Adamu Issifu

We develop a self-consistent dark matter admix neutron star framework based on a contact vector current-current interaction that couples the chemical potentials of both sectors through mutual mean-field shifts, with the dark matter (DM) fraction ${F}_{D}={N}_{D}/{N}_{B}$ fixed as a global input parameter. This formulation provides a physically motivated alternative to fixed-density prescriptions, allowing the local DM density to follow the baryonic matter (BM) density throughout the stellar interior. As an application, we consider a mirror-DM scenario with exact symmetry between the dark and visible sectors and investigate neutron star (NS) matter using the $\mathrm{NL}3\ensuremath{\omega}\ensuremath{\rho}$, FSU2R, NL3, and DDME2 equations of state. We find that the amount of DM introduced through ${F}_{D}$ weakens the binding of dense matter, reduces its incompressibility, and softens the equation of state, while the DM-BM interaction governs the microscopic behavior of the DM in the dense BM medium. Consequently, DM increases the central density and compactness of NSs, lowers their maximum masses, and shifts the onset of the direct Urca process to higher stellar densities. As a consequence, the onset of rapid cooling is shifted to more massive stars for models with a stiff symmetry energy and to less massive stars for models with a soft symmetry energy, depending on the extra compactness that results from the DM admixture. These results demonstrate that mirror-DM admixtures modify both the microscopic composition and macroscopic structure of NSs, with potential implications for their thermal evolution and multimessenger observational signatures.

This paper studies radial and non-radial oscillations of protoneutron stars (PNSs) evolving from hot, neutrino-rich states to cold, catalyzed configurations, using a density-dependent relativistic mean-field equation of state (EoS) with nucleonic and hyperonic matter. The fundamental ( f ) and first pressure ( $$p_1$$ p 1 ) modes are computed in both the Cowling approximation and full general relativity (GR). For the f -mode, the Cowling approximation overestimates the frequency by $$\sim 24\%$$ ∼ 24 % in the hot phase, increasing to $$\sim 28\%$$ ∼ 28 % at $$T=0$$ T = 0 for $$M_B=1.5\,M_\odot $$ M B = 1.5 M ⊙ , and by $$\sim 19\%$$ ∼ 19 % (hot/intermediate) rising to $$\sim 22\%$$ ∼ 22 % at $$T=0$$ T = 0 for $$M_B=2.3\,M_\odot $$ M B = 2.3 M ⊙ . For the $$p_1$$ p 1 -mode, deviations are smaller: $$\sim 6.7\%$$ ∼ 6.7 % (hot), peaking at $$\sim 10\%$$ ∼ 10 % during deleptonization, and decreasing to $$\sim 6.6\%$$ ∼ 6.6 % at $$T=0$$ T = 0 . Hyperons slightly increase oscillation frequencies. Stage-dependent f -mode scaling shows that expressing $$M\omega $$ M ω in terms of the effective compactness $$\tilde{\eta }=\sqrt{M^3/I}$$ η ~ = M 3 / I significantly reduces thermal scatter, bringing all evolutionary stages onto a tighter curve. Radial oscillations of a $$1.4\,M_\odot $$ 1.4 M ⊙ PNS show strong sensitivity of displacement and pressure perturbations to thermal state, composition, and compactness, with hyperonic EoSs yielding higher frequencies and modified node structures. Differences in $$\nu _0$$ ν 0 and $$\Delta \nu _n$$ Δ ν n between nucleonic and hyperonic models provide potential observational constraints on the dense matter EoS.

We investigate the evolution of magnetized protoneutron stars (PNSs) across four schematic stages: neutrino-trapped, deleptonization, neutrino-transparent, and the final cold, catalyzed neutron star (NS). Using a quasi-static approximation on the Kelvin–Helmholtz timescale, we model strongly magnetized configurations ( $$B \sim 10^{17}\,\text {G}$$ B ∼ 10 17 G ) using axisymmetric XNS 4.0 with Equations of State (EoS) derived from relativistic mean-field theory calibrated by the DDME2 parameterization. We analyze the gravitational mass, equatorial radius, shape deformation, magnetic flux, and magnetic-to-binding energy ratio as functions of thermodynamic and compositional changes. Our results show that increasing entropy per baryon and decreasing lepton fraction raise core temperatures, which in turn enhance magnetic deformation, flux confinement, and the magnetic-to-binding energy ratio. Magnetic field dissipation is most efficient during the deleptonization and neutrino-transparent stages, a process that ultimately determines the observable field strength of the mature NS. This work presents a systematic general-relativistic characterization of how thermal and compositional evolution reshapes magnetic-field structure, deformation, and magnetic energetics across multiple stages of PNS evolution.

In this paper, we investigate the Quantum Chromodynamics (QCD)-like running coupling, ${\alpha }_s^{AdS}\left(Q^2\right)$, and its associated $\beta$-function within a tachyonic Anti-de Sitter (AdS)/QCD framework. The ${\mathrm{AdS}}_5$ bulk geometry is deformed through the introduction of a color dielectric function $G\left(\varphi \right(z\left)\right)$, associated with a tachyon field $\varphi \left(z\right)$. This function governs the behavior of ${\alpha }_s^{AdS}\left(Q^2\right)$ across all momentum scales by modifying the AdS background at both small and large values of the holographic coordinate z. In the ultraviolet (UV) regime (small z), the deformation is driven by free tachyons and reproduces features consistent with perturbative QCD. In contrast, in the infrared (IR) regime (large z), tachyon condensation dominates, yielding behavior characteristic of nonperturbative QCD. This construction enables a unified description of the running coupling and its $\beta$-function over the full range of momentum transfer $Q^2$, where $Q^2$ denotes the space-like momentum scale.

We present the first systematic study of rigidly rotating protoquark stars based on isentropic equations of state (EOS) within the density-dependent quark mass (DDQM) framework. Using a quasi-static equilibrium approach, we follow the Kelvin--Helmholtz evolution from hot, lepton-rich matter to a cold, catalyzed quark star. Rotation substantially enhances the maximum stable mass (by up to $\sim 40\%$), equatorial radius, and key rotational observables, with the ratio of rotational kinetic to gravitational potential energy, $T_{\rm kin}/|W|$, reaching $0.18$--$0.19$ near the Keplerian limit, indicating a heightened susceptibility to gravitational-wave--emitting instabilities. Thermal evolution introduces a clear ordering: all stellar properties peak during the lepton-rich stages and decrease monotonically as the star cools. Compared to hadronic stars, rotating protoquark stars exhibit larger radii, higher moments of inertia, and stronger quadrupolar deformation, producing a distinct signature in the mass--radius--spin plane that can accommodate objects such as HESS~J1731--347 and PSR~J0740+6620. These results demonstrate that future multimessenger observations must account for both thermal history and rotation to robustly identify quark matter in compact stars.

We develop a unified framework in which the dynamics of a scalar glueball field, originating from phenomenological nonperturbative QCD confinement, simultaneously governs the deconfinement transition of strongly interacting matter and drives cosmological inflation. Starting from a temperature-dependent effective potential $V_{eff}(φ, T)$, we show that the glueball mass vanishes at a critical temperature $T_{cφ}$, signaling a first-order phase transition characterized by supercooling and a transient metastable vacuum. In the high-temperature regime $T > T_{cφ}$, the deconfined phase naturally produces an exponential expansion of the scale factor, providing the correct conditions for inflation. By computing the slow-roll parameters and the resulting spectral index $n_s$, tensor-to-scalar ratio $r_s$, and running $α_s$, we confront the model with the Planck observations. The predicted values of $n_s$ and $r_s$ fall within the Planck confidence contours for a broad and physically motivated range of the parameter $γ$ and for $N \approx 50\text{--}60$ e-folds. A distinctive linear relation, $r_s = 4(1-n_s)-72γ$, emerges as a testable signature of the model. Normalization to the observed scalar amplitude further constrains the thermal correction parameter $σ^2$ and the coupling $γ$, linking cosmological data directly to QCD-scale dynamics. These results demonstrate that a confinement-inspired potential can naturally reproduce the observed inflationary phenomenology and offer a novel bridge between early-universe cosmology and the nonperturbative sector of QCD.