Once more on the W-loop contribution to the Higgs decay into two photons

TL;DR

This paper revisits the W-loop contribution to Higgs decay into two photons, providing a finite, unambiguous amplitude calculation that suggests a smaller decay rate than observed, hinting at potential new physics.

Contribution

It offers a new, dispersion-based calculation of the W-loop amplitude that challenges previous assumptions and results in a different decay rate prediction.

Findings

Finite and unambiguous imaginary part of the amplitude

Reproduces the GWW amplitude via dispersion integral

Predicts a smaller Higgs to two photons decay rate than current observations

Abstract

The imaginary part of the Feynman amplitude of the $W$-loop contribution to the Higgs decay into two gammas (viewed as a function of the square of the off shell Higgs momentum) is finite and unambiguous. It is presented as the product of an invariant amplitude ${\cal A}$ times a bilinear in the components of the (on shell) photon momenta factor which takes the Ward identity into account. The unsubtracted dispersion integral of ${\cal A}$ is convergent and reproduces the amplitude computed by R. Gastmans, S.L. Wu and T.T. Wu [GWW]. In particular, the decoupling theorem, criticized as an unjustified assumption in a subsequent paper [SVVZ12], is obtained as a corollary. By contrast with the currently used value (computed in [SVVZ]) our calculation provides a smaller Higgs decay rate into 2 photons than the currently observed. If accepted as a true prediction of the Standard Model, it would be a first indication for the need of a New Physics.