Events Daily

Friday, April 28, 2023

Building locally finite two-loop QCD amplitudes
Babis Anastasiou, ETH Zurich
Event Type: Informal HEP Talk
Time: 2:00 PM - 3:15 PM
Location: 726 Broadway, 940, CCPP Seminar
Abstract: The Large Hadron Collider (LHC) experiments have remarkable statistical power that enables the observation and study of rare processes. Measurements of hard scattering in hadron collisions with multiple electroweak bosons, heavy quarks, or jets in the final state play a critical role in testing the Standard Model and constraining its extensions. In the last five years, significant progress has been made in deriving next-to-next-to-leading-order (NNLO) cross-sections for these complex processes, but the computational cost remains a challenge. In this presentation, we introduce a novel approach for computing necessary two-loop amplitudes based on QCD factorization. We discuss the origin of infrared singularities in QCD Feynman diagrams and how they can be organized into universal factors in QCD amplitudes. We demonstrate that we can identify these infrared singular factors in a class of two-loop QCD amplitudes, subtracting them from the integrand and leading to finite expressions for the physically significant and process-dependent factor of the amplitude that describes the hard scattering process. The latter can be computed with numerical methods, which is a complementary approach to traditional analytic or semi-analytic methods. This work represents the first example of a subtraction method for QCD amplitudes beyond the next-to-leading-order and paves the way for building the next generation of computer algorithms for high-precision theoretical predictions in QCD.

Link to the Event Video

Event Type: HEP Discussion Sessions
Time: 3:30 PM - 5:30 PM
Location: 726 Broadway, 901, Sm Conf

Conformal field theory at large fermion charge
Simeon Hellerman, IPMU
Event Type: Informal HEP Talk
Time: 4:00 PM - 5:30 PM
Location: 726 Broadway, 940, CCPP Seminar
Abstract: Recent years have seen a systematic study of conformal field theories at large quantum number, finding a pattern of semiclassicalization of the theory in low-lying states of large quantum number, even when the underlying theory is strongly coupled. Most concrete analyses so far have considered the case where all the large quantum number is carried by bosonic fields; in essentially all these cases the large-charge ground state is in some kind of superfluid phase or closely related effective description. In this talk I will describe recent results on theories in which fermions carry the charge of interest. In some cases the large-charge ground state is described by a superfluid; in some cases it is described by a fermi surface, either exactly or to all orders in perturbation theory. I will discuss some implications of these results.

Link to the Event Video