Positivity Bounds on Higgs-Portal Dark Matter

TL;DR

This paper uses positivity bounds on higher-dimensional operators to constrain Higgs-portal dark matter models, revealing parameter space restrictions and potential observable cosmic ray signals from dark matter annihilation.

Contribution

It introduces the application of positivity bounds to effective Higgs-portal dark matter models up to dimension-8 operators, providing new theoretical constraints.

Findings

Positivity bounds exclude certain effective couplings unconstrained by phenomenology.

Relic density, detection experiments, and positivity bounds together restrict parameter space.

Potential cosmic ray signals from dark matter annihilation are predicted.

Abstract

We consider the positivity bounds for WIMP scalar dark matter with effective Higgs-portal couplings up to dimension-8 operators. Taking the superposed states for Standard Model Higgs and scalar dark matter, we show that the part of the parameter space for the effective couplings, otherwise unconstrained by phenomenological bounds, is ruled out by the positivity bounds on the dimension-8 derivative operators. We find that dark matter relic density, direct and indirect detection and LHC constraints are complementary to the positivity bounds in constraining the effective Higgs-portal couplings. In the effective theory obtained from massive graviton or radion, there appears a correlation between dimension-8 operators and other effective Higgs-portal couplings for which the strong constraint from direct detection can be evaded. Nailing down the parameter space mainly by relic density, direct detection and positivity bounds, we find that there are observable cosmic ray signals coming from the dark matter annihilations into a pair of Higgs bosons, $WW$ or $ZZ$.