arXiv subjects

N. Heidari

Publications and source records attributed to N. Heidari.

At least 37 records · Page 2Linked to original sources

arXiv2026

The Flight of the Bumblebee in a Non-Commutative Geometry: A New Black Hole Solution

This paper investigates a new black hole solution within the framework of bumblebee gravity, incorporating non-commutative corrections parameterized by $Θ$ and implemented through the Moyal twist $\partial_r \wedge \partial_θ$. Notably, the event horizon remains unaffected by $Θ$, while the surface gravity becomes ill-defined, in agreement with the behavior previously reported for the non-commutative Schwarzschild black hole [1]. The propagation of light is examined by analyzing null geodesics, identifying critical orbits, and determining the resulting black hole shadow. To complement these analyses, we explore gravitational lensing by evaluating the deflection angle in both the weak- and strong-field regimes. Using these results, constraints are derived for the lensing observables by comparing with the Event Horizon Telescope data for $Sgr A^{*}$ and $M87^{*}$. Finally, we close the analysis by deriving additional constraints from standard Solar System experiments, including Mercury's orbital precession, gravitational light bending, and time-delay measurements.

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arXiv2026

Particle production, absorption, scattering, and geodesics in a Schwarzschild-Hernquist black hole

We investigate quantum and classical signatures of a Schwarzschild black hole embedded in a Hernquist dark matter halo. Starting from the exact spherically symmetric solution describing this composite system, we analyze particle production for both bosonic and fermionic fields using semiclassical techniques. Hawking radiation is derived through Bogoliubov transformations and independently via the tunneling method with energy conservation, allowing us to identify the effective temperature, emission spectrum, and the role of dark matter parameters in suppressing particle creation. The evaporation process is examined in the high-frequency regime, leading to modified evaporation times and emission rates relative to the vacuum Schwarzschild case. We further study absorption and scattering of massless scalar waves employing a partial-wave analysis, computing phase shifts, partial and total cross sections, and assessing the impact of the Hernquist scale radius and density on these observables. Finally, null and timelike geodesics are explored to characterize light propagation and particle motion in the presence of the dark matter halo.

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arXiv2026

Spin effects on particle creation and evaporation in $f(R,T)$ gravity

In this work, we study how the spin of particle modes influences particle creation, greybody factors, absorption, and evaporation of a black hole within the framework of modified electrodynamics in $f(R,T)$ gravity, recently proposed in Ref. [1]. All spin sectors -- scalar, vector, tensor, and spinorial -- are analyzed to obtain the corresponding features. For particle creation, we consider massless bosonic and fermionic perturbations to determine the respective particle densities. Analytical expressions for the greybody factors are derived, with suitable approximations for the tensor and spinorial cases. The absorption cross section is computed numerically, and using the Stefan-Boltzmann law, we estimate the black hole evaporation lifetime. The associated energy and particle emission rates are also discussed, along with the correspondence between quasinormal modes and greybody factors.

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arXiv2026

Gravitational aspects of a new bumblebee black hole

In this paper, we examine the physical consequences of a recently introduced black hole solution in bumblebee gravity [1]. The geometry is first presented and then reformulated through suitable coordinate adjustments, which make its global conical character evident. We then study the propagation of particles by solving the geodesic equations for null and timelike trajectories. The associated critical orbits (or photon spheres) are obtained, and shadow radius are computed and compared with other Lorentz-violating configurations in bumblebee and Kalb-Ramond models, including their charged and cosmological extensions. Massive particle motion is analyzed separately, followed by the construction of the effective potentials for scalar, vector, tensor, and spinor perturbations. These potentials allow the calculations of quasinormal frequencies and the corresponding time-domain evolution. Gravitational lensing phenomena are investigated in the weak and strong deflection regimes, and the light-travel time delay is also evaluated. The study concludes with bounds on the Lorentz-violating parameter based on classical Solar System experiments.

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arXiv2026

Gravitational waves in a minimal gravitational SME

In this work, we investigate the generation and propagation of gravitational waves within a minimal gravitational SME (Standard Model Extension). Starting from the modified graviton dispersion relation derived in the linearized gravity sector, we analyze the polarization properties of gravitational waves in the transverse-traceless tensor sector. We then construct the retarded Green function associated with the Lorentz-violating wave operator, explicitly verifying the causal structure of the theory and identifying the modified propagation speeds of the tensorial modes. In addition, we study the source-induced emission of gravitational waves from a binary black-hole system. We show that the gravitational waveform preserves the standard quadrupolar amplitude and polarization structure, while Lorentz-violating effects enter exclusively through a modification of the retarded time. As a result, the spatial components of the metric perturbation $h_{ij}(t,r)$ acquire a phase shift determined by the SME coefficients. Finally, we estimate phenomenological bounds to the model under consideration.

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arXiv2026

Imprints of non-commutativity on charged black holes

This work presents a comprehensive investigation of the gravitational phenomena that correspond to a non-commutative (NC) charged black hole, by incorporating NC geometry through a Moyal twist. We derive the deformed metric up to the second order of the NC parameter, utilizing the Seiberg-Witten map for the Reissner-Nordstrom black hole. We explore how non-commutativity modifies key thermodynamic properties, such as the Hawking temperature and heat capacity, and the existence of a remnant mass at the final stage of evaporation. Additionally, the study of Hawking radiation for bosonic and fermionic particles is discussed. Applying a perturbative method, scalar quasinormal modes are analyzed numerically. Furthermore, null geodesics and photon sphere stability are explored via curvature and topological methods. The shadow radius and deflection angle are computed to understand observational signatures. Lensing observables are compared to Event Horizon Telescope observations to provide probable constraints on the non-commutativity parameter. This study bridges theoretical predictions with astrophysical observations, offering insights into quantum gravity effects on black hole physics.

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arXiv2025

Some perspective of thermodynamical and optical properties of black holes in Maxwell-dilaton-dRGT-like massive gravity

Motivated by integrating the dilaton field (as a UV correction) with dRGT-like massive gravity (as an IR correction) into Einstein gravity, we investigate the thermodynamic and optical properties of black holes within this gravitational framework. We begin by reviewing the black hole solutions in Maxwell-dilaton-dRGT-like massive gravity, followed by an analysis of how various parameters influence on the asymptotical behavior of the spacetime and the event horizon of these black holes. In the subsequent section, we examine the conserved and thermodynamic quantities associated with these black holes, paying particular attention to the effects of parameters like $β$, $α$, and the massive parameters ($η_{1}$ and $η_{2}$) on their local stability by simultaneously evaluating the heat capacity and temperature. We also adopt an alternative method to study phase transitions using geometrothermodynamics. Furthermore, we explore how the parameters of Maxwell-dilaton-dRGT-like massive gravity impacts the optical characteristics and radiative behavior of black holes. In particular, we analyze the effects of the dilaton coupling constant ($α$), charge ($q$), the massive gravity parameter ($η_1$), and the graviton mass ($m_g$) on the radius of the photon sphere and the resulting black hole shadow. Moreover, the theoretical shadow radius is compared to the observational data from $Sgr A^*$. Additionally, we investigate the energy emission rate of these black holes, revealing that these parameters substantially influence the emission peak.

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arXiv2025

Quantum particle production and radiative properties of a new bumblebee black hole

In this work, we investigate the quantum and radiative properties of a recently proposed static bumblebee black hole arising from a general Lorentz-violating vacuum configuration. The analysis begins with the geometric structure of the solution and the thermodynamic temperature obtained from the surface-gravity prescription. The associated thermodynamic topological structure is also examined. Quantum particle production is then analyzed for bosonic and fermionic fields using the tunneling method. Analytic greybody bounds are derived for spin-0, spin-1, spin-2, and spin-1/2 fields. Furthermore, full greybody factors are computed with the sixth-order WKB method, together with the corresponding absorption cross sections and their characteristic spin-dependent peak patterns. These results support the evaluation of the evaporation lifetimes and the emission rates of energy and particle modes associated with each spin contribution, followed by a comparison of the high-frequency regime with other Lorentz-violating geometries, including the \textit{metric} bumblebee, \textit{metric-affine} bumblebee, Kalb-Ramond, and non-commutative Kalb-Ramond black holes. In addition, greybody factors are obtained using a quasinormal-mode-based prescription.

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arXiv2025

Giant Outer Transiting Exoplanet Mass (GOTEM) Survey.VII. TOI-6041: a multi-planet system including a warm Neptune exhibiting strong TTVs

We present the characterization of the TOI-6041 system, a bright ($V = 9.84 \pm 0.03$) G7-type star hosting at least two planets. The inner planet, TOI-6041b, is a warm Neptune with a radius of $4.55^{+0.18}_{-0.17}\,R_\oplus$, initially identified as a single-transit event in \textit{TESS} photometry. Subsequent observations with \textit{TESS} and \textit{CHEOPS} revealed additional transits, enabling the determination of its $26.04945^{+0.00033}_{-0.00034}$~d orbital period and the detection of significant transit timing variations (TTVs), exhibiting a peak-to-peak amplitude of about 1~hour. Radial velocity (RV) measurements obtained with the APF spectrographs allow us to place a $3σ$ upper mass limit of $28.9\,M_\oplus$ on TOI-6041b. In addition, the RV data reveal a second companion, TOI-6041c, on an 88~d orbit, with a minimum mass of $0.25\,M_{\mathrm{Jup}}$. A preliminary TTV analysis suggests that the observed variations could be caused by gravitational perturbations from planet c; however, reproducing the observed amplitudes requires a relatively high eccentricity of about 0.3 for planet c. Our dynamical stability analysis indicates that such a configuration is dynamically viable and places a $1σ$ upper limit on the mass of TOI-6041c at $0.8\,M_{\mathrm{Jup}}$. An alternative is the presence of a third, low-mass planet located between planets b and c, or on an inner orbit relative to planet b -- particularly near a mean-motion resonance with planet b -- which could account for the observed variations. These findings remain tentative, and further RV and photometric observations are essential to better constrain the mass of planet b and to refine the TTV modeling, thereby improving our understanding of the system's dynamical architecture.

astro-ph.EP↗

arXiv2025

Axisymmetric black hole in a non-commutative gauge theory: classical and quantum gravity effects

This work explores both classical and quantum aspects of an axisymmetric black hole within a non-commutative gauge theory. The rotating solution is derived using a modified Newman-Janis procedure. The analysis begins with the horizon structure, ergospheres, and angular velocity. The thermodynamic properties are examined through surface gravity, focusing on the Hawking temperature, entropy, and heat capacity. In addition, the remnant mass is calculated. The Hawking radiation is treated as a tunneling process for bosonic and fermionic particles, along with the corresponding particle creation density. Geodesic motion is explored, emphasizing null geodesics, radial accelerations, the photon sphere, and black hole shadows. Finally, the gravitational lensing in the strong deflection limit is investigated.

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arXiv2025

A Non-Commutative Kalb-Ramond Black Hole

This work presents a new black hole solution within the framework of a non-commutative gauge theory applied to Kalb-Ramond gravity. Using the method recently proposed in the literature [Nucl.Phys.B 1017 (2025) 116950], we employ the Moyal twist $\partial_r \wedge \partial_θ$ to implement non-commutativity, being encoded by parameter $Θ$. We begin by verifying that the resulting black hole no longer possesses spherical symmetry, while the event horizon remains unaffected by non-commutative corrections. The Kretschmann scalar is computed to assess the corresponding regularity. It turns out that the solution is regular, provided that the Christoffel symbols and related quantities are not expanded to second order in $Θ$. We derive the thermodynamic quantities, including the Hawking temperature $T^{(Θ,\ell)}$, entropy $S^{(Θ,\ell)}$, and heat capacity $C_V^{(Θ,\ell)}$. The remnant mass $M_{\text{rem}}$ is estimated by imposing $T^{(Θ,\ell)} \to 0$, although the absence of a physical remnant indicates complete evaporation. Quantum radiation for bosons and fermions is analyzed via the tunneling method, where divergent integrals are treated using the residue theorem. Notably, in the low-frequency regime, the particle number density for bosons surpasses that of fermions (at least within the scope of the methods considered here). The effective potential for a massless scalar field is obtained perturbatively, enabling the computation of quasinormal modes and the time-domain profiles. Finally, further bounds on $Θ$ and $\ell$ (Lorentz-violating paramter) are derived from solar system tests, including the perihelion precession of Mercury, light deflection, and the Shapiro time delay.

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arXiv2025

Gravitational signatures of a nonlinear electrodynamics in $f(R,T)$ gravity

In this work, we investigate a nonlinear electrodynamics model within the framework of $f(R,T)$ gravity. We begin by outlining the general features of the theory and analyzing the event horizon under conditions ensuring its real and positive definiteness. We then examine light trajectories, focusing on critical orbits, shadow radii, and geodesics of massless particles. The parameters $α$ and $β$, associated with the nonlinear extension of the Reissner-Nordström spacetime, are constrained using observational data from the Event Horizon Telescope (EHT). Subsequently, we analyze the thermodynamic properties of the system, including Hawking temperature, entropy, and heat capacity. Quasinormal modes are computed for scalar, vector, tensor, and spinorial perturbations, with the corresponding time-domain profiles explored as well. Gravitational lensing is then studied in both weak and strong deflection limits, along with the stability of photon spheres. Finally, we examine additional topological aspects, including topological thermodynamics and the topological photon sphere.

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arXiv2025

Characterizing planetary systems with SPIRou: Detection of a sub-Neptune in a 6-day period orbit around the M dwarf Gl 410

The search for exoplanets around nearby M dwarfs represents a crucial milestone in the census of planetary systems in the vicinity of our Solar System. Since 2018 our team is carrying a radial-velocity blind search program for planets around nearby M dwarfs with the near-IR spectro-polarimeter and velocimeter SPIRou at the CFHT and the optical velocimeter SOPHIE at the OHP in France. Here we present our results on Gl 410, a 0.55 Msun 480+-150 Myr old active M dwarf distant 12 pc. We used the line-by-line (LBL) technique to measure the RVs with SPIRou and the template matching method with SOPHIE. Three different methods were employed, two based on principal component analysis (PCA), to clean the SPIRou RVs for systematics. We applied Gaussian processes (GP) modeling to correct the SOPHIE RVs for stellar activity. The l1 and apodize sine periodogram analysis was used to search for planetary signals in the SPIRou data taking into account activity indicators. We analyzed TESS data and searched for planetary transits. We report the detection of a M sin(i)=8.4+-1.3 Mearth sub-Neptune planet at a period of 6.020+-0.004 days in circular orbit with SPIRou. The same signal, although with lower significance, was also retrieved in the SOPHIE RV data after correction for activity using a GP trained on SPIRou's longitudinal magnetic field (Bl) measurements. The TESS data indicate that the planet is not transiting. Within the SPIRou wPCA RVs, we find tentative evidence for two additional planetary signals at 2.99 and 18.7 days. In conclusion, infrared RVs are a powerful method to detect extrasolar planets around active M dwarfs. Care should be taken however to correct/filter systematics generated by residuals of the telluric correction or small structures in the detector plane. The LBL technique combined with PCA offers a promising way to reach this objective. Further monitoring of Gl 410 is necessary.

astro-ph.EP↗

arXiv2025

The Hot-Neptune Initiative (HONEI) I. Two hot sub-Neptunes on a close-in, eccentric orbit (TOI-5800 b) and a farther-out, circular orbit (TOI-5817 b)

Neptune-sized exoplanets are key targets for atmospheric studies, yet their formation and evolution remain poorly understood due to their diverse characteristics and limited sample size. The so-called "Neptune desert", a region of parameter space with a dearth of short-period sub- to super-Neptunes, is a critical testbed for theories of atmospheric escape and migration. The HONEI program aims to confirm and characterize the best Neptune-sized candidates for composition, atmospheric and population studies. By measuring planetary masses with high precision, we want to provide the community with optimal targets whose atmosphere can be effectively explored with the JWST or by ground-based high-resolution spectroscopy. For this purpose, we started a radial velocity follow-up campaign, using the twin high-precision spectrographs HARPS and HARPS-N, to measure the masses of TESS Neptune-sized candidates and confirm their planetary nature. In this first paper of the series, we confirm the planetary nature of two candidates: TOI-5800b and TOI-5817b. TOI-5800b is a hot sub-Neptune ($R_p=2.44\pm0.29$ $R_\oplus$, $M_p=9.4\pm1.8$ $M_\oplus$, $T_{eq} = 1108\pm20$ K) located at the lower edges of the Neptune desert ($P=2.628$ days) and is the most eccentric planet ($e\sim0.3$) ever found within $P<3$ d. TOI-5800b is expected to be still in the tidal migration phase with its parent star, a K3 V dwarf ($V=9.6$ mag), although its eccentricity could arise from interactions with another object in the system. Having a high-transmission spectroscopy metric ($TSM\sim103$), it represents a prime target for future atmospheric characterization. TOI-5817b is a relatively hot sub-Neptune ($R_p=3.08\pm0.14$ $R_\oplus$, $M_p=10.3\pm1.4$ $M_\oplus$, $T_{eq}=950\pm21$ K) located in the Neptune savanna ($P=15.610$ d) [...]

astro-ph.EP↗

arXiv2025

Non-commutativity in Hayward spacetime

In this work, we propose a new black hole solution, namely, a Hayward-like metric incorporating corrections due to non-commutativity by taking into account $\partial_r\wedge\partial_θ$ Moyal twist. We begin by deriving this solution using the non-commutative gauge theory framework. The general properties of the metric are then analyzed, including the event horizon structure and the Kretschmann scalar. Analogous to the standard Hayward solution, the modified black hole remains regular, provided that additional dependence on the angle $θ$. Next, we examine the thermodynamic properties, computing the Hawking temperature, entropy, and heat capacity. From the temperature profile, we verify that there is no physical remnant mass when $T^{(Θ,l)} \to 0$, indicating a complete evaporation process. Quantum radiation is analyzed by considering both bosonic and fermionic particle modes, with an estimation of the particle creation density provided for each case. The effective potential is evaluated perturbatively to accomplish the analysis of quasinormal modes and the time-domain response for scalar perturbations. The study of null geodesics is explored to enable the characterization of the photon sphere and black hole shadows. Additionally, constraints on the shadows are estimated based on EHT (Event Horizon Telescope) data. Furthermore, the Gaussian curvature is determined to assess the stability of critical orbits, followed by an analysis of gravitational lensing using the Gauss-Bonnet theorem. Finally, the constraints (bounds) on the parameters $Θ$ (non-commutativity) and $l$ (``Hayward parameter'') are derived based on solar system tests, including the perihelion precession of Mercury, light deflection, and the Shapiro time delay effect.

gr-qc↗

arXiv2025

Quantum gravity effects on particle creation and evaporation in a non-commutative black hole via mass deformation

In this work, we explore a gravitational non-commutative black hole by gauging the de Sitter SO(4,1) group and employing the Seiberg-Witten map. Specifically, we examine modifications of non-commutativity represented through mass deformation. Initially, we address modifications to Hawking radiation for bosonic particle modes by analyzing the Klein-Gordon equation in curved spacetimes. We compute the Bogoliubov coefficients, showing how $Θ$ introduces a correction to the amplitude associated with particle creation. Additionally, we derive the power spectrum and the Hawking temperature within this framework. We also derive Hawking radiation from a tunneling perspective, leading to expressions for the power spectrum and particle number density. A similar analysis is performed for fermion particles. Remarkably, we obtain an analytical expression for black hole evaporation lifetime and compare our results with recent estimates of non-commutativity in the literature.

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arXiv2025

EBLM XV -- Revised dynamical masses for the circumbinary planet host Kepler-16 AB, using the SOPHIE spectrograph

Eclipsing binaries are perfect laboratories to measure precise, accurate and model-independent stellar radii and stellar masses, so long as both components are spectroscopically resolved. Resolving both components is difficult in high-contrast binaries, for instance, those composed of an FGK main-sequence star with an M-type companion. In those cases, the secondary can contribute <1% of the total flux in optical wavelengths. This makes measuring dynamical masses challenging and has typically only been attempted with large-aperture telescopes (8-10-m). The High-Resolution Cross-Correlation Spectroscopy (HRCCS) method was developed to extract weak emission and transmission spectra for exoplanet atmospheres. This method was recently adapted and applied to measure dynamical masses in high-contrast binaries. In this work, we apply the HRCCS method to optical spectra of the high-contrast binary and circumbinary planet host Kepler-16AB, obtained with the SOPHIE spectrograph at the 1.93-m telescope at the Observatoire de Haute-Provence. The secondary, which has a contrast ratio of ~ 6 x 10-3, is resolved with a detection significance of 9.5-sigma. We derive dynamical masses with a precision of 1.5% and 0.9% for the primary and secondary respectively. These are comparable, but slightly higher (within 2-7%) to previous mass-measurements, which has -- within the uncertainties -- no implication for the mass of the known circumbinary planet. This work demonstrates that dynamical mass measurements of high-contrast binaries can be done with 2-m class telescopes. We also investigate different analysis protocols to ensure we derive robust uncertainties for dynamical masses.

astro-ph.EP↗

arXiv2025

Geodesics, accretion disk, gravitational lensing, time delay, and effects on neutrinos induced by a non-commutative black hole

This paper explores gravitational phenomena associated with a non-commutative black hole. Geodesic equations are derived, and a thin accretion disk is analyzed to model the black hole shadow image, considering an optically thin, radiating, and infalling gas. Retrolensing effects are examined to trace photon emission configurations, while gravitational lensing is investigated through weak and strong deflection limits, with lensing equations and observables applied to Sagittarius A*. The study also includes calculations of time delay, energy deposition rate from neutrino annihilation, phase and probability of neutrino oscillation, and neutrino gravitational lensing.

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