Phenomenology of TeV-scale scalar leptoquarks in the EFT

We examine new aspects of leptoquark (LQ) phenomenology using effective field theory (EFT). We construct a complete set of leading effective operators involving SU(2) singlets scalar LQ and the Standard Model fields up to dimension six. We show that, while the renormalizable LQ-lepton-quark interaction Lagrangian can address the persistent hints for physics beyond the Standard Model in the B-decays (B) over bar -> D(*)tau(nu) over bar, (B) over bar -> (K) over barl(+)l(-) and in the measured anomalous magnetic moment of the muon, the LQ higher dimensional effective operators may lead to new interesting effects associated with lepton number violation. These include the generation of one-loop and two-loops sub-eV Majorana neutrino masses, mediation of neutrinoless double-beta decay and novel LQ collider signals. For the latter, we focus on third generation LQ (phi(3)) in a framework with an approximate Z(3) generation symmetry and show that one class of the dimension five LQ operators may give rise to a striking asymmetric same-charge phi(3)phi(3) pair-production signal, which leads to low background same-sign leptons signals at the LHC. For example, with M-phi 3 similar to 1 TeV and a new physics scale of Lambda similar to 5 TeV, we expect at the 13 TeV LHC with an integrated luminosity of 300 fb(-1), about 5000 positively charged tau(+)tau(+) events via pp -> phi(3)phi(3) -> tau(+)tau(+) + 2 . j(b) (j(b) = b-jet), about 500 negatively charged tau(-)tau(-) events with a signature pp -> phi(3)phi(3 )-> + tau(-)tau(-) 4 . j + 2.j(b) (j = light jet) and about 50 positively charged l(+)l(+) events via pp -> l(+)l(+ )+ 2. j(b) (sic)T for any of the three charged leptons, l(+)l+ = e(+)e(+), mu(+)mu(+), tau(+)tau(+). It is interesting to note that, in the LQ EFT framework, the expected same-sign lepton signals have a rate which is several times larger than the QCD LQ-mediated opposite-sign leptons signals, gg, q (q) over bar -> phi(3)phi(3)* -> l(+)l(-) + X. We also consider the same-sign charged lepton signals in the LQ EFT framework at higher energy hadron colliders such as a 27 TeV HE-LHC and a 100 TeV FCC-hh.