Observational Evidence for Cosmological-Scale Extra Dimensions

TL;DR

This paper suggests that cosmological observations indicating faster structure formation and anomalies in CMB data can be explained by models with large extra dimensions affecting gravity on cosmological scales.

Contribution

It introduces a model with infinite-volume extra dimensions where a resonance graviton mediates an additional scalar force, explaining several large-scale cosmological anomalies.

Findings

Explains excess power in Lyman-alpha and CMB data.

Accounts for large bulk flows and ISW cross-correlation anomalies.

Proposes a small graviton Compton wavelength of 300-600 Mpc.

Abstract

We present a case that current observations may already indicate new gravitational physics on cosmological scales. The excess of power seen in the Lyman-alpha forest and small-scale CMB experiments, the anomalously large bulk flows seen both in peculiar velocity surveys and in kinetic SZ, and the higher ISW cross-correlation all indicate that structure may be more evolved than expected from LCDM. We argue that these observations find a natural explanation in models with infinite-volume (or, at least, cosmological-size) extra dimensions, where the graviton is a resonance with a tiny width. The longitudinal mode of the graviton mediates an extra scalar force which speeds up structure formation at late times, thereby accounting for the above anomalies. The required graviton Compton wavelength is relatively small compared to the present Hubble radius, of order 300-600 Mpc. Moreover, with certain assumptions about the behavior of the longitudinal mode on super-Hubble scales, our modified gravity framework can also alleviate the tension with the low quadrupole and the peculiar vanishing of the CMB correlation function on large angular scales, seen both in COBE and WMAP. This relies on a novel mechanism that cancels a late-time ISW contribution against the primordial Sachs-Wolfe amplitude.