Sounds Discordant: Classical Distance Ladder and ΛCDM-based Determinations of the Cosmological Sound Horizon

Abstract

Type Ia supernovae, calibrated by classical distance ladder methods, can be used, in conjunction with galaxy survey two-point correlation functions, to empirically determine the size of the sound horizon r s. Assumption of the ΛCDM model, together with data to constrain its parameters, can also be used to determine the size of the sound horizon. Using a variety of cosmic microwave background (CMB) data sets to constrain ΛCDM parameters, we find the model-based sound horizon to be larger than the empirically determined one with a statistical significance of between 2σ and 3σ, depending on the data set. If reconciliation requires a change to the cosmological model, we argue that change is likely to be important in the two decades of scale factor evolution prior to recombination. Future CMB observations will therefore likely be able to test any such adjustments; e.g., a third-generation CMB survey like SPT-3G can achieve a threefold improvement in the constraints on r s in the ΛCDM model extended to allow additional light degrees of freedom.

A Future Percent-level Measurement of the Hubble Expansion at Redshift 0.8 with Advanced LIGO

“…This demonstrates an absolute distance measure to z 0.8 at percent-level precision; combining this inference on H(z) with other data sets such as observations of baryon acoustic oscillations (Aubourg et al 2015) or Type Ia supernovae (Scolnic et al 2018) can translate this absolute distance measure to other redshifts (at z = 0 it would correspond to an uncertainty on H 0 of ±2.0 km s −1 Mpc −1 ) (Aubourg et al 2015;Cuesta et al 2015;Feeney et al 2019). For example, one can independently calibrate the Type Ia supernova distance scale without a distance ladder (Feeney et al 2019;Scolnic et al 2018), or compare the GW-determined distance scale with one derived from the photon-baryon sound horizon (Cuesta et al 2015;Aylor et al 2019) in the early universe (Planck Collaboration et al 2016) or at late times (Aubourg et al 2015). Our anticipated constraint on H(z) at the pivot redshift z 0.8 is about a factor of two wider than the per-bin anticipated constraint from the contemporaneous DESI (DESI Collaboration et al 2016) at comparable redshifts (the combined constraint from DESI is about a factor of three better than the per-bin constraint, or a factor of six better than our anticipated measurement).…”

Early Dark Energy from Massive Neutrinos as a Natural Resolution of the Hubble Tension

“…To illustrate this mechanism, consider a simple model for EDE coupled to a single neutrino species via a conformal coupling to the metricg µν = e 2β φ M pl g µν . (One could extend this theory to one with several different couplings 1 The field need not lie strictly at its minimum in order for this mechanism to be effective. Alternatively, the field might initially be over-damped but then be kicked up the potential to a new position where its mass is larger than the Hubble parameter.…”

Gravity in the infrared and effective nonlocal models

“…The minimal RT model differs a bit more, and in particular predicts a slightly higher value of H 0 , which in any case is not enough to significantly relieve the tension with the local H 0 measurement [137,138]. Indeed, as discussed in [139,140], it might not be possible to solve the H 0 tension, together with other potential tensions within ΛCDM, with a modification of only the late-Universe dynamics (as in our nonlocal model). The other difference of the minimal RT model is that it predicts a non-zero value for the sum of the neutrino masses, while all other models considered only give an upper bound.…”