Article
Astronomy & Astrophysics
Tanmoy Paul, Soumitra Sengupta
Summary: This article presents an ekpyrotic bounce scenario driven by a second rank antisymmetric Kalb-Ramond field, where the universe undergoes contraction through an ekpyrotic stage with a non-singular bouncing behavior, and smoothly transitions to an expanding phase. The article provides important insights into the early evolution of the universe.
PHYSICS OF THE DARK UNIVERSE
(2023)
Article
Astronomy & Astrophysics
David Benisty, Moshe M. Chaichian, Markku Oksanen
Summary: This passage studies the phenomenological implications of the Mimetic Tensor-Vector-Scalar theory (MiTeVeS). The theory extends the vector field model of mimetic dark matter by incorporating a scalar field, which is known to be ghost instability-free. When there is no interaction between the scalar field and the vector field, the obtained cosmological solution corresponds to the General Theory of Relativity (GR) with a minimally-coupled scalar field. However, introducing an interaction term between the scalar field and the vector field results in interesting dynamics.
PHYSICS OF THE DARK UNIVERSE
(2023)
Article
Physics, Mathematical
A. R. Lalke, G. P. Singh, A. Singh
Summary: In this paper, the late-time accelerated universe evolution in a flat, homogeneous and isotropic model is investigated in the context of f(Q,T) gravity. The model unifies an ekpyrotic, non-singular bounce with the present dark energy-dominated epoch. The theoretical value of the equation of state (EoS) parameter is found to be consistent with the estimated value from observational data.
INTERNATIONAL JOURNAL OF GEOMETRIC METHODS IN MODERN PHYSICS
(2023)
Article
Astronomy & Astrophysics
Cristian Erices, Pantelis Filis, Eleftherios Papantonopoulos
Summary: The study demonstrates the avoidance of the no-hair theorem in scalar-tensor theories with bimetric structure by introducing an electric charge, leading to black hole solutions with rich thermodynamic behavior. The interplay of stability and phase transitions between different black hole configurations resembles a solid-liquid-gas system, with an electric potential acting as pressure and a triple point where three phases coexist equally probable.
Article
Physics, Multidisciplinary
Jose Edgar Madriz Aguilar, M. Montes, A. Bernal
Summary: In this paper, we present cosmological solutions that represent the current accelerating expansion of the Universe using a geometrical gauge scalar-tensor theory of gravity. The background geometry is Weyl integrable, and we find a class of power law solutions for the Weyl scalar field in a power law expanding universe with an invariant metric. For specific parameters of the model, we obtain a deceleration parameter and equation of state parameters (EoS) that are consistent with PLANCK 2018 observational data. The deceleration parameter asymptotically approaches -1/2, and the EoS parameter can cross the phantom divide line in this model.
Article
Physics, Particles & Fields
Jackie C. H. Liu
Summary: Based on the ratio gravity theory, we propose a mechanism to generate dynamical dark energy by coupling gravity with a quintessence field. This model leads to different behaviors of dark energy in the early and late universe, with the quintessence field starting as a constant and oscillating as the universe expands.
EUROPEAN PHYSICAL JOURNAL C
(2022)
Article
Physics, Multidisciplinary
Xian Gao
Summary: The authors made a comprehensive classification of scalar monomials and covariant derivatives up to the third order, emphasizing their importance in effective field theory and exploring their complementarity; through systematic classification and derivation, a complete basis of monomials was derived with the potential for novel ghostfree Lagrangians; in addition, diagrammatic representations were developed to simplify the analysis process.
SCIENCE CHINA-PHYSICS MECHANICS & ASTRONOMY
(2021)
Article
Physics, Multidisciplinary
Manuel Gonzalez-Espinoza, Giovanni Otalora, Yoelsy Leyva, Joel Saavedra
Summary: We investigate the cosmological dynamics of dark energy in a scalar-vector-torsion theory, where the vector field is described by the cosmic triad and the scalar field has a non-minimal coupling to gravity. The coupling to gravity is introduced through the interaction between the scalar field and torsion, defined in the context of teleparallel gravity. We obtain the full set of field equations for the Friedmann-Lemaitre-Robertson-Walker space-time background and analyze the critical points, stability conditions, and cosmological properties. We find that the thermal history of the universe is successfully reproduced and identify new scaling solutions that behave similarly to radiation and matter.
EUROPEAN PHYSICAL JOURNAL PLUS
(2023)
Article
Astronomy & Astrophysics
Murat Korunur
Summary: In this study, a correspondence between quintessence, tachyon, and dilaton scalar field definitions and the generalized ghost dark energy model was established in a five-dimensional framework. Numerical analysis of equation of state parameters, kinetic energy, and scalar potential terms was conducted.
CLASSICAL AND QUANTUM GRAVITY
(2021)
Article
Astronomy & Astrophysics
Spyros Konitopoulos, Emmanuel N. Saridakis, P. C. Stavrinos, A. Triantafyllopoulos
Summary: This work explores the foundations of generalized scalar-tensor theories derived from vector bundle constructions, defining a space with two scalar fields over a pseudo-Riemannian base manifold. The novel geometrical structure leads to modified Friedmann equations in a cosmological context, introducing extra terms and enabling the appearance of an effective dark energy sector.
Article
Astronomy & Astrophysics
Da Huang, Chao-Qiang Geng, Hao-Jui Kuan
Summary: Spontaneous scalarization in massive scalar-tensor theories introduces extra polarizations in gravitational waves, offering valuable probes into gravity theories. Self-coupling effects suppress scalarization magnitude and reduce gravitational wave signals' amplitude. Self-interacting effects are negligible in gravitational waveforms, resulting in characteristic inverse-chirp patterns observed on Earth. Detection of scalarization-induced gravitational waves may be possible with future detectors at a signal-to-noise ratio level of O(100).
CLASSICAL AND QUANTUM GRAVITY
(2021)
Article
Astronomy & Astrophysics
Celine Boehm, Xiaoyong Chu, Jui-Lin Kuo, Josef Pradler
Summary: The study revisited the possibility of light-scalar dark matter coupled to electrons through fermion or vector mediators, and established new limits and loop-induced processes strengths. Various constraints were considered, largely excluding the explanation of the International Gamma-Ray Astrophysics Laboratory excess of 511 keV photons by galactic annihilation of these particles.
Article
Astronomy & Astrophysics
Giorgos Anastasiou, Ignacio J. Araya, Mairym Busnego-Barrientos, Cristobal Corral, Nelson Merino
Summary: We investigate a conformally coupled scalar-tensor theory with a quartic potential and local conformal symmetry. By restoring the full local conformal symmetry, we determine the counterterms that make the on-shell action finite. The resulting action contains a conformally covariant tensor constructed from the metric and scalar field, which has the same conformal weight as the Weyl tensor. Adding conformal gravity and the Einstein-AdS action to the theory, we find that the action can still be renormalized even with broken conformal symmetry.
Article
Astronomy & Astrophysics
Alfredo D. Millano, Genly Leon, Andronikos Paliathanasis
Summary: In this study, we investigate the dynamics of the field equations in a four-dimensional isotropic and homogeneous spatially flat Friedmann-Lemaitre-Robertson-Walker geometry, using the Einstein-Gauss-Bonnet theory. We consider a matter source and a scalar field coupled to the Gauss-Bonnet scalar. The theory can explain the acceleration phases of the Universe and may be used as a model for studying inflation or as a candidate for dark energy.
Article
Astronomy & Astrophysics
Tae Hoon Lee
Summary: The study proposes an f(R) gravity model within the framework of scalar-tensor theory, obtaining a solution for an accelerating universe in the late-time and discussing the future evolution of the universe.
MODERN PHYSICS LETTERS A
(2021)
Article
Astronomy & Astrophysics
Indrani Banerjee, Tanmoy Paul, Soumitra SenGupta
Summary: This study investigates how the interaction between the radion potential and kinetic term in a warped braneworld scenario leads to the transition of the universe from a contracting to an expanding phase during a non-singular bounce. The analysis shows that the predicted primordial observables are consistent with the constraints reported by the Planck satellite.
JOURNAL OF COSMOLOGY AND ASTROPARTICLE PHYSICS
(2021)
Article
Physics, Mathematical
I Brevik, A. Timoshkin, Tanmoy Paul
Summary: By considering an inhomogeneous viscous dark fluid coupled with dark matter in the Friedmann-Robertson-Walker flat universe, the study examines the thermal effects caused by Hawking radiation on the visible horizon and their connection with Types I and III singularities. With the allowance of thermal effects, the possibility of a transition to a Type II singularity in a finite time is explored. The inclusion of a bulk viscosity of the dark fluid reveals a qualitative change in the singular universe of Type I, where it may transition into a singularity of Type III or avoid a singularity altogether.
INTERNATIONAL JOURNAL OF GEOMETRIC METHODS IN MODERN PHYSICS
(2021)
Article
Astronomy & Astrophysics
Shin'ichi Nojiri, Sergei D. Odintsov, Tanmoy Paul
Summary: In this study, the holographic cut-off in the formalism of generalized holographic dark energy (HDE) is generalized to depend on the particle horizon, future horizon, and scale factor of the universe. It is shown that the Barrow entropic dark energy (DE) model is equivalent to the generalized HDE, where the holographic cut-off is determined by the first-order derivative of the particle horizon or future horizon. The equivalence is extended to consider the variation of the Barrow entropy exponent with the cosmological expansion.
Article
Multidisciplinary Sciences
Tanmoy Paul
Summary: In this study, we investigate the consistency and viability of the curvature coupling helical magnetogenesis scenario. We find that the model parameters that satisfy the constraints of perturbative quantum field theory and the restrictions on the curvature perturbation power spectrum can also predict the magnetic field strength at large scales.
Article
Astronomy & Astrophysics
Kazuharu Bamba, Sergei D. Odintsov, Tanmoy Paul, Debaprasad Maity
Summary: We investigate the generation of helical magnetic fields and address the baryon asymmetry of the universe from an inflationary magnetogenesis scenario. Depending on the reheating mechanism, we consider two different cases - (1) instantaneous reheating scenario, in which the reheating e-fold number is zero, and (2) Kamionkowski reheating scenario. It is demonstrated that for both the reheating mechanisms, the generated magnetic fields can be compatible with the observations for suitable range of the model parameter present in the non-minimal coupling of the electromagnetic field. However, the current magnetogenesis model does not produce sufficient hierarchy between the electric and magnetic fields at the end of inflation, resulting in the electric field not being able to sufficiently induce or enhance the magnetic field during the Kamionkowski reheating stage.
PHYSICS OF THE DARK UNIVERSE
(2022)
Article
Astronomy & Astrophysics
Sergei D. Odintsov, Tanmoy Paul
Summary: This work explores the influence of a Type-IV singularity on the dynamics of a bouncing universe in the context of a ghost-free Gauss-Bonnet theory of gravity. It is found that when the singularity has a global effect on spacetime, the scalar power spectrum becomes red-tilted and the tensor-to-scalar ratio is incompatible with observational data. However, if the singularity only locally affects spacetime around the time of occurrence, the observable quantities are compatible with Planck data.
Article
Astronomy & Astrophysics
Shin'ichi Nojiri, Sergei D. Odintsov, Tanmoy Paul
Summary: The study introduces a new four-parameter entropy function that unifies the early inflation and late dark energy era of the universe. It reveals that the parameters values for early inflation and late dark energy are consistent in this unified scenario. Additionally, the entropic cosmology from the proposed entropy function is equivalent to holographic cosmology.
Article
Astronomy & Astrophysics
Indrani Banerjee, Tanmoy Paul, Soumitra SenGupta
Summary: The scenario of a bouncing universe is a highly active field of research aiming to develop singularity-free cosmological models. In this work, three different approaches are considered to address this problem, each going beyond General Relativity while remaining within the framework of classical cosmology. The common feature of these approaches is that the bouncing mechanism naturally arises within the geometrical framework of the model, without the need for external sources. Various constraints that these viable cosmological models need to satisfy are also discussed in the context of these scenarios.
GENERAL RELATIVITY AND GRAVITATION
(2022)
Article
Astronomy & Astrophysics
Shin'ichi Nojiri, Sergei D. Odintsov, Tanmoy Paul
Summary: In this study, the Bekenstein-Hawking entropy is modified and a new entropy function is developed to derive the usual FLRW equations for matter fluids with different equation of state parameters. The research finds that by using a general entropy based on the Bekenstein-Hawking entropy, the Friedmann equations of the apparent horizon cosmology can be modified, leading to interesting cosmological consequences.
Article
Astronomy & Astrophysics
Sergei D. Odintsov, Tanmoy Paul
Summary: We propose a new entropy function that avoids singularities throughout the cosmic evolution of the universe and generalizes several known entropies. Unlike existing entropies, the new function remains nonsingular even when the Hubble parameter is zero, making it useful for describing bouncing scenarios in cosmology. The nonsingular behavior allows for symmetric bounce scenarios, and the parameters of the entropy function affect observable quantities such as the spectral tilt and the tensor-to-scalar ratio. The new entropic cosmology is also shown to be equivalent to generalized holographic cosmology. (c) 2022 Elsevier B.V. All rights reserved.
PHYSICS OF THE DARK UNIVERSE
(2023)
Article
Astronomy & Astrophysics
Shin'ichi Nojiri, Sergei D. Odintsov, Tanmoy Paul
Summary: In the formalism of generalized holographic dark energy, the infrared cut-off L-IR is generalized to the form, L-IR = L-IR(L-p, L-p, L-p, center dot center dot center dot, L-f, L-f, L-f, center dot center dot center dot, a, H, H, H, center dot center dot center dot). Based on such formalism, we establish a holographic realization of constant roll inflation during the early universe, where the corresponding cut-off depends on the Hubble parameter and its derivatives (up to the second order). The viability of this holographic constant roll inflation with respect to the Planck data in turn puts a certain bound on the infrared cut-off at the time of horizon crossing.
Article
Astronomy & Astrophysics
Tanmoy Paul, Soumitra Sengupta
Summary: This article presents an ekpyrotic bounce scenario driven by a second rank antisymmetric Kalb-Ramond field, where the universe undergoes contraction through an ekpyrotic stage with a non-singular bouncing behavior, and smoothly transitions to an expanding phase. The article provides important insights into the early evolution of the universe.
PHYSICS OF THE DARK UNIVERSE
(2023)
Article
Astronomy & Astrophysics
Sergei D. Odintsov, Simone D'Onofrio, Tanmoy Paul
Summary: The increasing interest in different entropy functions in cosmology raises the question of whether there is a generalized entropy that can unify all known entropies. A four-parameter generalized entropy has recently been formulated, which reduces to different known entropies in specific parameter limits. In this paper, the authors investigate the early phase of the universe's evolution, particularly from inflation to reheating, using the concept of entropic energy density. The results show that entropic energy can drive an early inflationary phase and the theoretical expectations are consistent with recent observational data.
PHYSICS OF THE DARK UNIVERSE
(2023)
Article
Astronomy & Astrophysics
Sergei D. Odintsov, Tanmoy Paul
Summary: We investigate the inflation and reheating phenomenology in scalar-Einstein-Gauss-Bonnet theory of gravity and find that the inflationary predictions are consistent with the recent Planck data and the presence of the GB coupling function allows for w(eff) to go beyond 1, potentially affecting the amplitude of primordial gravitational waves observed today.
PHYSICS OF THE DARK UNIVERSE
(2023)