Electroweak scale

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 Λ4πf ~ 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 (g2, λt2), 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.

Abstract: We consider the novel Kaluza-Klein (KK) scenario where gravity propagates in the $(4+n)$-dimensional bulk of spacetime, while gauge and matter fields are confined to the $(3+1)$-dimensional world volume of a brane configuration. For simplicity we assume compactification of the extra n dimensions on a torus with a common scale $R,$ and identify the massive KK states in the four-dimensional spacetime. For a given KK level $\stackrel{\ensuremath{\rightarrow}}{n}$ there is one spin-2 state, $(n\ensuremath{-}1)$ spin-1 states, and $n(n\ensuremath{-}1)/2$ spin-0 states, all mass degenerate. We construct the effective interactions between these KK states and ordinary matter fields (fermions, gauge bosons, and scalars). We find that the spin-1 states decouple and that the spin-0 states only couple through the dilaton mode. We then derive the interacting Lagrangian for the KK states and standard model fields, and present the complete Feynman rules. We discuss some low-energy phenomenology for these new interactions for the case when $1/R$ is small compared to the electroweak scale, and the ultraviolet cutoff of the effective KK theory is on the order of 1 TeV.

Abstract: Five-dimensional models where the bulk is a slice of AdS have the virtue of solving the hierarchy problem. The electroweak scale is generated by a ``warp'' factor of the induced metric on the brane where the standard model fields live. However, it is not necessary to confine the standard model fields on the brane and we analyze the possibility of having the fields actually living in the slice of AdS. Specifically, we study the behaviour of fermions, gauge bosons and scalars in this geometry and their implications on electroweak physics. These scenarios can provide an explanation of the fermion mass hierarchy by warp factors. We also consider the case of supersymmetry in the bulk, and analyze the conditions on the mass spectrum. Finally, a model is proposed where the warp factor generates a small (TeV) supersymmetry-breaking scale, with the gauge interactions mediating the breaking to the scalar sector.