Speaker
Description
We present the first lattice QCD determination of the Λ → N vector and axial-vector form factors, which are essential inputs for studying the semileptonic decay $\Lambda\rightarrow p \ell \overline{\nu}_\ell$. This channel provides a clean, theoretically controlled avenue for extracting the CKM matrix element |$V_{us}$| from the baryon sector. Our analysis uses a gauge ensemble with physical light, strange, and charm quark masses and yields the most precise determination to date of the full set of transition form factors—including second-class contributions—as well as the associated couplings, radii, and the ratio of muon-toelectron decay rates, an observable sensitive to possible non-standard scalar and tensor interactions. We compare our non-perturbative results with next-to-next-to-leading order expansions in the small parameter δ = $(m_Λ − m_N )/m_Λ$ ≈ 0.16. We find that the common phenomenological approximation of neglecting the $q^2$-dependence of the form factors leads to a ∼ 4% deviation in the decay rate. This underscores the critical importance of precise, fully non-perturbative form factor inputs for achieving the sub-percent precision targets of upcoming experimental programs.
