Quintessence Models Research Articles

Do cosmological observations allow a negative Λ?

ABSTRACT In view of the recent measurement of H0 from the Hubble Space Telescope and Supernova H0 for the Equation of State (SH0ES) team, we explore the possibility of existence of a negative cosmological constant [anti-de Sitter (AdS) vacua in the dark energy sector] in the Universe. In this regard, we consider quintessence fields on top of a negative cosmological constant and compare such construction with Λ cold dark matter (ΛCDM) model using a different combination of cosmic microwave background, Type Ia supernova, baryon acoustic oscillation, and H0 data. Various model comparison estimators show that quintessence models with a negative Λ are either preferred over ΛCDM or perform equally as the ΛCDM model. This suggests that the presence of a negative Λ (AdS ground state) in our Universe, which can naturally arise in string theory, is consistent with cosmological observations.

Coupled quintessence with a generalized interaction term

In this paper, we investigate a cosmological model in which dark energy, represented by a quintessential scalar field, is directly coupled to a dark-matter perfect fluid. We are interested in solutions of cosmological relevance, namely those for which a dark-matter-dominated era long enough to allow for structure formation is followed by an era of accelerated expansion driven by dark energy. For the coupling between these two dark components of the universe, we choose forms that generalize the one most commonly used in the literature. Resorting to powerful methods of qualitative analysis of dynamical systems, we show that, for certain generalized forms of the coupling, final states of our coupled quintessential model correspond to solutions in which the evolution of the universe is completely dominated by dark energy. In this case, there are no scaling solutions. Interestingly, however, for certain values of a relevant parameter, during the approach to the final state of evolution, the cosmological parameters change so slowly that, for all practical purposes, the solution appears to be stuck in a state corresponding to a scaling solution.

Accelerating Universe scenario in anisotropic f(Q) cosmology

In this paper, we investigate the exact solution of an anisotropic space-time in the context of $f(Q)$ gravity, where $f\left( Q\right) $ is the arbitrary function of the non-metricity scalar $Q$. Here, we consider a specific power-law form as $f\left( Q\right) =\alpha Q^{n+1}+\beta $, where $\alpha $, $\beta $, and $n$ are free model parameters. Using power-law cosmology ($a\left( t\right) \propto t^{m}$), we analyze the physical behavior of cosmological parameters such as the energy density, pressure, EoS parameter, skewness parameter. Further, we validated the model with energy conditions and found that our $f\left( Q\right) $\ cosmological model behaves like the quintessence model in the present and $% \Lambda $CDM in the future.

Probing Quintessence using BAO imprint on the cross-correlation of weak lensing and post-reionization H i 21 cm signal

ABSTRACT In this work, we investigate the possibility of constraining a thawing Quintessence scalar field model for dark energy. We propose using the imprint of baryon acoustic oscillation on the cross-correlation of post-reionization 21-cm signal and galaxy weak lensing convergence field to tomographically measure the angular diameter distance DA(z) and the Hubble parameter H(z). The projected errors in these quantities are then used to constrain the Quintessence model parameters. We find that independent 600 h radio interferometric observation at four observing frequencies 916, 650, 520, and 430 MHz with an SKA-1-Mid like radio telescope in cross-correlation with a deep weak lensing survey covering half the sky may measure the binned DA and H at a few per cent level of sensitivity. The Monte Carlo analysis for a power-law thawing Quientessence model gives the 1 − σ marginalized bounds on the initial slope λi, dark energy density parameter Ωϕ0 and the shape of the potential Γ at 8.63, 10.08, and $9.75{{\ \rm per\ cent}}$, respectively. The constraints improve to 7.66, 4.39, and $5.86{{\ \rm per\ cent}}$, respectively, when a joint analysis with supernovae and other probes is performed.

Geodesic deviation in Sáez–Ballester theory

We study the geodesic deviation (GD) equation in a generalized version of the Sáez–Ballester (SB) theory in arbitrary dimensions. We first establish a general formalism and then restrict to particular cases, where (i) the matter-energy distribution is that of a perfect fluid, and (ii) the spacetime geometry is described by a vanishing Weyl tensor. Furthermore, we consider the spatially flat FLRW universe as the background geometry. Based on this setup, we compute the GD equation as well as the convergence condition associated with fundamental observers and past directed null vector fields. Moreover, we extend that framework and extract the corresponding geodesic deviation in the modified Sáez–Ballester theory (MSBT), where the energy–momentum tensor and potential emerge strictly from the geometry of the extra dimensions. In order to examine our herein GD equations, we consider two novel cosmological models within the SB framework. Moreover, we discuss a few quintessential models and a suitable phantom dark energy scenario within the mentioned SB and MSBT frameworks. Noticing that our herein cosmological models can suitably include the present time of our Universe, we solve the GD equations analytically and/or numerically. By employing the correct energy conditions plus recent observational data, we consistently depict the behavior of the deviation vector η ( z ) and the observer area distance r 0 ( z ) for our models. Concerning the Hubble constant problem, we specifically focus on the observational data reported by the Planck collaboration and the SH0ES collaboration to depict η ( z ) and r 0 ( z ) for our herein phantom model. Subsequently, we contrast our results with those associated with the Λ CDM model. We argue that the MSBT can be considered as a fitting candidate for a proper description of the late evolution of the universe.

Momentum transfer models of interacting dark energy

We consider two models of interacting dark energy, both of which interact only through momentum exchange. One is a phenomenological one-parameter extension to wCDM, and the other is a coupled quintessence model described by a Lagrangian formalism. Using a variety of high and low redshift data sets, we perform a global fitting of cosmological parameters and compare to ΛCDM, uncoupled quintessence, and wCDM. We find that the models are competitive with ΛCDM, even obtaining a better fit when certain data sets are included.

Could trapped quintessence account for the laser-detuning-dependent acceleration of cold atoms in varying-frequency time-of-flight experiments?

Using a trapped quintessence model, a series of time-of-flight (TOF) experiments with a different frequency of probe light were designed and performed. The varying-frequency TOF (VFTOF) experiments demonstrated that the fall acceleration of test atoms is dependent on the detuning of the probe light frequency with respect to the atomic transition frequency. In appropriately designed experiments, if the scalar field in the model accounts for the accelerated expansion of the Universe entirely, the field will result in an observable fifth force. Meanwhile, the trapped quintessence model still satisfies all experimental bounds on deviations from general relativity due to both the saturation effect and the short interaction range of the scalar field. The scalar saturates at a value corresponding to the cosmological constant when the microscopic nonrelativistic matter density is large enough. The interaction range of the scalar is inversely proportional to the square root of the microscopic nonrelativistic matter density. The interaction range has been estimated to be several $\mu \rm{m}$ in the current cosmic density. The Universe is assumed to be permeated with fuzzy dark matter, which means that the microscopic nonrelativistic matter density defined through the quantum wavefunctions of the ultralight particles can be used on the cosmic scale. By measuring the fall acceleration of the test atoms with the TOF method step-by-step in the detuning frequency domain of the probe light, we derived the dispersion curves of the measured acceleration versus the frequency detuning of the probe light. When the nonrelativistic matter density of the source increased due to the energy gained from the laser light, the test atoms were pulled to the center of the source, and vice versa.

Fast full N-body simulations of generic modified gravity: conformal coupling models

We present mg-glam, a code developed for the very fast production of full N-body cosmological simulations in modified gravity (MG) models. We describe the implementation, numerical tests and first results of a large suite of cosmological simulations for three classes of MG models with conformal coupling terms: the f(R) gravity, symmetron and coupled quintessence models. Derived from the parallel particle-mesh code glam, mg-glam incorporates an efficient multigrid relaxation technique to solve the characteristic nonlinear partial differential equations of these models. For f(R) gravity, we have included new variants to diversify the model behaviour, and we have tailored the relaxation algorithms to these to maintain high computational efficiency. In a companion paper, we describe versions of this code developed for derivative coupling MG models, including the Vainshtein- and K-mouflage-type models. mg-glam can model the prototypes for most MG models of interest, and is broad and versatile. The code is highly optimised, with a tremendous speedup of a factor of more than a hundred compared with earlier N-body codes, while still giving accurate predictions of the matter power spectrum and dark matter halo abundance. mg-glam is ideal for the generation of large numbers of MG simulations that can be used in the construction of mock galaxy catalogues and the production of accurate emulators for ongoing and future galaxy surveys.

Variational Density Functional Calculations of Excited States: Conical Intersection and Avoided Crossing in Ethylene Bond Twisting.

Theoretical studies of photochemical processes require a description of the energy surfaces of excited electronic states, especially near degeneracies, where transitions between states are most likely. Systems relevant to photochemical applications are typically too large for high-level multireference methods, and while time-dependent density functional theory (TDDFT) is efficient, it can fail to provide the required accuracy. A variational, time-independent density functional approach is applied to the twisting of the double bond and pyramidal distortion in ethylene, the quintessential model for photochemical studies. By allowing for symmetry breaking, the calculated energy surfaces exhibit the correct topology around the twisted-pyramidalized conical intersection even when using a semilocal functional approximation, and by including explicit self-interaction correction, the torsional energy curves are in close agreement with published multireference results. The findings of the present work point to the possibility of using a single determinant time-independent density functional approach to simulate nonadiabatic dynamics, even for large systems where multireference methods are impractical and TDDFT is often not accurate enough.

Observational constraints on inflection point quintessence with a cubic potential

We examine the simplest inflection point quintessence model, with a potential given by V(ϕ)=V0+V3ϕ3. This model can produce either asymptotic de Sitter expansion or transient acceleration, and we show that it does not correspond to either pure freezing or thawing behavior. We derive observational constraints on the initial value of the scalar field, ϕi, and V3/V0 and find that small values of either ϕi or V3/V0 are favored. While most of the observationally-allowed parameter space yields asymptotic de Sitter evolution, there is a small region, corresponding to large V3/V0 and small ϕi, for which the current accelerated expansion is transient. The latter behavior is potentially consistent with a cyclic universe.

The momentum constraint equation in parameterised post-Newtonian cosmology

Abstract We derive a theory-independent version of the momentum constraint equation for use in cosmology, as a part of the parameterised post-Newtonian cosmology framework. Our equations are constructed by adapting the corresponding quantities from formalisms constructed for testing and constraining gravity in isolated astrophysical systems, thereby extending the domain of applicability of these approaches up to cosmological scales. Our parameterised equations include both scalar and divergenceless-vector gravitational potentials, and can be applied to both conservative and non-conservative theories of gravity. They can also be used to describe the gravitational fields of both non-linear structures and super-horizon perturbations. We apply the parameterised equations we propose to quintessence models of dark energy, as well as scalar-tensor and vector-tensor theories of gravity. We find them to work well in each case. Our equations are highly compact, and are intended to be useful for constraining gravity in a theory-independent fashion in cosmology.

Generalizing the constant-roll condition in scalar inflation

In this work, we generalize the constant-roll condition for minimally coupled canonical scalar field inflation. Particularly, we shall assume that the scalar field satisfies the condition [Formula: see text], and we derive the field equations under this assumption. We call the framework extended constant-roll framework. Accordingly, we calculate the inflationary indices and the corresponding observational indices of inflation. In order to demonstrate the inflationary viability, we choose three potentials that are problematic in the context of slow-roll dynamics, namely, chaotic, linear power-law and exponential inflation, and by choosing a simple power-law form for the smooth function [Formula: see text], we show that in the extended constant-roll framework, the models are compatible with the latest 2018 Planck constraints on inflation. We also justify appropriately why we called this new framework extended constant-roll framework, and we show that the condition [Formula: see text] is equivalent to the condition [Formula: see text], with the latter condition being a simple generalization of the constant-roll condition. Finally, we examine an interesting physical situation, in which a general extended constant-roll scalar field model is required to satisfy the cosmological tracker condition used in quintessence models. In contrast to the slow-roll and ordinary constant-roll cases, in which case the tracker condition is not compatible with neither the slow-roll or the ordinary constant-roll conditions, the extended constant-roll condition can be compatible with the tracker condition. This feature leads to a new inflationary phenomenological framework, the essential features of which we develop in brief. The main feature of the new theoretical framework is that the function [Formula: see text] and the potential [Formula: see text] are no longer free to choose, but these are directly functionally related.

Quintessential constant-roll inflation

We investigate a single field model in the context of the constant-roll inflation in which inflaton moves down to the minimum point of the potential with a constant rate of rolling. We use a quintessential inflationary model obtained by a Lorentzian function which is dependent on the number of e-folds. We present the inflationary analysis for the model and find the observational constraints on the parameters space using the observations of CMB anisotropies i.e. the Planck and Keck/array datasets. We find the observationally acceptable values of the Width of the Lorentzian function as 0.3<Γ≤0.5 at the 68% CL and Γ≤0.3 at the 95% CL when ξ=120, |β|=0.02 and N=60. Also, we acquire the observationally favoured values of the amplitude of the Lorentzian function as 400<ξ≤600 at the 68% CL and ξ≤400 at the 95% CL when Γ=0.1, |β|=0.02 and N=60. Moreover, we study the model from the Weak Gravity Conjecture approach using the swampland criteria.

A simple parametrisation for coupled dark energy

As an alternative to the popular parametrisations of the dark energy equation of state, we construct a quintessence model where the scalar field has a linear dependence on the number of e-folds. Constraints on more complex models are typically limited by the degeneracies that increase with the number of parameters. The proposed parametrisation conveniently constrains the evolution of the dark energy equation of state as it allows for a wide variety of time evolutions. We also consider a non-minimal coupling to cold dark matter. We fit the model with Planck and KiDS observational data. The CMB favours a non-vanishing coupling with energy transfer from dark energy to dark matter. Conversely, gravitational weak lensing measurements slightly favour energy transfer from dark matter to dark energy, with a substantial departure of the dark energy equation of state from -1.

Yoga Dark Energy: natural relaxation and other dark implications of a supersymmetric gravity sector

We construct a class of 4D 'yoga' (naturally relaxed) models for which the gravitational response of heavy-particle vacuum energies is strongly suppressed. The models contain three ingredients: (i) a relaxation mechanism driven by a scalar field (the 'relaxon'), (ii) a very supersymmetric gravity sector coupled to the Standard Model in which supersymmetry is non-linearly realised, and (iii) an accidental approximate scale invariance expressed through the presence of a low-energy dilaton supermultiplet. All three are common in higher-dimensional and string constructions and although none suffices on its own, taken together they can dramatically suppress the net vacuum-energy density. The dilaton's vev τ determines the weak scale M W ∼ M p/√τ. We compute the potential for τ and find it can be stabilized in a local de Sitter minimum at sufficiently large field values to explain the size of the electroweak hierarchy, doing so using input parameters no larger than O(60) because the relevant part of the scalar potential arises as a rational function of lnτ. The de Sitter vacuum energy at the minimum is order c M 8 W α 1/τ 4, with a coefficient c ≪ \U0001d4aa(M W -4). We discuss ways to achieve c ∼ 1/M p 4 as required by observations. Scale invariance implies the dilaton couples to matter like a Brans-Dicke scalar with coupling large enough to be naively ruled out by solar-system tests of gravity. Yet because it comes paired with an axion it can evade fifth-force bounds through the novel screening mechanism described in arXiv:2110.10352. Cosmological axio-dilaton evolution predicts a natural quintessence model for Dark Energy, whose evolution might realize recent proposals to resolve the Hubble tension, and whose axion contributes to Dark Matter. We summarize inflationary implications and some remaining challenges, including the unusual supersymmetry breaking regime used and the potential for UV completions of our approach.

KiDS-1000 cosmology: machine learning – accelerated constraints on interacting dark energy with CosmoPower

ABSTRACT We derive constraints on a coupled quintessence model with pure momentum exchange from the public ∼1000 deg2 cosmic shear measurements from the Kilo-Degree Survey and the Planck 2018 cosmic microwave background data. We compare this model with Lambda cold dark matter and find similar χ2 and log-evidence values. We accelerate parameter estimation by sourcing cosmological power spectra from the neural network emulator CosmoPower. We highlight the necessity of such emulator-based approaches to reduce the computational runtime of future similar analyses, particularly from Stage IV surveys. As an example, we present Markov Chain Monte Carlo forecasts on the same coupled quintessence model for a Euclid-like survey, revealing degeneracies between the coupled quintessence parameters and the baryonic feedback and intrinsic alignment parameters, but also highlighting the large increase in constraining power Stage IV surveys will achieve. The contours are obtained in a few hours with CosmoPower, as opposed to the few months required with a Boltzmann code.

A 3D Phase Space Analysis of Scalar Field Potentials

In this study, we present the phase-space analysis of Quintessence models specified by the choice of two potentials, namely the Recliner potential and what we call the broken exponential-law potential, which is a new proposal. Using a dynamical system analysis we provide a systematic study of the cosmological evolution of the two models and their properties. We find new scaling solutions characterised by a constant ratio between the energy density of the scalar field and that of the matter component. These solutions are of high interest in light of the possibility to alleviate the coincidence problem. Additionally, the models also show attractor solutions. We finally construct concrete models built using a double potential according to which one potential realises the early-time scaling regime and the second one allows to exit this regime and to enter in the epoch of cosmic acceleration driven by a scalar-field dominated attractor point.

Quintessential inflation and nonlinear effects of the tachyonic trap mechanism

With the help of the tachyonic trapping mechanism one can potentially solve a number of problems affecting quintessential inflation models. In this mechanism we introduce a trapping field with a spontaneous symmetry breaking potential. When the quintessential inflaton passes the critical point, a sudden burst of particle production is able to reheat the Universe and trap the inflaton away from theminimum of its potential. However, self-interactions of the trapping field suppress particle production and reduce the efficiency of this process. We develop a method to compute the magnitude of the suppression and explore the parameter space in which the mechanism can be applied effectively.

Quintessence and the Swampland: The Numerically Controlled Regime of Moduli Space

AbstractWe provide a detailed discussion of the main theoretical and phenomenological challenges of quintessence model building in any numerically controlled regime of the moduli space of string theory. We argue that a working quintessence model requires a leading order non‐supersymmetric (near) Minkowski vacuum with an axionic flat direction. This axion, when lifted by subdominant non‐perturbative effects, could drive hilltop quintessence only for highly tuned initial conditions and a very low inflationary scale. Our analysis has two important implications. Firstly, scenarios which are in agreement with the swampland conjectures, such as those that include runaways, or supersymmetric AdS and Minkowski vacua, cannot give rise to phenomenologically viable quintessence with full computational control. This raises doubts on the validity of the swampland dS conjecture since it would imply a strong tension between quantum gravity and observations. Secondly, if data should prefer dynamical dark energy, axion models based on alignment mechanisms look more promising than highly contrived hilltop scenarios.

Reconstructing scalar field models of the Sharma–Mittal holographic dark energy

In this paper, we investigate the Sharma–Mittal holographic dark energy (SMHDE) model in the context of a spatially homogeneous and isotropic flat Friedmann–Robertson–Walker (FRW) Universe by taking various values of model parameters [Formula: see text] and [Formula: see text] and the Hubble horizon is taken as the infrared cut-off. We have analyzed the deceleration parameter [Formula: see text] and the EoS parameter. According to the deceleration parameter, the Universe is in an accelerating and expanding phase, which is compatible with the observational data. The EoS parameter depicts that presently the Universe is lying in the quintessence region and at a late time it will show [Formula: see text]CDM behavior. It is also concluded by the stability analysis that SMHDE model is classically stable at present and future. To understand the dynamics of our Universe, we have established a correspondence among SMHDE and the quintessence, tachyon and K-essence scalar-field models. Our results show that the Universe is in an accelerating expansion mode described by quintessence like behavior. We go further and estimate the model parameters by using the distance modulus measurement of the recent Union 2.1 dataset of supernovae.