Enhanced Peculiar Velocities in Brane-Induced Gravity

TL;DR

This paper demonstrates that brane-induced gravity theories can significantly increase peculiar velocities and the likelihood of high-velocity merging systems like the Bullet Cluster, addressing anomalies challenging the LCDM model.

Contribution

It introduces brane-induced gravity as a modification to general relativity that explains large-scale velocity anomalies and increases the probability of rare cosmic events.

Findings

Peculiar velocities are enhanced by 24-34% in these theories.

The probability of the Bullet Cluster occurrence is increased by a factor of 10^4.

The anomalies are nearly consistent with observations at the 2 sigma level.

Abstract

The mounting evidence for anomalously large peculiar velocities in our Universe presents a challenge for the LCDM paradigm. The recent estimates of the large scale bulk flow by Watkins et al. are inconsistent at the nearly 3 sigma level with LCDM predictions. Meanwhile, Lee and Komatsu have recently estimated that the occurrence of high-velocity merging systems such as the Bullet Cluster (1E0657-57) is unlikely at a 6.5-5.8 sigma level, with an estimated probability between 3.3x10^{-11} and 3.6x10^{-9} in LCDM cosmology. We show that these anomalies are alleviated in a broad class of infrared-modifed gravity theories, called brane-induced gravity, in which gravity becomes higher-dimensional at ultra large distances. These theories include additional scalar forces that enhance gravitational attraction and therefore speed up structure formation at late times and on sufficiently large scales. The peculiar velocities are enhanced by 24-34% compared to standard gravity, with the maximal enhancement nearly consistent at the 2 sigma level with bulk flow observations. The occurrence of the Bullet Cluster in these theories is 10^4 times more probable than in LCDM cosmology.