Reconstructing the Peculiar Velocity of the Local Group with Modified Gravity and 2MASS

TL;DR

This study tests if modified gravity theories can explain the mismatch between the Local Group's reconstructed velocity from galaxy surveys and the velocity inferred from the CMB dipole, finding they cannot.

Contribution

Introduces a formalism for calculating peculiar velocities in modified gravity theories and applies it to the Local Group using 2MASS data.

Findings

Modified gravity models do not resolve the velocity discrepancy.

Reconstructed velocities align with General Relativity predictions.

The angular difference remains unexplained by the considered theories.

Abstract

The peculiar velocity of the Local Group, reconstructed from inhomogeneities in the local density field, differs in direction and magnitude from the velocity inferred from the Cosmic Microwave Background dipole. We investigate whether generalized theories of gravity, which predict a modified growth of perturbations, are able to alleviate this discrepancy. We introduce a general formalism for calculating the real-space peculiar-velocity field for modified gravity and theories with interactions in the dark sector. For different classes of theories - scalar tensor and higher-dimensional gravity - we reconstruct the Local Group peculiar velocity using groups of galaxies identified in the 2MASS Redshift Survey. We show that, for realistic parameters, modifications to General Relativity cannot account for the angular discrepancy between the reconstructed Local Group velocity and the dipole in the Cosmic Microwave Background.