Two-loop renormalization group profile of the standard model and a new generation

TL;DR

This paper analyzes the two-loop renormalization group behavior of the Standard Model, exploring Higgs mass constraints, the impact of an additional chiral generation, and the viability of a vector-like generation within experimental bounds.

Contribution

It provides a detailed two-loop profile of the Standard Model with new bounds on the Higgs mass and explores the implications of adding a new chiral generation or a vector-like pair.

Findings

Higgs mass must be between 140.7 and 161.3 GeV for Planck-scale cutoff.

A single new chiral generation is excluded under current experimental constraints.

A pair of chiral generations forming a vector-like pair could exist.

Abstract

The two-loop renormalization group global profile of the Standard Model (SM) in its full parameter space is investigated. Restrictions on the Higgs boson mass as a function of a cutoff scale are obtained from the stability of the electroweak vacuum and from the perturbative validity both in the Higgs and Yukawa sectors. The cutoff equal to the Planck scale requires the Higgs mass to be M=(161.3+-20.6)+4-10 GeV and M>=140.7+-10 GeV, where the M corridor is the theoretical one and the errors are due to the top mass uncertainty. Modification of the two-loop global profile of the SM extended by one new chiral generation is studied, and bounds on the masses of the generation are derived. Under the precision experiment restriction M<=200 GeV, the forth chiral generation, taken alone, is excluded. Nevertheless a pair of the chiral generations constituing the vector-like one could exist.