Saeed Fakhry

PDAT Laboratory · K.N. Toosi University of Technology

In this study, we investigate the impact of modified gravity (MG) on the merger rate of compact binaries within dark matter spikes surrounding supermassive black holes (SMBHs). Specifically, we calculate the binary merger rates involving primordial black holes (PBHs) and/or neutron stars (NSs) in Hu–Sawicki f(R) gravity and the normal branch of Dva...

In this work, we investigate the merger rate of primordial black hole–neutron star (PBH-NS) binaries in two widely studied modified gravity (MG) models: Hu–Sawicki f(R) gravity and the normal branch of Dvali–Gabadadze–Porrati gravity. In our analysis, we take into account the effects of MG on the halo properties, including halo mass function, halo...

Primordial black holes (PBHs) are known as one of the potential candidates for dark matter. They are expected to have formed due to the direct gravitational collapse of density fluctuations in the early Universe. In this regard, examining the merger rate of PBHs within modified theories of gravity can offer a deeper insight into their abundance. In...

In this study, we investigate gravitational lensing within modified gravity frameworks, focusing on the Hu-Sawicki $f(R)$ and normal branch Dvali-Gabadadze-Porrati (nDGP) models, and we compare these results with those obtained from general relativity (GR). Our results reveal that both modified gravity models consistently enhance key lensing parame...

In this study, we investigate the impact of modified gravity on the merger rate of compact binaries within dark-matter spikes surrounding super-massive black holes (SMBHs). Specifically, we calculate binary merger rates involving primordial black holes (PBHs) and/or neutron stars (NSs) in Hu-Sawicki $f(R)$ gravity and the normal branch of Dvali-Gab...

In this study, we investigate gravitational lensing within the framework of more realistic dark matter halo models, transcending the limitations of spherical-collapse approximations. Through analytical computations utilizing diverse mass functions, we address critical factors typically overlooked in the standard Press-Schechter formalism, including...

In this study, we expand upon White's model proposed in [1], which explores the post-collapse evolution of density peaks while incorporating the influence of angular momentum. Within a time scale smaller than the peak collapse, denoted as t0, the inner regions of the peak reach an equilibrium state, forming a cuspy profile, consistent with White's...

In this study, we expand upon White's model proposed in [1], which explores the post-collapse evolution of density peaks while incorporating the influence of angular momentum. Within a time scale smaller than the peak collapse, denoted as , the inner regions of the peak reach an equilibrium state, forming a cuspy profile, consistent with White's fi...

In this work we investigate the merger rate of primordial black hole-neutron star (PBH-NS) binaries in two widely-studied modified gravity (MG) models: Hu-Sawicki f (R) gravity and the normal branch of Dvali-Gabadadze-Porrati (nDGP) gravity. In our analysis, we take into account the effects of MG on the halo properties including: halo mass function...

Ultradense dark matter halos (UDMHs) are high concentrations of dark matter which are assumed to have formed from amplified primordial perturbations, alongside the primordial black holes (PBHs). In this work we calculate the abundance of UDMHs and improve the previous works by elaborating on the formation process of these halos through including va...

Primordial black holes (PBHs) are known as one of the potential candidates for dark matter. They are expected to have formed due to the direct gravitational collapse of density fluctuations in the early Universe. Therefore, the study of the merger rate of PBHs in modified theories of gravity can provide more detailed information about their abundan...

In this work, we extend the model proposed by White concerning the post-collapse evolution of density peaks while considering the role of angular momentum. On a timescale smaller than the peak collapse, $t_{0}$, the inner regions of the peak reach the equilibrium forming a cuspy profile, as in White’s paper, but the power-law density profile is fla...

Cosmic voids are known as underdense substructures of the cosmic web that cover a large volume of the Universe. It is known that cosmic voids contain a small number of dark matter halos, so the existence of primordial black holes (PBHs) in these secluded regions of the Universe is not unlikely. In this work, we calculate the merger rate of PBHs in...

Today, the existence of supermassive black holes (SMBHs) in the center of galactic halos is almost confirmed. An extremely dense region referred to as dark-matter spike is expected to form around central SMBHs as they grow and evolve adiabatically. In this work, we calculate the merger rate of compact binaries in dark matter spikes while considerin...

In this work, we study the effect of a high-precision semianalytical mass function on the merger rate of primordial black holes (PBHs) in dark matter halos. For this purpose, we first explain a theoretical framework for dark matter halo models and introduce relevant quantities such as the halo density profile, the concentration parameter, and a hig...

In this work, we calculate the merger rate of primordial black hole-neutron star binaries in ellipsoidal-collapse dark matter halo models and compare the results with the corresponding findings derived from spherical-collapse dark matter halo models. Our findings demonstrate that the merger rate of primordial black hole-neutron star binaries is con...

Nowadays, the existence of supermassive black holes (SMBHs) in the center of galactic halos is almost confirmed. An extremely dense region referred to as dark-matter spike is expected to form around central SMBHs as they grow and evolve adiabatically. In this work, we calculate the merger rate of compact binaries in dark-matter spikes while conside...

In this work, we study the effect of a high-precision semi-analytical mass function on the merger rate of primordial black holes (PBHs) in dark matter halos. For this purpose, we first explain a theoretical framework for dark matter halo models and introduce relevant quantities such as halo density profile, concentration parameter, and a high-preci...

In this work, we calculate the merger rate of primordial black hole–neutron star (PBH–NS) binaries within the framework of ellipsoidal-collapse dark matter models and compare it with that obtained from spherical-collapse dark matter halo models. Our results exhibit that ellipsoidal-collapse dark matter halo models can potentially amplify the merger...

Interacting dark matter-dark energy (IDMDE) models can be taken to account as one of the present challenges that may affect the cosmic structures. In this work, we study the integrated Sachs-Wolfe (ISW) effect in IDMDE models. To this end, we initially introduce a theoretical framework for IDMDE models. Moreover, we briefly discuss the stability co...

Cosmic voids are known as underdense substructures of the cosmic web that cover a large volume of the Universe. It is known that cosmic voids contain a small number of dark matter halos, so the existence of primordial black holes (PBHs) in these secluded regions of the Universe is not unlikely. In this work, we calculate the merger rate of PBHs in...

Primordial black holes (PBHs), as a potential macroscopic candidate for dark matter, can encounter other compact objects in dark matter halos because of their random distribution. Besides, the detection of gravitational waves (GWs) related to the stellar-mass black hole-neutron star (BH-NS) mergers raises the possibility that the BHs involved in su...

We study the cosmological inflation within the context of f(Q, T) gravity, wherein Q is the nonmetricity scalar and T is the trace of the matter energy-momentum tensor. By choosing a linear combination of Q and T, we first analyze the realization of an inflationary scenario driven via the geometrical effects of the linear f(Q, T) gravity and then,...

Interacting dark matter-dark energy models (IDMDE) can provide solutions to the current challenges that may affect cosmic structures. The main idea of such models is that the mass of dark matter particles can be specified by their interactions with a scalar field whose energy density is characterized by dark energy. In this work, we propose to stud...

Interacting dark matter-dark energy (IDMDE) models can be taken to account as one of the present challenges that may affect the cosmic structures. In this work, we study the integrated Sachs-Wolfe (ISW) effect in IDMDE models. To this end, we initially introduce a theoretical framework for IDMDE models. Moreover, we briefly discuss the stability co...

A novel 4-dimensional Einstein-Gauss-Bonnet (4D EGB) gravity has been proposed that asserts to bypass Lovelock's theorem and result in a non-trivial contribution to the gravitational dynamics in four-dimensional spacetime [1]. Although inconsistencies have been raised for this theory in nonlinear perturbation limits, the results of the consistent 4...

We study the cosmological inflation within the context of f(Q, T) gravity, wherein Q is the nonmetricity scalar and T is the trace of the matter energy-momentum tensor. By choosing a linear combination of Q and T, we first analyze the realization of an inflationary scenario driven via the geometrical effects of the linear f(Q, T) gravity and then,...

We study the merger rate of primordial black holes (PBHs) in self-interacting dark matter (SIDM) halo models. To explore a numerical description of the density profile of SIDM halo models, we use the result of a previously performed simulation for SIDM halo models with σ/m=10 cm^{2} g^{−1}. We also propose a concentration-mass-time relation that ca...

We investigate inflation in the framework of a special model of f (R, T) gravity in the presence of the inflaton field and Chern-Simons higher curvature corrections. With the calculation of the slow-roll parameters and the specification of inflationary observables, i.e., the scalar spectral index, the tensorial spectral index, and the tensor-to-...

Baryonic matter manages many energetic events in galactic halos such as active galactic nuclei and supernova explosions. Also, one of the most prominent effects of the baryonic matter is its effect on the number density of dark matter halos. In this study, we investigate the effect of baryonic matter on the merger rate of primordial black holes (...

We study the cosmological inflation within the context of f(Q, T) gravity, wherein Q is the nonmetricity scalar and T is the trace of the matter energy-momentum tensor. By choosing a linear combination of Q and T, we first analyze the realization of an inflationary scenario driven via the geometrical effects of f(Q, T) gravity and then, we obtain t...

A novel 4-dimensional Einstein-Gauss–Bonnet (4D EGB) gravity has been proposed that asserts to bypass the Lovelock’s theorem and to result in a non-trivial contribution to the gravitational dynamics in four-dimensional spacetime. Although inconsistencies have been raised for this theory in nonlinear perturbation limits, the results of the consisten...

We study numerically the nonlinear stability of excited fermion–boson stars in spherical symmetry. Such compound hypothetical stars, composed by fermions and bosons, are gravitationally bound, regular, and static configurations described within the coupled Einstein–Klein–Gordon–Euler theoretical framework. The excited configurations are characteriz...

A novel 4-dimensional Einstein-Gauss-Bonnet (4D EGB) gravity has been proposed that asserts to bypass the Lovelock’s theorem and to result in a non-trivial contribution to the gravitational dynamics in four-dimensional spacetime. In this work, we study the integrated Sachs-Wolfe (ISW) effect in the 4D EGB model. For this purpose, we calculate the e...

We study the merger rate of primordial black holes (PBHs) in the self-interacting dark matter (SIDM) halo models. To explore a numerical description for the density profile of the SIDM halo models, we use the result of a previously performed simulation for the SIDM halo models with $\sigma/m=10~cm^{2}g^{-1}$. We also propose a concentration-mass-ti...

We have studied the merger rate of primordial black holes (PBHs) in the ellipsoidal-collapse model of halo to explain the dark matter abundance by the PBH merger estimated from the gravitational waves detections via the Advanced LIGO (aLIGO) detectors. We have indicated that the PBH merger rate within each halo for the ellipsoidal models is more si...

We study numerically the nonlinear stability of {\it excited} fermion-boson stars in spherical symmetry. Such compound hypothetical stars, composed by fermions and bosons, are gravitationally bound, regular, and static configurations described within the coupled Einstein-Klein-Gordon-Euler theoretical framework. The excited configurations are chara...

We obtain analytic approximate black hole solutions for higher derivative gravity in the presence of Maxwell electromagnetic sources. We construct near horizon and asymptotic solutions and then use these to obtain an approximate analytic solution using a continued fraction method to get a complete solution. We compute the thermodynamic quantities a...

We have studied the merger rate in the ellipsoidal collapse model of halo to explain the dark matter abundance by the primordial black holes (PBHs) estimated from the gravitational waves detections via the LIGO detectors. We have indicated that the PBHs merger rate within each halo for the ellipsoidal models is more significant than for the spheric...

We obtain analytical approximate black hole solutions for higher derivative gravity in the presence of Maxwell electromagnetic source. We construct near horizon and asymptotic solutions and then use these to obtain an approximate analytic solution using a continued fraction method to get a complete solution. We compute the thermodynamic quantities...

Gravitationally bound structures composed by fermions and scalar particles known as fermion-boson stars are regular and static configurations obtained by solving the coupled Einstein-Klein-Gordon-Euler (EKGE) system. In this work, we discuss one possible scenario through which these fermion-boson stars may form by solving numerically the EKGE syste...

Gravitationally bound structures composed by fermions and scalar particles known as fermion-boson stars are regular and static configurations obtained by solving the coupled Einstein-Klein-Gordon-Euler (EKGE) system. In this work, we discuss one possible scenario through which thesefermion-boson stars may form by solving numerically the EKGE system...

By using the higher-order geodesic deviation equations for charged particles, we apply the method described by Kerner et.al. to calculate the perihelion advance and trajectory of charged test particles in the Reissner-Nordstrom space-time. The effect of charge on the perihelion advance is studied and we compared the results with those obtained earl...

By using the higher-order geodesic deviation equations for charged particles, we apply the method described by Kerner et.al. to calculate the perihelion advance and trajectory of charged test particles in the Riessner-Nordstrom spacetime. The effect of charge on the perihelion advance is studied and compared the results with those obtained earlier...

In this paper, the shape, sound, and current of an electrical discharge in the air between a metal pin and an electrolyte solution are studied. Two different situations are considered: A) without, and, B) with inclusion of a dielectric wall in the discharge circuit. It is found that: 1) the discharge A has a cylindrical shape rather than a branched...