Amplitudes, sum rules and positivity bounds in the SMEFT

by Dr Jiayin Gu (Johannes Gutenberg University Mainz)

Tuesday 9 Mar 2021, 10:00 → 11:00 Asia/Shanghai

Tsung-Dao Lee library/Fourth Floor-410 - 410# Meeting Room (Tsung-Dao Lee Library)

Abstract: 

The dispersion relation of an elastic 4-point amplitude in the forward direction leads to a sum rule that connects the low energy amplitude to the high energy observables.  We discuss the implication of these sum rules on the dimension-6 operators in the SMEFT, and point out their interesting connections with the custodial symmetry of the SM Higgs and fermion sectors.  These dispersion relations also lead to positivity bounds on certain dimension-8 operator coefficients.  While these dimension-8 operators are generally difficult to probe, we point out a special channel, e+e-  ->  gamma gamma, for which the leading contribution comes from dimension-8 operators, and the corresponding positivity bounds can be directly probed.   We also demonstrate the usefulness of the helicity amplitude formalism in both cases. 

Biography：

Jiayin Gu obtained his PhD at the University of California, Davis in 2014.  He has worked as a postdoctoral researcher at IHEP, DESY and is now at Johannes Gutenberg University Mainz.  In recent years, his work mainly focuses on the Standard Model Effective Field Theory (SMEFT) and its applications on precision Higgs and electroweak measurements at future colliders.  He is also an active contributor to various future collider projects, with a major contribution to the EFT analysis in the CEPC conceptual design report.

Meeting room:  https://zoom.com.cn/j/93579891950 

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sumpos4.pdf