Narrow Results

In contrast to the folklore that Technicolor (TC) is a "Higgsless theory", we shall discuss existence of a composite Higgs boson, Techni-Dilaton (TD), a pseudo-Nambu-Goldstone boson of the scale invariance in the Scale-invariant/Walking/Conformal TC (SWC TC) which generates a large anomalous dimension γ_m ≃ 1 in a wide region from the dynamical mass of the techni-fermion all the way up to the intrinsic scale Λ_TC of the SWC TC (analogue of Λ_QCD), where Λ_TC is taken typically as the scale of the Extended TC scale Λ_ETC: Λ_TC ≃ Λ_ETC ~ 10³TeV (≫ m). All the techni-hadrons have mass on the same order , which in SWC TC is extremely smaller than the intrinsic scale Λ_TC ≃ Λ_ETC, in sharp contrast to QCD where both are of the same order. The mass of TD arises from the non-perturbative scale anomaly associated with the techni-fermion mass generation and is typically 500-600 GeV, even smaller than other techni-hadrons of the same order of , in another contrast to QCD which is believed to have no scalar bound state lighter than other hadrons. We discuss the TD mass in various methods, Gauged NJL model via ladder Schwinger-Dyson (SD) equation, straightforward calculations in the ladder SD/ Bethe-Salpeter equation, and the holographic approach including techni-gluon condensate. The TD may be discovered in LHC.

We review recent progress in the lattice investigations of near-conformal non-Abelian gauge theories relevant for dynamical symmetry breaking and model building of composite Higgs models. The emphasis is placed on the mass spectrum and the running renormalized coupling. The role of a light composite scalar isosinglet particle as a composite Higgs particle is highlighted.

The dynamical origin of electroweak symmetry breaking is an open question with many possible theoretical explanations. Strongly coupled systems predicting the Higgs boson as a bound state of a new gauge-fermion interaction form one class of candidate models. Due to increased statistics, LHC run II will further constrain the phenomenologically viable models in the near future. In the meanwhile it is important to understand the general properties and specific features of the different competing models.

In this work we discuss many-flavor gauge-fermion systems that contain both massless (light) and massive fermions. The former provide Goldstone bosons and trigger electroweak symmetry breaking, while the latter indirectly influence the infrared dynamics. Numerical results reveal that such systems can exhibit a light $0^{++}$ isosinglet scalar, well separated from the rest of the spectrum. Further, when we set the scale via the vev of electroweak symmetry breaking, we predict a 2 TeV vector resonance which could be a generic feature of SU(3) gauge theories.

A fully dynamical origin for the masses of weak gauge bosons and heavy quarks of the Standard Model is considered. Electroweak symmetry breaking and the gauge boson masses arise from new strong dynamics, which leads to the appearance of a composite scalar in the spectrum of excitations. In order to generate mass for the Standard Model fermions, we consider extended gauge dynamics, effectively represented by four fermion interactions at presently accessible energies. By systematically treating these interactions, we show that they lead to a large reduction of the mass of the scalar resonance. Therefore, interpreting the scalar as the recently observed 125 GeV state, implies that the mass originating solely from new strong dynamics can be much heavier, of the order of 1 TeV. The couplings of the scalar resonance with the Standard Model gauge bosons and fermions are evaluated, and found to be compatible with the current LHC results.

We review the interplay between collider searches for vector-like quarks and dark matter direct detection experiments in composite Higgs models. With focus on a future 100 TeV collider, we also extend previous analyses to improve the reach for heavy quarks in the low mass region.

This paper examines the Standard Model under the strong–electroweak symmetry group $S{U}_S(3)\times U_{\mathit{\text{EW}}}(2)$ subject to the Lie algebra condition ${\text{𝔲}}_{\mathit{\text{EW}}}(2)\ncong {\text{𝔰}\text{𝔲}}_I(2)\oplus {\text{𝔲}}_Y(1)$. Physically, the condition ensures that all electroweak gauge bosons interact with each other prior to symmetry breaking — as one might expect from $U(2)$ invariance. This represents a crucial shift in the identification of physical gauge bosons: Unlike the Standard Model which posits a change of Lie algebra basis induced by spontaneous symmetry breaking, here the basis is unaltered and A, $Z^0$, $W^{\pm }$ represent the physical bosons both before and after spontaneous symmetry breaking.

Our choice of ${\text{𝔲}}_{\mathit{\text{EW}}}(2)$ requires some modification of the matter field representation of the Standard Model. The group $U_{\mathit{\text{EW}}}(2)$ admits two pertinent defining representations, $2$ and its $U(2)$-conjugate $2^c$, related by a large gauge transformation. Accordingly, the product group structure calls for strong–electroweak degrees of freedom in the $(3,2)$ and the $(3,2^c)$ of $S{U}_S(3)\times U_{\mathit{\text{EW}}}(2)$ that possess integer electric charge just like leptons. These degrees of freedom play the role of quarks, and they lead to a modified Lagrangian that nevertheless reproduces transition rates and cross-sections equivalent to the Standard Model. In particular, they reproduce the fractional electric charge of quark currents.

The close resemblance between quark and lepton electroweak doublets in this picture suggests a mechanism for a speculative phase transition between quarks and leptons that stems from the product structure of the symmetry group. Our hypothesis is that the strong and electroweak bosons see each other as a source of decoherence. In effect, lepton representations get identified with the $SU(3)$-trace-reduced quark representations. This mechanism allows for possible extensions of the Standard Model that do not require large inclusive multiplets of matter fields and might explain the Higgs as a pseudo Nambu–Goldstone boson.

We consider a possibility that electroweak symmetry breaking (EWSB) is triggered by a fundamental Higgs and a composite Higgs arising in a dynamical symmetry breaking mechanism induced by a new strong dynamics. The resulting Higgs sector is a partially composite two-Higgs doublet model with specific boundary conditions on the coupling and mass parameters originating at a compositeness scale Λ. The phenomenology of this model is discussed including the collider phenomenology at LHC and ILC.

The dynamical origin of electroweak symmetry breaking is an open question with many possible theoretical explanations. Strongly coupled systems predicting the Higgs boson as a bound state of a new gauge-fermion interaction form one class of candidate models. Due to increased statistics, LHC run II will further constrain the phenomenologically viable models in the near future. In the meanwhile it is important to understand the general properties and specific features of the different competing models.

In this work we discuss many-flavor gauge-fermion systems that contain both massless (light) and massive fermions. The former provide Goldstone bosons and trigger electroweak symmetry breaking, while the latter indirectly influence the infrared dynamics. Numerical results reveal that such systems can exhibit a light 0⁺⁺ isosinglet scalar, well separated from the rest of the spectrum. Further, when we set the scale via the vev of electroweak symmetry breaking, we predict a 2 TeV vector resonance which could be a generic feature of SU(3) gauge theories.

A fully dynamical origin for the masses of weak gauge bosons and heavy quarks of the Standard Model is considered. Electroweak symmetry breaking and the gauge boson masses arise from new strong dynamics, which leads to the appearance of a composite scalar in the spectrum of excitations. In order to generate mass for the Standard Model fermions, we consider extended gauge dynamics, effectively represented by four fermion interactions at presently accessible energies. By systematically treating these interactions, we show that they lead to a large reduction of the mass of the scalar resonance. Therefore, interpreting the scalar as the recently observed 125 GeV state, implies that the mass originating solely from new strong dynamics can be much heavier, of the order of 1 TeV. The couplings of the scalar resonance with the Standard Model gauge bosons and fermions are evaluated, and found to be compatible with the current LHC results.

In contrast to the folklore that Technicolor (TC) is a "Higgsless theory", we shall discuss existence of a composite Higgs boson, Techni-Dilaton (TD), a pseudo-Nambu-Goldstone boson of the scale invariance in the Scale-invariant/Walking/Conformal TC (SWC TC) which generates a large anomalous dimension γ_m ≃ 1 in a wide region from the dynamical mass of the techni-fermion all the way up to the intrinsic scale Λ_TC of the SWC TC (analogue of Λ_QCD), where Λ_TC is taken typically as the scale of the Extended TC scale Λ_ETC: Λ_TC ≃ Λ_ETC ~ 10³TeV (≫ m). All the techni-hadrons have mass on the same order , which in SWC TC is extremely smaller than the intrinsic scale Λ_TC ≃ Λ_ETC, in sharp contrast to QCD where both are of the same order. The mass of TD arises from the non-perturbative scale anomaly associated with the techni-fermion mass generation and is typically 500-600 GeV, even smaller than other techni-hadrons of the same order of , in another contrast to QCD which is believed to have no scalar bound state lighter than other hadrons. We discuss the TD mass in various methods, Gauged NJL model via ladder Schwinger-Dyson (SD) equation, straightforward calculations in the ladder SD/ Bethe-Salpeter equation, and the holographic approach including techni-gluon condensate. The TD may be discovered in LHC.

Based on Refs. 1 and 2, we study the couplings of the scalar bound state to the fermions and the weak bosons in walking gauge theories.

We present a minimal candidate model for the composite Higgs mechanism with fermion doublet in the two-index symmetric (sextet) representation of the SU(3) color gauge group.³ The model is known to be close to the conformal window with a small β-function.⁴ Chiral symmetry breaking with vacuum condensate becomes the origin of electroweak symmetry breaking from compositeness. Close to the conformal window, a light scalar state with Higgs quantum numbers is emerging. Associations with the recently observed 126 GeV Higgs boson, or with a dilaton state from broken scale invariance, are subjects of ongoing investigations.