Oct 2022 - Sept 2023
# Dave Sutherland: Geometric maps from the action to the S-matrix

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Europe/London

OC218
### OC218

Description

In (effective) field theories, the lagrangian has a field

redefinition redundancy, meaning many different lagrangians can generate

the same amplitudes. Just like gauge redundancy in a gauge theory, this

makes the map from lagrangians to amplitudes difficult: observable

physics is obscured behind a combinatorially large set of Feynman

diagrams, each of them unphysical, and of which pieces will generally

cancel against each other.

I will describe briefly how - in a scalar field theory - concepts from

geometry can cut through this noise by a) identifying field redefinition

invariant quantities in lagrangians that map neatly onto coefficients in

amplitudes and b) identifying one of the many equivalent lagrangians

that is objectively better for calculating amplitudes.