Abstract
We present an exceptional twin-Higgs model with the minimal symmetry structure for an exact implementation of twin parity along with custodial symmetry. Twin particles are mirrors of the Standard Model yet they carry hypercharge, while the photon is identified with its twin. We thoroughly explore the phenomenological signatures of hypercharged naturalness: long-lived charged particles; a colorless twin top with electric charge 2/3 that once pair-produced, bounds via twin-color interactions and can annihilate to dileptons or a Higgs plus a photon or a Z; and glueballs produced from Higgs decays and twin-quarkonium annihilation that either decay displaced or are stable on collider scales and eventually decay to diphotons. Prospects for detection of these signatures are also discussed.
Highlights
Mass should exceed a TeV [10, 11], and similar bounds apply to colored supersymmetric particles
We thoroughly explore the phenomenological signatures of hypercharged naturalness: long-lived charged particles; a colorless twin top with electric charge 2/3 that once pair-produced, bounds via twin-color interactions and can annihilate to dileptons or a Higgs plus a photon or a Z; and glueballs produced from Higgs decays and twin-quarkonium annihilation that either decay displaced or are stable on collider scales and eventually decay to diphotons
Instead of collider signals associated with production of colored particles, e.g. top partners, stops and gluinos, that subsequently decay to top/bottom and Higgs/EW gauge bosons or missing energy, in the twin-Higgs scenario the phenomenology at low energies is dominated by states that predominantly couple to the SM via the Higgs, giving rise for instance to exotic Higgs decays or heavy Higgs-like signatures [76,77,78]
Summary
The twin-Higgs mechanism relies on the Higgs arising as a NGB from the spontaneous breaking of a global symmetry. The novel features of our scenario stem from a different global symmetry breaking pattern, SO(7) → G2, with respect to previous twin-Higgs models. This breaking has the peculiarity of being the smallest that gives rise to seven NGBs while leaving an unbroken custodial symmetry, SU(2)L × SU(2)R ⊂ G2.1 The twin-Higgs mechanism can still be operative in this coset, with the Higgs complex doublet H and its twin H embedded in the. It follows that under the custodial SU(2)L × SU(2)R symmetry, the Higgs has the proper quantum numbers, i.e. H ∼ (2, 2), while the twin Higgs decomposes as H ∼ (1, 1) ⊕ (1, 3), which correspond to the singlet radial component, σ, and a triplet of SU(2)R Their kinetic terms take the same form as in other spherical cosets, f2 2. The coset SO(7)/G2 has been explored in [22, 23] in the context of ordinary composite-Higgs models
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