arXiv subjects

Hosein Gholami

Publications and source records attributed to Hosein Gholami.

13 recordsLinked to original sources

arXiv2026

A doubly critical point in the color-superconducting regime of the RG-consistent NJL model

Nambu--Jona-Lasinio (NJL) models of color-superconducting quark matter suffer from cutoff artifacts once temperature or quark chemical potential become comparable to the model cutoff. These artifacts can be removed employing a renormalization-group (RG) consistent regularization scheme. In this article we perform a systematic study of neutral beta-equilibrated quark matter within the three-flavor NJL model with RG consistent regularization. Varying the coupling constant in the scalar diquark channel, we map out the phase diagram in the plane of chemical potential and temperature, and identify the gapless domains. We particularly focus on the melting pattern of the color-flavor locked (CFL) phase. At larger couplings the CFL phase melts through a so-called $d$SC phase, as expected from leading-order Ginzburg--Landau analyses. Lowering the coupling, the phase structure becomes markedly richer: While at large densities the CFL phase still melts through a $dSC$ phase, we find a $uSC$ phase at lower chemical potential. These phases, $uSC$ and $dSC$ meet at a doubly critical point whose existence had been anticipated long ago but was never demonstrated explicitly in a model.

hep-ph↗

arXiv2026

The petit four of color-superconducting phases in proto-neutron star evolution

At high densities and moderate temperatures, hadronic matter is expected to undergo a first-order phase transition into a color-superconducting (CSC) state. A proto-neutron star describes the earliest evolutionary stages during the first seconds to minutes after core-collapse supernovae and therefore has the potential to assess the appearance of CSC phases at such high densities and moderate temperatures. To address this, we incorporate proto-neutron star conditions, considering neutrino-trapped and neutrino-transparent ones, into the equation of state including color-superconducting phases in a recently developed RG-consistent NJL model. Since the total baryon number of a proto-neutron star is conserved during its later evolution, tracking stellar configurations from an initial mass of the hot proto-neutron star to the final cold neutron star along isolines of baryon number allows us to investigate whether color-superconducting phases can form at any point along this trajectory. By mapping this multidimensional transition in the hot furnace of a core-collapse supernovae cooling from a neutrino-trapped birth state to a cold, neutrino-transparent final state, we reveal four distinct core evolution scenarios-our "petit four" of proto-neutron star evolution: a delayed collapse from the CSC phase to a black hole, a persistent CSC phase, a vanishing CSC phase, and a fleeting CSC phase. For our specific parameterization of the hadronic and the CSC equation of state, we find that a stable color-superconducting phase can only be sustained in the final cold neutron star for a narrow, high-mass region.

nucl-th↗

arXiv2026

Studying the QCD Matter produced in Heavy-Ion Collisions using the MUSES Calculation Engine

The equation of state of hot and dense matter is essential for describing heavy-ion collisions at all collision energies. Here, we explore the capabilities of the latest version of the MUSES Calculation Engine, $\textit{Calliope}$, focusing on software modules and workflows that compute the equation of state and observable properties of the matter produced in heavy-ion collisions. These include several equations of state, ranging from first-principles lattice QCD to phenomenological approaches, with or without a critical point, and with phase-space dimensionality ranging from two dimensions defined by temperature $T$ and baryon chemical potential $\mu_B$, to four dimensions after the addition of strangeness and electric-charge chemical potentials $\mu_S$ and $\mu_Q$. We also discuss modules that provide additional thermodynamic quantities and observables relevant for heavy-ion modeling, including elements of the pressure Hessian matrix and transport coefficients. Workflow examples are constructed that merge two equations of state thermodynamically consistently to extend phase-diagram coverage, and feed the results into an equation of state inverter to produce inputs suitable for hydrodynamic simulations. Finally, we apply this framework to perform a relativistic viscous hydrodynamic simulation with equations of state with an extended $T$ and $\mu_B$ coverage and a movable critical point, including effects from transport coefficients that phenomenologically encode critical scaling, at collision energies $\sqrt{s_{NN}}=7.7, 19.6$, and $39$ GeV.

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arXiv2026

Scalar diquarks in the QCD vacuum

While QCD fundamentally only depends on the values of the strong coupling and the quark masses, it exhibits a rich nonperturbative structure at low energies, where composite fields emerge as the relevant degrees of freedom. In this work, we present a first-principles framework that captures the transition from fundamental QCD to its low-energy sector in vacuum. It builds on the dynamical hadronization technique within the functional renormalization group approach to two-flavor QCD. In this framework, the low-energy constants relevant for effective models, including effective masses and coupling strengths, naturally emerge from the underlying renormalization group flow without introducing free parameters beyond those of QCD itself. We investigate the dynamical emergence of the pion, the $\sigma$-meson and the scalar diquark in both imaginary and real time, and determine a set of QCD low-energy constants which can be used to fix the free parameters of models of dense quark matter with a two-flavor color superconducting phase. In particular, this includes previously unknown properties of the scalar diquark. Our results provide important microscopic input for constraining color superconducting phases, which are expected to play a key role in our understanding of dense neutron star matter.

hep-ph↗

arXiv2026

Interplay between inhomogeneous chiral and crystalline color-superconducting phases in the two-flavor NJL model

We study the interplay between the chiral density wave (CDW) and the single-plane-wave Larkin-Ovchinnikov-Fulde-Ferrell (LOFF) phase of color-superconducting matter in two-flavor quark matter at vanishing and non-vanishing temperature $T$, quark number chemical potential $\mu$ and isospin chemical potential $\delta\mu$. The analysis is performed within the two-flavor Nambu--Jona-Lasinio (NJL) model in the chiral limit, using a three-momentum cutoff scheme. Treating the CDW wave vector $\vec{q}$ and the LOFF pair momentum $\vec{q}\,'$ as independent variational parameters, we minimize the mean-field effective potential with respect to both amplitudes and both wave vectors, without constraining their relative orientation, and map out the $T$-$\mu$ and $\mu$-$\delta\mu$ phase diagrams for a range of diquark couplings $G_D$. Our central result is that $\vec{q}$ and $\vec{q}\,'$ are never simultaneously nonzero: inhomogeneous chiral and diquark condensates do not coexist across the entire parameter range.

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arXiv2025

A finite temperature framework for quark matter with color-superconducting phases

Current observations of neutron stars and measurements of gravitational waves only provide constraints on the zero temperature ($T=0$) equation of state (EoS) of dense matter. The detection of the post-merger gravitational-wave signal from a binary neutron star merger would additionally provide access to finite-temperature properties of the EoS which contain more information about the composition and the interactions of dense matter than the cold EoS alone. In particular deconfined quark matter may be probed by its characteristic finite temperature effects. This is especially the case for color-superconducting phases, in which the quasiparticle contribution to the thermal pressure is exponentially suppressed at low temperatures. Here we develop a new finite $T$ framework to model the thermal EoS for dense quark matter based on the cold quark matter EoS which is useful for numerical relativity simulations. We test the validity of the framework against a three-flavor NJL mean-field calculation, both with and without diquark pairing. We find that even for the complicated phase diagram of the NJL model including multiple different phases the framework is accurate to the few percent level for temperatures up to $T\sim 50\,$MeV.

astro-ph.HE↗

arXiv2025

Neutrino absorption in two-flavor color-superconducting quark matter

We calculate the absorption mean free paths of electron and muon neutrinos in two-flavor color-superconducting (2SC) quark matter in the density and temperature range that is relevant to binary neutron star mergers. We model the strong interaction between quarks using a Nambu--Jona-Lasinio model, performing calculations self-consistently in the mean-field approximation. Since the 2SC gap is large we restrict our analysis to the contribution of unpaired quarks. We find that at low temperatures absorption by a down quark $ν+d \to u+e^-/μ^-$ is kinematically not allowed, so absorption by a strange quark $ν+s \to u+e^-/μ^-$ dominates the mean free path. As temperature or neutrino energy rises, the $d$ quark absorption channel becomes active, and the mean free path shrinks. We find that in equilibrated 2SC matter with an electron lepton fraction $Y_{L_e}=0.1$, the neutrinos form a degenerate gas with a mean free path of meters or less, independent of the temperature.

nucl-th↗

arXiv2025

Removing cutoff artifacts in the NJL model by a Renormalization Group consistent treatment

We summarize how a renormalization-group (RG)-consistent treatment removes well-known artifacts in NJL-model descriptions of color-superconducting quark matter. We introduce two RG-consistent schemes, "minimal" and "massless", and present analytic solutions for the diquark gap at $T=0$ and for the phase boundary $T_c(μ)$ in symmetric massless matter, representing the high-density limit of the model. We compare the pairing gaps, phase diagram, and speed of sound with results obtained using conventional regularization.

hep-ph↗

arXiv2025

Renormalizing the Quark-Meson-Diquark Model

We present a comprehensive study of the two-flavor Quark--Meson--Diquark (QMD) model by comparing a renormalization approach with a renormalization-group (RG) consistent mean-field formulation based on the functional renormalization group (FRG). The renormalized QMD model allows analytical investigations of key quantities such as the zero-temperature diquark gap and the critical temperature for color superconductivity, ultimately reproducing the exact BCS relation in the high-density limit. We carry out the same analysis for different schemes of RG-consistent QMD models. We show that the RG-consistent approach yields a phase diagram and thermodynamic properties qualitatively similar to those of the renormalized model, provided both are embedded within a unified scheme that ensures consistent vacuum properties. In particular, both treatments recover the Stefan--Boltzmann limit at high densities. On the other hand, whether the BCS relation for the critical temperature is satisfied depends on the details of the RG-consistent setup. Our results highlight the relevance of renormalization and RG-consistent methods for accurately capturing the thermodynamics of QMD and related effective models with diquark degrees of freedom.

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arXiv2025

Comprehensive Analysis of Constructing Hybrid Stars with an RG-consistent NJL Model

In this work, we investigate the properties of hadronic and quark matter that would allow for a first order phase transition between them within neutron stars. To this end, we use a parameterizable Relativistic Mean-Field (RMF) description for the hadronic phase and a Renormalization Group-consistent Nambu-Jona-Lasino (RG-NJL) model for the quark phase. This also enables us to consider sequential phase transitions involving a two-flavor color-superconducting (2SC) and a color-flavor-locked (CFL) phase. We find large ranges for all parameters that facilitate a phase transition, even when constrained by current astrophysical data. We further attempt to filter out stars with a high chance of detectability by mass-radius measurement, i.e., stars with identical mass but different radii, so-called twin stars. However, we find that such configurations are outside the constrained parameter spaces. Instead, most of the mass-radius relations that feature a phase transition appear to be indistinguishable from a purely hadronic description.

astro-ph.HE↗

arXiv2025

On the Calculation of Pressure Derivatives in Mean-Field Thermal Field Theories

Accurate determination of higher-order pressure derivatives with respect to temperature $T$ and chemical potential $μ$ is essential for analyzing critical phenomena, transport properties, and phase transitions in strongly interacting matter. However, standard numerical differentiation methods often suffer from large numerical instabilities, especially in more complex mean-field thermal field theories. In this work, we present an approach that systematically derives symbolic expressions for these higher-order derivatives, bypassing the numerical instabilities commonly encountered in conventional methods. Our formalism is based on a Jacobian technique, which ensures that the dependence of internal mean-field parameters is fully incorporated into the final symbolic expressions. We illustrate the effectiveness of this method using the two-flavor Nambu-Jona-Lasinio model as an example and show that it is particularly advantageous near phase transitions and at low temperatures, where numerical differentiation becomes highly sensitive.

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arXiv2024

Renormalization-group consistent treatment of color superconductivity in the NJL model

The Nambu-Jona-Lasinio (NJL) model and specifically its extension to color superconductivity (CSC) is a popular effective model for investigating dense quark matter. However, the reliability of its results is challenged by cutoff artifacts, which emerge if temperature or chemical potential are of the order of the cutoff energy scales. In this work, we generalize an idea from [Braun et al. SciPost Phys., 6:056, 2019], which is based on the requirement of renormalization-group (RG) consistency and has successfully been applied to the two-flavor Quark-Meson-Diquark model, to the NJL model for electrically and color-neutral three-flavor color-superconducting quark matter. To this end, we analyze the medium divergences of the model and eliminate them by appropriate counterterms, introducing three different schemes. We show that the RG-consistent treatment removes the cutoff artifacts of the conventional regularization and enables the investigation of CSC matter at higher densities by the model. Our studies reveal the emergence of a so-called d-quark superconducting (dSC) phase within the melting pattern of the Color-Flavor Locked (CFL) phase at high chemical potentials, consistent with earlier Ginzburg-Landau analyses.

hep-ph↗

arXiv2024

Astrophysical constraints on color-superconducting phases in compact stars within the RG-consistent NJL model

We determine parameters of the renormalization group-consistent three-flavor color-superconducting Nambu-Jona-Lasinio (NJL) model that are suited to investigate possible compact-star configurations. Our goal is to provide quark-matter equations of state (EoS) that can be used for hadron-quark hybrid-star constructions. To that end, we mainly focus on the parameters of the quark-matter model. By varying the vector and diquark coupling constants, we analyze their impact on the EoS, the speed of sound, the maximum diquark gap, and the mass-radius relation. In almost all configurations, a stable color-flavor-locked (CFL) phase appears in the core of the maximum-mass configurations, typically spanning several kilometers in radius. In other cases, the star's two-flavor color-superconducting (2SC) branch of the EoS becomes unstable before reaching the CFL transition density. At neutron-star densities, the speed of sound squared reaches up to $c_s^2 \sim 0.6$ and the CFL gap up to $Δ\sim250\,$MeV. We argue that adding a hadronic EoS at lower densities by performing a Maxwell construction does not increase the maximum mass substantially. Thus we use the $2.0 M_{\odot}$ constraint to constrain the NJL model parameters that are suited for the construction of hybrid-star EoS. We construct three examples of the hybrid-star model, demonstrating that there is room for different color-superconducting compositions. The hybrid EoSs obtained in this way can have no 2SC matter or different ratios of 2SC and CFL quark matter in the core. We show that early hadron-quark transitions are possible that can modify the tidal deformability at 1.4 $M_\odot$. We find that these EoSs are consistent with the imposed constraints from astrophysics and perturbative QCD. They allow for different hybrid-star scenarios with a hadronic EoS that is soft at low to intermediate densities ($\sim 1-3\, n_{\text{sat}}$).

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