Unanswered Questions in the Electroweak Theory

TL;DR

This paper reviews the current status of the electroweak theory before LHC experiments, highlighting the unconfirmed Higgs boson prediction, experimental constraints, and alternative symmetry-breaking mechanisms.

Contribution

It provides a comprehensive overview of electroweak theory, its experimental tests, and discusses potential new physics needed at the TeV scale.

Findings

Electroweak theory predicts a Higgs boson with mass less than 200 GeV.

Experimental tests have confirmed many aspects of the theory.

Alternative mechanisms for electroweak symmetry breaking are considered.

Abstract

This article is devoted to the status of the electroweak theory on the eve of experimentation at CERN's Large Hadron Collider. A compact summary of the logic and structure of the electroweak theory precedes an examination of what experimental tests have established so far. The outstanding unconfirmed prediction of the electroweak theory is the existence of the Higgs boson, a weakly interacting spin-zero particle that is the agent of electroweak symmetry breaking, the giver of mass to the weak gauge bosons, the quarks, and the leptons. General arguments imply that the Higgs boson or other new physics is required on the TeV energy scale. Indirect constraints from global analyses of electroweak measurements suggest that the mass of the standard-model Higgs boson is less than 200 GeV. Once its mass is assumed, the properties of the Higgs boson follow from the electroweak theory, and these inform the search for the Higgs boson. Alternative mechanisms for electroweak symmetry breaking are reviewed, and the importance of electroweak symmetry breaking is illuminated by considering a world without a specific mechanism to hide the electroweak symmetry. For all its triumphs, the electroweak theory has many shortcomings. . . .