Strange Matter Research Articles

Study of strange matter in STAR with express analysis

The STAR experiment provides a perfect machinery for studying strange matter for more than two decades. Recently, we developed the express procedure, which allows online monitoring of the collected physics data. The high quality of express calibration and reconstruction provides a unique possibility to run the express production and observe almost in real time strange particles including mesons, hyperons, resonances and even hypernuclei.The STAR Beam Energy Scan II program, including fixed target Au+Au collisions taken in 2018–2021, is particularly suited to study hypernuclei. Light hypernuclei are expected to be abundantly produced in low energy heavy-ion collisions. Measurements of hypernuclei production and their properties will provide information on the hyperon-nucleon interactions, which are essential ingredients for understanding nuclear matter equation of state at high net-baryon densities, such as inside neutron stars.With the heavy fragment trigger introduced for the 2021 data taking, we were able to run the express production at the STAR High Level Trigger farm. The collected data were suffcient to observe the decay process ofΛ5He →4Hepπ−with more than 11σ significance, measure binding energy as a function of hypernuclei mass, and study hypernuclei decay properties with the Dalitz plot technique.

From Nuggets of SQM to Domains of Broken Symmetry (In memoriam of Jack Sandweiss)

For the last 20 years of his remarkable career, Jack Sandweiss was an enthusiastic leader in heavy-ion physics, especially excited about two main topics: the search for stable or metastable strange quark matter and the possibility of local parity violation in heavy-ion collisions. I take a look back at some of Jack’s contributions in the context of the current state of both of these very active areas.

Recent progress on few-body hypernuclei

Few-body Λ hypernuclei provide valuable information towards understanding strange matter. Recent experimental progress by the STAR Collaboration at the RHIC facility and by the ALICE Collaboration at the LHC has been matched by theoretical progress reviewed here: (i) lifetimes of the hypertritonΛ3H,Λ3n if particle-stable,Λ4H andΛ4He and their charge symmetry breaking, and (ii) the onset of ΛΛ hypernuclear binding.

Study of Strange Quark Matter and Variable ∧ in Bianchi VI Universe

The present paper deals with strange quark matter i.e. ( 4 ) in the presence of variable cosmological term in Bianchi VI universe. Here we adopt the physical conditions (i)The shear scalar is proportional to expansion scalar and ( ii ) The time dependent cosmological term of the type 2 for the simplification of field equations. We observed some cosmological parameters such as deceleration parameter, quark density, quark pressure etc. Lastly we conclude with the discussion of cosmological perturbations of resultant universe. Also graphs are plotted for the detail study of the resultant model.

Bianchi V I_0 Universe with Magnetized Strange Quark Matter in f(R, T) Theory

This study discusses f(R,T) theory, one of the alternative theories. It then studies magnetized strange quark matter in the universe model Bianchi V I0, homogeneous and anisotropic. Afterwards, it has determined whether the energy conditions are provided by using the deceleration parameter while obtaining the solutions. Moreover, the evolution of the cosmic universe is examined with the help of graphics and tables.

Improved Λp Elastic Scattering Cross Sections between 0.9 and 2.0 GeV/c as a Main Ingredient of the Neutron Star Equation of State.

Strange matter is believed to exist in the cores of neutron stars based on simple kinematics. If this is true, then hyperon-nucleon interactions will play a significant part in the neutron star equation of state. Yet, compared to other elastic scattering processes, there is very little data on Λ-N scattering. This experiment utilized the CEBAF Large Acceptance Spectrometer (CLAS) detector to study the Λp→Λp elastic scattering cross section in the incident Λ momentum range 0.9-2.0 GeV/c. These are the first data on this reaction since the 1970s. The new cross sections have significantly better accuracy and precision than the existing world data, and the techniques developed here can also be used in future experiments.

Tidal deformability of strange quark planets and strange dwarfs

Strange quark matter, which is composed of u, d, and s quarks, could be the true ground of matter. According to this hypothesis, compact stars may actually be strange quark stars, and there may even be stable strange quark dwarfs and strange quark planets. The detection of the binary neutron star merger event GW170817 provides us new clues on the equation of state of compact stars. In this study, the tidal deformability of strange quark planets and strange quark dwarfs are calculated. It is found that the tidal deformability of strange quark objects is smaller than that of normal matter counterparts. For a typical 0.6 M$_\odot$ compact star, the tidal deformability of a strange dwarf is about 1.4 times less than that of a normal white dwarf. The difference is even more significant between strange quark planets and normal matter planets. Additionally, if the strange quark planet is a bare one (i.e., not covered by a normal matter curst), the tidal deformability will be extremely small, which means bare strange quark planets will hardly be distorted by tidal forces. Our study clearly proves the effectiveness of identifying strange quark objects via searching for strange quark planets through gravitational-wave observations.

Identifying QCD Phase Transitions via the Gravitational Wave Frequency from a Supernova Explosion

Abstract We investigate the nonradial oscillations of newly born neutron stars (NSs) and strange quark stars (SQSs). This is done with the relativistic nuclear field theory with hyperon degrees of freedom employed to describe the equation of state (EoS) for the stellar matter in NSs, and with both the MIT bag model and the Nambu–Jona-Lasinio model adopted to construct the configurations of the SQSs. We find that the gravitational-mode (g-mode) eigenfrequencies of newly born SQSs are significantly lower than those of NSs, which is independent of models implemented to describe the EoS for the strange quark matter. Meanwhile, the eigenfrequencies of the other modes of nonradial oscillations, e.g., fundamental (f)- and pressure (p)-modes, are much larger than those of the g-mode, and are related to the stiffness of the EoSs. In light of the first direct observation of gravitational waves (GWs), it is promising to employ GWs to identify the QCD phase transition in high-density strong-interaction matter.

Quark matter and quark stars within the quasiparticle model under magnetic fields

We investigate the properties of the equation of state (EOS), the quark fraction, and the isospin asymmetry for strange quark matter (SQM) under constant magnetic field within the quasiparticle model. Our results indicate that the effect of the magnetic field is important for the properties of strange quark matter, and the recently discovered heavy compact stars PSR $\mathrm{J}0348+0432$, MSR $\text{J0740}+6620$, PSR $\text{J2215}+5135$, and especially the GW190814s secondary component ${m}_{2}$ can be well described as quark stars within the quasiparticle model under magnetic fields by approximately using spherically symmetric Tolman-Oppenheimer-Volkov (TOV) equations.

Fully general-relativistic simulations of isolated and binary strange quark stars

The hypothesis that strange quark matter is the true ground state of matter has been investigated for almost four decades, but only a few works have explored the dynamics of binary systems of quark stars. This is partly due to the numerical challenges that need to be faced when modelling the large discontinuities at the surface of these stars. We here present a novel technique in which the EOS of a quark star is suitably rescaled to produce a smooth change of the specific enthalpy across a very thin crust. The introduction of the crust has been carefully tested by considering the oscillation properties of isolated quark stars, showing that the response of the simulated quark stars matches accurately the perturbative predictions. Using this technique, we have carried out the first fully general-relativistic simulations of the merger of quark-star binaries finding several important differences between quark-star binaries and hadronic-star binaries with the same mass and comparable tidal deformability. In particular, we find that dynamical mass loss is significantly suppressed in quark-star binaries. In addition, quark-star binaries have merger and post-merger frequencies that obey the same quasi-universal relations derived from hadron stars if expressed in terms of the tidal deformability, but not when expressed in terms of the average stellar compactness. Hence, it may be difficult to distinguish the two classes of stars if no information on the stellar radius is available. Finally, differences are found in the distributions in velocity and entropy of the ejected matter, for which quark-stars have much smaller tails. Whether these differences in the ejected matter will leave an imprint in the electromagnetic counterpart and nucleosynthetic yields remains unclear, calling for the construction of an accurate model for the evaporation of the ejected quarks into nucleons.

Bulk viscosity of interacting magnetized strange quark matter

Bulk viscosity of interacting magnetized strange quark matter

Possible nature of dark matter

We present a study of neutron star models that contain dark matter (DM) in the core. The DM is assumed to have a particle nature and to be self-interacting. Using constraints on the mass and radius of neutron stars, we investigate the allowed properties of either bosonic or fermionic DM particles. We consider cases where it constitutes up to 15% of the mass of the star, even though conventional mechanisms cannot generate such large fractions. For this purpose three different models of neutron stars are considered, the first involving nucleons only, the second including hyperons, and the last involving strange matter in the core. Different EoSs are constructed for the various cases of fermionic and bosonic DM. These EoSs are solved for selected properties of the DM particles and the results are tested against mass, radius and tidal deformability constraints for neutron stars. The distribution of energy density of DM and ordinary matter inside the neutron stars is also presented. It is found that if the DM is fermionic in nature it does not just sit in the core but it is present everywhere in the star, from the centre to outside the surface and may even envelop it.

Study on anisotropic charged strange stars within the framework of Rastall–Maxwell theory: Conformal Killing vector

The strange quark matter (SQM) for which the distribution is governed by the equation of state of the simplified MIT bag model such as: [Formula: see text], with [Formula: see text] the bag constant, in the presence of a load distribution given by [Formula: see text] has been the subject of a series of investigations within the framework of Rastall–Maxwell theory. We used the Modified Tolman–Oppenheimer–Volkoff (TOV) equation in Rastall gravity to generate the solutions by make using the conformal Killing vector. In order to check the physical acceptability of our solutions from conformal Killing vector method, we investigated around the Energy conditions, the Mass–Radius relation, Modified TOV equation, redshift and the stability of the system through Adiabatic Index, the Compactification factor and Causality condition. For physical values of Rastall parameters, we noticed that the stellar systems become more massive in proportion to their size. Then, this leads them into less dense compact objects which reveals that the alternative theory of Rastall is appropriate to better explain the behavior of massive stellar objects.

Search for nuclearites with the KM3NeT detector

Strange quark matter (SQM) is a hypothetical type of matter composed of almost equal quantities of up, down and strange quarks. Edward Witten presented the SQM as a denser and more stable matter that could represent the ground state of Quantum Chromodynamics (QCD). Massive SQM particles are commonly called nuclearites. These particles could have been produced in violent astrophysical processes, such as neutron star collisions and could be present in the cosmic radiation. Nuclearites with masses greater than 1013 GeV/c2 and velocities of about 250 km/s (typical galactic velocities) could reach the Earth and interact with atoms and molecules of sea water within the sensitive volume of the deep-sea neutrino telescopes. The SQM particles can be detected with the KM3NeT telescope (whose first lines are already installed and taking data in the Mediterranean Sea) through the visible blackbody radiation generated along their path inside or near the instrumented area. In this work the results of a study using Monte Carlo simulation of down-going nuclearites are discussed.

Study on anisotropic strange stars in Rastall gravity

The strange quark matter (SQM) whose distribution is governed by the simplified MIT bag model equation of state has been the subject of a series of investigations within the framework of Rastall’s theory. We obtain an exact solution of the modified form of the Tolman–Oppenheimer–Volkoff (TOV) equation in the Rastall gravity theory and study the dependence of different physical properties (the total mass, radius, energy density, and pressure) for the chosen values of the Rastall parameter $$\lambda_{ \scriptscriptstyle{\mathrm{Ras}} }$$ . To examine physical acceptability of the proposed stellar model, we conduct different tests in detail: the energy conditions, the the mass–radius relation, the Compactification factor, the redshift, the system stability, the modified TOV equation, the causality condition, and the adiabatic index in terms of $$\lambda_{ \scriptscriptstyle{\mathrm{Ras}} }$$ . We precisely explain the effects arising due to the Rastall parameter and geometry on the compact stellar system. We find that as the factor $$\lambda_{ \scriptscriptstyle{\mathrm{Ras}} }$$ decreases, the strange star candidates become gradually massive and larger in size with a less dense stellar configuration. But when $$\lambda_{ \scriptscriptstyle{\mathrm{Ras}} }$$ increases, the stars shrink gradually and become less massive, turning into a more compact stellar system. For $$\lambda_{ \scriptscriptstyle{\mathrm{Ras}} }>0$$ , our proposed model is therefore suitable for explaining the ultradense compact stars well within the observational limits; for $$\lambda_{ \scriptscriptstyle{\mathrm{Ras}} }<0$$ , it allows representing the recent massive pulsars and super-Chandrasekhar stars. For $$\lambda_{ \scriptscriptstyle{\mathrm{Ras}} }=1$$ , we retrieve the standard results of general relativity.

Properties of strange quark matter and strange quark stars

A Polyakov chiral text {SU(3)} quark mean-field (PCQMF) model is applied to study the properties of strange quark matter (SQM) and strange quark star (SQS) in beta -equilibrium. The effect of increasing the strength of vector interactions on the effective constituent quark mass, particle fractions, and the thermodynamical properties such as pressure, energy density, and the speed of sound is investigated. We investigate the above properties for the SQM relevant for various stages of star evolution, i.e., considering with/without trapped neutrinos and zero/finite entropy. The finite lepton fraction and the entropy of the medium is observed to cause the stiffness in the equation of state (EoS). Finally, we calculate the mass-radius relation and the dimensionless tidal deformability within the present model calculations and compare the results to the recent studies.

Nuclearite search with ANTARES

The ANTARES detector is a Cherenkov underwater neutrino telescope operating in the Mediterranean Sea. Its construction was completed in 2008. Even though optimised for the search of cosmic neutrinos, this telescope is also sensitive to nuclearites (massive nuggets of strange quark matter) trough the black body radiation emitted along their path.We discuss here the possible detection of non-relativistic down-going nuclearites with the ANTARES telescope and present the results of an analysis using data collected from 2009 till 2017.

Nambu–Jona-Lasinio SU(3) model constrained by lattice QCD: thermomagnetic effects in the magnetization

We use a three-flavor Nambu--Jona-Lasinio model to study the thermodynamics of strange quark matter under a strong magnetic field. The model Lagrangian features flavor SU(3) four-quark interactions and six-quark interactions that break the UA(1) symmetry. We incorporate thermomagnetic effects in the four-quark coupling. The model predicts magnetic catalysis at low temperatures and inverse magnetic catalysis at temperatures close to the pseudocritical temperature of the QCD transition, in agreement with lattice QCD results. We compute the pressure at the mean field level and obtain the magnetization of quark matter. We adopt the recently proposed vacuum magnetic regularization (VMR) scheme, in that divergent quark mass independent contributions are not subtracted, thereby avoiding unphysical results for the magnetization. We devote special attention to the renormalized magnetization, a projected quantity that allows for direct comparisons with lattice QCD simulations. Our results are in very good agreement with lattice data indicating a paramagnetic behavior for quark matter.

Low mass strange stars and the compact star 1E1207.4-5209 in the field correlator method

We investigate the possible existence of anomalous mass defects in the low mass region of stellar sequences of strange stars. We employ the nonperturbative equation of state derived in the framework of the field correlator method to describe the hydrostatic equilibrium of the strange matter. The large distance static $Q\overline{Q}$ potential ${V}_{1}$ and the gluon condensate ${G}_{2}$ are the main parameters of the model. We use the surface gravitational redshift measurements as a probe to determine the ratio $(\mathcal{P}/\mathcal{E}{)}_{C}$ at the center of strange stars. For ${V}_{1}=0$ and ${G}_{2}\ensuremath{\gtrsim}0.035\text{ }\text{ }{\mathrm{GeV}}^{4}$, we show that $(\mathcal{P}/\mathcal{E}{)}_{C}\ensuremath{\simeq}0.262$ and the corresponding redshift ${z}_{S}\ensuremath{\simeq}0.47$ are limiting values at the maximum mass of the highest mass stellar sequence. As a direct application of our study, we try to determine the values of ${V}_{1}$ and ${G}_{2}$ from astrophysical observations of the compact star 1E 1207.4-5209. Due to the uncertainties in the surface redshift determination, we made two attempts to obtain the model parameters. Our findings show that $(\mathcal{P}/\mathcal{E}{)}_{C}=0.07{3}_{+0.024}^{+0.029}$ at 68% confidence, ${V}_{1}=0.44\ifmmode\pm\else\textpm\fi{}0.10\text{ }\text{ }\mathrm{GeV}$ at 90% confidence and ${G}_{2}=0.008\ifmmode\pm\else\textpm\fi{}0.001\text{ }\text{ }{\mathrm{GeV}}^{4}$ at 95% confidence in the first attempt; and $(\mathcal{P}/\mathcal{E}{)}_{C}=0.087\ifmmode\pm\else\textpm\fi{}0.028$ at 71% confidence, ${V}_{1}=0.43\ifmmode\pm\else\textpm\fi{}0.085\text{ }\text{ }\mathrm{GeV}$ at 94% confidence and ${G}_{2}=0.0093\ifmmode\pm\else\textpm\fi{}0.00092\text{ }\text{ }{\mathrm{GeV}}^{4}$ at 94% confidence in the second attempt. These values of ${V}_{1}$ and ${G}_{2}$ are in reasonable agreement with the lattice and QCD sum rules calculations. As a consequence of the high values of ${V}_{1}$ and ${G}_{2}$, the anomalous mass defects of 1E 1207.4-5209 are $|{\mathrm{\ensuremath{\Delta}}}_{2}M|\ensuremath{\simeq}2.56\ifmmode\times\else\texttimes\fi{}{10}^{53}\text{ }\text{ }\mathrm{erg}$ in the first attempt and $|{\mathrm{\ensuremath{\Delta}}}_{2}M|\ensuremath{\simeq}2.94\ifmmode\times\else\texttimes\fi{}{10}^{53}\text{ }\text{ }\mathrm{erg}$ in the second attempt.

Repeating fast radio bursts from collapses of the crust of a strange star

SummaryStrange stars (SSs) are compact objects made of deconfined quarks. It is hard to distinguish SSs from neutron stars as a thin crust composed of normal hadronic matter may exist and obscure the whole surface of the SS. Here we suggest that the intriguing repeating fast radio bursts (FRBs) are produced by the intermittent fractional collapses of the crust of an SS induced by refilling of materials accreted from its low-mass companion. The periodic/sporadic/clustered temporal behaviors of FRBs could be well understood in our scenario. Especially, the periodicity is attributed to the modulation of accretion rate through the disk instabilities. To account for a ~16-day periodicity of the repeating FRB source of 180916.J0158+65, a Shakura-Sunyaev disk with a viscosity parameter of 0.004 and an accretion rate of 3 × 1016 g s−1 is invoked. Our scenario, if favored by future observations, will serve as indirect evidence for the strange quark matter hypothesis.