No Miracle in Gravity Portals

TL;DR

This paper critically examines the gravity portal model for dark matter, revealing that previous claims of enhanced decay rates are canceled out, showing decay rates are actually suppressed by the strong coupling scale.

Contribution

The study corrects prior misconceptions by demonstrating that decay rate enhancements in the gravity portal model are canceled, emphasizing the importance of proper amplitude calculations.

Findings

Decay rates are suppressed by the strong coupling scale.

No significant phenomenological signatures from decay rate enhancement.

Previous claims of large decay rates due to longitudinal gauge bosons are invalid.

Abstract

The idea of dark matter particles coupled only gravitationally is minimalist yet viable. Assuming an additional $Z_2$-breaking linear coupling of scalar curvature to the dark matter scalar (gravity portal) Refs. arXiv:1603.03696 and arXiv:1611.00725 claimed a strong parametric growth of the dark matter particle decay rate with its mass, which implies pronounced phenomenological signatures for the model. This peculiarity was attributed by the authors to the enhancement due to the presence of longitudinal gauge bosons in the final state. Quite unfortunately there were overlooked cancellations in the tree-level amplitudes. There is no miracle: all perturbative decay rates are suppressed by the strong coupling scale.