Article
Astronomy & Astrophysics
Daniele Oriti, Xiankai Pang
Summary: The analysis of emergent cosmological dynamics in mean field hydrodynamics of quantum gravity condensates reveals accelerated expansion of the universe at both early and late times. Although it does not support a compelling inflationary scenario in the early universe, it naturally produces a phantom-like dark energy dynamics at late times, which crosses the phantom divide and avoids any Big Rip singularity, approaching a de Sitter universe asymptotically.
JOURNAL OF COSMOLOGY AND ASTROPARTICLE PHYSICS
(2021)
Article
Physics, Multidisciplinary
Ahmad Sheykhi, Maral Sahebi Hamedan
Summary: The thermodynamics-gravity conjecture suggests a strong connection between the gravitational field equations and the first law of thermodynamics, meaning any changes in entropy expression directly impact the field equations. By considering the modified Barrow entropy associated with the apparent horizon, the Friedmann equations are altered as well. This paper explores the implications of this modification on the holographic dark energy (HDE) model, highlighting changes in energy density and the Friedmann equations. The study also investigates the cosmological consequences of using the Hubble horizon and future event horizon as infrared cutoffs, including interactions between dark matter (DM) and dark energy (DE), and the impact of the Barrow exponent on the cosmological behavior of HDE, such as crossing the phantom line and shifting the universe phase transition time.
Article
Astronomy & Astrophysics
H. R. M. Zarandi, E. Ebrahimi
Summary: This paper studies the cosmic age problem in holographic and generalized ghost dark energy models, and finds that non-linear interactions can alleviate the age problem. By analyzing age tests and data sets, the study also discovers a new bound for a parameter and shows that the generalized ghost dark energy can completely alleviate the cosmic age problem.
MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY
(2022)
Article
Astronomy & Astrophysics
Miguel Cruz, Samuel Lepe, German E. Soto
Summary: In this article, we review a dynamical dark energy model that has rarely been studied in the literature and propose two possible generalizations. By exploring the behavior of the original model and a minimal extension, we find that the cosmic components are related to their parameter states. In order to investigate the phantom regime, we present two dark energy densities inspired by the holographic approach and the emergent entropic forces model. We discover a type-III singularity in the first case and a transition from decelerated to accelerated cosmic expansion in the second proposal, ultimately leading to a de Sitter state.
Article
Astronomy & Astrophysics
Leandros Perivolaropoulos, Ioannis Antoniou, Demetrios Papadopoulos
Summary: This study generalizes the result of Rindler-Ishak by considering the lensing deflection angle in a Schwarzschild-deSitter (SdS) space-time with a general spherically symmetric fluid. An analytical expression for the deflection angle to first post-Newtonian order is derived, which is further verified by numerical derivation and reduces to previous results in special cases. The density and pressure of the spherically symmetric fluid that induces this metric are derived in terms of constants, and observational constraints on these constants are obtained using data from distant clusters of galaxies.
MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY
(2023)
Article
Astronomy & Astrophysics
Andreas Lymperis
Summary: By investigating the features of a non-metricity scalar Q function, the cosmological implications of f(Q) gravity are explored, and analytical expressions for the dark energy density, equation-of-state, and deceleration parameters are obtained. The study reveals that even in the absence of a cosmological constant, the universe follows the usual thermal history with matter and dark energy eras, and the dark energy equation-of-state parameter remains in the phantom regime. Additionally, the scenario shows excellent agreement with observational data from Supernovae type Ia. Furthermore, it is demonstrated that f(Q) gravity can effectively mimic the behavior of a cosmological constant.
JOURNAL OF COSMOLOGY AND ASTROPARTICLE PHYSICS
(2022)
Article
Astronomy & Astrophysics
Hoavo Hova
Summary: In this paper, the geometric effects of pressureless matter and modifications of the Riemann manifold on late-time cosmic acceleration are investigated. It is found that the expansion of the universe can undergo acceleration and even enter a phantom stage due to inhomogeneous modifications of generalized fluids. The cosmological parameters derived in this study are roughly consistent with the latest astrophysical data, and the corresponding f(R)-gravity is derived.
INTERNATIONAL JOURNAL OF MODERN PHYSICS D
(2022)
Article
Astronomy & Astrophysics
Alexander B. Balakin, Alexei S. Ilin
Summary: We propose a new self-consistent model that couples cosmic dark energy and dark matter using the rheological approach. This model represents the equations of state as integral operators of the Volterra type. We classify the exact solutions of the model based on the roots of the characteristic polynomial. The pressure, energy density, Hubble function, and acceleration parameter of dark energy and dark matter are expressed explicitly as functions of the dimensionless scale factor. We discuss two intriguing cosmological solutions that describe superexponential expansion and symmetric bounce, as well as new solutions corresponding to quasiperiodic behavior.
Review
Astronomy & Astrophysics
Veronica Motta, Miguel A. Garcia-Aspeitia, Alberto Hernandez-Almada, Juan Magana, Tomas Verdugo
Summary: The article summarizes the characteristics of dark energy models and some commonly used cosmological samples, discusses how to constrain model parameters using observational data, and finally provides an overview of the status of dark energy modeling.
Article
Astronomy & Astrophysics
Ricardo G. Landim
Summary: The study extends the fractional dark energy model by considering a nonzero chemical potential, showing that it can thermodynamically describe a phantom regime. Furthermore, the Planck constraints on the equation of state parameter provide upper limits on the allowed value of the ratio of the chemical potential to the temperature. Additionally, the investigation into the system of fractional dark energy particles with negative absolute temperatures reveals a connection between FDE and NAT when FDE is composed of fermions.
Article
Astronomy & Astrophysics
George Lazarides, Rinku Maji, Rishav Roshan, Qaisar Shafi
Summary: Inspired by the recent determination of the W-boson mass, this study revisits an SO(10) axion model and finds that a scalar SU(2)(L) triplet field can significantly contribute to the W mass, thereby resolving the discrepancy between the Standard Model prediction and the experimental measurement. The model also satisfies gauge coupling unification and observable proton decay, and predicts the existence of axion and stable intermediate mass fermion as dark matter candidates. Furthermore, the model predicts the gravitational wave spectrum from topologically stable cosmic strings.
Article
Astronomy & Astrophysics
Mariana Jaber, Gustavo Arciniega, Luisa G. Jaime, Omar Abel Rodriguez-Lopez
Summary: This study explores the hypothesis of accelerated cosmic expansion by introducing additional fields or modifications to General Relativity. A parameterization form is proposed to reproduce the generic behavior of widely used physical models with infrared corrections. Different combinations of data are analyzed to constrain the specific cases embedded in the parameterization form.
PHYSICS OF THE DARK UNIVERSE
(2022)
Article
Physics, Multidisciplinary
Ibrar Hussain, G. Mustafa, Kashif Ammar Yasir, Allah Ditta
Summary: This study is devoted to exploring the physical properties of wormhole geometry under the phantom regime in f(T, tau) gravity. The shape function in the phantom regime is calculated for the first time, and the validity region of the energy conditions is discussed using specific shape functions.
CHINESE JOURNAL OF PHYSICS
(2022)
Article
Physics, Nuclear
Mihai Marciu, Dana Maria Ioan
Summary: This paper extends the basic Einstein-Hilbert action by introducing a non-minimal coupling between the space-time geometry and matter fields. It formulates a cosmological model based on specific associations between the matter energy-momentum tensor and the Einstein tensor. The dynamics of the model and its physical implications are explored through a dynamical system analysis.
Article
Astronomy & Astrophysics
Yuewei Wen, Eva Nesbit, Dragan Huterer, Scott Watson
Summary: Standard cosmological data analyses can't easily determine the presence of modified gravity. This study presents a quantitative mapping showing how modified gravity models appear within standard analyses, reporting specific biases in standard-parameter spaces. The implications for measurements of mass fluctuations are also discussed.
JOURNAL OF COSMOLOGY AND ASTROPARTICLE PHYSICS
(2022)
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
Astronomy & Astrophysics
Shreya Banerjee, Sayantani Bera, David F. Mota
Summary: The Lambda-Cold Dark Matter model is currently the most accurate model for explaining cosmological observations, but there are still issues at galactic scales. Various models of dark matter, such as superfluid dark matter, Bose-Einstein Condensate (BEC) dark matter, and fuzzy dark matter, have been proposed to address these shortcomings. This study investigates these models using the constraint on gravitational wave propagation speed from the detection of the binary neutron star GW170817 by the LIGO-Virgo detector network. The findings suggest that the fuzzy dark matter model is the most feasible scenario to be tested in the near future, especially with detection frequencies < 10-9 Hz.
JOURNAL OF COSMOLOGY AND ASTROPARTICLE PHYSICS
(2023)
Article
Astronomy & Astrophysics
Theodoros Papanikolaou, Andreas Lymperis, Smaragda Lola, Emmanuel N. Saridakis
Summary: Primordial black holes (PBHs) can be formed through non-canonical inflation, and can provide observational evidence of the early Universe. Constraints on the non-canonical exponents are extracted by requiring significant PBH production. Asteroid-mass PBHs can explain the dark matter, and solar-mass PBHs within the LIGO-VIRGO detection band can be produced. The collapse of enhanced cosmological perturbations that form PBHs can also generate a detectable stochastic gravitational wave (GW) background.
JOURNAL OF COSMOLOGY AND ASTROPARTICLE PHYSICS
(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)
