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Astronomy & Astrophysics
Mingzhe Li, Haomin Rao
Summary: The Nieh-Yan modified teleparallel gravity is a model that modifies the general relativity equivalent teleparallel gravity by introducing a coupling between the Nieh-Yan density and an axion-like field. This model predicts parity violations in gravitational waves and avoids the pathologies found in other models. In this paper, the symmetry constraint on the connection is relaxed, leading to a new flat universe solution where scalar and tensor perturbations are coupled.
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Astronomy & Astrophysics
Asanka Amarasinghe, Tianye Liu, Daniel A. Norman, Philip D. Mannheim
Summary: This paper investigates cosmological perturbation theory in the context of the fourth-order derivative conformal gravity theory and provides an exact solution from the recombination era until the present era.
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Astronomy & Astrophysics
Payel Sarkar, Prasanta Kumar Das
Summary: In this study, we investigated the bouncing universe scenario in the case of modified gravity represented by f(R,T) = R + 2 lambda T, where R is the Ricci scalar and T is the trace of energy momentum tensor. Two different types of scale factors were considered, which were non-zero at t = 0 (the bounce point). The initial non-vanishing values of the scale factors resolved the singularity problem. The behaviors of the Hubble parameter H and the deceleration parameter q were examined for two different models corresponding to the two scale factors. Violation of energy conditions was observed, and both models were highly unstable at the bounce point, but the perturbation decayed rapidly away from the bounce and became stable at late times.
PHYSICS OF THE DARK UNIVERSE
(2023)
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Astronomy & Astrophysics
Tom Rudelius
Summary: A popular proposal for resolving the Hubble tension involves early dark energy models driven by an axion field. However, these models are tightly constrained by the axion weak gravity conjecture, making it challenging to realize them in a UV complete theory of quantum gravity.
JOURNAL OF COSMOLOGY AND ASTROPARTICLE PHYSICS
(2023)
Article
Physics, Multidisciplinary
M. J. Luo
Summary: This article proposes and reviews a framework of quantum spacetime reference frame, in which the quantum spacetime is deformed by the Ricci flow at the Gaussian approximation. It is found that the Ricci flow can be applied to the high curvature region near the local singularity of the early universe, and can naturally reproduce an inflationary deSitter universe without introducing any inflaton field. The deviation from exact deSitter can be calculated by a small deviation from the singular flow-time via the Ricci flow, and the power spectrum of the scalar perturbation agrees with current observations.
Article
Astronomy & Astrophysics
Marvin Sipp, Bjoern Malte Schaefer
Summary: We reconsider the gravitational wave spectrum induced by scalar perturbations in flat space-time, focusing on matter- and dark energy-dominated epochs. During matter domination, the commonly applied approximation for the derivative of tensor perturbation is flawed, resulting in an overestimation of the energy density spectrum. Additionally, non-oscillating tensor perturbations appear in the presence of a cosmological constant. Numerical calculations for a Planck-like ACDM cosmology show the presence of non-oscillating growing modes during the transition between matter and dark energy domination in conformal Newtonian gauge.
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Physics, Multidisciplinary
A. I. Keskin
Summary: This study investigates the inflationary era of the Universe in the context of f(R) gravity, considering scalar perturbation equations and assuming specific parameter values to achieve inflation. The findings suggest that this inflation scenario for the early universe is possible, as observed parameters align with latest observational data.
EUROPEAN PHYSICAL JOURNAL PLUS
(2021)
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Physics, Mathematical
Archana Dixit, Anirudh Pradhan, Dinesh Chandra Maurya
Summary: This paper investigates the physical behavior of cosmological models in modified Teleparallel gravity with a general function f(T), and finds that the second term of f(T) behaves similarly to the cosmological term Lambda in late-time universe, causing acceleration in expansion and acting like dark energy candidates.
INTERNATIONAL JOURNAL OF GEOMETRIC METHODS IN MODERN PHYSICS
(2021)
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Astronomy & Astrophysics
Shang Li, Ji-Ping Dai, Xiu-Hui Tan, Yang-Jie Yan, Jun-Qing Xia
Summary: The bounce scenario in cosmology is a research topic that addresses the singularity problem and trans-Planckian issue left by the standard inflationary theory. In this work, the authors extend the analysis to large-scale structure measurements and find that the model parameters can be constrained effectively. The constraints become even stronger when combined with the measurements from the Planck satellite.
MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY
(2023)
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Astronomy & Astrophysics
Antonio De Felice, Shinji Mukohyama
Summary: This paper introduces a new cosmological framework integrating dark matter into a minimally modified gravity model, maintaining the same number of gravitational degrees of freedom through a series of transformations. The framework includes two time-dependent free functions to achieve desired evolutions of Hubble expansion rate and effective gravitational constant for dark matter.
JOURNAL OF COSMOLOGY AND ASTROPARTICLE PHYSICS
(2021)
Article
Astronomy & Astrophysics
Yusuke Mikura, Yuichiro Tada, Shuichiro Yokoyama
Summary: By incorporating local conformal symmetry and broken global SO(1,1) symmetry in the metric-affine geometry, a minimal realization of slow-roll k-inflation is motivated. Predictions of this model, with n(s) around 0.96, r around 0.005, and c(s) around 0.03, are not only consistent with current observational data but also have potential for future testing.
Article
Physics, Mathematical
Rashid Zia, Dinesh Chandra Maurya, Anil Kumar Shukla
Summary: The paper presents the f(Q,T) gravity theory and investigates a cosmological model based on it, determining the best fit model parameters using observational data and revealing the transition from decelerating to accelerating expansion of the Universe. The calculated signature-flipping point and universe's age are also provided in the study.
INTERNATIONAL JOURNAL OF GEOMETRIC METHODS IN MODERN PHYSICS
(2021)
Article
Astronomy & Astrophysics
Sunny Vagnozzi
Summary: New physics increasing the expansion rate before recombination is a possible solution to the Hubble tension, but there is currently no clear evidence for it in the CMB. General consistency tests of the ΛCDM model show that it fits CMB data well, posing a challenge for early-time new physics models.
Article
Astronomy & Astrophysics
Manuel Gonzalez-Espinoza, Giovanni Otalora, Joel Saavedra
Summary: This study investigates the conditions for eliminating ghost, gradient, and tachyonic instabilities in scalar-torsion f(T, phi) gravity theories, with a general barotropic perfect fluid. By analyzing the gravity and matter sectors separately, it is confirmed that the theory is free from ghost and gradient instabilities, with the propagation speed meeting the standard criteria. The study also provides general expressions for mass eigenvalues in the presence of tachyonic instability, leading to the identification of a parameter space where stable configurations can exist in line with constraints from CMB measurements and BBN. Numerical analysis further supports the stability of the system throughout cosmic evolution.
JOURNAL OF COSMOLOGY AND ASTROPARTICLE PHYSICS
(2021)
Article
Astronomy & Astrophysics
Lorenzo Sebastiani
Summary: We investigate the thermodynamics of the apparent horizon in (non-flat) FLRW spacetime in different theories of modified gravity and in the presence of a perfect fluid. We focus on theories that have second order differential field equations on the FLRW background. Our findings suggest that it is possible to express the entropy solely in terms of the radius of the apparent horizon, which allows for the reconstruction of the gravitational lagrangian consistent with the first law.
PHYSICS OF THE DARK UNIVERSE
(2023)
Article
Physics, Particles & Fields
Parviz Goodarzi, H. Mohseni Sadjadi
EUROPEAN PHYSICAL JOURNAL C
(2017)
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Astronomy & Astrophysics
H. Mohseni Sadjadi, A. P. Khosravi Karchi
JOURNAL OF COSMOLOGY AND ASTROPARTICLE PHYSICS
(2018)
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Astronomy & Astrophysics
H. Mohseni Sadjadi, V Anari
JOURNAL OF COSMOLOGY AND ASTROPARTICLE PHYSICS
(2018)
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Astronomy & Astrophysics
H. Mohseni Sadjadi
PHYSICS OF THE DARK UNIVERSE
(2018)
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Physics, Particles & Fields
Parviz Goodarzi, H. Mohseni Sadjadi
EUROPEAN PHYSICAL JOURNAL C
(2019)
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Astronomy & Astrophysics
M. Khodaei, H. Mohseni Sadjadi
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Astronomy & Astrophysics
H. Mohseni Sadjadi, M. Khodaei
JOURNAL OF COSMOLOGY AND ASTROPARTICLE PHYSICS
(2019)
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Astronomy & Astrophysics
H. Mohseni Sadjadi, M. Khodaei
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Astronomy & Astrophysics
H. Mohseni Sadjadi, V. Anari
PHYSICS OF THE DARK UNIVERSE
(2020)
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Astronomy & Astrophysics
H. Mohseni Sadjadi
PHYSICS OF THE DARK UNIVERSE
(2020)
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Astronomy & Astrophysics
V. Anari, H. Mohseni Sadjadi
Summary: We propose a model to describe the late-time cosmic acceleration by considering a coupling between massive neutrinos and quintessence. The quintessence potential evolves under the constant-roll condition, resulting in persistent late-time acceleration.
JOURNAL OF COSMOLOGY AND ASTROPARTICLE PHYSICS
(2022)
Article
Astronomy & Astrophysics
H. Yazdani Ahmadabadi, Mohseni Sadjadi
Summary: In this study, we investigate the flavor transition of neutrinos in the context of screening models with scalar-matter conformal coupling. By employing an analytical method, we analyze the oscillation phase in a spherically symmetric spacetime filled with a scalar field. Our findings demonstrate the influence of the scalar field on the neutrino oscillations, which is attributed to the indirect environmental effect resulting from the behavior of the scalar field determined by the ambient matter density. Furthermore, we discuss the implications of our results within the framework of screening mechanisms and compare them with observational data.
PHYSICS OF THE DARK UNIVERSE
(2022)
Article
Physics, Multidisciplinary
H. Mohseni Sadjadi, V. Anari
Summary: In the early Universe, dark energy may have a significant contribution. By proposing a process involving a conformal coupling of quintessence to dark matter and based on screening models, the early dark energy can be reduced to its ultimate value in the late time, unifying both early and late-time dark energies into a single component.
EUROPEAN PHYSICAL JOURNAL PLUS
(2023)
Article
Astronomy & Astrophysics
H. Mohseni Sadjadi, Yazdani Ahmadabadi
Summary: The flavor transitions of neutrinos with nonstandard interactions are influenced by a scalar field that is conformally coupled to matter and neutrinos, altering their effective mass and wave function. The matter density plays a role in determining the behavior of the scalar field, indirectly affecting flavor conversion. The study examines the deficit in the total flux of electron-neutrinos produced in the Sun and compares the results with observational data.
Article
Astronomy & Astrophysics
H. Mohseni Sadjadi, V. Anari
