Friday, July 27, 2012
The Higgs boson and condensed matter physics
One of the key ideas first emphasized by Phil Anderson in 1963 was that a massless gauge field can aquire a mass in the presence of a coupling to a spontaneously broken field. A concrete realisation of this occurs in superconductors. In the Meissner effect a superconductor thicker than the penetration depth expels magnetic fields. This is like the photon acquires a mass.
In the electro-weak theory of Weinberg-Salam there is a combined U(1) x SU(2) gauge symmetry. Due to coupling to the Higgs field (whose symmetry is spontaneously broken)
one gauge field remains massless (the photon) and the other three become massive. These massive particles are the W+, W-, and Z bosons.
In a type II superconductor, vortices are allowed in the superconducting order parameter field. Can such vortices occur in the Higgs field? They may have been important in the early universe.
On fascinating thing I learnt is that for the Higgs field the crucial ratio [between the London penetration length and the superconducting coherence length] that determines whether type II behaviour is possible is the ratio of Higgs boson mass to W mass. The LHC results suggest that type II behaviour is possible!
In summary, here is an extract from Coleman's book (page 246).
Shortly after the importance of this mechanism for relativistic Yang Mills theories was noted by Higgs and Anderson, Weinberg and Salem independently applied the idea to develop the theory of “electro-weak” interactions. According to this picture, the universe we live is a kind of cosmological Meissner phase, formed in the early universe, which excludes the weak force by making the vector bosons which carry it, become massive. It is a remarkable thought that the very same mechanism that causes superconductors to levitate lies at the heart of the weak nuclear force responsible for nuclear fusion inside stars. In trying to discover the Higg’s particle, physicists are in effect trying to probe the cosmic superconductor above its gap energy scale.
