Strange Matter Research Articles

Anisotropic strange quark star in Finch-Skea geometry and its maximum mass for non-zero strange quark mass (m s ≠ 0)* *BD and KBG thank the CSIR for providing the fellowship vide No 09/1219(0005)/2019-EMR-I and 09/1219(0004)/2019-EMR-I, respectively.

A class of relativistic astrophysical compact objects is analyzed in the modified Finch-Skea geometry described by the MIT bag model equation of state of interior matter, , where B is known as the bag constant. B plays an important role in determining the physical features and structure of strange stars. We consider the finite mass of the strange quark () and study its effects on the stability of quark matter inside a star. We note that the inclusion of strange quark mass affects the gross properties of the stellar configuration, such as maximum mass, surface red-shift, and the radius of strange quark stars. To apply our model physically, we consider three compact objects, namely, (i) VELA X-1, (ii) 4U 1820-30, and (iii) PSR J 1903+327, which are thought to be strange stars. The range of B is restricted from 57.55 to (), for which strange matter might be stable relative to iron (). However, we also observe that metastable and unstable strange matter depend on B and . All energy conditions hold well in this approach. Stability in terms of the Lagrangian perturbation of radial pressure is studied in this paper.

Five-dimensional strange quark matter cosmological model with string cloud

The work in this paper is devoted to the study of Kaluza–Klein (KK) cosmological model with strange quark matter attached to string cloud in the framework of metric version of [Formula: see text] gravity. By utilizing hybrid expansion law for average scale factor of the model i.e. [Formula: see text], here [Formula: see text] and [Formula: see text] are positive constants, we derive the solution of the field equations of KK model in the [Formula: see text] gravity. Various dynamical parameters of the model are obtained and their behavior is analyzed through graphical representation. We observe that the analysis of deceleration parameter exhibits a smooth transition of the universe from early decelerated phase to current accelerated epoch. Also, we discussed well-known state-finder parameters [Formula: see text] and [Formula: see text] planes which are analyzed by graphical representation.

Self-gravitating electrically charged anisotropic strange star model

The main focus of this paper is devoted to exploring the physical aspects of compact stars with the presence of electric charge under an embedded Class I approach in the arena of Bardeen geometry. We derive the embedded Class I solutions by taking spherically symmetric static spacetime with an anisotropic source of matter. We also look at the equation of state (EoS) for strange quark matter (SQM), which inspired the phenomenological MIT-Bag model as a free Fermi gas of quarks. The unknown constants are evaluated through the boundary conditions along with the Bardeen model to portray as an exterior space–time. Bardeen’s model becomes very interesting in an entertaining and unique way with great precision as it could be interpreted as the analytical solutions of some appropriate nonlinear electrodynamics associated with the gravitational field. In this concern, we thoroughly explored the dependence of several physical parameters, such as the metric potentials, energy density, pressure constituents, anisotropy, and electric charge, etc., on the chosen varied values of n. Finally, we discuss the physical viability and stability of the stellar model through various physical tests. It is important to mention here that the obtained stellar configuration is in agreement with the physical viability and stability criteria under the effect of the electric charge and anisotropic fluid source of matter.

Limits on the nuclearite flux using the ANTARES neutrino telescope

In this work, a search for nuclearites of strange quark matter by using nine years of ANTARES data taken in the period 2009–2017 is presented. The passage through matter of these particles is simulated taking into account a detailed description of the detector response to nuclearites and of the data acquisition conditions. A down-going flux of cosmic nuclearites with Galactic velocities (β = 10-3) was considered for this study. The mass threshold for detecting these particles at the detector level is 4 × 1013 GeV/c 2. Upper limits on the nuclearite flux for masses up to 1017 GeV/c 2 at the level of ∼ 5 × 10-17 cm-2 s-1 sr-1 are obtained. These are the first upper limits on nuclearites established with a neutrino telescope and the most stringent ever set for Galactic velocities.

Does magnetized strange quark matter exist in the early universe?

In this paper, we have examined the magnetized strange quark matter (MSQM) distribution in the inhomogeneous anisotropic Einstein–Rosen universe model within the framework of [Formula: see text] theory and General Relativity (GR) in order to investigate whether there was a magnetic field in the first moments of the universe. With the help of the arbitrary [Formula: see text] function, we researched for solutions in both theories for various cases. We have seen that the cubic function [Formula: see text] gives meaningful results in both theories. We have obtained magnetic field-free strange quark matter solutions for the quadratic and constant states of the arbitrary function [Formula: see text]. It is seen that the choice of geometry (selection of the [Formula: see text] function) has an effect on the presence of the magnetic field. Finally, the physical results are examined on 3D graph.

Counting states: A combinatorial analysis of SQM fragmentation

AbstractThe Strange Quark Matter (SQM) hypothesis states that at extreme pressure and density conditions, a new ground state of matter would arise, in which half of the down quarks become strange quarks. If true, it would mean that at least the core of neutron stars is made of SQM. In this hypothesis, SQM would be released in the interstellar medium when two of these objects merge. It is estimated that of SQM would be released this way. This matter will undergo a sequence of processes that should result in a fraction of the released SQM becoming heavy nuclei through the r‐process. In this work, we are interested in characterizing the fragmentation of SQM, with the novelty of keeping track of the quark configuration of the fragmented matter. This is accomplished by developing a methodology to estimate the energy of each fragment as the sum of its constituent quarks, the Coulomb interaction among the quarks and fragments' momenta.

Quark stars with 2.6 M_odot in a non-minimal geometry-matter coupling theory of gravity

This work analyses the hydrostatic equilibrium configurations of strange stars in a non-minimal geometry-matter coupling (GMC) theory of gravity. Those stars are made of strange quark matter, whose distribution is governed by the MIT equation of state. The non-minimal GMC theory is described by the following gravitational action: f(R,L)=R/2+L+sigma RL, where R represents the curvature scalar, L is the matter Lagrangian density, and sigma is the coupling parameter. When considering this theory, the strange stars become larger and more massive. In particular, when sigma =50 km^2, the theory can achieve the 2.6 M_odot , which is suitable for describing the pulsars PSR J2215+5135 and PSR J1614-2230, and the mass of the secondary object in the GW190814 event. The 2.6 M_odot is a value hardly achievable in General Relativity, even considering fast rotation effects, and is also compatible with the mass of PSR J0952-0607 (M = 2.35 pm 0.17 ~M_odot ), the heaviest and fastest pulsar in the disk of the Milky Way, recently measured, supporting the possible existence of strange quark matter in its composition. The non-minimal GMC theory can also give feasible results to describe the macroscopical features of strange star candidates.

Formation and evaporation of strangelets during the merger of two compact stars

We study the partial fragmentation of a strange quark star into strangelets during the process of merger of two strange quark stars. We discuss the fate of the fragments considering their possible evaporation into nucleons. We show that only a rather small amount of large size strangelets, ejected from the spiral arms in the postmerger, survives a total evaporation into nucleons. In this way we demonstrate that (1) the density of strangelets in the galaxy is too low to trigger the conversion of all neutron stars into strange quark stars, and it allows the coexistence of both types of compact objects; (2) the probability of direct detection of a strangelet is negligible, and therefore its nondetection is compatible with the strange quark matter hypothesis; (3) most of the matter ejected during and after the merger of two strange quark stars evaporates into nucleons, and therefore it can generate a kilonova-like signal.

Observation of night-time emissions of the Earth in the near UV range from the International Space Station with the Mini-EUSO detector

Mini-EUSO (Multiwavelength Imaging New Instrument for the Extreme Universe Space Observatory) is a telescope observing the Earth from the International Space Station since 2019. The instrument employs a Fresnel-lens optical system and a focal surface composed of 36 Multi-Anode Photomultiplier tubes, 64 channels each, for a total of 2304 channels with single photon counting sensitivity. Mini-EUSO also contains two ancillary cameras to complement measurements in the near infrared and visible ranges. The scientific objectives of the mission range from the search for Extensive Air Showers (EAS) generated by Ultra-High Energy Cosmic Rays (UHECRs) with energies above 1021eV, the search for nuclearites and Strange Quark Matter (SQM), up to the study of atmospheric phenomena such as Transient Luminous Events (TLEs), meteors and meteoroids. Mini-EUSO can map the night-time Earth in the near UV range (predominantly between 290–430 nm) with a spatial resolution of about 6.3 km (full field of view equal to 44°) and a maximum temporal resolution of 2.5μs, observing our planet through a nadir-facing UV-transparent window in the Russian Zvezda module. The detector saves triggered transient phenomena with a sampling rate of 2.5μs and 320μs, as well as continuous acquisition at 40.96 ms scale. In this paper we discuss the detector response and the flat-fielding and calibration procedures. Using the 40.96 ms data, we present ≃6.3 km resolution night-time Earth maps in the UV band, and report on various emissions of anthropogenic and natural origin. We measure ionospheric airglow emissions of dark moonless nights over the sea and ground, studying the effect of clouds, moonlight, and artificial (towns, boats) lights. In addition to paving the way forward for the study of long-term variations of light of natural and artificial origin, we also estimate the observation live-time of future UHECR detectors.

Strange quark matter from a baryonic approach

We construct a model for dense matter based on low-density nuclear matter properties that exhibits a chiral phase transition and that includes strangeness through hyperonic degrees of freedom. Empirical constraints from nuclear matter alone allow for various scenarios, from a strong first-order chiral transition at relatively low densities through a weaker transition at higher densities, even up to a smooth crossover not far beyond the edge of the allowed range. The model parameters can be chosen such that at asymptotically large densities the chirally restored phase contains strangeness and the speed of sound approaches the conformal limit, resulting in a high-density phase that resembles deconfined quark matter. Additionally, if the model is required to reproduce sufficiently massive compact stars, the allowed parameter range is significantly narrowed down, resulting for instance in a very narrow range for the poorly known slope parameter of the symmetry energy, $L\ensuremath{\simeq}(88--92)\text{ }\text{ }\mathrm{MeV}$. We also find that for the allowed parameter range strangeness does not appear in the form of hyperons in the chirally broken phase and the chiral transition is of first order. Due to its unified approach and relative simplicity---here we restrict ourselves to zero temperature and the mean-field approximation---the model can be used in the future to study dense matter under compact star conditions in the vicinity of the chiral phase transition, for instance to compute the surface tension or to investigate spatially inhomogeneous phases.

GW190814: Circumstantial evidence for up-down quark star

Within a confining quark matter model which considers phenomenologically the quark confinement and asymptotic freedom as well as the chiral symmetry restoration and quark deconfinement at high baryon density, we find that if the up-down quark matter ($ud\mathrm{QM}$) is more stable than nuclear matter and strange quark matter (SQM), the maximum mass of static quark stars with $ud\mathrm{QM}$ is $2.87\text{ }\text{ }{M}_{\ensuremath{\bigodot}}$ under agreement with both the constraints on star tidal deformability from gravitational wave signal GW170817 and the mass-radius of PSR $\mathrm{J}0030+0451$ and PSR $\mathrm{J}0740+6620$ measured by NICER. In contrast, the conventional strange quark star with the SQM that is more stable than nuclear matter while the nuclear matter is more stable than $ud\mathrm{QM}$, has a maximum static mass of only $1.87\text{ }\text{ }{M}_{\ensuremath{\bigodot}}$ and its radius significantly deviates from NICER's constraint. Our results thus provide circumstantial evidence suggesting the recently reported GW190814's secondary component with a mass of ${2.59}_{\ensuremath{-}0.09}^{+0.08}\text{ }\text{ }{M}_{\ensuremath{\bigodot}}$ could be an up-down quark star.

Vector dark boson mediated feeble interaction between fermionic dark matter and strange quark matter in quark stars

Abstract We study the structural properties like the gravitational mass, radius, and tidal deformability of dark matter (DM) admixed strange quark stars (SQSs). For the purpose we consider the vector MIT Bag model to describe the strange quark matter (SQM) and investigate the possible presence of accreted DM in the SQSs consequently forming DM admixed SQSs. We introduce feeble interaction between SQM and the accreted fermionic DM via a vector dark boson mediator. Considering the present literature, in the context of possible presence of DM in SQSs, this work is the first to consider interaction between DM and SQM in the DM admixed SQSs. The mass of the DM fermion (mχ) and the vector mediator (mξ) and the coupling (yξ) between them are determined in accordance with the constraint from Bullet cluster and the present day relic abundance, respectively. We find that the presence of DM reduces both the mass and radius of the star compared to the no-DM case. The massive the DM fermion, the lower the values of maximum mass and radius of the DM admixed SQSs. For the chosen values of mχ and corresponding values of mξ and yξ, the computed structural properties of the DM admixed SQSs satisfy all the various present day astrophysical constraints. We obtain massive DM admixed SQSs configurations consistent with the GW190814 observational data. Hence the secondary compact object associated with this event may be a DM admixed SQS.

Properties of Strange Quark Matter in the Context of Diquark Correlation

AbstractProperties of strange quark matter (SQM) have been studied as diquark matter with diquark correlation. The dense SQM is under strong magnetic field due to electroweak interaction of quarks. Here it is suggested that u, d, s quarks get correlated to form diquark matter of different flavors. The diquarks are suggested to behave like quasiparticles under the influence of strong magnetic field inside the dense quark matter. In the current work diquarks are described as the composite fermions which behave like quasiparticle under the strong magneticfield in an analogy with the electrons behaving in strong magnetic field. The thermodynamic potential for SQM has been estimated and behavior is studied with respect to chemical potential. The equation of state and the velocity of sound through SQM are also studied. Some interesting observations are made. It is suggested that the composite fermion picture of diquark correlation lowers the binding energy of the system making the SQM a more stable state.

Open bottom mesons and upsilon states in hot magnetized strange hadronic matter

The masses of open bottom mesons ([Formula: see text]([Formula: see text],[Formula: see text]), [Formula: see text]([Formula: see text],[Formula: see text]), [Formula: see text]([Formula: see text], [Formula: see text])) and upsilon states ([Formula: see text], [Formula: see text], [Formula: see text], [Formula: see text] and [Formula: see text]) are investigated in the isospin asymmetric strange hadronic medium at finite temperature in the presence of strong magnetic fields using a chiral effective Lagrangian approach. Here the chiral SU(3) Lagrangian is generalized to include the bottom sector to incorporate the interactions of the open bottom mesons with the magnetized medium. At finite temperature, the number density and scalar density of baryons are expressed in terms of thermal distribution functions. For charged baryons, the magnetic field introduces contribution from Landau energy levels. The masses of the open bottom mesons get modified through their interactions with the baryons and the scalar mesons, which undergo modifications in a magnetized medium. The charged [Formula: see text], [Formula: see text] mesons have additional positive mass shifts due to Landau quantization in the presence of the magnetic field. The medium mass shift of the upsilon states originates from the modification of the gluon condensates simulated by the variation of dilaton field ([Formula: see text]) and a quark mass term in the magnetized medium. The open bottom mesons and upsilon states experience a mass drop in the magnetized medium. The masses of these mesons initially increase with a rise in temperature, and beyond a high value of temperature, their masses are observed to drop. When the temperature is below 90[Formula: see text]MeV, the in-medium masses of the mesons increase with an increase in the magnetic field. However, at high temperatures (T > 90 MeV), the masses are observed to drop with an increase in the magnetic field. These in-medium modifications can have observable effects in asymmetric heavy-ion collisions experiments.

Gravitational Waves from Strange Star Core–Crust Oscillation

According to the strange quark matter hypothesis, pulsars may actually be strange stars composed of self-bound strange quark matter. The normal matter crust of a strange star, unlike that of a normal neutron star, is supported by a strong electric field. A gap is then presented between the crust and the strange quark core. Therefore, peculiar core–crust oscillation may occur in a strange star, which can produce distinctive gravitational waves. In this paper, the waveforms of such gravitational waves are derived using a rigid model. We find that the gravitational waves are extremely weak and undetectable, even for the next-generation detectors. Therefore, the seismology of a strange star is not affected by the core–crust oscillation. Observers will have to search for other effects to diagnose the existence of the crust.

Is the remnant of GW190425 a strange quark star?

This study investigates the effects of different QCD models on the structure of strange quark stars (SQS). In these models, the running coupling constant has a finite value in the infrared region of energy. By imposing some constraints on the strange quark matter (SQM) and exploiting the analytic and background perturbation theories, the equations of states for the SQM are obtained. Then, the properties of SQSs in general relativity are evaluated. By using component masses of GW190425 [1] as well as some conversion relations between the baryonic mass and the gravitational mass, the remnant mass of GW190425 is obtained. Our results for the maximum gravitational mass of SQS are then compared with the remnant mass of GW190425. The results indicate that the obtained maximum gravitational masses are comparable to the remnant mass of GW190425. Therefore, it is proposed that the remnant mass of GW190425 might be a SQS.

Dependence of maximum mass of strange star on finite strange quark mass (m s ≠ 0)

In this article we analyze a class of compact object in spheroidal geometry described by Vaidya–Tikekar model and MIT bag model equation of state considering the finite mass of strange quark (m s). The maximum mass and radius is found by maximizing the square of radial sound velocity at the centre. For monotonically decreasing nature of the sound velocity we note that an upper limit of the spheroidal parameter (λ) exists. Therefore for the calculation of maximum mass arbitrary choice of λ is not possible. The effect of strange quark mass on the maximum mass is found to satisfy previously obtained result (Li et al 2021 Eur. Phys. J. C 81 921). To apply the present model we consider the compact stars 4U 1608-52 and 4U 1820-30. The stability of strange quark matter inside these compact objects is explored by taking different values of the bag constant B. It is found that 4U 1608-52 may be categorized as strange star with wider stability window for three-flavor quark matter whereas 4U 1820-30 only shows metastability. The model is found to be stable against small radial perturbation. One possible drawback of the present model is the prediction of maximum mass from mass-radius plot. For this reason we have predicted the maximum mass from alternative approach.

Open charm mesons and charmonia in magnetized strange hadronic matter * *A.J.C.S acknowledges the support towards this work from the Department of Science and Technology, Government of India, via an INSPIRE fellowship (INSPIRE Code IF170745). AM acknowledges financial support from Department of Science and Technology (DST), Government of India (CRG/2018/002226)

We investigate the in-medium masses of open charm mesons (D( , ), ( , ), ( , )) and charmonium states ( , , , , ) in strongly magnetized isospin asymmetric strange hadronic matter using a chiral effective model. In the presence of a magnetic field, the number and scalar densities of charged baryons have contributions from Landau energy levels. The mass modifications of open charm mesons result from their interactions with nucleons, hyperons, and the scalar fields (the non-strange field σ, strange field ζ, and isovector field δ) in the presence of a magnetic field. The mass modifications of the charmonium states result from the modification of gluon condensates in a medium simulated by the variation in the dilaton field (χ) in the chiral effective model. The effects of finite quark masses are also incorporated in the trace of the energy-momentum tensor in quantum chromodynamics to investigate the mass shifts of charmonium states. The in-medium masses of open charm mesons and charmonia are observed to decrease with an increase in baryon density. The charged , , , and mesons have additional positive mass shifts due to Landau quantization in the presence of a magnetic field. The effects of the strangeness fraction are observed to be more dominant for mesons compared with D mesons. The mass shifts of charmonia are observed to be larger in hyperonic media compared with nuclear media when the effect of the finite quark mass term is neglected. These medium mass modifications can have observable consequences on the production of the open charm mesons and charmonia in high-energy asymmetric heavy-ion collision experiments.

Strange Quark Matter and the Astrophysical Nature of Anomalous Effects in 1–100 PeV Cosmic Rays

The composition of cosmic rays is of decisive importance for the determination of reasons for change in the slope of the spectra of extensive air showers (knee) at energies of 1–100 PeV. The characteristics of the extensive air showers, where the highest energy secondary hadrons are concentrated, have been analyzed. Some anomalous effects such as an increase in the absorption length of hadron showers, scaling violation in the spectra of secondary hadrons, an excess of muons in extensive air showers with gamma-ray families, the appearance of the halos, and the alignment of energy centers along a straight line are observed in X-ray emulsion chambers in the knee region. At the same energies equivalent to 1–100 PeV in the laboratory system, LHC and RHIC data demonstrate a scaling behavior of the hadron spectrum, which means that new nuclear processes are absent. These data imply that anomalies observed in cosmic rays are due to astrophysical reasons, i.e., changes in the composition of cosmic rays. The analysis of the data on the EAS cores suggests that the knee in their spectrum is formed by a nonnuclear component of cosmic rays, possibly consisting of particles of strange quark matter.

Thermal relaxation and cooling of quark stars with a strangelet crust

Context. In this article we explore the cooling of isolated quark stars. These objects are structured from a homogeneous quark matter core and crusted by ordinary matter or by strangelets. Aims. Our main purpose is to quantify the effects of a strangelet crust on the cooling and relaxation times of these strange stars. Methods. We adopt two kinds of crust: (i) a crust made of purely nuclear matter following the Baym-Pethick-Sutherland equation of state (EOS) and (ii) a crust made of nuggets of strange quark matter (strangelets). Both models have the same quark matter core, described by the MIT bag model EOS. Our study also includes the possible effects of color superconductivity in the quark core. Results. We have found that objects with a strangelet crust have a significantly different thermal relaxation time.