Why Unparticle Models with Mass Gaps are Examples of Hidden Valleys

Abstract

Hidden valleys, hidden sectors with multi-particle dynamics and a mass gap, can produce striking and unusual final states at the LHC. Unparticle models, hidden-sectors with conformal dynamics and no (or a very small) mass gap, can result in unusual kinematic features that indirectly reflect the conformal dynamics. When sufficiently large mass gaps are added to unparticle models, they become hidden valley models. Predictions using unparticle propagators alone overlook the most striking signals, which are typically of hidden-valley type. Inclusive signatures often cannot be predicted from unparticle dimensions, and exclusive signatures are often visible and can be spectacular. Among possible signatures are: Higgs decays to pairs of particles that in turn decay to two quarks, leptons or gauge bosons, possibly with displaced vertices; Higgs, top, and neutralino decays to more than six particles; resonances below an ``unparticle'' continuum which produce multi-body final states; etc. The Stephanov model is deconstructed, reconstructed, and shown to be a hidden valley model. Some effects of strong dynamics on hidden valley observables, not predictable using unparticle methods, are discussed, including resonances, reduced flavor symmetry breaking, reduced supersymmetry breaking, and a strongly enhanced hidden parton shower.

Figures (26)

• Figure 1: In the hidden valley scenario, a hidden sector couples at or near the TeV scale to the standard model sector. In the simplest hidden valleys, a barrier limiting production of hidden-sector particles will be breached in the near future. The number of particles increases through a multi-particle production process in the hidden sector. A mass gap prevents decays within the hidden sector, allowing hidden-sector particles to decay to visible particles, often with long lifetimes due to the barrier. Events with high multiplicity and/or displaced vertices naturally result.
• Figure 2: The unparticle scenario is similar to the hidden valley scenario, but specifically assumes the hidden sector is conformal, which is not a necessary assumption for a hidden valley. In standard unparticle models, the mass gap is very low, so that standard model particles reflect the hidden physics only indirectly. If the mass gap is higher, the unparticle model becomes a hidden valley model, with the same signals.
• Figure 3: An unparticle mixing with the Higgs boson is produced in $gg$ collisions.
• Figure 4: In our toy models at weak coupling, the unparticle propagator is a $\phi$ loop, corrected by hidden gauge boson exchange, and the imaginary part of the unparticle propagator contains the process $gg\to \phi\phi^\dagger$.
• Figure 5: The hidden sector is interacting: a hidden gauge boson can be radiated off the $\phi$ particles. This is also present in the imaginary part of the unparticle propagator.