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EPP Theory Seminar: Soft-collinear gravity: an emergent gauge symmetry and the soft theorem - Patrick Hager (TUM)

Abstract: 
Soft theorems give important insights into the all-order structure of Quantum Field Theory,
revealing universal properties of soft radiation.
Since the fundamental work of Low, Burnett, Kroll, and Weinberg, proving the universal behaviour of soft emission
by identifying the leading and subleading terms in the soft momentum expansion,
there have been many advances in the study of next-to-soft terms. 
For instance, in the gravitational case, the use of amplitude methods recently revealed the existence of a third, sub-subleading term.
In addition, potent effective theories, like soft-collinear effective theory, are now available for gauge theory,
which can shed light on the origin of these theorems.
 
In this talk, I outline the construction of the subleading soft-collinear Lagrangian for gravity, in the position-space formalism, 
emphasizing the fundamental role played by the gravitational gauge symmetry.
From the EFT point of view, the soft theorems are then an immediate implication of the emergent soft gauge symmetry
and can already be identified at the Lagrangian level. I explain how these theorems arise in both the gauge-theory and gravitational case 
and how the soft gauge symmetry in the effective theory constrains these emissions.
In this way, soft-collinear effective theory provides an intuitive explanation for both the form as well as the number of universal terms.

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