arXiv subjects

Mohammad Reza Shojaei

Publications and source records attributed to Mohammad Reza Shojaei.

10 recordsLinked to original sources

arXiv2026

From Voids to Clusters: Mergers and Evolutionary Pathways of Star-Forming and Quenched Low-Mass Galaxies

The evolution of low-mass galaxies is shaped by both internal processes and environmental factors, yet the role of environment and mergers in regulating their growth and star formation rates remains poorly understood, especially in the low-density regime. This study aims to compare the evolutionary pathways and merger histories of star-forming and quenched galaxies in dense (cluster) and under-dense (void) environments, focusing on galaxies with stellar masses in the range $10^{8.5} \leq M_\star/M_\odot \leq 10^{10.5}$. It presents the first statistical analysis within this stellar mass range, explicitly distinguishing between mini, minor, and major mergers across varying environments. Using the high-resolution TNG300-1 simulation from the IllustrisTNG project, we classify galaxies as star-forming and quenched based on sSFR and UVJ criteria. We track their physical properties over the last $\sim 10.5$ Gyr ($z < 2$), follow their complete merger histories, distinguishing between major, minor, and mini mergers, and assess the statistical impact of these mergers on star formation and gas content.

astro-ph.GA↗

arXiv2025

From QCD-Based Descriptions to Direct Fits: A Unified Study of Nucleon Electromagnetic Form Factors

We present a detailed study of the nucleon electromagnetic form factors in the spacelike region by combining three complementary approaches: two GPD-based contributions and a vector-meson exchange component. By fitting experimental data, we extract the optimal weights and shape parameters describing the proton and neutron form factors. Global Padé-based fits are then constructed for four distinct groups of form factors, starting from local Taylor expansions and yielding stable analytic parametrizations over the analyzed $t$ range. The combined framework provides an accurate and physically motivated description of nucleon structure within a controlled model-dependent setting across a wide range of momentum transfers.

hep-ph↗

arXiv2025

Star-Forming vs. Quenched Galaxies in Voids: Insights into the Role of Mergers

Cosmic voids, the largest under-dense structures in the Universe, are crucial for exploring galaxy evolution. These vast, sparsely populated regions are home to void galaxies -- predominantly gas-rich, star-forming, and blue -- that evolve more slowly than those in denser environments. Additionally, the correlation between galaxy mergers and specific properties of galaxies, such as the star formation rate (SFR), is not fully understood, particularly in these under-dense environments. Quenched void galaxies exhibit high SFRs at high redshifts, significantly decreasing at lower redshifts (z < 0.5). These galaxies have higher dark matter halos than star-forming galaxies across all redshifts, leading to rapid gas consumption. They formed earlier and experienced more major mergers in earlier epochs but fewer recent mergers, resulting in a lack of fresh gas for sustained star formation. Also, star-forming and high-mass quenched void galaxies show higher SFRs in mergers compared to non-merger galaxies. This study highlights that formation time, merger rates, and dark matter halos play a crucial role in the star formation history of void galaxies. Rapid and earlier gas consumption due to earlier formation time and the absence of recent mergers could lead to quenched void galaxies at lower redshifts, providing valuable insights into galaxy evolution in low-density environments.

astro-ph.GA↗

arXiv2024

Examining the structure functions of nucleons by introducing new Ansatz and their consequences on parton distribution functions in higher approximation

By introducing ansatz and using a PDF at the $N^3LO$ approximation in this paper, we have studied the structure of the nucleons in generalized parton distributions (GPDs). For this purpose, the form factors and the electric radius of nucleons, as well as the quark's form factors, are calculated in this paper. These calculations give important new information about the nucleons and the distribution of partons within them. The results are analyzed, and to validate them, the abstract emphasizes the importance of comparing the results with existing research and experimental data. By varying the free appropriate parameters of the new ansatz, the study seeks to optimize the model, ensure its suitability for accurately describing the nucleon's internal structure, and provide valuable insights about the distribution of partons.

hep-ph↗

arXiv2023

Form factors of the nucleon by using the t dependence of parton distribution functions

This paper calculates the elastic form factors for nucleons based on generalized parton distributions using an extended new ansatz introduced in http://dx.doi.org/10.1103/PhysRevC.105.025202 (Phys. Rev. C 105, no.2, 025202 (2022)). Different parton distribution functions (PDFs) are considered, and modifications are made to the free parameters of the new ansatz. The obtained results are systematically compared among the combinations of different PDFs and ansatzes for high ranges of momentum transfer, with $-t < 35 GeV^{-2}$. The minimum suitable parameters are used to parametrize the model. After obtaining the form factors, we proceed to compute the electric radius and the transversely unpolarized densities for the nucleon. In addition, we derive the parton distribution functions (PDFs) that depend on the impact parameter. Finally, we analyze the results by comparing them with the findings from other research and experimental data.

hep-ph↗

arXiv2019

Calculation Binding energy for 223,225,227Ra isotopes in relativistic heavy cluster model

14C is a stable isotope and emitted from medium and heavy mass nuclei. The 14C result is in excellent agreement with a favored ground-state-to-ground-state transition according to the cluster model of Blendowske et al. We study Ra isotopes in relativistic core-cluster model, solve the Dirac equation with the new phenomenological potential by parametric Nikiforov-Uvarov method, and obtain wave function and binding energy.

nucl-th↗

arXiv2019

Investigation of the energy levels and the structure of the different states of the 24Mg nucleus

In this work, the 24Mg nucleus is considered in the cluster model by solving the Schrodinger and Klein- Gordon equations from the Nikiforov- Uvarov (NU) method. A local potential is used for these two equations that is compatible with the Hafstad-Teller potential. By substituting this potential in the Schrodinger and Klein- Gordon equations, the energy levels and wave functions are obtained from NU method. We obtain a first order equation in terms of E for the Schrodinger equation and a fourth-order equation in terms of ER for the Klein-Gordon equation. Therefore, the obtained equation from the Klein-Gordon equation has both the real solutions and imaginary solutions that we consider only the real solutions for this equation. For more accuracy, the spin-orbit and tensor potentials are added to the central potential as the perturbed terms and the first-order correction value of the energy levels is calculated. These energy levels are used for 24Mg nucleus and the good results are obtained in agreement with the experimental data. Of course, one can see that the calculated results from the Schrodinger and Klein-Gordon equations, i.e. non-relativistic and relativistic respectively, are nearly the same. By using the Coulomb repulsive potential, it is shown that the structure of the ground state and the first excited state of this nucleus is as octahedral and the configuration of the alpha particles for the second excited state is as pentahedral, i.e. as 12C +12C . Finally, we obtain the critical point for the calculation of maximum energy of this nucleus in the cluster model.

nucl-th↗

arXiv2018

Calculation Energy levels and charge radius for odd $^{41-49}$Ca Isotopes by using the analytical approach

In the present study, some static properties of odd isotopes of Ca were investigated in the non-relativistic shell model. We also suggested a novel suitable local potential model for the non-microscopic investigation of the mentioned nuclei. We modeled the odd $^{41-49}$Ca nuclei as doubly-magic isotopes, with further nucleons (valence) in the lf7/2 and 2p3/2 levels. Then the modified Eckart potential as well as Hulthen potential were chosen for the interaction between core and nucleons. We also used the Parametric Nikiforov Uvarov method to calculate the values of energy, the radius of charge and wave function. The obtained results showed a good agreement with the experimental data, so this model is applicable for the similar nuclei.

nucl-th↗

arXiv2017

The effect of tensor interaction in splitting the energy levels of relativistic systems

In this paper we solve analytically Dirac equation for Eckart plus Hulthen potentials with Coulomb-like and Yukawa-like tensor interaction in the presence of Spin and Pseudo-spin Symmetry for any k number. The Parametric Nikiforov-Uvarov method is used to obtain the energy Eigen-values and wave functions. We also discuss the energy Eigen-values and the Dirac spinors for the Eckart plus Hulthen potentials for the spin and pseudo-spin symmetry with PNU method. To show the accuracy of the present model, some numerical results are shown in both pseudo-spin and spin symmetry limits.

nucl-th↗

arXiv2016

Calculation of Energy Spectrum of 12C Isotope by Relativistic Cluster model

In this paper, we have calculated the energy spectrum of 12C isotope by cluster model. The experimental results show that the "Hoyle" state at 7.65 MeV in 12C isotope has a well-developed three-alpha structure. Hence, we select a three-body system and for interaction between the clusters we use modified Yukawa potential plus coulomb potential. Then, we solve the relativistic Klein-Gordon equation using Nikiforov-Uvarov method to calculate the energy spectrum. Finally, the calculated results are compared with the experimental data. The results show that the isotope 12C should be considered as consisting of three-alpha cluster and the modified Yukawa potential is adaptable for cluster interactions.

nucl-th↗