arXiv subjects

Manda Malekpour

Publications and source records attributed to Manda Malekpour.

4 recordsLinked to original sources

arXiv2026

Brans Dicke scalar-tensor gravity and unimodular FRW cosmology with Coleman-Weinberg potential

As alternative gravity theories with respect to the general relativity, the Brans-Dicke (BD) scalar tensor model is well known for which the BD parameter is controller the best fit observational data and so its cosmological model is studied in the literature well. On the other side, the Coleman Weinberg (CW) self-interaction scalar field potential coming from radiation corrections of Feynman diagrams is used to describe the best fit cosmic inflation phase and reheating phase. This has a logarithmic term with respect to the Higgs potential and it is applicable even for massless bosons. From particle physics point of view, this is used usually to describe the Higgs mechanism and creation of massive Goldstone bosons. As a basic model to describe the cosmic inflation the cosmological constant is used to describe the de Sitter space where the cosmological constant play as dark energy density. Since, the cosmological constant is a hierarchy problem and it is added in the Einstein equation without to describe that where that is come originally? at a first time the Albert Einstein himself proposed a uni-modular frame for which the cosmological constant generate from a integral constant. This idea is very well because it resolve `fine tuning` problem of the cosmological constant parameter. Hence we use this idea for the BD theory in presence of the CW potential and obtained suitable solutions of the field equations for a flat Robertson-Walker space time by regarding the slow roll parameters of cosmic inflation and then we find the best fit correspondence between the theoretical predictions of the parameters of the solutions and the Planck2018, DESI2024, and ACT2025 observational data.

gr-qc↗

arXiv2026

Reheating after the Higgs Inflation

Since the discovery of the Higgs particle in the LHC, numerous inflationary models utilize it as the inflaton. In this study, after establishing that Higgs inflation can be a viable model in the context of unimodular gravity, we address a scenario related to reheating, which plays a crucial role in connecting the inflationary era to a hot Big Bang universe. Also, we calculate essential parameters such as the temperature and the e-folds number according to the equation of the state parameter ($\omega_{re}$) in this regime of reheating. The physics behind the reheating process are extremely imprecise at present, and we have only a very limited range of acceptable values for $\omega_{re}$. We analyze the compatibility with Planck2018, BICEP/Keck2021, DESI2024, and ACT array bounds and find that within this model, $\omega_{re}$ is restricted to the range $ -1 \leq \omega_{re} \leq \frac{1}{6} $.

physics.gen-ph↗

arXiv2026

Non-minimal Unimodular Inflation

We study an extension of the unimodular cosmological inflation in the context of the non-minimal coupling of a generic scalar field with gravitational sector. We consider the non-minimal coupling of the scalar field and gravity as the only source of energy-momentum tensor in this setup. Without introducing new particles other than those already existing in electroweak theory, the generic scalar field's non-minimal coupling is responsible for the generation of the seeds of perturbations for structure formation and the observed Cosmic Microwave Background anisotropies in this scenario. We calculate inflation parameters in both the Jordan and Einstein frames, and then we study primordial spectral indices for slow-roll parameters in Einstein's frame at the first and second orders. The numerical results of this model are consistent with the Planck2018 and BICEP/Keck joint data sets in some subspaces of the model parameters space. By considering a sufficient amount of inflation, we estimate the strength of the non-minimal coupling parameter, $\xi$, to find appropriate new constraints on the values of this parameter. By comparing the numerical values of the inflation observables in two frames and also with observation, we comment on the issue of frames in this framework.

astro-ph.CO↗

arXiv2024

Higgs Inflation in Unimodular Gravity

The discovery of Higgs mechanism within the context of spontaneous symmetry breaking has offered a new perspective on the early time cosmic inflation and also on the relationship between elementary particles and dark energy, believed to drive the universe's accelerating expansion. We suggest an inflation scenario driven by the Higgs boson within the framework of unimodular gravity, where the Higgs field acts as the inflaton and has a significant non-minimal coupling to the gravity. We present a detailed analysis of the problem in the Jordan and then Einstein frame for a unimodular Higgs inflation, followed by a comparison of our findings with the Cosmic Microwave Background observations made by the Planck Collaboration and other joint data sets. Therefore, new constraints are imposed on the non-minimal coupling parameter, $\xi$, by determining the magnitudes required for effective cosmic inflation. We demonstrate that a substantial non-minimal coupling of order $\xi\sim 10^{2}-10^{4}$ is required for this model to match with the observed primordial spectrum.

hep-th↗