Article
Astronomy & Astrophysics
Shaswata Chowdhury, Tapobrata Sarkar
Summary: The study investigates the effects of modified gravity beyond Horndeski theory in the interior of a population II star, finding that reduced gravity may result in decreased luminosity and increased radius of the star, but some effects are reversed near the core. The model provides a constraint on the modified gravity parameter within its limitations.
JOURNAL OF COSMOLOGY AND ASTROPARTICLE PHYSICS
(2021)
Article
Astronomy & Astrophysics
Eanna. E. Flanagan
Summary: Blanchet and Marsat proposed a relativistic version of modified Newtonian dynamics, which has consistent nonrelativistic limit and stable solutions for stationary systems with certain symmetry. In the low acceleration regime, the theory introduces an order unity correction to the modified Newtonian dynamics.
ASTROPHYSICAL JOURNAL
(2023)
Review
Astronomy & Astrophysics
Sreekanth Harikumar
Summary: The MOG theory modifies gravity by introducing dynamical scalar fields and a massive vector field, explaining cosmological phenomena, galaxy rotation curves, and solar system observations successfully. It associates matter with a fifth force and a modified equation of motion, eliminating the need for dark matter.
Article
Astronomy & Astrophysics
Antonio De Felice, Kei-ichi Maeda, Shinji Mukohyamaa, Masroor C. Pookkillatha
Summary: We study the collapse of a spherically symmetric dust cloud in the VCDM gravitational theory and find that it corresponds to a specific foliation of the Oppenheimer-Snyder solution in general relativity. The resulting collapse leads to a static configuration with a vanishing lapse function at a radius inside the apparent horizon. This implies the need for a UV completion to describe the physics inside the resulting black hole.
JOURNAL OF COSMOLOGY AND ASTROPARTICLE PHYSICS
(2023)
Article
Physics, Particles & Fields
H. R. Fazlollahi
Summary: This study investigates the conservation of stress-energy tensor in curved spacetime and examines the application of modified gravity. The spherically symmetric solutions and evolution of the Universe for early and late time are explored, showing that there are no new results compared to Einstein gravity in vacuum solutions. However, during inflation, the scalar spectra index deviates from the standard model. Late-time and constraint models are also considered using the MCMC algorithm.
EUROPEAN PHYSICAL JOURNAL C
(2023)
Article
Astronomy & Astrophysics
Kazufumi Takahashi, Rampei Kimura, Hayato Motohashi
Summary: This paper discusses the impact of generalized, non-invertible disformal transformations on the coupling of fermionic matter, finding that an additional condition is required for consistent fermionic matter coupling. A subclass of the generalized disformal Horndeski class is identified that allows for the consistent coupling of ordinary matter fields, including standard model particles.
Article
Physics, Multidisciplinary
M. Z. Bhatti, Z. Yousaf, T. Ashraf
Summary: This paper discusses the viable and analytic solution of the spherically symmetric gravastar model under the influence of modification of Gauss-Bonnet gravity, f(G) gravity. The mathematical formalism of the gravastar's three regions and the analysis of different physical features are presented, resulting in an exact and singularity-free model within an alternative theory framework.
CHINESE JOURNAL OF PHYSICS
(2021)
Article
Physics, Multidisciplinary
Amir H. Rezaei, T. Azizi, N. Rashidi
Summary: In this paper, an exponential form of modified gravity is considered. The theory is consistent with local tests and various aspects of the model are investigated, including the static solution, scalar field potential, and stability of critical points. The realization of inflation and its graceful exit in this model are also studied.
Article
Astronomy & Astrophysics
Haomin Rao
Summary: The paper explores the use of the Nieh-Yan modified teleparallel gravity model in the Solar System, finding that it shares the same post-Newtonian parameters as general relativity and is compatible with Solar System experiments.
Article
Astronomy & Astrophysics
S. G. Vilhena, S. B. Duarte, M. Dutra, P. J. Pompeia
Summary: We examine compact objects in modified teleparallel gravity with realistic equations of state. A modification of Teleparallel Equivalent to General Relativity is proposed, and a suitable tetrad is applied to the field equations. A specific set of relations demonstrating an equivalency between our gravitational model and the New General Relativity is discovered. This study includes numerical analysis using realistic equations of state and investigates the behavior of mass, radius, and the mass-radius relation as functions of a free parameter in our model.
JOURNAL OF COSMOLOGY AND ASTROPARTICLE PHYSICS
(2023)
Article
Physics, Multidisciplinary
D. Bazeia, A. S. Lobao Jr
Summary: This study examines braneworld models in a five-dimensional warped geometry with a single infinite extra dimension in the presence of scalar fields. The research considers generalized models involving the Ricci scalar, the trace of the stress-energy tensor, and the cuscuton contribution. The findings show that the brane can become thinner while maintaining gravitational stability and strict control over the gravity zero mode.
Article
Physics, Multidisciplinary
Sofia Qvarfort, Dennis Raetzel, Stephen Stopyra
Summary: In this study, we derive the best possible bounds on Yukawa- and chameleon-like modifications to the Newtonian gravitational potential using a cavity optomechanical quantum sensor. We take into account the size of the optomechanical probe and investigate the screening effect when both the source and probe are spherical.
NEW JOURNAL OF PHYSICS
(2022)
Article
Physics, Particles & Fields
Christian G. Bohmer, Erik Jensko, Ruth Lazkoz
Summary: When considering a homogeneous and isotropic cosmological model, the field equations of modified gravity theories can be transformed into autonomous differential equations, which is a successful approach to study such models. We propose a perspective that is applicable to many different modified gravity models and relies on the standard cosmological density parameters, allowing for the extraction of generic information before considering a specific model.
EUROPEAN PHYSICAL JOURNAL C
(2022)
Article
Astronomy & Astrophysics
J. Bezerra-Sobrinho, L. G. Medeiros
Summary: In the context of effective theories of gravity, this paper proposes a minimalist bottom-up approach that considers 1-loop quantum corrections. It introduces four extra terms in the Einstein-Hilbert action to ensure renormalizability and accounts for the integration of massless/light matter fields. The focus is on analyzing the impact of the nonlocal term R ln (square) R on Starobinsky inflation, where it is treated as a small correction to the R-2 term. The model is shown to behave like a local model in this context, with a canonical scalar field minimally coupled to general relativity in the approximate Einstein frame. The inflationary regime of the model is studied and its free parameters are constrained through observations of CMB anisotropies.
JOURNAL OF COSMOLOGY AND ASTROPARTICLE PHYSICS
(2023)
Article
Astronomy & Astrophysics
J. R. Nascimento, A. Yu Petrov, P. J. Porfirio
Summary: The paper explores the contribution of the Dirac field in a torsion background to the fermionic one-loop effective action, revealing its topological nature. A novel modified theory of gravity is proposed by incorporating this contribution into the Einstein-Cartan action, leading to nontrivial solutions distinct from those of General Relativity.
Article
Physics, Particles & Fields
Emmanuel N. Saridakis, Weiqiang Yang, Supriya Pan, Fotios K. Anagnostopoulos, Spyros Basilakos
Summary: Soft cosmology extends the standard cosmology by allowing for different equation-of-state parameters for dark matter and dark energy at different scales. Data analysis suggests that soft cosmology is favored by observational constraints.
Article
Physics, Nuclear
Farruh Atamurotov, Mubasher Jamil, Kimet Jusufi
Summary: In this study, the optical properties of a renormalization group improved Schwarzschild black hole in a plasma medium are investigated. The deflection angle of light in the weak gravity regime is computed for uniform and non-uniform plasma media, revealing the modifications caused by the plasma medium. The effects of plasma media play an important role in the optical appearance of black holes.
Article
Astronomy & Astrophysics
Maria Mylova, Jackson Levi Said, Emmanuel N. Saridakis
Summary: This paper constructs the effective field theory (EFT) of the teleparallel equivalent of general relativity (TEGR). The EFT contains more terms compared to the EFT of general relativity (GR) and possesses minor but non-zero differences. However, these differences are suppressed by a heavy mass scale ? and may not be measurable in future experiments and observations.
CLASSICAL AND QUANTUM GRAVITY
(2023)
Article
Physics, Multidisciplinary
G. G. L. Nashed, Emmanuel N. Saridakis
Summary: In this study, new classes of anisotropic solutions are extracted within the framework of mimetic gravity. By applying the Tolman-Finch-Skea metric and a specific anisotropy unrelated to it, and smoothly matching the interior solution to the exterior Schwarzschild solution, the authors investigate various properties of these solutions. The results show positive energy density, decreasing pressures towards the center of the star, repulsive anisotropic force, and monotonically increasing equation-of-state parameters. The stability of the solutions is also examined, and it is found that the stars in all cases are stable.
EUROPEAN PHYSICAL JOURNAL PLUS
(2023)
Article
Chemistry, Multidisciplinary
Shreya Banerjee, Sunil K. Gupta, Erode N. Prabhakaran
Summary: The presence of sinusoidal synchronicity between rotational motion along C-alpha-C ' sigma bond and the concomitant pyramidalization of C ' in amides is demonstrated for the first time in solution. It has been found that synchronicity is perturbed when tau-rotation is 'locked' with interactions, resulting in a strain on the amide bond and a decrease in energy barrier for the amide bond cis/trans isomerism by approximately 1.68 kcal/mol.
Article
Astronomy & Astrophysics
Maria Petronikolou, Emmanuel N. Saridakis
Summary: In this study, we investigate scalar-tensor and bi-scalar-tensor modified theories of gravity that can alleviate the H-0 tension. We show that by choosing particular models with specific features, such as a shift-symmetric friction term or phantom behavior of the effective dark-energy equation-of-state parameter, the tension can be alleviated. These theories provide known mechanisms for alleviating the H0 tension.
Article
Astronomy & Astrophysics
Shreya Banerjee, Maria Petronikolou, Emmanuel N. Saridakis
Summary: We investigate the cosmological applications of gravitational scalar-tensor theories and analyze them in the context of the H0 tension. Two specific models are explored, showing negligible effects at high redshifts but an increasing deviation as time passes. At low redshifts, the Hubble parameter takes on higher values in a controlled manner. This behavior is attributed to the phantom nature of the effective dark-energy equation-of-state parameter, providing a possible solution to the H0 tension. Comparison with cosmic chronometer data demonstrates full agreement within 1σ confidence level.
Article
Astronomy & Astrophysics
Petros Asimakis, Spyros Basilakos, Andreas Lymperis, Maria Petronikolou, Emmanuel N. Saridakis
Summary: This study constructs new classes of modified theories that couple the matter sector with the Einstein tensor, specifically considering direct couplings to the energy-momentum tensor and its trace derivatives. The general field equations, without higher-order derivatives, are derived and applied in a cosmological framework, resulting in Friedmann equations with additional terms that give rise to an effective dark energy sector. The study shows successful description of the thermal history of the universe at the background level, with matter and dark energy epochs, and the dark energy equation-of-state parameter can approach -1 as time progresses. Comparison with cosmic chronometer data demonstrates a very good agreement. Detailed investigations of scalar and tensor perturbations validate the predicted behavior of the matter overdensity.
Article
Chemistry, Multidisciplinary
Mita Dutta, Shreya Banerjee, Mahitosh Mandal, Manish Bhattacharjee
Summary: A self-healable metallohydrogel of Mn(ii) has been successfully prepared using a low molecular weight gelator, Na2HL. It has been characterized by various techniques and encapsulated with drugs IND and GEM. The GEM-loaded metallogel showed enhanced delivery and cytotoxicity against breast cancer cells, while the MOG_IND exhibited improved anti-inflammatory response compared to the drug alone.
Article
Astronomy & Astrophysics
Wompherdeiki Khyllep, Jibitesh Dutta, Emmanuel N. Saridakis, Kuralay Yesmakhanova
Summary: Motivated by the success of f(Q) gravity in fitting observational data, we analyze the behavior of two studied f(Q) models, power-law and exponential, through dynamical system analysis. We find that both models have a matter-dominated saddle point followed by a stable dark-energy-dominated accelerated universe. The models fit observational data well and can be considered as promising alternatives to the ACDM concordance model.
Article
Physics, Particles & Fields
Sebastian Bahamonde, Konstantinos F. Dialektopoulos, Manuel Hohmann, Jackson Levi Said, Christian Pfeifer, Emmanuel N. Saridakis
Summary: This study focuses on the cosmological perturbation theory in f(T) gravity, which is a simple extension of the teleparallel equivalent of general relativity. The authors examine the possibility of a non-flat FLRW background solution and perform perturbations for different spatial geometries. They determine the behavior of the perturbative modes in this non-flat FLRW setting for arbitrary f(T) models and identify propagating modes.
EUROPEAN PHYSICAL JOURNAL C
(2023)
Article
Physics, Particles & Fields
Fotios K. Anagnostopoulos, Viktor Gakis, Emmanuel N. Saridakis, Spyros Basilakos
Summary: The f(Q) theories of modified gravity, based on non-metricity as the fundamental geometric quantity, have shown great effectiveness in describing the late-time Universe. By using Big Bang Nucleosynthesis (BBN) formalism and observations, constraints on various classes of f(Q) models are obtained. The deviations on the freeze-out temperature caused by f(Q) terms are calculated and constraints on the model parameters are imposed by applying the observational bound on |delta Tf/Tf|. It is found that f(Q) gravity can pass the BBN constraints, distinguishing itself from many other gravitational modifications that fail to do so.
EUROPEAN PHYSICAL JOURNAL C
(2023)
Article
Physics, Particles & Fields
Theodoros Papanikolaou, Charalampos Tzerefos, Spyros Basilakos, Emmanuel N. Saridakis
Summary: Research shows that the fluctuations of primordial black holes can be used as a novel tool to test general relativity and constrain possible modified gravity deviations in the framework of f(T) gravity. By investigating three viable mono-parametric models, we find that the deviations from general relativity in terms of the gravitational-wave source and propagation are negligible within the observationally allowed range of f(T) model parameters. Therefore, we conclude that realistic and viable f(T) theories can safely pass the primordial black hole constraints, providing additional support for them.
EUROPEAN PHYSICAL JOURNAL C
(2023)
Article
Astronomy & Astrophysics
Yu-Min Hu, Yaqi Zhao, Xin Ren, Bo Wang, Emmanuel N. Saridakis, Yi-Fu Cai
Summary: This study investigates the scalar perturbations and possible strong coupling issues of f(T) gravity using the effective field theory (EFT) approach. The generalized EFT framework of modified teleparallel gravity is revisited and applied to examine both linear and second-order perturbations in f(T) theory. The results suggest that there is no new scalar mode present in f(T) gravity, indicating a strong coupling problem. However, an estimation of the strong coupling scale based on the ratio of cubic to quadratic Lagrangians shows that the strong coupling problem can be avoided for certain modes.
JOURNAL OF COSMOLOGY AND ASTROPARTICLE PHYSICS
(2023)
Article
Astronomy & Astrophysics
Ali Dehghani, Behnam Pourhassan, Soodeh Zarepour, Emmanuel N. Saridakis
Summary: This study investigates the thermodynamic schemes of charged BTZ-like black holes in arbitrary dimensions. Two possible thermodynamic schemes are identified with different outcomes. In the traditional scheme, the charged black holes violate the reverse isoperimetric inequality and have a fundamental thermodynamic instability. In the second scheme, the black holes are thermodynamically stable and can explain the van der Waals critical phenomenon.
PHYSICS OF THE DARK UNIVERSE
(2023)
