The Littlest Higgs

Abstract

We present an economical theory of natural electroweak symmetry breaking, generalizing an approach based on deconstruction. This theory is the smallest extension of the Standard Model to date that stabilizes the electroweak scale with a naturally light Higgs and weakly coupled new physics at TeV energies. The Higgs is one of a set of pseudo Goldstone bosons in an SU (5)/SO(5) nonlinear sigma model. The symmetry breaking scale f is around a TeV, with the cutoff Λ < ∼ 4πf ∼ 10 TeV. A single electroweak doublet, the "little Higgs", is automatically much lighter than the other pseudo Goldstone bosons. The quartic self-coupling for the little Higgs is generated by the gauge and Yukawa interactions with a natural size O(g 2 , λ 2 t ), while the top Yukawa coupling generates a negative mass squared triggering electroweak symmetry breaking. Beneath the TeV scale the effective theory is simply the minimal Standard Model. The new particle content at TeV energies consists of one set of spin one bosons with the same quantum numbers as the electroweak gauge bosons, an electroweak singlet quark with charge 2/3, and an electroweak triplet scalar. One loop quadratically divergent corrections to the Higgs mass are cancelled by interactions with these additional particles.

A vector-like heavy quark in the Littlest Higgs model

“…The Littlest Higgs (LH) model begins with SU (5) global symmetry, with a locally gauged subgroup [SU (2) × U (1)] 2 [1]. The SU (5) global symmetry is spontaneously broken down to its subgroup SO(5) at the scale f ∼ 1 TeV.…”

“…A new theory for electroweak symmetry breaking was developed from deconstruction theory two years ago [1,2]. This theory is named as "the Littlest Higgs (LH) model" because it is the smallest extension of the SM to date that stabilizes the mass of the SM Higgs boson on the electroweak scale.…”

Search for Heavy Resonances in the Dimuon Channel with the DØ Detector

“…THEORY particles are cancelled by new particles with masses ∼ 1 − 3 TeV that contribute with an opposite sign at the 1-loop level. The "littlest" Higgs model [37] is the simplest example of such a theory. It has a continuous global symmetry group SU(5), and a [SU (2) …”

The little hierarchy in Universal Extra Dimensions

“…The successful attempts in this direction in four dimensional extensions of the SM require, in addition to having a spontaneously broken global symmetry, an extension of the gauge group as well as new fermions. In these scenarios, called Little Higgs models [2], gauge and Yukawa couplings explicitly break the global symmetry giving the Higgs a mass that is smaller than the Nambu-Goldstone boson (NGB) decay constant f by a loop factor. The new particle content is forced by the global symmetries to cancel the quadratic divergences in the Higgs mass, leaving only milder logarithmic divergences.…”

“…Several ideas along this line have been implemented in 4D in the last few years. Here we will implement a Little Higgs model [2,3,4] and a Twin Higgs model [5,6,7] in UED.…”