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We provide a pedagogical introduction to extensions of the Standard Model in which the Higgs is composite. These extensions are known as models of dynamical electroweak symmetry breaking or, in brief, Technicolor. Material covered includes: motivations for Technicolor, the construction of underlying gauge theories leading to minimal models of Technicolor, the comparison with electroweak precision data, the low energy effective theory, the spectrum of the states common to most of the Technicolor models, the decays of the composite particles and the experimental signals at the Large Hadron Collider. The level of the presentation is aimed at readers familiar with the Standard Model but who have little or no prior exposure to Technicolor. Several extensions of the Standard Model featuring a composite Higgs can be reduced to the effective Lagrangian introduced in the text. We establish the relevant experimental benchmarks for Vanilla, Running, Walking, and Custodial Technicolor, and a natural fourth family of leptons, by laying out the framework to discover these models at the Large Hadron Collider.
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We analyze the potential of the Large Hadron Collider (LHC) to observe signatures of phenomenologically viable Walking Technicolor models. We study and compare the Drell-Yan (DY) and Vector Boson Fusion (VBF) mechanisms for the production of composite heavy vectors. We find that the heavy vectors are most easily produced and detected via the DY processes. The composite Higgs phenomenology is also studied. If Technicolor walks at the LHC its footprints will be visible and our analysis will help uncovering them.
In multiscale models of walking technicolor, relatively light color-singlet technipions are produced in $q ol q$ annihilation in association with longitudinal $W$ and $Z$ bosons and with each other. The technipions decay as $tpiz ra b ol b$ and $tpip ra c ol b$. Their production rates are resonantly enhanced by isovector technirho vector mesons with mass $M_W + M_{tpi} simle M_{tro} simle 2 M_{tpi}$. At the Tevatron, these associated production rates are 1--10 picobarns for $M_{tpi} simeq 100,gev$. Such a low mass technipion requires topcolor-assisted technicolor to suppress the decay $t ra tpip b$. Searches for $tpitpi$ production will also be rewarding. Sizable rates are expected if $M_{tro} simge 2M_{tpi} + 10,gev$. The isoscalar $omega_T$ is nearly degenerate with $tro$ and is expected to be produced at roughly the same rate. The $omega_T$ should have the distinctive decay modes $omega_T ra gamma tpiz$ and $Z tpiz$.
In multiscale and topcolor-assisted models of walking technicolor, relatively light spin-one technihadrons $rho_T$ and $omega_T$ exist and are expected to decay as $rho_T to W pi_T, Z pi_T$ and $omega_T to gamma pi_T$. For $M_{rho_T} simeq 200 GeV$ and $M_{pi_T} simeq 100 GeV$, these processes have cross sections in the picobarn range in $bar p p$ colisions at the Tevatron and about 10 times larger at the Large Hadron Collider. We demonstrate their detectability with simulations appropriate to Run II conditions at the Tevatron.
We study the potential of the LHCb experiment to discover, for the first time, the $mu^+mu^-$ true muonium bound state. We propose a search for the vector $1^3S_1$ state, $mathcal{T!M}$, which kinetically mixes with the photon and dominantly decays to $e^+e^-$. We demonstrate that a search for $eta to gamma mathcal{T!M}$, $mathcal{T!M}to e^+e^-$ in a displaced vertex can exceed a significance of 5 standard deviations assuming statistical uncertainties. We present two possible searches: an inclusive search for the $e^+e^-$ vertex, and an exclusive search which requires an additional photon and a reconstruction of the $eta$ mass.
We perform a lattice study of the topological susceptibility and instanton size distribution of the $su{2}$ gauge theory with two adjoint Dirac fermions (also known as Minimal Walking Technicolor), which is known to be in the conformal window. In the theory deformed with a small mass term, by drawing a comparison with the pure gauge theory, we find that topological observables are decoupled from the fermion dynamics. This provides further evidence for the infrared conformality of the theory. A study of the instanton size distribution shows that this quantity can be used to detect the onset of finite size effects.
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