arXiv subjects

Taimur Mohammadi

Publications and source records attributed to Taimur Mohammadi.

5 recordsLinked to original sources

arXiv2025

The Power Spectrum Of Gravitational Waves in Anisotropic Universe (\emph{Bianchi type--I})

One of the predictions from simple inflation models is stochastic background of Gravitational Waves (\textbf{GW}), or literally what is called Primordial Gravitational Waves (\textbf{PGW}) with a nearly scale--invariant spectrum. To discuss a possible direct detection of PGW, the quantity so--called Spectral Energy Density (\textbf{SED}) has crucial role. In this work, we consider PGW produced in the Radiation-Dominate(\textbf{RD}) era and generated by perturbing the isotropic and Anisotropic (\emph{Bianchi type--I}) metrics and focusing on the SED generated by these GW. This study was done because the power spectrum of GW from the RD epoch is one of the most important topics in early cosmology, as GW produced during this period can provide us with direct information about very High Energies and fundamental phases of the universe (e.g. inflation and phase transition)The results show that the power spectrums in the early universe are diffetent for isotropic and anisotropic universe, but they coincide at the present time.

gr-qc↗

arXiv2024

One-Dimensional Primordial Gravitational Waves In Pure Quadratic Gravity

The almost scale-invariant spectrum for the stochastic background wave (in primordial Universe) is a firm prediction of inflationary scenarios. In the present work, to study of primordial Gravitational Waves, one dimensional toy model in generalizations of the Einstein-Hilbert frame, described by second order curvature invariant (called pure Quadratic Gravity) is considered. Solutions to the primordial perturbations are more varied than Einstein-Hilbert frame and include simple incoming and outcoming waves. By examining the spectrum diagram of the perturbation solutions, it can be seen that the oscillating solutions are ruled out due to not having the necessary spectral power, but the solutions as damping exponential have the ability to produce a scale-invariant spectrum (confirmed by CMB data).

gr-qc↗

arXiv2023

Magnetic Dipole and Noncommutativity

The noncommutativity concept has wide range of applications in physical and mathematical theories. Noncommutativity in the position-time coordinates concerns the microscale structure of space-time. the noncommutativity is an intrinsic property of the space-time and it could be different from usual properties when one encounters the high energy phenomena. on the other hand, the space-time is assumed to be as a background for the occurrence of physical events. therefore, it is not far-fetched to expect the emergence of new physics or dynamics when the fine geometric structure of space-time is deformed. In this work, we consider a common form of this deformation and try to answer the question as: a physical (or dynamical) model can be described by the noncommutative effects?. This can also be asked this way: dose the noncommutativity could have a physical manifestations in the nature?. Our model here is a magnetic dipole.

gr-qc↗

arXiv2022

The Power Spectrum Of Gravitational Waves In Anisotropic Universe

One of the predictions from simple inflation models is a stochastic background of gravitational waves (or literally what is called the Primordial Gravitational Waves (\textbf{PGW})) with a nearly scale--invariant spectrum. In this work, we consider these waves arising from perturbing the Anisotropic background (Bianchi type--I) metric by focus on their power spectrums.The intended frameworks are the Einstein's and modified gravity frames. The investigations indicate that in the modified gravity context, the results have more ability to adapt to physical conditions or constraints. Especially, the scale--invariant character of the spectrum is much more pronounced in the modified framework.

gr-qc↗

arXiv2021

About the Power Spectrum Of Primordial Gravitational Waves

The primordial gravitational waves (\textbf{PGW}) have been generated by inflationary amplification of the primordial (quantum) fluctuations. It is true that they have not been recorded directly so far, but their spectrum can help a lot in solving the basic puzzles of the early universe as Inflation (high) energy scale. In the present work, we give a straightforward method to calculate the spectral energy density (\textbf{SED}) of the relic gravitons different from that used in e.g. \cite{ mirza04,Latham 2005, Yuki 2006}. In our approach, the evolution equations are in terms of the scale factor (instead of conformal time) through the Lagrange formalism (instead of the transfer function). The presence of the Hubble parameter allows to calculate the power spectrum in the different dynamical regimes.

gr-qc↗