The flavor of a minimal composite S 1 leptoquark and the b → cτ ν ¯ $$ b\to c\tau \overline{\nu} $$ anomaly

Abstract

Abstract Several experiments have measured a deviation in B → D (∗) semileptonic decays, that point to new physics at the TeV scale violating lepton flavor universality. A scalar leptoquark S 1, with a suitable structure of couplings in flavor space, is known to be able to solve this anomaly modifying b → cτ ν ¯ $$ b\to c\tau \overline{\nu} $$ . In the context of composite Higgs models, we consider a theory containing H and S 1 as Nambu-Goldstone bosons (NGBs) of a new strongly interacting sector, with ordinary resonances at a scale O 10 $$ \mathcal{O}(10) $$ TeV. Assuming anarchic partial compositeness of the Standard Model (SM) fermions we calculate the potential of the NGBs that is dominated by the fermions of the third generation, we compute R D ∗ $$ {R}_{D^{\left(\ast \right)}} $$ and estimate the corrections to flavor observables by the presence of S 1. We find that the SM spectrum and m S 1 $$ {m}_{S_1} $$ ∼ TeV can be obtained with a NGB decay constant of order ∼ 5 TeV. We obtain a robust correlation between the main corrections to R D ∗ $$ {R}_{D^{\left(\ast \right)}} $$ , B K ∗ νν $$ {B}_{K^{\left(\ast \right)}\nu \nu} $$ and g τ /g μ , that leads to a sever bound on R D ∗ $$ {R}_{D^{\left(\ast \right)}} $$ , roughly 2σ below the experimental value. Besides the bounds on the flavor observables g τ W $$ {g}_{\tau}^W $$ , BR(τ → μγ) and ∆ m B s $$ \Delta {m}_{B_s} $$ are saturated, with the first one requiring a coupling between resonances g * ≲ 2, whereas the second one demands m S 1 $$ {m}_{S_1} $$ ≳ 1.7 TeV, up to corrections of O 1 $$ \mathcal{O}(1) $$ .

Keywords

• Bottom Quarks
• Compositeness
• Lepton Flavour Violation (charged)
• Theories of Flavour