investigate how vector and isovector interactions can be determined within the density regime of neutron stars (NSs) while fulfilling nuclear and astrophysics constraints. We make use of the Chiral Mean Field (CMF) model, a SU(3) nonlinear realization of the sigma model within the mean-field approximation, for the first time within a Bayesian analysis framework. We show that neutron-matter...
X-ray pulses of rapidly rotating neutron stars (NSs) can be used to probe both the properties of heated surface regions of a NS and the equation of state (EoS) of high-density matter inside a NS. Constraints on the EoS are obtained by measuring the mass and radius of the NS based on the relativistic effects when photons travel from the stellar surface to the observer. During the last few...
By taking the nucleon-to-quark phase transition within a neutron star as an example, we present a thermodynamically consistent method to calculate the equation of state of ambient matter so that transitions that are intermediate to those of the familiar Maxwell and Gibbs constructions can be described. This method does not address the poorly known surface tension between the two phases...
I will summarize our works in Refs. [1]-[3] in which we studied neutron star property based on the PDM-NJL crossover model. In the low-density region, we construct an EoS using a hadronic model based on the parity doublet structure with the chiral invariant mass of nucleons. In the high density region, an EoS is obtained in an NJL-type quark model. By interpolating two EoSs with assuming the...
The recent discovery of a central compact object (CCO) within the supernova remnant HESS J1731-347, characterized by a mass of approximately and a radius of about
km, has opened up a new window for the study of compact objects. This CCO is particularly intriguing because it is the lightest and smallest compact object ever observed, raising questions and challenging the existing theories. To...
We study the effect of the isovector-scalar meson (980) on the properties of nuclear matter and the neutron star (NS) matter by constructing a parity doublet model with including the meson based on the chiral SU(2)L x SU(2)_R symmetry. We also include the - mixing contribution to adjust the slope parameter at the saturation. We find that, when the chiral invariant mass of nucleon is smaller...
Large uncertainties in the determinations of the equation of state of dense stellar matter allow the intriguing possibility that the bulk quark matter in beta equilibrium might be the true ground state of the matter at zero pressure. And quarks will form Cooper pairs very readily since the dominant interaction between quarks is attractive in some channels. As a result, quark matter will...
We study the Nambu-Jona-Lasinio (NJL) model and its extension to color superconductivity (CSC) by incorporating the Renormalization Group (RG)-consistent treatment. This refinement leads to significant updates in the understanding of the CSC phases including an improved speed of sound at higher densities.
For modeling the dense quark matter EoS, we determine and constrain the vector and...
In this model holographic model, we will use the Gauss-Bonnet gravity the baryonic matter correspond to the dilute instanton gas and the color superconductivity (CSC) phase is in deconfinement region. We will calculate this and find the equation of state of the CSC phase
We derived an equation of state for neutron stars using a bottom-up holographic QCD model. Our calculations included mass-radius relationships of neutron stars and the sound velocity in high-density QCD matter.
In the inner crust of neutron stars, a Coulomb lattice of nuclei exists, immersed in a sea of superfluid neutron gas. The interplay between these nuclear crystals and the background neutrons may significantly alter nuclear dynamics, a phenomenon known as the "entrainment" effect, which is crucial for understanding several astronomical phenomena.
In our study, we have developed new...
I outline the origin of the hypothesis for Quarkyonic Matter and discuss the generic characteristics of such matter. A specific IdylliQ model is presented corresponding to an ideal gas of nucleons with a constraint that the quark phase space density does not exceed 1, that is the maximal occupancy for quark states, This model is dual between quarks and nucleons, and in the Quarkyonic phase...
We examine which first order phase transitions are consistent with today's astrophysical constraints. In particular, we explore how a well-constrained mass-radius data point would restrict the admissible parameter space and to this end, we employ the most likely candidates of the recent NICER limits of PSR J0030+0451. To systematically vary the stiffness of the equation of state, we employ a...
The merger of two neutron stars can form a system composed of a central object (either a neutron star or black hole) and a centrifugally supported disk. Inside the disk, magnetorotational instability generates a turbulent state, which then induces an effective viscosity. The viscous angular momentum transport and heating can evolve the system and trigger mass ejection from the disk on a...
We study the damping of density oscillations in the quark matter phase that might occur in compact stars. To this end we compute the bulk viscosity and the associated damping time in three-flavor quark matter, considering both nonleptonic and semileptonic electroweak processes. We use two different equations of state of quark matter, more precisely, the MIT bag model and perturbative QCD,...
Possibility of kaon-condensed phase (KC) in hyperon-mixed matter is considered in high-density multi-strangeness system, which may be realized in neutron stars.
The interaction model is based on effective chiral Lagrangian for kaon-baryon and kaon-kaon interactions, being combined with the relativistic mean-field theory for two-body baryon-baryon (B-B) interaction. In addition, universal...
An analytic technique of inverting the TOV equation with accuracies within 1% in both energy density and pressure is presented. In addition, a method using correlations connecting M,R data and energy density,pressure information is presented, giving a method of inferring the EOS from observations that does not contain the usual prior uncertainties stemming from the use of parameterized or...
It has been suggested [1] that the observation of pulsars with the same mass but significantly different radii (twin stars) would prove that the existence of a critical endpoint in the QCD phase diagram since this phenomenon requires a strong phase transition in cold neutron star matter [2].
We explore whether such a phase transition in neutron star cores, possibly coupled with a secondary...
At the beginning of the talk, I will reflect on my memories with my supervisor, Prof. Akira Ohnishi. Then, I will present our research on the Lambda potential strongly repulsive at high densities that is capable of avoiding the hyperon puzzle of neutron stars. The Lambda potential is shown to be consistent with the Lambda binding energies of hypernuclei and the Lambda directed flows in...
At the extreme densities reached in the core of neutron stars and related astrophysical phenomena, quark deconfined matter may take place. The formation of this new phase of strongly interacting matter is likely to occur via a first-order phase transition for the typical temperatures reached in astrophysical processes. For example, quark deconfinement could occur within the hot remnant of a...
Current anisotropic star models often overlook the effects of shear modulus and phase transitions. In our study, we propose a new anisotropic model for hybrid stars with an elastic quark matter core and a fluid nuclear matter envelope with a sharp phase transition in between. We incorporate the effects of shear deformation characterized by the shear modulus into the structural equations of...
Neutron Stars (NSs) make a unique physical laboratory with extreme physical conditions irreproducible in experiments, capable of producing a hadron-to-quark deconfinement phase transition in their interior. Owing to the high densities reached by the cold nuclear matter at the core of NSs, it is speculated that NS cores may be composed of deconfined quark matter (QM). Using state-of-the-art...
Including the effects of the chiral anomaly within Chiral Perturbation Theory at finite baryon chemical potential, it has been shown that neutral pions form an inhomogeneous phase dubbed the "Chiral Soliton Lattice" (CSL) above a certain critical magnetic field that could possibly be reached in magnetars and heavy-ion collisions. Beyond a second critical field, the CSL becomes unstable to...
We investigate the effects of dark matter (DM) on neutron star (NS) properties using the relativistic mean-field (RMF) theory. By integrating a DM model, we analyze how DM parameters, specifically DM mass and Fermi momentum, influence nuclear saturation properties, the equation of state (EoS), and the mass-radius relationship of NSs. Our research also examines the universal relation between...
It is believed that de-confined quark matter is more energetically stable than hadronic matter at extreme densities, such as those occurring in neutron stars. We thus believe that an explosive phase transition between hadronic and quark matter can occur in neutron star cores. Past studies have shown that the interface between hadronic and quark matter can develop wrinkles as the phase...
The massive stars end their lives by supernova explosions, leaving central compact objects that may evolve into neutron stars. Initially, after birth, the star remains hot and gradually cools down. We explore the matter and star properties during this initial stage of the compact stars, considering the possibility of the appearance of deconfined quark matter in the core of the star. Nonradial...
Neutrinos play essential roles in the evolution of core-collapse supernovae. However, the conventional neutrino kinetic theory violates the basic tenet of low-energy effective theories in that it does not respect the symmetry (or parity violation) due to the chirality of neutrinos. In this talk, we discuss the formulation of the chiral radiation transport theory for neutrinos with parity...
The Bodmer-Witten conjecture proposes that strange quark matter (SQM) is the true ground state of strong interaction matter, suggesting that self-bound strange quark stars could be the physical nature of all compact stars. However, distinguishing between quark stars and neutron stars remains challenging with current astronomical observations. In this talk, I will explore the properties of the...
During the binary quark star merger, segment quark nuggets could be ripped out. The emission of neutrons and protons from quark nugget makes the environment differ from the standard binary neutron star merger. When temperature drops below 1 MeV, the nucleosynthesis path will be different compare with the well-know r-process nucleosynthesis in binary neutron star merger. here in this talk, I...
Due to the nonperturbative QCD dynamics in the density regime of neutron stars, new alternatives of strong matter and related stellar structure are possible. Recently, we proposed that up-down quark stars, inverted hybrid stars, hybrid strangeon stars can possibly exist, based on the hypothesis that either quark matter or strangeon matter is the ground state of bulk strong matter. They can...
In this study, we investigate the structure of neutron stars within the framework of covariant gravity, an extension of general relativity that incorporates non-metricity. By adopting a static and spherically symmetric metric with perfect fluid matter, we derive the modified Tolman-Oppenheimer-Volkoff (TOV) equations specific to three models: quadratic, exponential, and logarithmic. We...
After an introduction to the status of the field, I present our results on how to discriminate equations of state with a quark-hadron crossover with respect to EOSs with purely hadronic matter or with a first-order quark-hadron transition through gravitational waves emitted in binary neutron star mergers.
A common alternative to the standard assumption of nucleonic composition of matter in the interior of a neutron star is to include strange baryons, particularly hyperons. Any change in composition of the neutron star core has an effect on 𝑔-mode oscillations of neutron stars, through the compositional dependence of the equilibrium and adiabatic sound speeds. Using a variety of relativistic...
I will discuss how multi-quark system confines quarks and propose a new string-type confinement for heavy-tetra-quark systems. It is tested by the fully-heavy tetra-quark (cc c-bar c-bar) system.
Recently the lattice simulation in two-color QCD at finite density clarified that the squared sound velocity cs2 exceeds the conformal limit 1/3 . We know that at mu -> infinity the conformal limit is realized, thus, a peak structure was numerically observed. Theoretically, on the other hand, the ChPT is known to predict a monotonic increment of cs2 to yield cs2 -> 1 at sufficiently dense...
A vast ensemble of equations of state (EoSs), developed within the framework of covariant density functional theory pertaining to hadronic matter and accommodating density-dependent couplings, is deployed to scrutinize the polar f- and p-oscillations in both cold and hot compact stars. The interplay between oscillation frequencies of cold purely nucleonic neutron stars (NSs), their global...
I will discuss the recent developments for the analysis of QCD phase structure with heavy-ion collisions with an emphasis on the QCD critical point search with event-by-event fluctuations. I will discuss the dynamical description of proton number cumulants and put these results in the context of new STAR data from phase II of Beam Energy Scan.
The Compressed Baryonic Matter (CBM) experiment is currently under construction at the Facility for Antiproton and Ion Research (FAIR).
Its goal is to explore the phase structure of strongly interacting (QCD) matter at high net-baryon densities and moderate temperatures through heavy-ion
and hadron collisions in the energy range of \sqrt{s_{NN}} = 2.9 - 4.9 GeV using the SIS100 beams.
As a...
Light (e.g. deuterons, tritons, helions, particles) 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. These clusters not only form in these astrophysical sites, but also in heavy-ion collisions.
The appearance of these clusters can modify the neutrino transport, and, therefore, consequences...
We draw an analogy between the materials condensed by the strong interaction (i.e., strong matter) and that by the electromagnetic force (simply, electric matter), both of which are condensed matters with almost continues mass spectrum, if Nature favors the quark-flavor symmetry. While strangeon stars could be manifested in the form of pulsar, gamma-ray bursts and fast radio bursts, strangeon...
Spatial inhomogeneous phases of nuclear and quark matter are a feature of the QCD Phase Map at intermediate densities/low temperatures, making them potential candidates for the inner phases of neutron stars. Yet, single-modulated chiral condensates, even when energetically favored over others at zero temperature, are wiped out by thermal fluctuations due to the Landau-Peierls instability. In...
Recent work has suggested that the magnetic dual chiral density wave (MDCDW), an inhomogeneous condensate that arises in dense QCD in a magnetic field, is an appealing candidate phase for the description of matter in the core of compact stars. For example, the nontrivial topology in its fermion spectrum gives it a high critical temperature and allows it to avoid the Landau-Peierls instability,...
Since the discovery of a two-solar-mass pulsar back in 2010, the field of neutron-star physics has been revolutionized along with great progress in the theory and modeling of strongly-interacting matter at supra-nuclear densities. In this talk, I will focus on the implications for limiting viable scenarios of high-density hadron-to-quark phase transitions in the inner cores of neutron stars,...
We compare two first-principles calculations of the QCD equation of state (EOS): the weak-coupling results and the recent lattice QCD data at finite isospin density.
Because both finite-baryon-density QCD and finite-isospin-density QCD have the same weak-coupling expansion, we can learn about the former case from the latter, in which the lattice data is available, and in this talk, we...
In physics, analogies are extremely powerful tools. They give the opportunity to look at physical phenomena from different perspectives, favoring connections between very disparate research fields. In a recent work, we established an intriguing analogy between the inner crust of neutron stars and ultracold dipolar supersolids and used it to investigate the anomalies in the rotation frequency...
We have attempted to mitigate the challenge of connecting the neutron star (NS) properties with the nuclear matter parameters that describe equations of state (EOSs). The efforts to correlate various neutron star properties with individual nuclear matter parameters have been inconclusive.
A Principal Component Analysis is employed as a tool to uncover the connection between multiple nuclear...
I will discuss how multi-quark system confines quarks and propose a new string-type confinement for heavy-tetra-quark systems. It is tested by the fully-heavy tetra-quark (cc c-bar c-bar) system.
Due to the nonperturbative QCD dynamics in the density regime of neutron stars, new alternatives of strong matter and related stellar
structure are possible. Recently, we proposed that up-down quark stars, inverted hybrid stars, hybrid strangeon stars can possibly exist, based on the hypothesis that either quark matter or strangeon matter is the ground state of bulk strong matter. They can...
We investigate the intricate relationships between the non-radial
𝑓 mode oscillation frequencies of neutron stars (NS)s and the corresponding nuclear matter equation of state (EOS) using a machine learning (ML) approach within the ambit of the relativistic mean field (RMF) framework for nuclear matter. With two distinct parameterizations of the Walecka model, namely, (1) with non-linear self...
