Implications of the discovery of a Higgs boson with a mass of 125 GeV

TL;DR

The paper explores the implications of discovering a 125 GeV Higgs boson for various theoretical models, analyzing constraints from flavor physics, electroweak symmetry breaking, and vacuum stability, with potential signals for LHC discovery.

Contribution

It provides a comprehensive analysis of how a 125 GeV Higgs constrains models like supersymmetry and composite Higgs, emphasizing flavor symmetry and vacuum stability implications.

Findings

Certain models can accommodate a 125 GeV Higgs with new particles accessible at the LHC.

The Higgs quartic coupling near criticality suggests the electroweak vacuum may be metastable.

Constraints from flavor physics and electroweak precision tests narrow down viable models.

Abstract

The rather precise knowledge of the mass of the Higgs boson and of its couplings has important consequences for the physical phenomena taking place at the Fermi scale. We analyze some of these implications in the most motivated frameworks for physics at that energies - supersymmetry, models of a composite Higgs boson, and the Standard Model itself. At the same time, precision experiments in flavour physics require a highly non-generic structure of flavour and CP transitions. In any model of electroweak symmetry breaking with a relatively low scale of new phenomena, as motivated by naturalness, some mechanism has to be found in order to keep unwanted flavour effects under control. We devote particular attention to the consequences of the approximate U(2)^3 symmetry exhibited by the quarks of the Standard Model. The combined analysis of the indirect constraints from flavour, Higgs and electroweak physics will allow us to outline a picture of some most natural models of physics near the Fermi scale. Although non trivially, a few models emerge that look capable of accommodating a 125 GeV Higgs boson, consistently with all the other constraints, with new particles in an interesting range for discovery at the LHC, as well as associated flavour signals. This is particularly interesting in view of the forthcoming improvements in the direct experimental investigation of that energies. Finally, the measurement of the last parameter of the Standard Model - the Higgs quartic coupling - has important consequences even if no new physics is present close to the Fermi scale: its near-critical value, which puts the electroweak vacuum in a metastable state close to a phase transition, may have an interesting connection with Planck-scale physics. We derive the bound for electroweak vacuum stability with full two-loop precision, and explore some possible implication of near-criticality.