Revisiting a Negative Cosmological Constant from Low-Redshift Data

Abstract

Persisting tensions between high-redshift and low-redshift cosmological observations suggest the dark energy sector of the Universe might be more complex than the positive cosmological constant of the ΛCDM model. Motivated by string theory, wherein symmetry considerations make consistent AdS backgrounds (i.e. maximally symmetric spacetimes with a negative cosmological constant) ubiquitous, we explore a scenario where the dark energy sector consists of two components: a negative cosmological constant, with a dark energy component with equation of state w φ on top. We test the consistency of the model against low-redshift Baryon Acoustic Oscillation and Type Ia Supernovae distance measurements, assessing two alternative choices of distance anchors: the sound horizon at baryon drag determined by the Planck collaboration, and the Hubble constant determined by the SH0ES program. We find no evidence for a negative cosmological constant, and mild indications for an effective phantom dark energy component on top. A model comparison analysis reveals the ΛCDM model is favoured over our negative cosmological constant model. While our results are inconclusive, should low-redshift tensions persist with future data, it would be worth reconsidering and further refining our toy negative cosmological constant model by considering realistic string constructions.tions between dark matter particles, or between dark matter and baryons, could alleviate these issues (see e.g. [17][18][19][20][21][22][23][24][25][26][27][28][29][30][31] for an incomplete list of proposed models).

Rastall gravity extension of the standard $$\Lambda $$CDM model: theoretical features and observational constraints

“…This situation achieved for > 0 is of particular interest and tempting for its further theoretical and observational investigation, as it has recently been reported in [31][32][33][34][35][36][37][38][39][40][41][42][43][44] that a number of persistent low-redshift tensions, including the H 0 tension, may be alleviated by a dynamical DE that assumes negative energy density values (or in cosmological models wherein the cosmological constant is dynamically screened) at finite redshift (see Sect. 1).…”

“…For example, the value of the Hubble constant H 0 predicted by the cosmic microwave background (CMB) Planck data [2,5] within the framework of the standard CDM model is in serious disagreement with the direct local distance ladder measurements [23][24][25][26]. This tension becomes even more compelling as it worsens (relieves only partially) when the is replaced by the simplest minimally coupled single-field quintessence (phantom or quintom models), see [27][28][29][30] and [31] for further references. Surprisingly, it has been reported that the H 0 tension -as well as a number of other persistent low-redshift tensions -may be alleviated by a dynamical dark energy (DE) whose density can assume negative values or vanish at high redshifts [31][32][33][34][35][36][37][38][39][40][41][42][43][44].…”

“…This tension becomes even more compelling as it worsens (relieves only partially) when the is replaced by the simplest minimally coupled single-field quintessence (phantom or quintom models), see [27][28][29][30] and [31] for further references. Surprisingly, it has been reported that the H 0 tension -as well as a number of other persistent low-redshift tensions -may be alleviated by a dynamical dark energy (DE) whose density can assume negative values or vanish at high redshifts [31][32][33][34][35][36][37][38][39][40][41][42][43][44]. The fact that the CMB Planck data favor positive spatial curvature -which imitates a negative energy density source -on top of the standard CDM model in contrast to the inflationary paradigm might also be signaling a need for such DE sources [5] (see also [45][46][47]).…”

Is the Hubble tension a hint of AdS phase around recombination?

“…Theoretically, one possibility is modifying postrecombination physics, such as the dark energy or modified gravity models, e.g. [9][10][11][12][13][14][15][16][17][18][19][20]. Such solutions are constrained tightly by late-time observations [1].…”

Cosmology with Relativistically Varying Physical Constants

“…Thus the staggering feature of the varying physical constant model VcGΛ is that it yields negative dark-energy density while still showing accelerated expansion of the universe. Possibility of such a scenarios has been explored by many researchers [37][38][39][40] who considered the varying cosmological constant to primarily resolve Hubble constant tension, which is due to the difference in its values obtained from CMB data and SNe Ia data. Such a scenario is extremely interesting from the string theory perspective as obtaining a vacuum solution with a positive value of Λ within moduli-fixed consistent and stable string theory compactifications has been a formidable task 41-44 . It is even more staggering that the spatial curvature of the universe is strongly negative rather than flat and thus contradicts all the theories, and observations derived assuming invariant physical constants.…”