Positivity Bounds on Dark Energy: When Matter Matters

Understand

Positivity bounds - constraints on any low-energy effective field theory imposed by the fundamental axioms of unitarity, causality and locality in the UV - have recently been used to constrain scalar-tensor theories of dark energy.

• However, the coupling to matter fields has so far played a limited role.
• We show that demanding positivity when including interactions with standard matter fields leads to further constraints on the dark energy parameter space.
• We demonstrate how implementing these bounds as theoretical priors affects cosmological parameter constraints and explicitly illustrate the impact on a specific Effective Field Theory for dark energy.