Fourth quark-lepton generation and precision measurements

TL;DR

This paper shows that adding a fourth quark-lepton generation can be consistent with precision electroweak measurements if the new particles are sufficiently heavy, challenging previous constraints on new physics models.

Contribution

It demonstrates that a fourth generation of fermions can satisfy electroweak precision constraints without requiring light new particles.

Findings

A fourth generation is compatible with Z, W, and top quark measurements.

Heavy masses for new particles still satisfy electroweak constraints.

Challenges previous assumptions about mass bounds for new fermions.

Abstract

Precise measurements of Z-boson parameters and W-boson and t-quark masses put strong constraints on non SU(2) * U(1) singlet New Physics. We demonstrate that one extra generation passes electroweak constraints even when all new particle masses are well above their direct mass bounds.