We show that the compact star XTE J1814-338 can be explained as a strange star admixed with self-interacting bosonic dark matter (BDM), provided the dark matter fraction exceeds approximately 70%. This interpretation leads to a robust constraint on the BDM particle mass: m chi less than or similar to 307(lambda/pi)1/4 MeV (lambda is the dimensionless coupling constant of the BDM). The result is independent of formation scenario and microphysical details and is falsifiable by future NICER and LIGO/Virgo observations.

Strong magnetic fields and anisotropic stresses can substantially modify the structure and observable properties of compact stars. In this review, we present a unified treatment of magnetically induced anisotropy across neutron stars, hybrid stars, and white dwarfs, connecting the microphysical equation of state effects to macroscopic structure and multimessenger observables. We demonstrate that magnetic-field geometry plays a decisive role: toroidally oriented (transverse) fields enhance the maximum mass by providing additional perpendicular pressure support, whereas radially oriented fields primarily increase central compression with comparatively small mass gain. In neutron stars, anisotropy and magnetic stresses can shift phase-transition thresholds in hybrid models and enable configurations in the lower mass gap with significantly smaller magnetic energy compared to the gravitational binding energy. We further show that continuous gravitational wave emission from magnetically deformed neutron stars provides a complementary probe of internal field geometry through ellipticity-driven strain evolution. In magnetized white dwarfs, super-Chandrasekhar masses arise from the spatial redistribution of magnetic stresses rather than from globally strong magnetic energy. Taken together, these results highlight that magnetic-field geometry and matter anisotropy are as important as field strength in determining mass–radius relations, tidal deformability, gravitational wave detectability, and the emergence of extreme compact-star configurations.

There is an ongoing discussion in the literature on the nature of long-period transients (LPTs), radio-emitting sources with periods ranging from hundreds to tens of thousands of seconds. Although some of these objects have been identified as white dwarf (WD) + M-dwarf binaries, this description currently does not fit the entire class. An example is GLEAM-X J162759.5-523504.3 (hereafter GLEAM-X J1627-5235), with a period of 1091 s, for which the lack of an optical counterpart disfavors the presence of such a binary system. In this case, GLEAM-X J1627-5235 could be interpreted as an isolated, massive, fast-rotating, and highly magnetized (similar to 109 G) WD pulsar. Its properties are consistent with a carbon-oxygen WD of mass similar to 1.3 M circle dot and radius similar to 2500 km, possibly supported by small-scale multipolar magnetosphere structures that keep it above the death line for WD-pulsars. We assess a double WD merger origin, modeling the post-merger rotational evolution under accretion, propeller, and magnetic braking torques. We find rotational age of similar to 572 Myr for GLEAM-X J1627-5235, i.e., the post-merger time required to reach its observed period. This result is consistent with current optical upper limits for GLEAM-X J1627-5235 and support the WD pulsar interpretation for this source. We also discuss how the same model can apply to other LPTs.

We develop a general framework for quantum field theory in curved spacetime based on Local Minkowski Coordinates (LMC), which incorporates curvature effects into local Feynman diagrammatics. Gravitational influence enters through a curvature-dependent normalization function B(x), derived from covariant current conservation, and a gravitational phase S(x), obtained via the WKB approximation. These quantities enter through local phase accumulation and observer-dependent normalization of external states, without modifying globally conserved fluxes. As a first application, we analyze the local redshift normalization and phase structure of quantum amplitudes in the vicinity of a Schwarzschild black hole. Within their range of validity, the curvature-dependent factors B(x) and S(x) reproduce the expected gravitational redshift of field amplitudes in general relativity. When amplitudes are propagated to asymptotic infinity and evaluated in a standard global quantum state (such as the Unruh state), the resulting flux is consistent with the standard Hawking result. The framework refines the local WKB structure and clarifies the separation between local normalization effects and globally conserved fluxes.

Abstract In Pseudo-Complex General Relativity (pcGR), the introduction of a repulsive core modifies the strong-field geometry of compact objects and alters the structure of null geodesics. In this work, we reformulate the exact radial motion of photons as an autonomous dynamical system and use phase-space methods to classify the resulting geometric regimes. We show that the existence of circular null orbits is controlled by a saddle-node bifurcation occurring at the critical coupling $B_4^{(\mathrm{ps})}= (2187/128)M^4$. Below this threshold, the spacetime supports an unstable photon sphere, while above it all real circular null geodesics are eliminated from the phase space. We further identify a finite intermediate regime, $10.125 < B_4/M^4 < 17.086$, in which the event horizon is absent but the photon sphere persists. This Naked Photon Sphere phase demonstrates that the loss of the horizon and the loss of circular null geodesics are distinct geometric transitions in pcGR. Finally, we examine the semiclassical thermodynamic evolution of the system. Within the standard continuation of the horizon branch, the evaporation trajectory approaches a stable remnant configuration whose mass satisfies $M_{\rm rem}>M_{\rm crit}$, where $M_{\rm crit}$ denotes the mass associated with the photon-sphere bifurcation. Consequently, within this semiclassical framework, the remnant endpoint lies above the photon-sphere bifurcation scale, so the physical trajectory does not reach the regime in which circular null orbits are eliminated. These results establish a direct link between phase-space dynamics, compact-object geometry, and remnant formation in pcGR.

Abstract We investigate the structure of strange dwarfs, modeled as hybrid compact stars composed of a self bound strange quark matter core surrounded by a white dwarf like crust, within a fully relativistic framework. Static configurations are constructed by solving the Tolman Oppenheimer Volkoff equations, and uniformly rotating configurations are modeled within the Hartle-Thorne slow rotation expansion (to $$\mathcal{O}(\Omega ^2)$$ O ( Ω 2 ) ). We therefore interpret results at large fractional spins conservatively, and use the Kepler frequency mainly as a reference scale for comparing different masses and models. The stellar matter is described using a hybrid equation of state, in which the crust is modeled by a degenerate electron-ion system and the core by the MIT Bag Model. By comparing strange dwarfs with conventional white dwarfs across a range of rotation rates, we show that rotation inflates the radius and can reduce (in a quantifiable way) the separation between the two families in the (M, R) plane, potentially masking structural signatures associated with the presence of a quark core. Our results highlight the importance of accounting for rotational effects when interpreting mass radius measurements and other global observables in the context of searches for exotic compact objects in current and future high precision surveys.

We explore gravity, a classical extension of general relativity, and evaluate its applicability to compact stars. As a modification of Einstein's theory, gravity serves as a useful framework for investigating gravitational effects in ultra-relativistic regimes where (standard) general relativity may break down, while remaining consistent with it in weak-field limits. In this work, we derive a second-order modified Tolman-Oppenheimer-Volkoff (MTOV) system, consisting of four coupled second-order differential equations, for general gravity. This formulation is applied to static, spherically symmetric strange quark stars modeled using the MIT Bag equation of state. We propose two models, each incorporating a single parameter that governs the deviation from general relativity. The MTOV equations are solved numerically using the Runge-Kutta-Fehlberg method, and the results are compared to those obtained in general relativity. Our findings demonstrate that gravity can yield distinct and physically meaningful modifications to the properties of compact stars. We further examine the contributions of second- and higher-order corrections in the scalar-tensor sector of the gravitational action.

In this paper, we explore a novel framework for explaining the mass and radius relationships of observed neutron stars by considering strange stars (SSs) admixed with mirror dark matter (MDM). We develop a theoretical model that incorporates non-commutative algebra to describe the interactions between ordinary strange quark matter (SQM) and MDM, which are predicted to form compact objects that could explain recent astrophysical data, including observations of PSR J0740+6620, PSR J0030+0451, PSR J0437-4715, and the central compact object in HESS J1731-347. Notably, we demonstrate that the exotic mass-radius measurement of XTE J1814-338 can be explained by the presence of a mirror SS with an ordinary SQM core. In contrast to other explanations based on boson stars, our SS+MDM model offers a natural explanation for this system. We provide detailed mass-radius comparisons with observational data and discuss future observations that could test the predictions of our model, offering new insights into neutron star structure and the role of dark matter in compact objects.

ABSTRACTWe explore the implications of Branch‐Cut Quantum Gravity (BCQG), a novel framework leveraging non‐commutative geometry within a symplectic phase‐space, on the accelerated expansion of the universe. Non‐commutativity, introduced through a deformation of the Poisson algebra and enhanced by a symplectic metric, provides a robust mechanism for addressing key challenges in cosmology, such as the youngness paradox and the fine‐tuning of initial conditions in standard inflationary models. By embedding quantum dual‐field dynamics within a Riemannian‐foliated spacetime, BCQG naturally integrates short‐ and long‐range spacetime effects into a unified formalism. This approach offers an alternative to standard inflationary models by predicting cosmic acceleration through geometric restructuring rather than finely‐tuned initial states. In contrast to models like ΛCDM or String Theory, BCQG introduces unique corrections to cosmic scale factors and predicts a novel transition between contraction and expansion phases via topological branch‐cuts, circumventing the singularity problem. Moreover, BCQG's non‐commutative formulation provides testable predictions, such as modifications in cosmic microwave background (CMB) anisotropies and large‐scale structure evolution. We discuss the mathematical foundation, observational implications, and future avenues for validating BCQG through astrophysical data, positioning it as a promising theoretical alternative for understanding the universe's accelerated growth.

The LIGO/Virgo collaboration detected a compact object in the GW190814 event on August 14, 2019, with an estimated mass of ∼ 2.59^+0.08_-0.09 M _⊙ , alongside a 23 M _⊙ black hole. This observation ignited a scientific discussion due to the object’s unique position in the mass gap between neutron stars and black holes. In our study, we investigate the upper limit of the central magnetic field of anisotropic magnetized neutron stars, contextualized by the GW190814 event. We employ the density-dependent relativistic mean-field theory equation of state and assume a specific density dependence for the magnetic field. Our findings indicate that the magnetic field strength, anisotropy, and the magnetic field’s orientation significantly affect the physical properties of neutron stars. We examine two orientations: radial (where local magnetic fields point radially) and transverse (where they are perpendicular to the radial direction). Notably, stars with a transverse magnetic field orientation exhibit increased mass with higher anisotropy and magnetic field strength. Additionally, we show that the magnetic field, its orientation, and anisotropy substantially influence the tidal deformability of neutron stars. We aim to constrain the central magnetic field of neutron stars based on the tidal deformability measurement for a canonical 1.4 M _⊙ neutron star, Λ _1.4=616^+273_-158 , obtained from GW190814, which suggests a preference for a stiffer equation of state.

We propose a novel extension to the recently developed non-commutative Riemannian foliated branch-cut quantum gravity (BCQG). Based on an extended Faddeev-Jackiw symplectic deformation of the conventional Poisson algebra, we investigate non-commutativity effects on a symplectic topological manifold that provides a natural isomorphic setting composed by a triad of canonically conjugate scalar complex fields which comprise quantum complementary dualities. Based on a complementary analytically continued Friedmann-type equation, combined with a quantum approach based on the Hořawa-Lifshitz quantum gravity, we describe the dynamic evolution of the universe's wave function, unfolding unprecedented predictions for the cosmic evolution and inflation. The non-commutative foliated quantum gravity approach offers a new perspective on explaining the accelerated cosmic expansion of the universe, strongly suggesting that non-commutative algebra induces the late accelerated growth of both the universe's wave function and the corresponding scale factor, along with their quantum counterparts. In contrast to the conventional inflationary model, where inflation requires a remarkably fine-tuned set of initial conditions in a patch of the universe, non-commutative foliated quantum gravity, analytically continued to the complex plane, captures short and long scales of spacetime, leading to an evolutionary cosmic dynamic through a topological reconfiguration of the primordial cosmic matter and energy content. This result introduces new speculative framework elements regarding the reconfiguration of matter and energy due to an underlying non-commutative spatio-temporal structure as a driver of spacetime cosmic acceleration.

Parametric representations of the high-density nuclear equation of state are used in constructing models for interpreting the astrophysical observations of neutron stars. This study explores how accurately equations of state with strong first-order phase transitions can be represented using spectral or piecewise analytic methods that assume no a priori knowledge of the location or the strength of the phase transition. The model equations of state used in this study have phase transitions strong enough to induce a gravitational instability that terminates the sequence of stable neutron stars. These equations of state also admit a second sequence of stable stars with core matter that has undergone this strong first-order phase transition (possibly driven by quark deconfinement). These results indicate that spectral representations generally achieve somewhat higher accuracy than piecewise analytic representations having the same number of parameters. Both types of representation show power-law convergence at approximately the same rate.

A novel approach to cosmic inflation within the framework of a noncommutative Riemannian foliated quantum gravity, built upon a reverse Faddeev-Jackiw symplectic spacetime deformation of the conventional Poisson algebra, is investigated. Friedmann-type dynamical equations, analytically continued to a complex noncommutative framework, incorporate a modified energy-momentum Riemann tensor and a noncommutative matter-energy potential, highlighting the emergence of quantum gravity topological fluctuation effects on the expansion dynamics of the universe. In this realm, the coupling of UV and IR scales plays a central role, providing a natural topological mechanism for inflation and recursal evidence for the generation of relic gravitational waves. These predictions align with a self-consistent description of the transition between the primordial mirror-universe deceleration and present-universe acceleration phases as predicted by the Riemann foliated quantum gravity, offering potential connections to observational cosmology.

We explore a noncommutative extension of branch-cut quantum gravity (BCQG), with a focus on its implications for early-universe inflation. Our framework builds on a three-field mini-superspace model involving a complex-valued cosmic-scale factor, a perfect-fluid field, and an inflaton-type scalar field. Using a Faddeev-Jackiw symplectic deformation of the conventional Poisson algebra, we construct a noncommutative phase space and derive a modified Wheeler-DeWitt equation. Analytic solutions to the wave function of the universe are obtained and analyzed. We show that noncommutativity induces coupling between ultraviolet and infrared modes, naturally leading to an inflationary phase without requiring fine-tuned initial conditions. This feature offers a novel alternative to standard inflationary models. We also discuss how the structure of the wave function in this framework may relate to primordial density perturbations. While some aspects of this theory remain speculative, the mathematical formulation provides a consistent path toward integrating quantum gravitational effects into early cosmological dynamics.

In this Letter, we study the structure of the strange stars admixed with bosonic dark matter, and find that these stars can well explain the mass and radius observations of XTE J1814-338. We also find that for the strong interaction coupling constant α_S=0.6 and B^1/4=135 MeV (B is the bag constant), the observations of XTE J1814-338 constrain the mass of the bosonic dark matter to m_χ≤ 307 (λ/π)^1/4 MeV (λ is the dimensionless coupling constant of the bosonic dark matter).

To model the structure of neutron stars (NSs) theoretically,it is common to consider layers with different density regimes. Matching the equation of state (EoS) for the crust and core and obtaining a suitable description of these extreme conditions are crucial for understanding the properties of these compact objects. In this work, we construct ten different NS EoSs incorporating three distinct crust models, which are connected to the core using a thermodynamically and causally consistent formalism. For cold NSs, we propose a linear relationship between pressure and energy density in a narrow region between the crust and core, effectively establishing an interpolation function in the pressure-baryonic chemical potential plane. We then compare this EoS matching method with the classical approach, which neglects causal and thermodynamic consistency. We solve the Tolman-Oppenheimer-Volkoff equation to obtain the mass-radius relationship and compare our results with observational constraints on NSs. Furthermore, we investigate the influence of the new matching formalism on non-radial oscillation frequencies and damping times. Our findings suggest that the method used to glue the crust and core EoS impacts NS observables, such as the radius, oscillation frequencies, and damping times of non-radial modes, which may be crucial for interpreting future gravitational wave observations from neutron star mergers or isolated pulsars. The effects are particularly noticeable for low-mass NSs, regardless of the specific EoS model chosen. In particular, we find that the p_1 oscillation mode exhibits significant differences in frequencies among alternative matching methods, whereas the fundamental f-mode remains unaffected by changes in crust models or interpolation schemes.

We present a study of relic gravitational waves based on a foliated gauge field theory defined over a spacetime endowed with a noncommutative algebraic–geometric structure. As an ontological extension of general relativity—concerning manifolds, metrics, and fiber bundles—the conventional space and time coordinates, typically treated as classical numbers, are replaced by complementary quantum dual fields. Within this framework, consistent with the Bekenstein criterion and the Hawking–Hertog multiverse conception, singularities merge into a helix-like cosmic scale factor that encodes the topological transition between the contraction and expansion phases of the universe analytically continued into the complex plane. This scale factor captures the essence of an intricate topological quantum-leap transition between two phases of the branching universe: a contraction phase preceding the now-surpassed conventional concept of a primordial singularity and a subsequent expansion phase, whose transition region is characterized by a Riemannian topological foliated structure. The present linearized formulation, based on a slight gravitational field perturbation, also reveals a high sensitivity of relic gravitational wave amplitudes to the primordial matter and energy content during the universe’s phase transition. It further predicts stochastic homogeneous distributions of gravitational wave intensities arising from the interplay of short- and long-spacetime effects within the non-commutative algebraic framework. These results align with the anticipated future observations of relic gravitational waves, expected to pervade the universe as a stochastic, homogeneous background.