Little Higgs

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In particle physics, little Higgs is a refined version of the Higgs boson based on the idea that the Higgs boson is a pseudo-Goldstone boson arising from some global symmetry breaking at a TeV energy scale. The main goal of little Higgs theories was to have electroweak symmetry breaking be the result of strong dynamics in the spirit of pions in QCD. The idea was initially studied by Nima Arkani-Hamed, Andy Cohen, and Howard Georgi in the spring of 2001. The idea was explored further in a scientific paper by Nima Arkani-Hamed, Andy Cohen, Thomas Gregoire, and Jay Wacker in the spring of 2002. In the spring of 2002 several papers appeared that refined the ideas of little Higgs theories, most notably the Littlest Higgs by Nima Arkani-Hamed, Andy Cohen, Emmanuel Katz, and Ann Nelson.

Little Higgs theories were an outgrowth of dimensional deconstruction. In these theories, the gauge group has the form of a direct product of several copies of the same factor, for example . Each SU(2) factor may be visualised as the SU(2) group living at a particular point along an additional dimension of space. Consequently, many virtues of extra-dimensional theories may be reproduced even though the little Higgs theory is 3+1-dimensional. The little Higgs models are able to predict a naturally-light Higgs particle.

The main idea behind the little Higgs models is that the one-loop contribution to the tachyonic Higgs boson mass coming from the top quark cancels. (The other one-loop contributions are small enough that they don't really matter; the top Yukawa coupling is huge and all the other Yukawa couplings and gauge couplings are small.) This protects the Higgs boson mass for about one order of magnitude, which is good enough to evade many of the precision electroweak constraints.