Abstract
We revisit the Twin Higgs scenario as a “dark” solution to the little hierarchy problem, identify the structure of a minimal model and its viable parameter space, and analyze its collider implications. In this model, dark naturalness generally leads to Hidden Valley phenomenology. The twin particles, including the top partner, are all Standard-Model-neutral, but naturalness favors the existence of twin strong interactions — an asymptotically-free force that confines not far above the Standard Model QCD scale — and a Higgs portal interaction. We show that, taken together, these typically give rise to exotic decays of the Higgs to twin hadrons. Across a substantial portion of the parameter space, certain twin hadrons have visible and often displaced decays, providing a potentially striking LHC signature. We briefly discuss appropriate experimental search strategies.
Highlights
The principle of Naturalness, the notion that the weak scale should be insensitive to quantum effects from physics at much higher mass scales, necessitates new TeV-scale physics beyond the Standard Model (SM)
The absence far of any signals in these experiments has disfavored the most popular scenarios, including supersymmetry (SUSY), Composite Higgs and Extra Dimensions, unless their mass scales are raised above natural expectations, leading to sub-percent level electroweak fine-tuning in complete models
The “Twin Higgs” mechanism provides an existence proof for the unsettling possibility that the solution to the hierarchy problem involves a sector of particles that carry no Standard Model quantum numbers, and are difficult to produce at the LHC
Summary
The principle of Naturalness, the notion that the weak scale should be insensitive to quantum effects from physics at much higher mass scales, necessitates new TeV-scale physics beyond the Standard Model (SM). For lower mass (typically below ∼ 40 GeV in the minimal model we describe) the decay of the G0+ may be macroscopically displaced from the interaction point Such displaced decays are a striking signature, spectacular enough to compensate for the relatively low production rate, and represent an excellent opportunity for the LHC. With a branching fraction of the Higgs to twin hadrons of order 0.1% or greater, our minimal Twin Higgs model should motivate further experimental searches for this signal of hidden naturalness. Hadronization in the twin sector is a complex and poorly understood process, and considerably more investigation will be needed before predictions of glueball and quarkonium multiplicity and kinematic distributions could be possible This solution to the naturalness problem requires further work on both experimental and theoretical fronts. In appendix E, the phenomenological effect of gauging twin hypercharge, as a non-minimal extension of the model, is considered
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