Found 712 results, showing the newest relevant preprints. Sort by relevancy only.Update me on new preprints

Nonlinear interacting **cosmological** **models** after Planck 2018 legacy
release and the $H_0$ tension

Interacting dark energy models are widely renowned for giving an explanation to the cosmic coincidence problem as well as several observational issues. Expand abstract.

Interacting dark energy

**models**are widely renowned for giving an explanation to the cosmic coincidence problem as well as several observational issues. According to the recent observational data, and so far we are concerned with the literature, the choice of the interaction function between dark matter and dark energy is always questionable since there is no such underlying theory that could derive it. Thus, in this work we have raised this issue by proposing two new nonlinear interaction functions and constrain them using cosmic microwave background (CMB) from Planck 2018, baryon acoustic oscillations (BAO), dark energy survey and a measurement of the Hubble constant $H_0$ from Hubble Space Telescope (HST) 2019. The dark energy equation of state is considered to be constant throughout the work and the geometry of the universe is assumed to be homogeneous and isotropic with zero spatial curvature. Our analyses report that a non-zero interaction is always allowed by the observational data and the dark energy equation of state is bent towards the phantom regime. In particular, when $H_0$ from HST is added to Planck 2018+BAO, we find an evidence for a non-zero coupling at more than $2\sigma$ confidence level. Our analyses also report that for both the models, $H_0$ is close to its local measurements and thus alleviating the $H_0$ tension. In particular, one of the interacting**models**perfectly solves the $H_0$ tension.12 days ago

10/10 relevant

arXiv

10/10 relevant

arXiv

Quadratic integrals of a multi-scalar **cosmological** **model**

In the context of FRW spacetime with zero spatial curvature, we consider a multi-scalar tensor cosmology model under the pretext of obtaining quadratic conservation laws. Expand abstract.

In the context of FRW spacetime with zero spatial curvature, we consider a multi-scalar tensor cosmology

**model**under the pretext of obtaining quadratic conservation laws. We propose two new interaction potentials of the scalar field. Integral to this task, is the existence of dynamical Noether symmetries which are Lie-B\"{a}cklund transformations of the physical system. Finally, analytical solutions of the field are found corresponding to each new**model**. In one of the models, we find that the scale factor mimics $\Lambda$-cosmology in a special case.44 days ago

7/10 relevant

arXiv

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arXiv

Disformally coupled quintessence

However, viable

**cosmological****models**seem to have suppressed disformal late-time contributions. Expand abstract. In this work we consider a

**cosmological****model**in which dark energy is portrayed by a canonical scalar field which is allowed to couple to the other species by means of a disformal transformation of the metric. We revisit the current literature by assuming that the disformal function in the metric transformation can depend both on the scalar field itself and on its derivatives, encapsulating a wide variety of scalar-tensor theories. This generalisation also leads to new and richer phenomenology, explaining some of the features found in previously studied**models**. We present the background equations and perform a detailed dynamical analysis, from where new disformal fixed points emerge, that translate into novel**cosmological**features. These include early scaling regimes between the coupled species and broader stability parameter regions. However, viable**cosmological****models**seem to have suppressed disformal late-time contributions.52 days ago

7/10 relevant

arXiv

7/10 relevant

arXiv

f(R)-gravity **models** constrained with **cosmological** data

In this work, we look at the cosmological constraints of four different f(R)-gravity models, which include 2 toy models and 2 more realistic models, such as the Starobinsky and Hu-Sawicki models. Expand abstract.

In this work, we look at the

**cosmological**constraints of four different f(R)-gravity models, which include 2 toy**models**and 2 more realistic models, such as the Starobinsky and Hu-Sawicki**models**. We use 359 low- and intermediate-redshift Supernovae Type 1A data obtained from the SDSS-II/SNLS3 Joint Light-curve Analysis (JLA). We then develop a Markov Chain Monte Carlo (MCMC) simulation to determine the best-fit for each f(R)-gravity model, as well as for the Lambda Cold Dark Matter ($\Lambda$CDM) model, to obtain the**cosmological**parameters ($\Omega_{m}$ and $\bar{h}$). We assume a flat universe with negligible radiation. Therefore, the only difference between these**model**are the dark energy term and the arbitrary free parameters. When do a statistical analysis on these models, (where we used the $\Lambda$CDM**model**as the "true model"), we found that the Starobinsky**model**obtained a larger likelihood function that the $\Lambda$CDM model, while still obtaining the**cosmological**parameters to be $\Omega_{m} = 0.268^{+0.027}_{-0.024}$ and $\bar{h} = 0.690^{+0.005}_{-0.005}$. We also found a reduced Starobinsky model, that explained the data, as well as being statistically significant. We also found a further 3**models**that can explain the data, even though they are not statistically significant, while also finding 3**models**that did not explain the data and was statistically rejected.99 days ago

4/10 relevant

arXiv

4/10 relevant

arXiv

Horizon thermodynamics in holographic **cosmological** **models** with a
power-law term

Thermodynamics on the horizon of a flat universe at late times is studied in holographic cosmological models that assume an associated entropy on the horizon. Expand abstract.

Thermodynamics on the horizon of a flat universe at late times is studied in holographic

**cosmological****models**that assume an associated entropy on the horizon. In such models, a $\Lambda(t)$**model**similar to a time-varying $\Lambda(t)$ cosmology is favored because of the consistency of energy flows across the horizon. Based on this consistency, a $\Lambda(t)$**model**with a power-law term proportional to $H^{\alpha}$ is formulated to systematically examine the evolution of the Bekenstein--Hawking entropy. Here, $H$ is the Hubble parameter and $\alpha$ is a free parameter whose value is a real number. The present**model**always satisfies the second law of thermodynamics on the horizon. In particular, the universe for $\alpha99 days ago

10/10 relevant

arXiv

10/10 relevant

arXiv

Extended FLRW **Models**: dynamical cancellation of **cosmological**
anisotropies

We investigate a corner of the Bianchi models that has not received much attention: "extended FLRW models" (eFLRW) defined as a cosmological model with underlying anisotropic Bianchi geometry that nevertheless expands isotropically and can be mapped onto a reference FLRW model with the same expansion history. Expand abstract.

We investigate a corner of the Bianchi

**models**that has not received much attention: "extended FLRW models" (eFLRW) defined as a**cosmological****model**with underlying anisotropic Bianchi geometry that nevertheless expands isotropically and can be mapped onto a reference FLRW**model**with the same expansion history. In order to investigate the stability and naturalness of such**models**in a dynamical systems context, we consider spatially homogeneous**models**that contain a massless scalar field $\varphi$ and a non-tilted perfect fluid obeying an equation of state $p=w\rho$. Remarkably, we find that matter anisotropies and geometrical anisotropies tend to cancel out dynamically. Hence, the expansion is asymptotically isotropic under rather general conditions. Although extended FLRW**models**require a special matter sector with anisotropies that are 'fine-tuned" relative to geometrical anisotropies, our analysis shows that such solutions are dynamically preferred attractors in general relativity. Specifically, we prove that all locally rotationally symmetric Bianchi type III universes with space-like $\nabla_\mu\varphi$ are asymptotically shear-free, for all $w\in[-1,1]$. Moreover, all shear-free equilibrium sets with anisotropic spatial curvature are proved to be stable with respect to all homogeneous perturbations for $w\geq -1/3$.100 days ago

4/10 relevant

arXiv

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arXiv

A Map Between Primordial Power Spectra and the Effective Field Theory of Inflation

We have developed a precise dictionary between the spectrum of primordial density fluctuations and the parameters of the effective field theory (EFT) of inflation that determine the primordial power spectrum (PPS). Expand abstract.

We have developed a precise dictionary between the spectrum of primordial density fluctuations and the parameters of the effective field theory (EFT) of inflation that determine the primordial power spectrum (PPS). At lowest order the EFT contains two parameters: the slow-roll parameter $\epsilon$, which acts as an order parameter, and the speed of sound $c_s$. Applying second-order perturbation theory, we provide maps from the PPS to the EFT parameters that are precise up to the cube of the fractional change in the PPS $(\Delta \mathcal{P}/\mathcal{P})^3$, or less than $1\%$ for spectral features that modulate the PPS by $20\%$. While such features are not required when the underlying

**cosmological****model**is assumed to be $\Lambda$CDM they are necessary for alternative**models**that have no**cosmological**constant/dark energy. We verify the dictionary numerically and find those excursions in the slow-roll parameter that reproduce the PPS needed to fit Planck data for both $\Lambda$ and no-$\Lambda$**cosmological****models**.100 days ago

5/10 relevant

arXiv

5/10 relevant

arXiv

Standard Sirens as a novel probe of dark energy

Cosmological models with a dynamical dark energy field typically lead to a modified propagation of gravitational waves via an effectively time-varying gravitational coupling $G(t)$. Expand abstract.

**Cosmological**

**models**with a dynamical dark energy field typically lead to a modified propagation of gravitational waves via an effectively time-varying gravitational coupling $G(t)$. The local variation of this coupling between the time of emission and detection can be probed with standard sirens. Here we discuss the role that Lunar Laser Ranging (LLR) and binary pulsar constraints play in the prospects of constraining $G(t)$ with standard sirens. In particular, we argue that LLR constrains the matter-matter gravitational coupling $G_N(t)$, whereas binary pulsars and standard sirens constrain the quadratic kinetic gravity self-interaction $G_{gw}(t)$. Generically, these two couplings could be different in alternative

**cosmological**models, in which case LLR constraints are irrelevant for standard sirens. We use the Hulse-Taylor pulsar data and show that observations are highly insensitive to time variations of $G_{gw}(t)$ yet highly sensitive to $G_N(t)$. We thus conclude that future gravitational waves data will become the best probe to test $G_{gw}(t)$, and will hence provide novel constraints on dynamical dark energy

**models**.

121 days ago

5/10 relevant

arXiv

5/10 relevant

arXiv

Connecting early and late epochs by f(z)CDM cosmography

The cosmographic approach is gaining considerable interest as a model-independent technique able to describe the late expansion of the universe. Expand abstract.

The cosmographic approach is gaining considerable interest as a

**model**-independent technique able to describe the late expansion of the universe. Indeed, given only the observational assumption of the**cosmological**principle, it allows to study the today observed accelerated evolution of the Hubble flow without assuming specific**cosmological****models**. In general, cosmography is used to reconstruct the Hubble parameter as a function of the redshift, assuming an arbitrary fiducial value for the current matter density, $\Omega_m$, and analysing low redshift**cosmological**data. Here we propose a different strategy, linking together the parametric cosmographic behavior of the late universe expansion with the small scale universe. In this way, we do not need to assume any "a priori" values for the**cosmological**parameters, since these are constrained at early epochs using both the Cosmic Microwave Background Radiation (CMBR) and Baryonic Acoustic Oscillation (BAO) data. In order to test this strategy, we describe the late expansion of the universe using the Pad\'e polynomials. This approach is discussed in the light of the recent $H(z)$ values indicators, combined with Supernovae Pantheon sample, galaxy clustering and early universe data, as CMBR and BAO. We found an interesting dependence of the current matter density value with cosmographic parameters, proving the inaccuracy of setting the value of $\Omega_m$ in cosmographic analyses, and a non-negligible effect of the cosmographic parameters on the CMBR temperature anisotropy power spectrum. Finally, we found that the cosmographic series, truncated at third order, shows a better $\chi^2$ best fit value then the vanilla $\Lambda$CDM**model**. This can be interpreted as the requirement that higher order corrections have to be considered to correctly describe low redshift data and remove the degeneration of the**models**.122 days ago

4/10 relevant

arXiv

4/10 relevant

arXiv

The simplest **cosmological** **model** in $f(R,T)$ gravity

In the present work, we search the simplest cosmological model in $f(R,T)$ gravity by considering its functional form $f(R,T) = R + \xi R T$ with $\xi$ being positive constant. Expand abstract.

In the present work, we search the simplest

**cosmological****model**in $f(R,T)$ gravity by considering its functional form $f(R,T) = R + \xi R T$ with $\xi$ being positive constant. We have constructed the Einstein's field equation in $f(R,T)$ gravity for homogeneous and isotropic space time. The explicit solution of the constructed**model**is obtained by considering the scale factor as $a = \alpha t^{\beta}$ with $\alpha$ and $\beta$ being free parameters. The values of $\alpha$ and $\beta$ are obtained by using Markov Chain Monte Carlo (MCMC) method to constraining the**model**under consideration with observational $H(z)$ data. Some physical and kinematic properties of the**model**are also discussed.123 days ago

7/10 relevant

arXiv

7/10 relevant

arXiv