Open Access Publications from the University of California

## New vector-like fermions and flavor physics

• Author(s): Ishiwata, K
• Ligeti, Z
• Wise, MB
• et al.

## Published Web Location

https://doi.org/10.1007/JHEP10(2015)027
Abstract

© 2015, The Author(s). Abstract: We study renormalizable extensions of the standard model that contain vector-like fermions in a (single) complex representation of the standard model gauge group. There are 11 models where the vector-like fermions Yukawa couple to the standard model fermions via the Higgs field. These models do not introduce additional fine-tunings. They can lead to, and are constrained by, a number of different flavor-changing processes involving leptons and quarks, as well as direct searches. An interesting feature of the models with strongly interacting vector-like fermions is that constraints from neutral meson mixings (apart from CP violation in K0−K¯0$${K}^0-{\overline{K}}^0$$ mixing) are not sensitive to higher scales than other flavor-changing neutral-current processes. We identify order 1/(4πM)2(where M is the vector-like fermion mass) one-loop contributions to the coefficients of the four-quark operators for meson mixing, that are not suppressed by standard model quark masses and/or mixing angles.