Article
Astronomy & Astrophysics
F. B. M. dos Santos, S. Santos da Costa, R. Silva, M. Benetti, J. S. Alcaniz
Summary: This paper updates previous constraints on the minimal coupled fl-exponential model and extends the results to derive the equations for the non-minimal coupled scenario. The predictions of both models are compared with observational data and the standard ACDM cosmology, and it is found that the data moderately prefer the non-minimally coupled fl-exponential inflationary model.
JOURNAL OF COSMOLOGY AND ASTROPARTICLE PHYSICS
(2022)
Article
Astronomy & Astrophysics
Elham Nouri, Hossein Motavalli, Amin Rezaei Akbarieh
Summary: This paper presents a generalized tachyonic dark energy scenario in a homogeneous and isotropic FLRW flat universe, where a noncanonical scalar field is nonminimally coupled to gravity. The tachyon field accelerates the evolution of the universe in the early times and plays a key role in dark energy in the late times. The study shows a cosmological degeneracy in the model, indicating the potential of the generalized tachyon field as a dark energy candidate.
INTERNATIONAL JOURNAL OF MODERN PHYSICS D
(2022)
Article
Physics, Particles & Fields
Yan Peng
Summary: We investigate the existence of scalar fields outside neutral reflecting shells by considering static massive scalar fields non-minimally coupled to the Gauss-Bonnet invariant. We analytically analyze the properties of scalar fields through the scalar field equation. In the regime of small scalar field mass, we derive a compact resonance formula for the allowed masses of scalar fields in the composed scalar field and shell configurations.
EUROPEAN PHYSICAL JOURNAL C
(2023)
Article
Physics, Multidisciplinary
Daniel G. Figueroa, Adrien Florio, Toby Opferkuch, Ben A. Stefanek
Summary: This paper investigates the important implications of scalar fields with non-minimal gravitational interactions for the physics of the early universe. A procedure is proposed to solve the dynamics of non-minimally coupled scalar fields directly in the Jordan frame, where the non-minimal couplings are explicitly maintained. The algorithm can be applied to lattice simulations that include minimally coupled fields and an arbitrary number of non-minimally coupled scalars, allowing for fully inhomogeneous and nonlinear dynamics and the domination of non-minimally coupled species in the expansion of the universe. As an example, geometric preheating with a non-minimally coupled scalar spectator field during the oscillations of the inflaton after inflation is studied.
Article
Physics, Multidisciplinary
Mithun Bairagi
Summary: In this work, we construct an inflationary model in the framework of Bianchi type-I spacetime by using a non-minimally coupled, homogeneous, self-interacting canonical scalar field. By employing the Lie symmetry method, we obtain new exact solutions to the Einstein field equations assuming a power-law relationship between the scalar field and average scale factor. These symmetry-based solutions are then used to determine the values of important parameters in an anisotropic universe. The model predicts that the volume of space expands with time, exhibiting the Universe's accelerating phases, and the spacetime evolves from anisotropy to isotropy, consistent with recent cosmological observations.
Article
Engineering, Mechanical
Shi-Xin Jin, Yi Zhang
Summary: In this paper, the approximate Noether theorems for approximate Birkhoffian systems are introduced and discussed. The approximate Birkhoff equations for the systems are established. The Noether identities for approximate Birkhoffian systems are derived based on Noether symmetry and quasi-symmetry, establishing the relationship between approximate Noether symmetries and approximate conservation laws. The results demonstrate that the results under approximate Hamiltonian systems are a special cases of the approximate Birkhoffian systems, while the results under approximate Lagrangian systems are equivalent to that under approximate Hamiltonian systems. Finally, two examples are provided to illustrate the application of the results.
NONLINEAR DYNAMICS
(2023)
Article
Astronomy & Astrophysics
Lei-Hua Liu, Tomislav Prokopec
Summary: This study investigates scalar cosmological perturbations generated through nonminimal coupling in two-field inflationary models with a focus on curvaton scenarios. It shows that small, negative nonminimal couplings can contribute to a redder curvature spectrum, potentially saving some curvaton scenarios that would otherwise be ruled out. The study also highlights the impact of nonminimal coupling on the postinflationary growth of the spectator perturbation and the effectiveness of the curvaton mechanism.
JOURNAL OF COSMOLOGY AND ASTROPARTICLE PHYSICS
(2021)
Article
Physics, Particles & Fields
Sebastian Garcia-Saenz, Aaron Held, Jun Zhang
Summary: This study investigates perturbations of massive and massless vector fields on a Schwarzschild black-hole background, with a focus on non-minimal coupling between the vector field and the curvature. The quasi-normal mode spectrum of the vector field is determined, and solutions corresponding to quasi-bound states and static configurations are considered.
JOURNAL OF HIGH ENERGY PHYSICS
(2022)
Article
Astronomy & Astrophysics
Seokcheon Lee
Summary: For the varying speed of light (VSL) models to be phenomenologically feasible, at least one dimensionless physical constant must change. Adiabaticity and the dependence of physical constants and quantities on cosmic time are also important. The minimally extended VSL (meVSL) model satisfies these conditions and the redshift-drift formula is the same as the standard model. However, the meVSL cannot be verified experimentally but can be tested using cosmological chronometers (CC).
MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY
(2023)
Article
Multidisciplinary Sciences
Cai Wang, Chuan-Jing Song
Summary: Research has been conducted on Noether figury and perturbation to Noether symmetry for Hamiltonian systems within generalized operators. The study includes four parts, each of which involves two kinds of generalized operator. Firstly, Hamilton equations are established. Secondly, the Noether symmetry method is used to find solutions and obtain conserved quantities. Thirdly, perturbation to Noether symmetry and adiabatic invariants are explored. Finally, two examples are given to illustrate the methods and results.
Article
Astronomy & Astrophysics
Mio Kubota, Kin-ya Oda, Stanislav Rusak, Tomo Takahashi
Summary: Double inflation can occur when a spectator field is non-minimally coupled to gravity. The non-minimal coupling results in the growth of the spectator field, which drives the second stage of inflation in a significant region of parameter space. The non-minimal coupling of the spectator field can modify the predictions for the spectral index and the tensor-to-scalar ratio.
JOURNAL OF COSMOLOGY AND ASTROPARTICLE PHYSICS
(2022)
Article
Astronomy & Astrophysics
Basabendu Barman, Nicolas Bernal, Ashmita Das, Rishav Roshan
Summary: We study a simple abelian vector dark matter model, where only the dark matter couples non-minimally to the scalar curvature of the background spacetime. By analyzing freeze-out, freeze-in, and scattering scenarios, we show that such non-minimally coupled dark matter can be probed in direct detection experiments, satisfying the observed relic abundance and perturbative unitarity.
JOURNAL OF COSMOLOGY AND ASTROPARTICLE PHYSICS
(2022)
Article
Astronomy & Astrophysics
Manuella C. Silva, Rudnei O. Ramos, Ricardo L. S. Farias
Summary: This paper studies the phase transition patterns of a model of two coupled complex scalar fields at finite temperature and chemical potential. Possible phenomena like symmetry persistence and inverse symmetry breaking at high temperatures are analyzed. The effect of finite density is also considered and studied in combination with the thermal effects. The nonperturbative optimized perturbation theory method is considered and the results contrasted with perturbation theory. Applications of the obtained results in the context of the condensation of kaons at high densities, which is important in the understanding of the color-flavor locked phase of quantum chromodynamics, are considered.
Article
Multidisciplinary Sciences
Chenwei Lv, Ren Zhang, Zhengzheng Zhai, Qi Zhou
Summary: The authors establish a duality between non-Hermiticity and curved spaces, revealing a geometric root of non-Hermitian phenomena and providing a method to study and tailor non-Hermiticity using curved spaces.
NATURE COMMUNICATIONS
(2022)
Article
Physics, Multidisciplinary
V. K. Oikonomou
Summary: This study focuses on k-inflation theories with non-minimal coupling of the scalar field to gravity, investigating the evolution of the scalar field under slow-roll or constant-roll conditions when a scalar potential is present or absent. The results show that the theory is compatible with the latest Planck data in the slow-roll models with scalar potential, but less appealing in models without potential. Additionally, it is suggested that the Einstein frame counterpart of non-minimal k-inflation models with scalar potential may be a viable theory due to the conformal invariance of the observational indices.
EUROPEAN PHYSICAL JOURNAL PLUS
(2021)
Article
Physics, Multidisciplinary
Gilberto M. Kremer
PHYSICA A-STATISTICAL MECHANICS AND ITS APPLICATIONS
(2020)
Article
Physics, Nuclear
Marlos O. Ribas, Fernando P. Devecchi, Gilberto M. Kremer
INTERNATIONAL JOURNAL OF MODERN PHYSICS A
(2020)
Article
Multidisciplinary Sciences
Adriano B. Barreto, Gilberto M. Kremer
Article
Physics, Multidisciplinary
Gilberto M. Kremer
Summary: A kinetic theory for relativistic gases in the presence of gravitational fields is developed in the second post-Newtonian approximation. By using the Boltzmann equation and equilibrium Maxwell-Juttner distribution function, the components of particle four-flow and energy-momentum tensor are obtained. The Eulerian hydrodynamic equations for mass density, mass-energy density, and momentum density are determined from the Boltzmann equation in the second post-Newtonian approximation.
Article
Physics, Nuclear
Marlos O. Ribas, Fernando P. Devecchi, Gilberto M. Kremer
Summary: This study introduces a model of the early universe involving a scalar field, relativistic fluid, and self-interacting fermionic field. Through classical analysis and quantum equations, it is found that the combination of scalar and fermionic fields can achieve a smooth transition from quantum to classical, with the key being the use of Bohmian mechanics and quantum potential. The influence of the scalar field on the results is also discussed.
INTERNATIONAL JOURNAL OF MODERN PHYSICS A
(2021)
Article
Physics, Particles & Fields
Gilberto M. Kremer
Summary: In this study, Jeans instability is analyzed within the framework of post-Newtonian Boltzmann and Poisson equations. It was found that the necessary mass for an overdensity to initiate gravitational collapse in the post-Newtonian theory is smaller than in the Newtonian theory.
EUROPEAN PHYSICAL JOURNAL C
(2021)
Article
Astronomy & Astrophysics
Gilberto M. Kremer
Summary: This study numerically shows Jeans instability in an expanding universe, indicating that the growth of density constrast is slower when considering particle collisions, and oscillations fade away over time for perturbations smaller than the Jeans wavelength.
INTERNATIONAL JOURNAL OF MODERN PHYSICS D
(2022)
Article
Physics, Multidisciplinary
Gilberto M. Kremer
Summary: The post-Newtonian hydrodynamic equations for a non-perfect fluid are derived from a post-Newtonian Boltzmann equation. The energy-momentum tensor components are determined using the relativistic Eckart decomposition for a viscous and heat conducting fluid. The post-Newtonian expression of the relativistic Grad distribution function is obtained. The hydrodynamic equations for mass density, mass-energy density, and momentum density are derived using a post-Newtonian transfer equation and Grad's distribution function. In the non-relativistic limit, the Newtonian hydrodynamic equations are recovered.
Article
Astronomy & Astrophysics
Gilberto Medeiros Kremer
Summary: The post-Newtonian Jeans equation is derived from the post-Newtonian Boltzmann equation in spherical coordinates for stationary self-gravitating systems. It is coupled with the three Poisson equations from the post-Newtonian theory, which are functions of the energy-momentum tensor components determined from the post-Newtonian Maxwell-Juttner distribution function. An application of this equation investigates the influence of a central massive black hole on the velocity dispersion profile of the host galaxy and determines the effects of post-Newtonian corrections.
Article
Physics, Mathematical
Gilberto M. Kremer, Andres Santos
Summary: The paper introduces the development and simplification of granular gas models, proposes a new inelastic rough Maxwell model, and provides exact solutions for the model. The proposed model allows for the evaluation of the dynamic properties of granular gases.
JOURNAL OF STATISTICAL PHYSICS
(2022)
Article
Astronomy & Astrophysics
Gilberto M. M. Kremer
Summary: This work analyzes the influence of post-Newtonian corrections on the equations of stellar structure and calculates the physical quantities for the Sun, white dwarf Sirius B, and neutron stars. The results show that the post-Newtonian corrections can be neglected for the Sun and Sirius B, but become important for stars with strong fields. For the analyzed neutron stars, the post-Newtonian corrections lead to higher central pressure and temperature, and slightly lower central mass density.
RESEARCH IN ASTRONOMY AND ASTROPHYSICS
(2022)
Article
Physics, Multidisciplinary
Gilberto M. M. Kremer
Summary: The influence of reactive cross sections on the reaction rate of a simple chemical reaction A + A -> products, where the products' concentrations are negligible compared to the reagents', is investigated using the Boltzmann equation. This reaction is considered slow, as the time between successive reactions is greater than the time between elastic collisions. The internal degrees of freedom of gas molecules are not considered. Two models for the reactive cross section, the line-of-centers energy model and the modified line-of-centers energy model, are examined. Explicit expressions for the reaction rate as a function of activation energy are provided, demonstrating how the reactant fields of particle number density and temperature evolve with time during the progress of the chemical reaction.
BRAZILIAN JOURNAL OF PHYSICS
(2023)
Article
Physics, Mathematical
Gilberto M. Kremer
Summary: The second post-Newtonian hydrodynamic equations are analyzed using a plane wave solution framework. The coupling of the hydrodynamic equations for mass and momentum density with the Poisson equations for Newtonian and post-Newtonian gravitational potentials is examined. Perturbations of the basic fields and gravitational potentials from a background state using plane wave representations yield a dispersion relation and the emergence of the Jeans instability condition. The study determines the influence of the first and second post-Newtonian approximations on the Jeans mass, showing that the second post-Newtonian approximation requires a smaller mass for an overdensity to initiate gravitational collapse compared to the Newtonian theory.
INTERNATIONAL JOURNAL OF GEOMETRIC METHODS IN MODERN PHYSICS
(2023)
Article
Physics, Multidisciplinary
Gilberto M. Kremer
Summary: The non-equilibrium contributions to the post-Newtonian hydrodynamic equations are determined using a relaxation-time model and the Chapman-Enskog method. The components of the energy-momentum tensor are found from the non-equilibrium and post-Newtonian equilibrium Maxwell-Jüttner distribution functions. The linearized field equations for mass, momentum, and internal energy densities, along with the three Poisson equations of the post-Newtonian approximation, are studied with a plane wave representation of the fields. Constitutive equations for the viscous stress and heat flux vector are obtained, showing that the transport coefficients depend on the Newtonian gravitational potential.
Article
Astronomy & Astrophysics
Gilberto M. Kremer, Leandro C. Mehret
Summary: The study aims to investigate the corrections to the spherical symmetric accretion of an infinity gas cloud into a massive object due to the post-Newtonian approximation. The analysis shows that the correction terms have a more significant impact at lower radial distances, while for alpha(infinity)/c > 10(-2), there is no continuous inflow and outflow velocity at the critical point.
