Relaxing cosmological tensions with a sign switching cosmological constant

Abstract

Inspired by the recent conjecture that the universe has transitioned from AdS vacua to dS vacua in the late universe made via graduated dark energy, we extend the standard ΛCDM model by a cosmological 'constant' (Λs) that switches sign at certain redshift, z † , and name it as ΛsCDM. We discuss in detail the construction and theoretical features of this model, and find out that, when the consistency of the ΛsCDM model with the cosmic microwave background (CMB) data is ensured, (i) z † 1.1 is implied by the condition that the universe monotonically expands, (ii) H0 is inversely correlated with z † and reaches ≈ 74.5 km s −1 Mpc −1 for z † = 1.5, (iii) H(z) presents an excellent fit to the Ly-α measurements provided that z † 2.34. We further investigate the model constraints by using the full Planck CMB data, with and without baryon acoustic oscillations (BAO) data. We find that the CMB data alone does not constrain z † but CMB+BAO dataset favors the sign switch of Λs providing the constraint: z † = 2.44 ± 0.29 (68% CL). Our analysis reveals that the lower and upper limits of z † are controlled by the Galaxy and Ly-α BAO measurements, respectively, and the larger z † values imposed by the Galaxy BAO data prevent the model from achieving the highest local H0 measurements. In general, the ΛsCDM model (i) relaxes the so-called H0 tension while being fully consistent with the TRGB measurement, (ii) removes the discrepancy with the Ly-α measurements, (iii) relaxes the so-called S8 tension, and (iv) finds a better agreement with the BBN constraints of physical baryon density. We find no strong statistical evidence to discriminate between the ΛsCDM and ΛCDM models. However, interesting and promising features of the ΛsCDM model, as turned out in our study, provide an upper edge over ΛCDM.

Dynamical analysis of logarithmic energy-momentum squared gravity

“…We have carried out the dynamical system analysis of a cosmological model in the energy-momentum squared gravity (EMSG) described by the functional f (T µν T µν ) = α ln(λT µν T µν ), which is known as energymomentum log gravity (EMLG) [12]. In this model, the new terms in the right-hand side of the Einstein field equations yield a constant inertial mass density and provide a dynamical dark energy with a density passing below zero at large redshifts, accommodating a mechanism for screening Λ in the past, suggested for alleviating some cosmological tensions such as the H 0 tension [12] (see also [7,10,[32][33][34][35][36][37][38][39][40][41][42][43][44].…”

“…[7] (see also Refs. [8][9][10][11]), which considers the minimal dynamical deviation from the null inertial mass density (corresponding to the minimal deviation from simple-graduated dark energy) of the form ∝ ρ λ < 0 (where λ is a ratio of two odd integers).…”

“…That is, this model accommodates a mechanism for screening Λ in the past, suggested for alleviating some cosmological tensions. It has been reported that the H 0 tension-as well as a number of other low-redshift discrepancies-may be alleviated by a dynamical dark energy that assumes negative or vanishing energy density values at high redshifts [7,10,[32][33][34][35][36][37][38][39][40][41][42]. See also Ref.…”

Towards early dark energy and $n_s$=1 with Planck, ACT and SPT

“…In an AdS phase with w > 1 the energy of EDE can redshift faster than that in oscillation phase, thus results less destruction to other measurement. 2 It is well-known that AdS vacua is ubiquitous in high energy theories, so the AdS-EDE model can be well-motivated, see also the applications of AdS vacua to late Universe [36][37][38][39][40][41][42].…”

Model selection applied to non-parametric reconstructions of the Dark Energy

“…Similarly, there have been, although not as many as for the equation of state (EoS), parameterizations for the dark energy density, i.e. the Generalised Emergent Dark Energy (GEDE) [16,22,23], the Graduated Dark Energy (gDE) [24][25][26], the Early Dark Energy (EDE) [27] and the Energy-Momentum Log-gravity (EMLG) [28]. Generally, in these models it can be obtained an associated EoS but the main assumptions come from the density, that is, the GEDE considers directly the evolution of the density parameter, and in the gDE model an inertial mass density is introduced which allows a possible transition to negative effective energy densities.…”