Electroweak precision constraints on the Lee-Wick Standard Model

TL;DR

This paper analyzes electroweak precision constraints on the Lee-Wick Standard Model, showing that the model generally predicts large positive S and negative T parameters, with certain parameter choices allowing lighter Lee-Wick fermions at the cost of fine-tuning.

Contribution

The study provides a detailed analysis of electroweak constraints on the Lee-Wick Standard Model and proposes an extension with a fourth fermion generation to relax these constraints.

Findings

Lee-Wick scale around 5 TeV for all masses equal

Light fermionic states as low as 2.4-3.5 TeV possible with heavier other masses

Extended model with fourth generation allows lighter Lee-Wick fermions (0.4-1.5 TeV)

Abstract

We perform an analysis of the electroweak precision observables in the Lee-Wick Standard Model. The most stringent restrictions come from the S and T parameters that receive important tree level and one loop contributions. In general the model predicts a large positive S and a negative T. To reproduce the electroweak data, if all the Lee-Wick masses are of the same order, the Lee-Wick scale is of order 5 TeV. We show that it is possible to find some regions in the parameter space with a fermionic state as light as 2.4-3.5 TeV, at the price of rising all the other masses to be larger than 5-8 TeV. To obtain a light Higgs with such heavy resonances a fine-tuning of order a few per cent, at least, is needed. We also propose a simple extension of the model including a fourth generation of Standard Model fermions with their Lee-Wick partners. We show that in this case it is possible to pass the electroweak constraints with Lee-Wick fermionic masses of order 0.4-1.5 TeV and Lee-Wick gauge masses of order 3 TeV.