Positivity Bounds: Building UV/IR Connections Using Scattering Amplitudes

The Effective Field Theory (EFT) framework has proven immensely successful in both particle physics and cosmology, providing a means of describing low-energy observations in the IR without reference to the (as yet unknown) high-energy physics in the UV.
But this decoupling of the UV from the IR also presents a major obstacle to uncovering new fundamental physics beyond the Standard Model and LambdaCDM - since it is not possible to probe the relevant energy scales directly, it is difficult to go beyond our low-energy effective descriptions.

In this talk, I will present new developments in overcoming this obstacle.
Certain fundamental properties in the UV (such as causality, locality and unitarity) leave characteristic imprints on the EFT scattering amplitude in the IR. These imprints, known as “positivity bounds”, can be used to bridge the gap between the UV and IR regimes.
I will show how features of the UV can be inferred from our low-energy measurements, and conversely how UV axioms can be used as priors to improve our IR parameter estimation of EFT coefficients.
These “positivity” connections between the UV and IR regimes provide us with a new way of analysing low-energy EFTs that will guide us towards a better understanding of the new physics which lies beyond our current models.

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