ITP |
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Teilchentee SS 2024
Seminar at the Institute for Theoretical Physics, Heidelberg University
Thursdays at 16:15 in Room 106 Philosophenweg 12
Before each seminar, the speaker gives an informal pre-talk, introducing the MSc and PhD students at the ITP to the broader context of the topic of the seminar.
Pre-talks start at 15:30.
Organizers: Caroline Heneka, Aleksas Mazeliauskas, Ayodele Ore
Date: 20.06.24
Speaker: Valentin Hirschi (Bern)
Title: Local Unitarity: unite and conquer Infrared Divergences
Abstract
It is well-known that perturbative expansions of QFT observable suffer from infrared (IR) divergences both in the phase-space of real-emission contributions and in the loop amplitudes of virtual contributions. Traditionally, the two are handled separately through a combination of local subtraction counterterm and dimensional regularisation. Local Unitarity is an alternative formulation, using the Loop-Tree Duality (LTD) theorem, and leveraging the Kinoshita–Lee–Nauenberg (KLN) cancellation pattern to achieve a direct cancellation of real-emission and loop IR divergences at the local level. Together with an automated local renormalization procedure based on the R-operation (~local BPHZ), the resulting expression is locally finite and thus amenable to a fully numerical integration at arbitrary perturbative orders and for processes with final-state singularities only. I will present an overview of the various ingredients involved in that construction and the challenges awaiting my new group at the University of Bern. A special emphasis will be put on the following more recent developments: a) Efficient momentum-space parameterization using tropical sampling. b) Fast and stable LTD integrated evaluations using the cross-free family representation. c) Threshold regularization using a subtraction method instead of contour deformations.
