Hubble sinks in the low-redshift swampland

Abstract

Local determinations of the Hubble constant H0 favour a higher value than Planck based on CMB and ΛCDM. Through a model-independent expansion, we show that low redshift (z 0.7) data comprising baryon acoustic oscillations (BAO), cosmic chronometers and Type Ia supernovae has a preference for Quintessence models that lower H0 relative to ΛCDM. In addition, we confirm that an exponential coupling to dark matter cannot alter this conclusion in the same redshift range. Our results leave open the possibility that a coupling in the matter-dominated epoch, potentially even in the dark ages, may yet save H0 from sinking in the string theory Swampland.

Cosmology of linear Higgs-sigma models with conformal invariance

“…In this case, there is a transition from the early period with Ω χ = 0, the effective equation of state given by w eff = w m but undetermined w, towards the cosmic acceleration with Ω χ = 1 and w = −1 + c 2 /3 for c 2 < 2 [23][24][25]. We remark that there was a recent discussion on the lower value of the Hubble constant H 0 in quintessence-like models as compared to ΛCDM [26,27], which would make the tension with the local determinations more serious.…”

A stringy perspective on the coincidence problem

“…For β ∼ O(1), this will occur within at most ln[M Pl /H 0 ln(M Pl /H 0 ))] ∼ 143 Hubble times, so our conclusions are unchanged, and the coincidence problem isn't as serious as we previously thought. Of course, the de Sitter conjecture is less well established than the distance conjecture, and, in the simplest scenarios, may even be at odds with local measurements of H 0 [64]. With this in mind, what can we say if we deny the validity of both criteria (2.2) and (2.3) and abandon the de Sitter conjecture altogether?…”

Reheating in holographic cosmology and connecting to Λ-MSSM constructions for particle physics

“…Moreover, for times t > t 0 , meaning in field theory energies U > U 0 , there are no more degrees of freedom "added in" (when going to the IR, we lose degrees of freedom, when going to the UV, we add them), so c is constant, and then by the formula from the previous subsection, Λ is also constant. Note also that experimentally, a (true) cosmological constant is better than quintessence (varying potential), in particular it solves better the Hubble tension (tension in measurement of H 0 at different scales), see [29].…”