Symmetry breaking and electroweak physics at Photon Linear Colliders

The physics potential of a high-energy photon collider is reviewed. The emphasis is put on aspects related to the symmetry breaking sector, including Higgs searches and production of longitudinal vector bosons.

Electroweak Symmetry Breaking and the Higgs Boson: Confronting Theories at Colliders

In this review, we discuss methods of parsing direct and indirect information from collider experiments regarding the Higgs boson and describe simple ways in which experimental likelihoods can be consistently reconstructed and interfaced with model predictions in pertinent parameter spaces. Ultimately these methods are used to constrain a five-dimensional parameter space describing a model-independent framework for electroweak symmetry breaking. We review prevalent scenarios for extending the electroweak symmetry breaking sector relative to the Standard Model and emphasize their predictions for nonstandard Higgs phenomenology that could be observed in LHC data if naturalness is realized in particular ways. Specifically we identify how measurements of Higgs couplings can be used to imply the existence of new physics at particular scales within various contexts, highlighting some parameter spaces of interest in order to give examples of how the data surrounding the new state can most effectively be used to constrain specific models of weak scale physics.

Electroweak symmetry breaking in Higgs mechanism with composite operators and solution of naturalness

Introducing a source for a bi-local composite operator motivated by the perturbative expansion in gauge couplings, we calculate its effective potential in the renormalization group of Standard Model with no involvement of technicolor. The potential indicates the breaking of electroweak symmetry below a scale M due to a nonzero vacuum expectation value of neutral component for the SU(2)-doublet operator. At virtualities below a cut off Lambda we introduce the local higgs approximation for the effective fields of sources coupled to the composite operators. The value of Lambdaapprox 600 GeV is fixed by the measured masses of gauge vector bosons. The exploration of equations for infrared fixed points of calculated Yukawa constants allows us to evaluate the masses of heaviest fermion generation with a good accuracy, so that m_t(m_t) = 165pm 4 GeV, m_b(m_b) = 4.18pm 0.38 GeV and m_tau(m_tau) = 1.78pm 0.27 GeV. After a finite renormalization of effective fields for the sources of composite operators, the parameters of effective Higgs field potential are calculated at the scale of matching with the local theory Lambda. The fixed point for the Yukawa constant of t quark and the matching condition for the null effective potential at M drive the M value to the GUT scale. The equation for the infrared fixed point of quartic self-action allows us to get estimates for two almost degenerate scalar particles with m_H= 306pm 5 GeV, while third scalar coupled with the tau lepton is more heavy: m_{H_tau} = 552pm 9 GeV. Some phenomenological implications of the offered approach describing the effective scalar field, and a problem on three fermion generations are discussed.

Hybrid dynamical electroweak symmetry breaking with heavy quarks and the 125 GeV Higgs

Existing models of dynamical electroweak symmetry breaking (EWSB) find it very difficult to get a Higgs of mass lighter than $m_t$. Consequently, in light of the LHC discovery of the ~125 GeV Higgs, such models face a significant obstacle. Moreover, with three generations those models have a superheavy cut-off around $10^{17}$ GeV, requiring a significant fine-tuning. To overcome these twin difficulties, we propose a hybrid framework for EWSB, in which the Higgs mechanism is combined with a Nambu-Jona-Lasinio mechanism. The model introduces a strongly coupled doublet of heavy quarks with a mass around 500 GeV, which forms a condensate at a compositeness scale $Lambda$ about a few TeV, and an additional unconstrained scalar doublet which behaves as a fundamental doublet at $Lambda$. This fundamental-like doublet has a vanishing quartic term at $Lambda$ and is, therefore, not the SM doublet, but should rather be viewed as a pseudo-Goldstone boson of the underlying strong dynamics. This setup is matched at the compositeness scale $Lambda$ to a tightly constrained hybrid two Higgs doublet model, where both the composite and unconstrained scalars participate in EWSB. This allows us to get a good candidate for the recently observed 125 GeV scalar which has properties very similar to the Standard Model Higgs. The heavier (mostly composite) CP-even scalar has a mass around 500 GeV, while the pseudoscalar and the charged Higgs particles have masses in the range 200 -300 GeV.

Strong Coupling Electroweak Symmetry Breaking

We review models of electroweak symmetry breaking due to new strong interactions at the TeV energy scale and discuss the prospects for their experimental tests. We emphasize the direct observation of the new interactions through high-energy scattering of vector bosons. We also discuss indirect probes of the new interactions and exotic particles predicted by specific theoretical models. [Working group summary report from the Snowmass `96 summer study, to appear in the proceedings.]