International Journal of Modern Physics D

In this paper, we review and update constraints on the Early Dark Energy (EDE) model from cosmological data sets, in particular Planck PR3 and PR4 cosmic microwave background (CMB) data and large-scale structure (LSS) data sets including galaxy clustering and weak lensing data from the Dark Energy Survey, Subaru Hyper Suprime-Cam and KiDS+VIKING-450, as well as BOSS/eBOSS galaxy clustering and Lyman-$\alpha$ forest data. We detail the fit to CMB data, and perform the first analyses of EDE using the CAMSPEC and Hillipop likelihoods for Planck CMB data, rather than Plik, both of which yield a tighter upper bound on the allowed EDE fraction than that found with Plik. We then supplement CMB data with LSS data in a series of new analyses. All these analyses are concordant in their Bayesian preference for $\mathrm{\Lambda }$CDM over EDE, as indicated by marginalized posterior distributions. We perform a series of tests of the impact of priors in these results, and compare with frequentist analyses based on the profile likelihood, finding qualitative agreement with the Bayesian results. All these tests suggest prior volume effects are not a determining factor in analyses of EDE. This work provides both a review of existing constraints and several new analyses.

We introduce a new class of two-dimensional gravity models using ideas motivated by the Teleparallel Equivalent of General Relativity. This leads to a rather natural formulation of a theory that has close links with Jackiw–Teitelboim gravity. After introducing the theory and discussing its vacuum solutions, we present the Hamiltonian analysis. This implies the presence of a single dynamical degree of freedom, which is in sharp contrast to General Relativity, where there are no degrees of freedom in two spacetime dimensions. Our approach can be extended to various other lower-dimensional gravity theories and thus could be of wider interest.

In this paper, we review the experimental constraints on the parameter $\alpha$ associated with the Generalized Uncertainty Principle (GUP) and the parameter $\beta$ associated with the Generalized Event Horizon (GEH). The Compton–Schwarzschild correspondence implies a relationship between $\alpha$ and $\beta$, with both parameters being of order 1. This presents a problem for our previous “$M+1∕M$” model since the extra gravitational force at sub-Planckian masses contravenes observations. Various resolutions of this problem are discussed.

The purpose of this study is to investigate the parametrization form of the deceleration parameter in relation to the redshift z. The parameter is represented by the equation $q(z)=q_0+q_1\frac{z(1+z)}{{(1+z)}^2}$, which offers the desirable quality of allowing the sign to be flipped from a decelerating phase to an accelerating phase. We have investigated the Hubble parameter by evaluating the specified parametric form of q and derived constraints on the related free parameters $H_0$, $q_0$ and $q_1$ with confidence limits of 1$\sigma$ and 2$\sigma$ by using the ${\chi }^2$-minimization approach. Furthermore, we have constrained the current value of the deceleration parameter $q_0=-0.457_{-0.0023}^{+0.0022}$ and obtained that the current universe is accelerating. We have examined the characteristics of our model by assuming the two distinct forms of $f(G)=\alpha G^{m+1}$ and $f=\frac{{\alpha }_1{G}^n+{\beta }_1}{{\alpha }_2{G}^n+{\beta }_2}$. In addition, we have examined the evolutionary paths of energy density, pressure and EoS parameters in order to deduce the universe’s accelerating behavior. In order to verify the feasibility of our cosmological model, we also investigate the behavior of various energy conditions.

We point out that time’s arrow is naturally induced by quantum mechanical evolution, whenever the systems have a very large number $\mathcal{𝒩}$ of nondegenerate states and a Hamiltonian bounded from below. When $\mathcal{𝒩}$ is finite, the arrow is imperfect, since evolution can resurrect past states. In the limit $\mathcal{𝒩}\to \infty$ the arrow is fixed by the “tooth of time”: the decay of excited states induced by spontaneous emission to the ground state, mediated by interactions and a large number of decay products which carry energy and information to infinity. This applies to individual isolated atoms, and does not require a coupling to a separate large heath bath.

Future research studies of cosmic microwave background (CMB) polarization seem likely to provide a more improved upper bound of $r\le 0$.03 on the tensor-to-scalar ratio (r). In this work, we present the reheating predictions of mutated hilltop inflation (MHI). We find that the model is well consistent with combined Planck+BK18+BAO observations over a range of effective equation of state (EoS) (${\overline{\omega }}_{\mathrm{\text{rh}}}$) and model parameter ($\mu$). For lower values of $\mu$, MHI generates considerably smaller r compared to normal hilltop potential by lying well within the observational bounds, making MHI a better choice as per recent and future observational studies.