Dense Quark Matter Research Articles

Dual symmetries of dense isotopically and chirally asymmetric QCD

In the present paper, the dual symmetries of dense quark matter phase diagram found in some massless three- and two-color NJL models in the mean field approximation have been shown to exist at a more fundamental level as dual transformations of fields and chemical potentials leaving the Lagrangian invariant. As a result, the corresponding dual symmetries of the full phase diagram can be shown without any approximation. And it has been shown not only in the NJL models, but also in framework of two- and three-color massless QCD itself. This is quite interesting, since one might say that it is not very common to show something completely non-perturbatively in QCD.

Topological susceptibility and axion potential in two-flavor superconductive quark matter

We study the potential of the axion, a, of Quantum Chromodynamics, in the two-flavor color superconducting phase of cold and dense quark matter. We adopt a Nambu-Jona-Lasinio-like model. Our interaction contains two terms, one preserving and one breaking the U(1)A symmetry: the latter is responsible of the coupling of axions to quarks. We introduce two quark condensates, hL and hR, describing condensation for left-handed and right-handed quarks respectively; we then study the loci of the minima of the thermodynamic potential, Ω, in the (hL,hR) plane, noticing how the instanton-induced interaction favors condensation in the scalar channel when the θ angle, θ=a/fa, vanishes. Increasing θ we find a phase transition where the scalar condensate rotates into a pseudoscalar one. We present an analytical result for the topological susceptibility, χ, in the superconductive phase, which stands both at zero and at finite temperature. Finally, we compute the axion mass and its self-coupling. In particular, the axion mass ma is related to the full topological susceptibility via χ=ma2fa2; hence our result for χ gives an analytical result for ma in the superconductive phase of high-density Quantum Chromodynamics. Published by the American Physical Society 2024

Dual chiral density wave induced oscillating Casimir effect

The Casimir effect is known to be induced from photon fields confined by a small volume, and also its fermionic counterpart has been predicted in a wide range of quantum systems. Here, we investigate what types of Casimir effects can occur from quark fields in dense and thin quark matter. In particular, in the dual chiral density wave, which is a possible ground state of dense quark matter, we find that the Casimir energy oscillates as a function of the thickness of matter. This oscillating Casimir effect is regarded as an analog of that in Weyl semimetals and is attributed to the Weyl points in the momentum space of quark fields. In addition, we show that an oscillation is also induced from the quark Fermi sea, and the total Casimir energy is composed of multiple oscillations. Published by the American Physical Society 2024

Analysis of charged hadrons’ transverse momentum distributions in p + Pb and Xe + Xe collisions at LHC energies

This paper is focused on comparative analysis of transverse momentum ( pT ) distributions across two different sets of experimental data from ALICE at the LHC, juxtaposing with the Monte-Carlo models EPOS-LHC and EPOS 1.99 simulations. The chosen collision sets have approximately same per nucleon energy. We analyze the transverse momentum spectra of hadrons ( π++π−, K++K− and p+p¯ ) in p+Pb collisions at sNN= 5.02 TeV, and Xe + Xe collisions at sNN= 5.44 TeV spanning a rapidity range of 0 < yCM < 0.5, centrality of 0 to 5% (the most central or head-on collisions). Analysis of the Hadrons yield is crucial for understanding the mechanism of underlying hadronization in the hot and dense quark matter produced in relativistic heavy ion collisions. The experimental results are compared with the predictions of hydrodynamic models EPOS-LHC and EPOS-1.99. It is notably found that the maximum yields of various particles occur at low pT. Furthermore, the comparison showed a slightly better agreement between experimental results and the predictions of the EPOS-LHC as opposed to that of EPOS-1.99. The EPOS-LHC model significantly shows an enhanced agreement with experimental results in the case of Xe+Xe collisions as compared to p+Pb collisions.

Quark matter and nuclear astrophysics: Recent developments

Does deconfined cold quark matter occur in nature? This is currently one of the fundamental open questions in nuclear astrophysics. In these proceedings, I review the current state-of-the-art techniques to address this question in a model-agnostic manner, by synthesizing inputs from astrophysical observations of neutron stars and their binary mergers, and first-principles calculations within nuclear and particle theory. I highlight recent improvements in perturbative calculations in asymptotically dense cold quark matter, as well as compelling evidence for a conformalizing transition within the cores of massive neutron stars.

Dual properties of dense quark matter with color superconductivity phenomenon

Dual properties of dense quark matter with color superconductivity phenomenon

Exploring the axion potential and axion walls in dense quark matter

Exploring the axion potential and axion walls in dense quark matter

Axion-polaritons in the magnetic dual chiral density wave phase of dense QCD

We investigate the propagation of electromagnetic radiation in the magnetic dual chiral density wave (MDCDW) phase of dense quark matter. Considering the theory of low-energy fluctuations in this phase, we show how linearly polarized photons reaching the MDCDW medium couple to the fluctuation field to produce two hybridized modes of propagation that we call in analogy with similar phenomenon in condensed matter physics axion polaritons, one of them being gapless and the other gapped. The gapped mode's gap is proportional to the background magnetic field and inversely proportional to the amplitude of the inhomogeneous condensate. The generation of axion polaritons can be traced back to the presence of the chiral anomaly in the low-energy theory of the fluctuations. Considering the Primakoff effect in the MDCDW medium, we argued that axion polaritons can be generated inside quark stars bombarded by energetic photons coming from gamma-ray bursts and point out that this mechanism could serve to explain the missing pulsar paradox in the galaxy center.

Impact of Multiple Phase Transitions in Dense QCD on Compact Stars

This review covers several recent developments in the physics of dense QCD with an emphasis on the impact of multiple phase transitions on astrophysical manifestations of compact stars. To motivate the multi-phase modeling of dense QCD and delineate the perspectives, we start with a discussion of the structure of its phase diagram and the arrangement of possible color-superconducting and other phases. It is conjectured that pair-correlated quark matter in β-equilibrium is within the same universality class as spin-imbalanced cold atoms and the isospin asymmetrical nucleonic matter. This then implies the emergence of phases with broken space symmetries and tri-critical (Lifshitz) points. The beyond-mean-field structure of the quark propagator and its non-trivial implications are discussed in the cases of two- and three-flavor quark matter within the Eliashberg theory, which takes into account the frequency dependence (retardation) of the gap function. We then construct an equation of state (EoS) that extends the two-phase EoS of dense quark matter within the constant speed of sound parameterization by adding a conformal fluid with a speed of sound cconf.=1/3 at densities ≥10nsat, where nsat is the saturation density. With this input, we construct static, spherically symmetrical compact hybrid stars in the mass–radius diagram, recover such features as the twins and triplets, and show that the transition to conformal fluid leads to the spiraling-in of the tracks in this diagram. Stars on the spirals are classically unstable with respect to the radial oscillations but can be stabilized if the conversion timescale between quark and nucleonic phases at their interface is larger than the oscillation period. Finally, we review the impact of a transition from high-temperature gapped to low-temperature gapless two-flavor phase on the thermal evolution of hybrid stars.

Photon propagation in magnetized dense quark matter. A possible solution for the missing pulsar problem.

In this paper it is reviewed the topological properties and possible astrophysical consequences of a spatially inhomogeneous phase of quark matter, known as the Magnetic Dual Chiral Density Wave (MDCDW) phase, that can exist at intermediate baryon density in the presence of a magnetic field. Going beyond mean-field approximation, it is shown how linearly polarized electromagnetic waves penetrating the MDCDW medium can mix with the phonon fluctuations to give rise to two hybridized modes of propagation called as axion polaritons because of their similarity with certain modes found in condensed matter for topological magnetic insulators. The formation of axion polaritons in the MDCDW core of a neutron star can serve as a mechanism for the collapse of a neutron star under the bombardment of the gamma rays produced during gamma ray bursts. This mechanism can provide a possible solution to the missing pulsar problem in the galactic center.

Causality violation and the speed of sound of hot and dense quark matter in the Nambu–Jona-Lasinio model

The Nambu--Jona-Lasinio model is widely used to study strong-interaction phenomena in vacuum and quark matter. Since the model is nonrenormalizable, one needs to work within a specific regularization scheme to obtain finite results. Here we show that a commonly used cutoff regularization scheme leads to unphysical results, such as superluminal speed of sound and wrong high-temperature behavior of the specific heat and other thermodynamical quantities. Such a troublesome feature of the cutoff regularization invalidates the model for temperature and baryon density values relevant to the phenomenology of heavy-ion collisions and compact stars. We show that the source of the problems stems from cutting off momentum modes in finite integrals depending on thermal distribution functions in the grand canonical potential. The problems go away when taking into account the full momentum range of those integrals. Explicit examples are worked out in the SU(2)-flavor version of the model.

Electrical conductivity of strongly magnetized dense quark matter - possibility of quantum Hall effect

We have pointed out the possibilities of quantum Hall effect (QHE) and Shubnikov-de Haas (SdH) oscillation in the transportation of strongly magnetized degenerate quark matter- expected inside the highly dense compact star, such as the neutron star. The anisotropic pattern of electrical conductivity and resistivity tensor is explored in classical to quantum cases by considering the Landau quantization of quarks in the presence of a finite magnetic field. With increasing magnetic field, classical to quantum transitions are realized through enhanced (reduced) resistivity (conductivity) with QHE/SdH type oscillatory patterns. Estimating QCD relaxation time for degenerate quark matter from Ref. [57], eB≈(1−4)mπ2 can be considered a strong magnetic field for massless and degenerate quark matter with quark chemical potential μ≈0.2−0.4 GeV. We discovered exotic quantum magnetic oscillating patterns associated with the QHE and SdH phenomena within the mentioned regimes.

Cold dense quark matter with phenomenological medium effects: A self-consistent formulation of the quark-mass density-dependent model

We revisit the quark-mass density-dependent model -- a phenomenological equation of state for deconfined quark matter in the high-density low-temperature regime -- and show that thermodynamic inconsistencies that have plagued the model for decades, can be solved if the model is formulated in the canonical ensemble instead of the grand canonical one. Within the new formulation, the minimum of the energy per baryon occurs at zero pressure, and the Euler's relation is verified. Adopting a typical mass-formula, we first analyze in detail a simple model with one particle species. We show that a ``bag'' term that produces quark confinement naturally appears in the pressure (and not in the energy density) due to density dependence of the quark masses. Additionally, the chemical potential gains a new term as in other models with quark repulsive interactions. Then, we extend the formalism to the astrophysically realistic case of charge-neutral three-flavor quark matter in equilibrium under weak interactions, focusing on two different mass formulae: a flavor dependent and a flavor blind one. For these two models, we derive the equation of state and analyze its behavior for several parameter choices. We systematically analyze the parameter space and identify the regions corresponding to self-bound 2-flavor and 3-flavor quark matter, hybrid matter and causal behavior.

Degenerate fermionic matter at N3LO : Quantum electrodynamics

We determine the pressure of a cold and dense electron gas to a nearly complete next-to-next-to-next-to-leading order (N$^3$LO) in the fine-structure constant $\alpha_e$, utilizing a new result for the two-loop photon self-energy from a companion paper. Our result contains all infrared-sensitive contributions to the pressure at this order, including the coefficient of the $O(\alpha_e^3 \ln \alpha_e^{ })$ term, and leaves only a single coefficient associated with the contributions of unresummed hard momenta undetermined. Moreover, we explicitly demonstrate the complete cancellation of infrared divergences according to the effective field theory paradigm by determining part of the hard contributions at this order. Our calculation provides the first improvement to a 45-year-old milestone result and demonstrates the feasibility of the corresponding N$^3$LO calculation for cold and dense quark matter.

Estimation of transport coefficients of dense hadronic and quark matter* *DS acknowledges the institute postdoctoral funding and research facilities at Indian Institute of Science Education and Research Berhampur, Odisha at the initial stage of this work. NA acknowledges the funding support of IFCPAR/CEFIPRA under Project (5804-3)

In this study, we calculated transport coefficients including the shear viscosity and electrical conductivity relative to the density of dense hadronic and quark matter. By considering the simple massless limit for the quark matter and two different effective models for the hadronic matter, we estimated the transport coefficients of the two phases separately. Accordingly, density profiles of the transport coefficients were depicted in two parts: the phase-space part and the relaxation time part. From calculating the shear viscosity to density ratio, we also explored the nearly perfect fluid domain of the quark and hadronic matter.

Cold dense quark matter for the Alcubierre drive model

The Alcubierre warp drive is a controversial theory by Miguel Alcubierre. Some arguments claim that it may not be physically possible. However, based on previous studies, this work suggests an extremely dense quark matter with a low-temperature limit of up to zero that can satisfy the requirements of the Alcubierre warp drive model considering the color interaction potential energy. The energy-momentum tensor and velocity of the warp drive model supported by the quark matter are also described.

Anomalous enhancement of dilepton production due to soft modes in dense quark matter

We explore how the dilepton production rate is modified near the critical temperature of color superconductivity and QCD critical point by the soft modes inherently associated with the phase transitions of second-order. It is shown that the soft modes affect the photon self-energy significantly through so called the Aslamasov-Larkin, Maki-Thompson and density of states terms, which are known responsible for the paraconductivity in the metalic superconductivity, and cause an anomalous enhancement of the production rate in the low energy/momemtum region.

Recovering the Conformal Limit of Color Superconducting Quark Matter within a Confining Density Functional Approach

We generalize a recently proposed confining relativistic density-functional approach to the case of density-dependent vector and diquark couplings. The particular behavior of these couplings is motivated by the non-perturbative gluon exchange in dense quark matter and provides the conformal limit at asymptotically high densities. We demonstrate that this feature of the quark matter EoS is consistent with a significant stiffness in the density range typical for the interiors of neutron stars. In order to model these astrophysical objects, we construct a family of hybrid quark-hadron EoSs of cold stellar matter. We also confront our approach with the observational constraints on the mass–radius relation of neutron stars and their tidal deformabilities and argue in favor of a quark matter onset at masses below 1.0M⊙.

Femtometreistä valovuosiin: neutronitähdet eksoottisen aineen laboratoriona

The Standard Model of particle physics describes the basic properties and interactions of all known elementary particles at an astonishingly good level, and predictions derived from it have time and again been experimentally verified. One of its parts, namely the theory of the strong nuclear interaction, Quantum Chromodynamics (QCD), has however proven to be computationally extremely demanding. In particular, the properties of matter described by QCD are at the moment still largely unknown in the limit of high baryon density.&#x0D; Very recently, the study of dense QCD matter has taken important steps forward owing largely to new observational data originating from a distant but very effective laboratory: neutron stars. The cores of these extremely compact stars contain the densest form of matter in our present-day Universe, and the properties of this matter are reflected on the measurable macroscopic properties of the stars themselves. In this review article, I will introduce this active field of research, placing particular emphasis on recent efforts to discover an entirely new phase of matter - cold and dense quark matter - inside the cores of the most massive neutron stars.

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.