The Z decay width in the SMEFT: y t and λ corrections at one loop
Abstract
We calculate one loop y t and λ dependent corrections to {\overline{Γ}}Z,{\overline{R}}_f^0 and the partial Z widths due to dimension six operators in the Standard Model Effective Field Theory (SMEFT), including finite terms. We assume CP symmetry and a U(3)5 symmetry in the UV matching onto the dimension six operators, dominantly broken by the Standard Model Yukawa matrices. Corrections to these observables are predicted using the input parameters {{\widehat{α}}_{ew},{\widehat{M}}_Z,{\widehat{G}}_F,{\widehat{m}}_t,{\widehat{m}}_h} extracted with one loop corrections in the same limit. We show that at one loop the number of SMEFT parameters contributing to the precise LEPI pseudo-observables exceeds the number of measurements. As a result the SMEFT parameters contributing to LEP data are formally unbounded when the size of loop corrections are reached until other data is considered in a global analysis. The size of these loop effects is generically a correction of order ∼ % to leading effects in the SMEFT, but we find multiple large numerical coefficients in our calculation at this order. We use a \overline{MS} scheme, modified for the SMEFT, for renormalization. Some subtleties involving novel evanescent scheme dependence present in this result are explained.
- Publication:
-
Journal of High Energy Physics
- Pub Date:
- March 2017
- DOI:
- 10.1007/JHEP03(2017)060
- arXiv:
- arXiv:1611.09879
- Bibcode:
- 2017JHEP...03..060H
- Keywords:
-
- Effective field theories;
- Beyond Standard Model;
- High Energy Physics - Phenomenology
- E-Print:
- 38 pages + refs, 11 figures, v3: Acknowledgement updated with grant numbers