Higgs field

Higgs field. A fundamental scalar field thought to permeate all space, giving elementary particles their mass via the Higgs mechanism. Its existence is a cornerstone of the Standard Model of particle physics, and its associated quantum excitation, the Higgs boson, was confirmed by experiments at the Large Hadron Collider in 2012. The field's non-zero vacuum expectation value breaks the electroweak symmetry of the electroweak interaction, differentiating the photon from the W and Z bosons.

Overview

The concept emerged from theoretical work in the 1960s by several physicists, including Peter Higgs, François Englert, and Robert Brout, to explain the origin of mass within gauge theory. It is unique within the Standard Model as a scalar field with a non-zero value even in its lowest energy state. This property is central to the Brout-Englert-Higgs mechanism, which describes how gauge bosons acquire mass while preserving the renormalizability of the theory. The 2012 discovery of a new particle by the ATLAS and CMS collaborations at CERN provided direct evidence for its quantum manifestation.

Theoretical background

The development was driven by challenges in unifying the electromagnetic force with the weak nuclear force into a single electroweak theory proposed by Sheldon Glashow, Steven Weinberg, and Abdus Salam. A key problem was that naive gauge invariance seemed to require force-carrying particles like the W boson and Z boson to be massless, contradicting experimental data. In 1964, independent papers by Peter Higgs, and by François Englert and Robert Brout, introduced a mechanism involving a self-interacting scalar field. This work was later incorporated into a full model by Steven Weinberg and Abdus Salam, showing how the mechanism gives mass to both gauge bosons and fermions via Yukawa coupling.

Properties and effects

It is characterized by a Mexican hat potential, leading to spontaneous symmetry breaking of the electroweak symmetry when the universe cooled after the Big Bang. Its vacuum expectation value is approximately 246 GeV, setting the scale for electroweak interaction masses. The field couples to particles with different strengths, resulting in varied mass; for instance, the top quark interacts strongly, while the photon does not interact at all, remaining massless. These interactions are mediated by the exchange of virtual Higgs boson quanta. The field's properties also have implications for the stability of the vacuum and potential connections to cosmic inflation.

Experimental confirmation

The search for its associated particle, the Higgs boson, was a primary goal of particle accelerators like the Large Electron–Positron Collider and, ultimately, the Large Hadron Collider at CERN. On July 4, 2012, the ATLAS and CMS collaborations announced the observation of a new boson with a mass around 125 GeV. Subsequent analysis of decay channels into particles like photons, Z bosons, and W bosons confirmed its properties were consistent with predictions. The discovery led to the 2013 Nobel Prize in Physics being awarded to Peter Higgs and François Englert.

Implications and open questions

The confirmation solidified the theoretical structure of the Standard Model, but it also raised new questions about physics beyond the Standard Model. Its measured mass suggests the vacuum may be metastable, a question tied to the hierarchy problem and the nature of dark matter. Experiments at the Large Hadron Collider continue to study the boson's couplings to fermions like the tau lepton and bottom quark for signs of deviation. Furthermore, its role in the early universe and potential connection to cosmic inflation remains an active area of research in cosmology and theories like supersymmetry.

Category:Quantum field theory Category:Standard Model Category:Physical fields