Minimal Conformal Technicolor and Precision Electroweak Tests

TL;DR

This paper proposes a minimal conformal technicolor model where electroweak symmetry breaking occurs via a composite Higgs arising from a strongly coupled SU(2) gauge theory, avoiding the need for top partners and little Higgs mechanisms, and demonstrating compatibility with electroweak precision tests.

Contribution

It introduces a novel minimal conformal technicolor model with a calculable composite Higgs mass and suppressed electroweak corrections, eliminating the need for top partners.

Findings

The composite Higgs mass is determined by the top loop and is independent of vacuum alignment.

The model achieves a good electroweak fit with v/f ~ 0.25, requiring about 10% fine tuning.

A heavier pseudoscalar A exists with suppressed LHC production.

Abstract

We study the minimal model of conformal technicolor, an SU(2) gauge theory near a strongly coupled conformal fixed point, with conformal symmetry softly broken by technifermion mass terms. Conformal symmetry breaking triggers chiral symmetry breaking in the pattern SU(4) -> Sp(4), which gives rise to a pseudo-Nambu-Goldstone boson that can act as a composite Higgs boson. The top quark is elementary, and the top and electroweak gauge loop contributions to the Higgs mass are cut off entirely by Higgs compositeness. In particular, the model requires no top partners and no "little Higgs" mechanism. A nontrivial vacuum alignment results from the interplay of the top loop and technifermion mass terms. The composite Higgs mass is completely determined by the top loop, in the sense that m_h/m_t is independent of the vacuum alignment and is computable by a strong-coupling calculation. There is an additional composite pseudoscalar A with mass larger than m_h and suppressed direct production at LHC. We discuss the electroweak fit in this model in detail. Corrections to Z -> bb and the T parameter from the top sector are suppressed by the enhanced Sp(4) custodial symmetry. Even assuming that the strong contribution to the S parameter is positive and usuppressed, a good electroweak fit can be obtained for v/f ~ 0.25, where v and f are the electroweak and chiral symmetry breaking scales respectively. This requires fine tuning at the 10% level.