Odd top partners at the LHC

Abstract

LHC searches for fermionic top partners T focus on three decay topologies: T → bW , T → tZ, and T → th. However, top partners may carry new conserved quantum numbers that forbid these decays. The simplest possibility is a conserved parity, under which the top partner is odd and all SM states are even. In this case, decays of top partners may involve new particle-odd scalars, leading to signal topologies more commonly associated with supersymmetry, either with or without R-parity conservation. We study a simplified model in which this possibility is realized, and estimate the bounds on the top partner mass in this model implied by LHC searches for supersymmetry. We find that the bounds can be significantly weaker than in the conventional top partner decay scenario. For example, if the new parity is exact, a 500 GeV top partner is allowed as long as the lightest parity-odd scalar mass is between 325 and 500 GeV. The lower allowed top partner mass reduces the need for fine-tuning in the Higgs mass parameter, compared to the conventional decay scenario. We also present an explicit model, the Oddest Little Higgs, which exhibits this phenomenology.

Forbidden dark matter at the weak scale via the top portal

“…Hence we find that while m MED ∈ [380, 690] GeV is excluded in tchFDM, the corresponding range is m MED ∈ [310, 920] GeV in tchSDM. The latter is in good agreement with the recasting performed by the authors of [68] for fermionic top partners that are odd under a parity.…”

“…Therefore to set bounds, we first generate the mediator pair production process pp → T¯ T in MadGraph5 [60] and obtain the production cross-sections at leading order. Then we apply a K-factor of 1.5 (see [68]) to obtain the NLO cross-section. Assuming similar acceptances for the production of a stop pair and T¯ T , we compare our rates with the 95% C.L.…”

Beyond the minimal top partner decay

“…However, the experimental searches could be recasted or adjusted to look for the different pattern of final state particles from the production and decay of these top partners. We expect that the corresponding analyses could reach comparable sensitivities as the current ones (see [31,32] where this subject is addressed). Nevertheless, the search for non-minimal top partner decays could also provide compelling information about the underlying symmetry structure of the electroweak scale.…”

Novel signatures for vector-like quarks

“…[22]. Additional decay modes of vector-like quarks T have been considered in composite Higgs [49], little Higgs [50] and two-Higgs doublet models [51]. We begin by writing in section 2 the interactions for a vector-like doublet extension when the scalar sector comprises two doublets H u and H d , as in the case of the MSSM.…”