Novel mechanism for CMB modulation in the Standard Model

TL;DR

This paper introduces a new indirect modulation mechanism in the Standard Model with right-handed neutrinos, showing it can generate large CMB anisotropies and impose bounds on Higgs and neutrino parameters.

Contribution

It proposes and analyzes the 'indirect modulation' mechanism for CMB anisotropy generation within the Standard Model framework.

Findings

The mechanism can produce perturbations four orders of magnitude larger than observed.

It establishes a lower bound on the Higgs quartic coupling.

It constrains neutrino Yukawa couplings to be below unity.

Abstract

We demonstrate that light spectator fields can source sizeable CMB anisotropies through modulated reheating even in the absence of direct couplings to the inflaton. The effect arises when the phase space of the inflaton decay is modulated by the spectator which generates masses for the decay products. We call the mechanism \textit{indirect modulation} and show that it can source perturbations even four orders of magnitude larger than the observed. Importantly, the indirect mechanism is present in the Standard Model extended with right-handed neutrinos. For a minimally coupled Higgs boson this leads to a novel lower bound on the quartic coupling and constrains the neutrino Yukawas below unity.