Cosmological constrains on minimally and non-minimally coupled scalar field models

Cosmological Data ◽

Local Determination ◽

The One

Abstract We study the minimally and non-minimally coupled scalar field models as possible alternatives for dark energy, the mysterious energy component that is driving the accelerated expansion of the universe. After discussing the dynamics at both the background and perturbation level, we confront the two models with the latest cosmological data. After obtaining updated constraints on their parameters we perform model selection using the basic information criteria. We found that the ΛCDM model is strongly favored when the local determination of the Hubble constant is not considered and that this statement is weakened once local H0 is included in the analysis. We calculate the parameter combination $S_8=\sigma _8\sqrt{\Omega _{m}/0.3}$ and show the decrement of the tension with respect to the Planck results in the case of minimally and non-minimally coupled scalar field models. Finally, for the coupling constant between DE and gravity, we obtain the constraint $\xi \simeq -0.06^{+0.19}_{-0.19}$, approaching the one from solar system tests |ξ| ≲ 10−2 and comparable to the conformal value ξ = 1/6 at 1σ uncertainty.

Heuristic determination of the cosmological constant

Modern Physics Letters A ◽

10.1142/s0217732321501145 ◽

2021 ◽

pp. 2150114

Author(s):

Manuel Urueña Palomo ◽

Fernando Pérez Lara

Keyword(s):

Field Theory ◽

Energy Density ◽

Cosmological Constant ◽

Accelerated Expansion ◽

Fundamental Constants ◽

Quantum Field ◽

Brute Force ◽

The vacuum catastrophe results from the disagreement between the theoretical value of the energy density of the vacuum in quantum field theory and the estimated one observed in cosmology. In a similar attempt in which the ultraviolet catastrophe was solved, we search for the value of the cosmological constant by brute-force through computation. We explore combinations of the fundamental constants in physics performing a dimensional analysis, in search of an equation resulting in the measured energy density of the vacuum or cosmological constant that is assumed to cause the accelerated expansion of the universe.

NEW HOLOGRAPHIC CHAPLYGIN GAS MODEL OF DARK ENERGY

International Journal of Modern Physics D ◽

10.1142/s0218271811018779 ◽

2011 ◽

Vol 20 (03) ◽

pp. 281-297 ◽

Cited By ~ 5

Author(s):

M. MALEKJANI ◽

A. KHODAM-MOHAMMADI

Keyword(s):

Dark Energy ◽

Scalar Field ◽

Chaplygin Gas ◽

Accelerated Expansion ◽

Linear Perturbation ◽

Generalized Chaplygin Gas ◽

Infrared Cutoff ◽

Scalar Field Models ◽

Linear Perturbation Theory ◽

Limiting Case

In this work, we investigate the holographic dark energy model with a new infrared cutoff (new HDE model), proposed by Granda and Oliveros. Using this new definition for the infrared cutoff, we establish the correspondence between the new HDE model and the standard Chaplygin gas (SCG), generalized Chaplygin gas (GCG) and modified Chaplygin gas (MCG) scalar field models in a nonflat universe. The potential and dynamics for these scalar field models, which describe the accelerated expansion of the universe, are reconstructed. According to the evolutionary behavior of the new HDE model, we derive the same form of dynamics and potential for the different SCG, GCG and MCG models. We also calculate the squared sound speed of the new HDE model as well as the SCG, GCG and MCG models, and investigate the new HDE Chaplygin gas models from the viewpoint of linear perturbation theory. In addition, all results in the nonflat universe are discussed in the limiting case of the flat universe, i.e. k = 0.

A novel teleparallel dark energy model

International Journal of Modern Physics D ◽

10.1142/s0218271816500255 ◽

2016 ◽

Vol 25 (02) ◽

pp. 1650025 ◽

Cited By ~ 12

Author(s):

Giovanni Otalora

Keyword(s):

Dark Energy ◽

Scalar Field ◽

Teleparallel Gravity ◽

Accelerated Expansion ◽

Late Time ◽

De Sitter ◽

Sitter Group ◽

Current State ◽

Although equivalent to general relativity, teleparallel gravity (TG) is conceptually speaking a completely different theory. In this theory, the gravitational field is described by torsion, not by curvature. By working in this context, a new model is proposed in which the four-derivative of a canonical scalar field representing dark energy is nonminimally coupled to the “vector torsion”. This type of coupling is motivated by the fact that a scalar field couples to torsion through its four-derivative, which is consistent with local spacetime kinematics regulated by the de Sitter group [Formula: see text]. It is found that the current state of accelerated expansion of the universe corresponds to a late-time attractor that can be (i) a dark energy-dominated de Sitter solution ([Formula: see text]), (ii) a quintessence-type solution with [Formula: see text], or (iii) a phantom-type [Formula: see text] dark energy.

Singularities in Inflationary Cosmological Models

Universe ◽

10.3390/universe7120491 ◽

2021 ◽

Vol 7 (12) ◽

pp. 491

Author(s):

Leonardo Fernández-Jambrina

Keyword(s):

Scalar Field ◽

Field Potential ◽

Fractional Power ◽

Scalar Fields ◽

Big Bang ◽

Cosmological Models ◽

Accelerated Expansion ◽

Type Iv ◽

Big Crunch ◽

Expansion Of The Universe

Due to the accelerated expansion of the universe, the possibilities for the formation of singularities has changed from the classical Big Bang and Big Crunch singularities to include a number of new scenarios. In recent papers it has been shown that such singularities may appear in inflationary cosmological models with a fractional power scalar field potential. In this paper we enlarge the analysis of singularities in scalar field cosmological models by the use of generalised power expansions of their Hubble scalars and their scalar fields in order to describe all possible models leading to a singularity, finding other possible cases. Unless a negative scalar field potential is considered, all singularities are weak and of type IV.

BRANS-DICKE COSMOLOGY WITH FERMIONS AND CHAMELEON MECHANISM

International Journal of Modern Physics Conference Series ◽

10.1142/s2010194512004242 ◽

2012 ◽

Vol 07 ◽

pp. 174-183

Author(s):

DAO-JUN LIU ◽

BIN YANG ◽

XING-HUA JIN

Keyword(s):

Scalar Field ◽

Interaction Potential ◽

The Self ◽

Accelerated Expansion ◽

Late Time ◽

Fermion Field ◽

Chameleon Mechanism ◽

Stable Solutions ◽

We study the cosmological dynamics of Brans-Dicke theory in which there are fermions with a coupling to BD scalar field as well as a self-interaction potential. The conditions that there exists a solution which is stable and represents a late-time accelerated expansion of the universe are found. It is shown that the late-time acceleration depends completely on the self-interaction of the fermion field if our investigation is restricted to the theory with positive BD parameter ω. Provided a negative ω is allowed, there will be another two class of stable solutions describing late-time accelerated expansion of the universe. Besides, we find that chameleon mechanism will be possessed in our theory when a suitable self-interaction of fermion field is considered.

Dimensional reduction and (Anti) de Sitter bounds

Journal of High Energy Physics ◽

10.1007/jhep08(2021)041 ◽

2021 ◽

Vol 2021 (8) ◽

Author(s):

Tom Rudelius

Keyword(s):

Scalar Field ◽

Cosmological Constant ◽

Dimensional Reduction ◽

Energy Condition ◽

Field Potential ◽

Limited Range ◽

Mass Scale ◽

Accelerated Expansion ◽

De Sitter ◽

Expansion Of The Universe

Abstract Dimensional reduction has proven to be a surprisingly powerful tool for delineating the boundary between the string landscape and the swampland. Bounds from the Weak Gravity Conjecture and the Repulsive Force Conjecture, for instance, are exactly preserved under dimensional reduction. Motivated by its success in these cases, we apply a similar dimensional reduction analysis to bounds on the gradient of the scalar field potential V and the mass scale m of a tower of light particles in terms of the cosmological constant Λ, which ideally may pin down ambiguous O(1) constants appearing in the de Sitter Conjecture and the (Anti) de Sitter Distance Conjecture, respectively. We find that this analysis distinguishes the bounds $$ \left|\nabla V\right|/V\ge \sqrt{4/\left(d-2\right)} $$ ∇ V / V ≥ 4 / d − 2 , m ≲ |Λ|1/2, and m ≲ |Λ|1/d in d-dimensional Planck units. The first of these bounds is equivalent to the strong energy condition in Einstein-dilaton gravity and precludes accelerated expansion of the universe. It is almost certainly violated in our universe, though it may apply in asymptotic limits of scalar field space. The second bound cannot be satisfied in our universe, though it is saturated in supersymmetric AdS vacua with well-understood uplifts to 10d/11d supergravity. The third bound likely has a limited range of validity in quantum gravity as well, so it may or may not apply to our universe. However, if it does apply, it suggests a possible relation between the cosmological constant and the neutrino mass, which (by the see-saw mechanism) may further provide a relation between the cosmological constant problem and the hierarchy problem. We also work out the conditions for eternal inflation in general spacetime dimensions, and we comment on the behavior of these conditions under dimensional reduction.

RECONSTRUCTION OF NEW HOLOGRAPHIC SCALAR FIELD MODELS OF DARK ENERGY IN BRANS–DICKE UNIVERSE

Modern Physics Letters A ◽

10.1142/s0217732311034682 ◽

2011 ◽

Vol 26 (03) ◽

pp. 191-204 ◽

Cited By ~ 12

Author(s):

WEI-QIANG YANG ◽

YA-BO WU ◽

LI-MIN SONG ◽

YANG-YANG SU ◽

JIAN LI ◽

...

Keyword(s):

Dark Energy ◽

Scalar Field ◽

Dark Energy Model ◽

Holographic Dark Energy ◽

Chaplygin Gas ◽

Energy Model ◽

Accelerated Expansion ◽

Holographic Dark Energy Model ◽

Special Cases ◽

Expansion Of The Universe

Motivated by the work: K. Karami and J. Fehri, Phys. Lett. B684, 61 (2010) and A. Sheykhi, Phys. Lett. B681, 205 (2009), we generalize their work to the new holographic dark energy model with [Formula: see text] in the framework of Brans–Dicke cosmology. Concretely, we study the correspondence between the quintessence, tachyon, K-essence, dilaton scalar field and Chaplygin gas model with the new holographic dark energy model in the non-flat Brans–Dicke universe. Furthermore, we reconstruct the potentials and dynamics for these models. By analysis we can show that for new holographic quintessence and Chaplygin gas models, if the related parameters to the potentials satisfy some constraints, the accelerated expansion can be achieved in Brans–Dicke cosmology. In particular, the counterparts of fields and potentials in general relativity can describe accelerated expansion of the universe. It is worth stressing that not only can we give some new results in the framework of Brans–Dicke cosmology, but also the previous results of the new holographic dark energy in Einstein gravity can be included as special cases given by us.

On quintessence star model and strange star

The European Physical Journal C ◽

10.1140/epjc/s10052-020-08433-6 ◽

2020 ◽

Vol 80 (9) ◽

Author(s):

Gabino Estevez-Delgado ◽

Joaquin Estevez-Delgado

Keyword(s):

Dark Matter ◽

Radial Pressure ◽

Strange Star ◽

Accelerated Expansion ◽

Anisotropic Fluid ◽

Stable Model ◽

Star Model ◽

Ordinary Matter ◽

The One

AbstractThe astronomical observations on the accelerated expansion of the universe generate the possibility that the internal matter of the stars is not only formed by ordinary matter but also by matter with negative pressure. We discuss the existence of stars formed by the coexistence of two types of fluids, one associated to quintessence dark matter described by the radial and tangential pressures $$(P_{rq},P_{tq})$$ ( P rq , P tq ) and the density $$\rho _{q}$$ ρ q characterized by a parameter $$-1<w<-\frac{1}{3}$$ - 1 < w < - 1 3 and ordinary matter described by an anisotropic fluid with radial pressure of a strange star given by the MIT Bag model $$P_r=\frac{1}{3}(c^2\rho -4B_g)$$ P r = 1 3 ( c 2 ρ - 4 B g ) and tangential pressure $$P_t=\frac{1}{3}(c^2\rho -4B_g)-\frac{3}{2}(1+w)c^2\rho _q$$ P t = 1 3 ( c 2 ρ - 4 B g ) - 3 2 ( 1 + w ) c 2 ρ q , in which the effect is reflected of the quintessence dark matter over the ordinary matter. Via a theorem we show that the geometry that describes this interaction is equivalent to that of a perfect fluid with ordinary matter. Taking as geometry the one associated with a model for neutron stars, a physically acceptable and stable model is obtained. The application to the star Her X-1, as a candidate to a strange quark star, generates for us a value of the MIT Bag constant $$B_g = 97.0048\,\mathrm{Mev}/\mathrm{fm}^3$$ B g = 97.0048 Mev / fm 3 , which is found to be inside the expected interval.

COSMOLOGICAL DYNAMICS OF f(R) GRAVITY SCALAR DEGREE OF FREEDOM IN EINSTEIN FRAME

International Journal of Modern Physics D ◽

10.1142/s0218271813500831 ◽

2013 ◽

Vol 22 (14) ◽

pp. 1350083 ◽

Cited By ~ 9

Author(s):

UMANANDA DEV GOSWAMI ◽

KABITA DEKA

Keyword(s):

Scalar Field ◽

Power Law ◽

Einstein Frame ◽

Degree Of Freedom ◽

Gravity Models ◽

Accelerated Expansion ◽

Power Law Model ◽

Starobinsky Model ◽

f(R) gravity models belong to an important class of modified gravity models where the late time cosmic accelerated expansion is considered as a manifestation of the large scale modification of the force of gravity. f(R) gravity models can be expressed in terms of a scalar degree of freedom by redefinition of model's variable. The conformal transformation of the action from Jordan frame to Einstein frame makes the scalar degree of freedom more explicit and can be studied conveniently. We have investigated the features of the scalar degree of freedoms and the consequent cosmological implications of the power-law (ξRn) and the Starobinsky (disappearing cosmological constant) f(R) gravity models numerically in the Einstein frame. Both the models show interesting behavior of their scalar degree of freedom and could produce the accelerated expansion of the universe in the Einstein frame with the negative equation of state of the scalar field. However, the scalar field potential for the power-law model is the well-behaved function of the field, whereas the potential becomes flat for higher value of field in the case of the Starobinsky model. Moreover, the equation of state of the scalar field for the power-law model is always negative and less than -1/3, which corresponds to the behavior of the dark energy, that produces the accelerated expansion of the universe. This is not always the case for the Starobinsky model. At late times, the Starobinsky model behaves as cosmological constant Λ as behaves by power-law model for the values of n → 2 at all times.

Kantowski–Sachs universe with dark energy fluid and massive scalar field

Canadian Journal of Physics ◽

10.1139/cjp-2019-0563 ◽

2020 ◽

Vol 98 (11) ◽

pp. 993-998

Author(s):

K. Deniel Raju ◽

M.P.V.V. Bhaskara Rao ◽

Y. Aditya ◽

T. Vinutha ◽

D.R.K. Reddy

Keyword(s):

Dark Energy ◽

Scalar Field ◽

Cosmological Parameters ◽

Accelerated Expansion ◽

Massive Scalar ◽

Field Equations ◽

Massive Scalar Field ◽

Anisotropic Dark Energy ◽

This study is mainly concerned with a spatially homogeneous and anisotropic Kantowski–Sachs cosmological model with anisotropic dark energy fluid and massive scalar field. We solve the field equations using (i) the shear scalar proportionality to the expansion scalar and (ii) a mathematical condition that is a consequence of the power law between the scalar field and the average scale factor of the universe, and the corresponding dark energy model is presented. The cosmological parameters of the model are computed and discussed, as well as the relevance of its dynamical aspects to the recent scenario of the accelerated expansion of the universe.