Towards consistent Electroweak Precision Data constraints in the SMEFT

• Published in: The journal of high energy physics Vol. 2015; no. 5; p. 1
• Main Authors: Berthier, Laure, Trott, Michael
• Format: Journal Article
• Language: English
• Published: Berlin/Heidelberg Springer Berlin Heidelberg 01.05.2015; Springer Nature B.V
• Subjects: Classical and Quantum Gravitation; Elementary Particles; High energy physics; Physics; Physics and Astronomy; Quantum Field Theories; Quantum Field Theory; Quantum Physics; Regular Article - Theoretical Physics; Relativity Theory; String Theory; Beyond Standard Model; Effective field theories
• ISSN: 1029-8479; 1029-8479
• DOI: 10.1007/JHEP05(2015)024

A bstract We discuss the impact of many previously neglected effects of higher dimensional operators when fitting to Electroweak Precision data (EWPD) in the Standard Model Effective Field Theory (SMEFT). We calculate the general case of 2 → 2 fermion scattering in the SMEFT to order O v T / Λ 2 valid on and off the Z pole, in the massless fermion limit. We demonstrate that previously neglected corrections scale as Γ Z M Z / v ¯ T 2 in the partial widths extracted from measured cross sections at LEPI, compared to the leading effect of dimension six operators in anomalous Z couplings. Further, constraints on leading effects of anomalous Z couplings are also modified by neglected perturbative corrections and dimension eight operators. We perform a minimal EWPD fit to illustrate the size of the error these corrections induce, when bounding leading effects. These considerations relax bounds compared to a naive leading order analysis, and show that constraints that rise above the percent level are subject to substantial theoretical uncertanties. We also argue that renormalization group running global constraints expressed through χ 2 functions to a common scale, and then minimizing and performing a global fit of all data allows more consistent constraints to be obtained in the SMEFT.