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H. Mohseni Sadjadi

Publications and source records attributed to H. Mohseni Sadjadi.

At least 19 recordsLinked to original sources
arXiv2026

Testing Modified Teleparallel Gravity by Neutrino Oscillations

In the framework of modified teleparallel gravity, we study neutrino flavor conversion. We show how the presence of spacetime torsion modifies both neutrino flavor oscillation and the matter-enhanced Mikheyev-Smirnov-Wolfenstein (MSW) resonance. Using data from solar neutrino experiments, we perform an analysis to place new bounds on the modified teleparallel model parameters and neutrino-torsion coupling. Our numerical results indicate that the resulting modifications to the neutrino survival probability may explain potential observational discrepancies in current and future observatories without invoking new physics or non-standard interactions.

hep-ph↗
arXiv2026

Mass-Varying Dark Matter Induced Scalarization and Scalar Clouds around Black Holes

We consider a black hole solution embedded in a mass varying dark matter (DM) halo and study scalarization induced by DM. We derive the required conditions on the scalar DM coupling that allow for a regular bound state scalar cloud. We find that such configurations exist only for quantized coupling values in terms of the halo's intrinsic parameters (for Hernquist, this reduces to the inverse of the compactness). This study provides a novel connection between DM phenomenology and scalarization around a black hole.

gr-qc↗
arXiv2026

Gravitational Baryogenesis in Rainbow Gauss-Bonnet gravity

The gravitational baryogenesis is studied in regularized four dimensional Einstein Gauss Bonnet model with rainbow gravity corrections. This combined framework generates a non vanishing time derivative of the Ricci scalar even during radiation domination era. We derive analytical expressions for the baryon to entropy ratio in both the high curvature and perturbative regimes. The Gauss Bonnet contribution produces nonzero asymmetry precisely at radiation era, where the Einstein Hilbert contribution vanishes. Numerical analysis identifies viable parameter spaces reproducing the observed baryon to entropy ratio, compatible with observations.

gr-qc↗
arXiv2026

Spontaneous scalarization around a black hole in a dark matter halo

We demonstrate that in a scalar-tensor theory where dark matter is conformally coupled to a scalar field, a black hole surrounded by a Hernquist dark matter halo can undergo spontaneous scalarization, acquiring a nontrivial scalar field configuration. The astrophysical properties of the dark matter halo directly dictate the quantum-like spectrum of scalar field configurations around the central black hole. Remarkably, the conformal coupling constant becomes discretized and is determined solely by the halo's compactness parameter.

gr-qc↗
arXiv2026

Mass Varying Neutrino Oscillation in Teleparallel Gravity

In the Cartan teleparallel formulation of gravity, a scalar field coupled to the torsion tensor can acquire an environment dependent effective mass. This gives rise to a screening effect: Inside dense bodies such as the Sun, the scalar field is suppressed, causing the mass varying neutrino mass to vary with local density. We investigate the impact of this torsion-induced screening on solar neutrino oscillations. The mechanism modifies the standard MSW resonance condition in a distinct way, leading to detectable shift in the flavor conversion probability. Using data from solar neutrino experiments (Super-Kamiokande, Borexino, SNO), we place constraints on the torsion-scalar coupling parameters. Our work provides concrete test of teleparallel gravity through mass varying neutrino oscillations.

hep-ph↗
arXiv2025

Mass Varying Neutrino Oscillation in Scalar-Gauss-Bonnet Gravity

We investigate how matter density affects neutrino oscillations by considering a mass-varying neutrino scenario where the neutrino mass depends on a scalar field. This scalar field is non-minimally coupled to the Gauss-Bonnet (GB) invariant, causing its profile to be implicitly influenced by the surrounding matter distribution. Using data from solar neutrino experiments, we derive constraints on the model parameters, providing new insights into the properties of mass-varying neutrino within the Gauss-Bonnet scalar-tensor framework.

hep-ph↗
arXiv2025

Onset of dark energy from cosmological scalarization and gravitational wave speed

This study investigates the emergence of dark energy during the matter-dominated era through spontaneous cosmological scalarization in the scalar-Ricci-Gauss-Bonnet model.Our model aligns with the conjecture that the speed of gravitational waves at low redshifts is nearly equal to the speed of light, implying that the Gauss-Bonnet invariant does not directly contribute to late-time acceleration and suggesting that scalarization begins in the radiation-dominated era. The Gauss-Bonnet coupling stabilizes the quintessence field at an initial fixed point with negligible dark energy density during the radiation era. As the Universe expands, the Ricci coupling induces a tachyonic transition in the quintessence field, driving the evolution of dark energy.

gr-qc↗
arXiv2024

Imprints of vector field non-standard couplings on solar neutrino flux

Regarding the proximity of dark energy scale and neutrino mass, one can get new insight into the probe signatures of vector field dark energy component on neutrino flavor conversion. A vector field is assumed to be conformally coupled to various matter components through a screening paradigm. We show how the oscillation probabilities evolve differently with a finite-size matter density like the Sun for different values of relevant model parameters. Considering existing neutrino flavor conversion data, we point out how this non-standard coupling affects neutrino fluxes and also we compute the discrepancy in the total flux of solar electron-neutrinos.

hep-ph↗
arXiv2024

Early dark energy and scalarization in a scalar-tensor model

We present a model in which the Gauss-Bonnet invariant holds the quintessence at a fixed point, respecting an initial $Z_2$ symmetry in the radiation-dominated era. This results in an early dark energy that becomes significant around the matter-radiation equality era. However, due to $Z_2$ symmetry breaking, scalarization occurs, leading to a rapid reduction in the early dark energy density. The model then quickly behaves like the $Λ$CDM model. This scenario may also explain the reduction of sound horizon and aligns with the assumption that the gravitational wave speed is infinitesimally close to the speed of light.

gr-qc↗
arXiv2024

Scalar-Gauss-Bonnet model, the coincidence problem and the gravitational wave speed

We introduce a dynamical dark energy model wherein quintessence interacts with both the Gauss-Bonnet invariant and dark matter. Initially, the Gauss-Bonnet invariant stabilizes the quintessence at a fixed point, resulting in a negligible density of dark energy. Subsequently, the conformal coupling to dark matter triggers the evolution of dark energy. This model proposes an explanation for the initial absence of dark energy in radiation era and its later emergence during the matter-dominated era, achieving a magnitude comparable to dark matter in the present epoch. In this scenario, the Gauss-Bonnet term does not directly influence late-time cosmic evolution. Our model aligns with the assumption that the speed of gravitational wave is infinitesimally close to the speed of light.

gr-qc↗
arXiv2024

Chameleon-neutrino conformal coupling and MSW-mediated solar neutrino deficit

A modified version of the MSW effect is studied within the framework of screening models through conformal couplings of a scalar field within matter. Such a coupling leads to a new, unknown interaction between the scalar field and the neutrino. We mainly look for the discrepancy in the total solar electron-neutrinos flux through this interaction. Since the scalar field behavior depends on the local density of matter, we observe an indirect effect of matter on flavor changes, and subsequently, on neutrino flux through neutrino decay. The paper ends by describing various probabilities and comparing the results with observational data.

hep-ph↗
arXiv2023

Early dark energy and the screening mechanism

In the early Universe, dark energy may have a non-negligible contribution. If this dark energy corresponds to an early cosmological constant, it leads to a late-time huge dark energy density which is much larger than what is expected for the current expansion of the Universe. Using a conformal coupling of the quintessence to the dark matter, and based on the screening models, we propose a process to reduce the early dark energy to its ultimate value in the late time. Early and late time dark energies can be unified in a single component, in this way.

gr-qc↗
arXiv2022

Screening models and neutrino oscillations

In screening models with scalar-matter conformal coupling, we study the flavor transition of neutrinos. We employ an analytical method for studying the oscillation phase in a spherically symmetric spacetime filled by a scalar field. Since the ambient matter density determines the scalar field's behavior, an indirect environmental effect contributes to the flavor conversion inside matter. We evaluate the survival probabilities and show that the existence of the scalar field affects the oscillations of neutrinos. We discuss the results in the framework of screening mechanisms and the end, confront our results with observational data.

hep-ph↗
arXiv2022

Constant-roll, cosmic acceleration, and massive neutrinos

We propose a model to describe the late-time cosmic acceleration in the context of the constant-roll model. By considering a coupling between massive neutrinos and the quintessence, the onset of evolution of the quintessence is related to the neutrinos' behavior. When the neutrinos become non-relativistic, the dark energy density increases from zero and results in late-time cosmic acceleration alleviating the coincidence problem. The quintessence potential is such that it evolves under the constant-roll condition giving rise to persistent late-time acceleration.

gr-qc↗
arXiv2021

Damped Neutrino Oscillations in a Conformal Coupling Model

Flavor transitions of Neutrinos with a nonstandard interaction are studied. A scalar field is conformally coupled to matter and neutrinos. This interaction alters the neutrino effective mass and its wavefunction leading to a damping factor, causing deficits in the probability densities and affecting the oscillation phase. As the matter density determines the scalar field's behavior, we also have an indirect matter density effect on the flavor conversion. We explain our results in the context of screening models and study the deficit in the total flux of electron-neutrinos produced in the Sun through the decay process and confront our results with observational data.

hep-ph↗
arXiv2020

On cosmic acceleration in four dimensional Einstein-Gauss-Bonnet gravity

We study the possibility that in the model introduced in \cite{GBN}, the Gauss-Bonnet term alone gives rise to the cosmic acceleration and super-acceleration in four-dimensional FLRW space-time at the late time. We also discuss transitions from deceleration to acceleration and acceleration to super-acceleration. We show that the Gauss-Bonnet invariant can drive the acceleration in the low redshift provided that its regularized coefficient has the same order as the squared of the ratio of the reduced Planck mass to the Hubble parameter.

gr-qc↗
arXiv2019

Regular scalar field around reflecting stars and black holes, and reflecting star polarization

The existence of a regular non-trivial scalar field in the background of an asymptotically flat static reflecting star is discussed. The scalar field is assumed to be conformally coupled to the outside matter. The induced scalar charge is determined and the required conditions to have regular field are obtained. The results are compared with the case of a black hole. Conditions to have regular non-trivial scalar field out of the black hole horizon are investigated. We show that in the presence of a scalar source, in contrast to the black holes, the reflecting star becomes polarized.

gr-qc↗