Exploring the accelerating black holes from the observations of quasi-periodic oscillations in X-ray binaries Hamza Rehman, Saddam Hussain, G. Abbas, Tao Zhu European Physical Journal C, 2026 Black holes in dense astrophysical environments, such as globular clusters or in the vicinity of other massive objects, may possess accelerations. Such acceleration would modulate the characteristics of the quasi-periodic oscillations (QPOs) observed in X-ray black hole binaries. In this paper, we explore the influence of spin-aligned acceleration of a black hole on QPOs observed in X-ray binaries. For this purpose, we compute the fundamental frequencies arising from the motion of test particles around an accelerating (spin-aligned) black hole and apply the relativistic precession, parametric resonance, and forced resonance models to establish their correspondence with several observed QPOs of X-ray binaries (GRO J1655-40, XTE J1550-564, XTE J1859+226, GRS 1915+105, H1743-322, M82 X-1, and Sgr A $$^{*}$$ ∗ ). We then employ the Bayesian Markov-Chain Monte Carlo method to constrain the black hole parameters. Our results show no evidence for spin-aligned acceleration in any of the analyzed sources, suggesting that most of these X-ray binaries reside in isolated environments and therefore experience only small perturbations to the background spacetime geometries.
Interacting k-essence field with non-pressureless dark matter: Cosmological dynamics and observational constraints Saddam Hussain, Qiang Wu, Tao Zhu Journal of Cosmology and Astroparticle Physics, 2026 We investigate a class of interacting dark energy and dark matter (DM) models, where dark energy is modeled as a k -essence scalar field with an inverse-square potential. Two general forms of interaction are considered: One proportional to the Hubble parameter, and another independent of the Hubble parameter, depending instead on combinations of the energy densities and pressures of the dark sectors. The cosmological evolution is reformulated in terms of an autonomous system of equations, which provides a convenient phase-space parametrization for the numerical integration of the background dynamics and for confronting the models with observations. The models are tested against a wide range of observational datasets, including cosmic chronometers (CC), BAO measurements from DESI DR2, compressed Planck data (PLA), Pantheon+ (PP), DES supernovae, Big Bang Nucleosynthesis (BBN), and strong lensing data from H0LiCOW (HCW). The analysis shows that the models consistently reproduce all major cosmological epochs and yield statistically competitive results compared to the flat ΛCDM model. The models exhibit late-time de-Sitter solutions, ensuring ghost-free evolution, with the Hubble constant in the range H 0 ∼ 67–70 km/s/Mpc.
Interacting bosonic dark energy and fermionic dark matter in Einstein scalar Gauss–Bonnet gravity Simran Arora, Saddam Hussain, Benjamin Rose, Anzhong Wang European Physical Journal C, 2026 We explore a cosmological framework in which a Gauss–Bonnet (GB) coupled scalar field, acting as dark energy, interacts with a fermionic dark matter field through a coupling obtained from the point of view of particle physics. This setup is inspired by string/M-theory, and two representative scalar field potentials are investigated: exponential and power-law. A distinctive feature of the GB-coupled models is their potential to alter the propagation speed of gravitational waves (GWs), a property with significant implications in light of recent multi-messenger astrophysical observations. To account for this, we analyze models under two scenarios: one where the GW speed differs from that of light and the other where they are equal, but all consistent with current observational constraints. The dynamical evolution of the system is investigated by reformulating the field equations into an autonomous dynamical system, enabling a detailed analysis of the Universe’s long-term behavior, including the radiation-, matter- and dark energy-dominated epochs. We constrain the model parameters using a broad set of recent observational data, including mock high-redshift measurements from the Roman Space Telescope. Our findings indicate that both potentials yield cosmologies that are in excellent agreement with current data, closely tracking the expansion history predicted by the standard $$\Lambda $$ Λ CDM model, while still allowing room for subtle deviations that could be tested by future observations.
Interacting scalar fields as Dark Energy and Dark Matter in Einstein scalar Gauss Bonnet gravity Saddam Hussain, Simran Arora, Yamuna Rana, Benjamin Rose, Anzhong Wang Journal of Cosmology and Astroparticle Physics, 2026 A Gauss-Bonnet (GB) coupled scalar field ϕ , responsible for the late-time cosmic acceleration and interacting with a coherent scalar field ψ through an interaction potential W ( ϕ,ψ ), is considered from the point of view of particle physics for two different models. The non-minimal coupling between the GB curvature term and the field ϕ leads to a time-dependent speed of gravitational waves (GWs), which is fixed to unity in order to be consistent with current GW observations, rendering the GB coupling function model-independent. We investigate the dynamical stability of the system by formulating it as an autonomous system, and provide a detailed discussion on the choice of initial conditions required to obtain stable background evolution of the models. We constrain the model parameters using various sets of observational data, including both early- and late-time probes. We incorporate the improved Dark Energy Survey (DES) 5-year Type Ia supernova sample (DES-SN5YR), referred to as DES-Dovekie, which exhibits substantially lower tension with the Pantheon+ supernova sample. We find that both models are physically viable and closely follow the ΛCDM trend for the Pantheon+ and DES samples. However, upon including the Roman mock data, a significant departure is observed at higher redshifts, yielding statistically strong preference over the flat ΛCDM model.
Probing the dynamics of Gaussian dark energy equation of state using DESI BAO Saddam Hussain, Simran Arora, Anzhong Wang, Benjamin Rose Monthly Notices of the Royal Astronomical Society, 2026 We present an updated reconstruction of the dark energy (DE) equation of state (EoS), $w(a)$, employing the newly released Dark Energy Spectroscopic Instrument (DESI) Data Release 2 (DR2) baryon acoustic oscillation (BAO) data. This analysis constrains the cosmological scenarios influenced by different models through the joint examination of a range of recently available cosmological probes, specifically the pantheon+ sample and the DESY5 sample of Type Ia supernovae, baryon acoustic oscillations, Hubble parameter measurements derived from cosmic chronometers, and cosmic microwave background distance priors based on the Planck 2018 data. Furthermore, we provide a concise perspective on the dynamical evolution of all models (CPL, PADE, GEDE, GDE, and BellDE) and their interrelations. A Bayesian inference procedure is adopted to estimate the models parameters that yield the best fit to the data. The EoS remains within the phantom regime at higher redshifts, while favouring the quintessence regime in the current epoch. In this context, we propose a new Gaussian-like form of EoS, termed BellDE, which avoids phantom behaviour ($w \\ge -1$) at higher redshifts while remaining precisely calibrated at lower redshifts. Interestingly, BellDE exhibits a transient phantom nature ($w < -1$) around the transition redshift $z \\sim 0.5$, subsequently evolving into a quintessential regime ($w > -1$). In particular, the BellDE model provides competitive statistical preference while offering greater flexibility in the redshift regime $z \\sim 0.5-1$, where DE is observationally significant.
Comprehensive study of k-essence model: dynamical system analysis and observational constraints from latest Type Ia supernova and BAO observations Saddam Hussain, Sarath Nelleri, Kaushik Bhattacharya Journal of Cosmology and Astroparticle Physics, 2025 We constrain the parameters of the k-essence scalar field model with inverse square and exponential potentials using data sets including Pantheon+SHOES and the Dark Energy Survey (DES) of Type Ia supernovae, Baryon Acoustic Oscillation (BAO) data from SDSS and DESI surveys, and direct measurements of the Hubble parameter and redshift obtained from the differential age method (CC). We also provide a brief perspective on the dynamical evolution of both models and derive stability constraints on the model parameters, which are then used to set appropriate priors. We adopt a Bayesian inference procedure to estimate the model parameters that best fit the data. A comprehensive analysis in light of observational data shows that the k-essence model fits well across all data combinations. However, according to the BIC criterion, the ΛCDM model provides a slightly better fit compared to the k-essence model.
Interacting models of dark energy and dark matter in Einstein scalar Gauss Bonnet gravity Saddam Hussain, Simran Arora, Yamuna Rana, Benjamin Rose, Anzhong Wang Journal of Cosmology and Astroparticle Physics, 2024 We study the dynamics of the interacting models between the Gauss-Bonnet (GB) coupled scalar field and the dark matter fluid in a homogeneous and isotropic background. A key feature of GB coupling models is the varying speed of gravitational waves (GWs). We utilize recent constraints on the GW speed and conduct our analysis in two primary scenarios: model-dependent and model-independent. In the model-dependent scenario, where determining the GW speed requires a specific GB coupling functional form, we choose an exponential GB coupling. We adopt a dynamical system analysis to obtain the necessary constraints on the model parameters that describe different phases of the universe and produce a stable late-time accelerating solution following the GW constraint, and find that to satisfy all these constraints, fine-tuning of the free parameters involved in the models is often needed. In the model-independent scenario, the GW speed is fixed to one, and we construct the autonomous system to identify the late-time stable accelerating critical points. Furthermore, we adopt a Bayesian inference method using late-time observational data sets, including 31 data points from cosmic chronometer data (Hubble data) and 1701 data points from Pantheon+ and find that all the observational constraints can be satisfied without fine-tuning. In addition, we also utilize simulated binned Roman and LSST data to study the evolution of the universe in the model-independent scenario. We find that the model shows significant deviation at higher redshifts from ΛCDM and fits the current data much better than ΛCDM within the error bars.
Exploring the accelerating black holes from the observations of quasi-periodic oscillations in X-ray binaries H Rehman, S Hussain, G Abbas, T Zhu The European Physical Journal C 86 (5), 568 , 2026 2026
Interacting bosonic dark energy and fermionic dark matter in Einstein scalar Gauss–Bonnet gravity S Arora, S Hussain, B Rose, A Wang The European Physical Journal C 86 (4), 420 , 2026 2026
Chasing Gamma-Ray Signals from Binary Neutron Star Coalescences with the Cherenkov Telescope Array: Prospects and Observing Strategies S Abe, J Abhir, A Abhishek, F Acero, A Acharyya, R Adam, ... arXiv preprint arXiv:2604.08748 , 2026 2026
Interacting scalar fields as Dark Energy and Dark Matter in Einstein scalar Gauss Bonnet gravity SU Nazreen, S Hussain, S Arora, Y Rana, B Rose JOURNAL OF COSMOLOGY AND ASTROPARTICLE PHYSICS , 2026 2026
Interacting scalar fields as Dark Energy and Dark Matter in Einstein scalar Gauss Bonnet gravity S Hussain, S Arora, Y Rana, B Rose, A Wang Journal of Cosmology and Astroparticle Physics 2026 (04), 070 , 2026 2026
Interacting k -essence field with non-pressureless dark matter: Cosmological dynamics and observational constraints S Hussain, Q Wu, T Zhu Journal of Cosmology and Astroparticle Physics 2026 (04), 067 , 2026 2026 Citations: 1
Probing Kerr black hole in a uniform Bertotti-Robinson magnetic field through astrophysical quasi-periodic oscillations H Rehman, S Shaymatov, S Hussain, T Zhu arXiv preprint arXiv:2603.18129 , 2026 2026 Citations: 2
Dynamical Systems Approach to Non-Slow-Roll Inflationary Models: S. Biswas et al. S Biswas, S Hussain, K Bhattacharya General Relativity and Gravitation 58 (2), 14 , 2026 2026
Constraints on extra charges in dyonic Kerr-Newman-Kasuya-Taub-NUT black hole from the observations of quasi-periodic oscillations H Rehman, S Hussain, G Abbas, T Zhu Journal of Cosmology and Astroparticle Physics 2026 (01), 060 , 2026 2026 Citations: 1
Probing the dynamics of Gaussian dark energy equation of state using DESI BAO S Hussain, S Arora, A Wang, B Rose Monthly Notices of the Royal Astronomical Society 545 (2), staf1924 , 2026 2026 Citations: 11
Prospects for dark matter observations in dwarf spheroidal galaxies with the Cherenkov Telescope Array Observatory K Abe, S Abe, J Abhir, A Abhishek, F Acero, A Acharyya, R Adam, ... Monthly Notices of the Royal Astronomical Society 544 (3), 2946-2986 , 2025 2025 Citations: 2
DESI BAO S Hussain, S Arora, A Wang, B Rose 2025
Particle production scenario in an algebraically coupled quintessence field with a dark matter fluid S Hussain Chinese Journal of Physics 97, 673-695 , 2025 2025 Citations: 5
Particle physics models of interacting bosonic dark energy and fermionic dark matter in Einstein scalar Gauss-Bonnet gravity S Arora, S Hussain, B Rose, A Wang arXiv preprint arXiv:2508.08638 , 2025 2025 Citations: 1
Yano-Schrödinger Hyperfluid: Cosmological Implications H Chaudhary, S Hussain Journal of High Energy Astrophysics, 100447 , 2025 2025 Citations: 1
Large scale structure constraints and matter power spectrum in gravity PK Dhankar, A Munyeshyaka, S Hussain, T Mutabazi arXiv preprint arXiv:2507.10631 , 2025 2025
Interacting Scalar Fields as Dark Energy and Dark Matter in Einstein scalar Gauss Bonnet Gravity S Hussain, S Arora, Y Rana, B Rose, A Wang arXiv preprint arXiv:2507.05207 , 2025 2025 Citations: 7
Avoidance of Big Crunch Singularity in the Q-SC-CDM model via nonminimal coupling: Theory and Data Analyses Y Myrzakulov, S Hussain, M Shahalam arXiv preprint arXiv:2506.11755 , 2025 2025 Citations: 2
Phase space and Data analyses of a non-minimally coupled scalar field system with decaying dark energy model Y Myrzakulov, S Hussain, M Shahalam arXiv preprint arXiv:2506.11755 , 2025 2025 Citations: 3
Dynamical systems approach to Cold and Warm Inflation within slow-roll and beyond S Biswas, S Hussain, K Bhattacharya arXiv preprint arXiv:2504.10454 , 2025 2025
MOST CITED SCHOLAR PUBLICATIONS
Dynamical stability of the -essence field interacting nonminimally with a perfect fluid A Chatterjee, S Hussain, K Bhattacharya Physical Review D 104 (10), 103505 , 2021 2021 Citations: 42
Dynamical systems analysis of tachyon-dark-energy models from a new perspective S Hussain, S Chakraborty, N Roy, K Bhattacharya Physical Review D 107 (6), 063515 , 2023 2023 Citations: 34
Dynamical stability in models where dark matter and dark energy are nonminimally coupled to curvature S Hussain, A Chatterjee, K Bhattacharya Physical Review D 108 (10), 103502 , 2023 2023 Citations: 31
Dynamical stability in presence of non-minimal derivative dependent coupling of k -essence field with a relativistic fluid K Bhattacharya, A Chatterjee, S Hussain The European Physical Journal C 83 (6), 488 , 2023 2023 Citations: 30
Interacting models of dark energy and dark matter in Einstein scalar Gauss Bonnet gravity S Hussain, S Arora, Y Rana, B Rose, A Wang Journal of Cosmology and Astroparticle Physics 2024 (11), 042 , 2024 2024 Citations: 23
Comprehensive study of k -essence model: dynamical system analysis and observational constraints from latest Type Ia supernova and BAO observations S Hussain, S Nelleri, K Bhattacharya Journal of Cosmology and Astroparticle Physics 2025 (03), 025 , 2025 2025 Citations: 21
Ghost Condensates and Pure Kinetic k -Essence Condensates in the Presence of Field–Fluid Non-Minimal Coupling in the Dark Sector S Hussain, A Chatterjee, K Bhattacharya Universe 9 (2), 65 , 2023 2023 Citations: 20
Stability analysis of warm quintessential dark energy model S Das, S Hussain, D Nandi, RO Ramos, R Silva Physical Review D 108 (8), 083517 , 2023 2023 Citations: 15
Probing the dynamics of Gaussian dark energy equation of state using DESI BAO S Hussain, S Arora, A Wang, B Rose Monthly Notices of the Royal Astronomical Society 545 (2), staf1924 , 2026 2026 Citations: 11
Interacting Scalar Fields as Dark Energy and Dark Matter in Einstein scalar Gauss Bonnet Gravity S Hussain, S Arora, Y Rana, B Rose, A Wang arXiv preprint arXiv:2507.05207 , 2025 2025 Citations: 7
Periodic fixed point theorems via rational type contraction in b-metric spaces S Hussain, M Sarwar, C Tunc Journal of Mathematical Analysis 10 (3), 61-67 , 2019 2019 Citations: 7
Particle production scenario in an algebraically coupled quintessence field with a dark matter fluid S Hussain Chinese Journal of Physics 97, 673-695 , 2025 2025 Citations: 5
Non-adiabatic particle production scenario in algebraically coupled quintessence field with dark matter fluid S Hussain arXiv e-prints, arXiv: 2403.10215 , 2024 2024 Citations: 5
In vivo and in vitro bioassay of potential insecticides against mealy bugs: A cotton worse catastrophe in Pakistan MJ Arif, S Hussain, MR Shahid, G Abbas, MD Gogi Proceedings of 2nd Congress on Insect Science-Pest management in global … , 2008 2008 Citations: 5
The nature of cosmological metric perturbations in presence of gravitational particle production K Bhattacharya, A Chatterjee, S Hussain arXiv preprint arXiv:2007.00904 , 2020 2020 Citations: 4
Phase space and Data analyses of a non-minimally coupled scalar field system with decaying dark energy model Y Myrzakulov, S Hussain, M Shahalam arXiv preprint arXiv:2506.11755 , 2025 2025 Citations: 3
Chasing gravitational waves with the Cherenkov Telescope Array JG Green, A Carosi, L Nava, B Patricelli, F Schüssler, M Seglar-Arroyo, ... arXiv preprint arXiv:2310.07413 , 2023 2023 Citations: 3
Fixed point theorems for multi-valued generalized contraction in b-metric spaces S Hussain, M Sarwar, C Tunc J. Math. Anal 9, 158-166 , 2018 2018 Citations: 3
Probing Kerr black hole in a uniform Bertotti-Robinson magnetic field through astrophysical quasi-periodic oscillations H Rehman, S Shaymatov, S Hussain, T Zhu arXiv preprint arXiv:2603.18129 , 2026 2026 Citations: 2
Prospects for dark matter observations in dwarf spheroidal galaxies with the Cherenkov Telescope Array Observatory K Abe, S Abe, J Abhir, A Abhishek, F Acero, A Acharyya, R Adam, ... Monthly Notices of the Royal Astronomical Society 544 (3), 2946-2986 , 2025 2025 Citations: 2
