Study of the Λ→pℓν[over ¯]_{ℓ} Semileptonic Decay in Lattice QCD

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 Λ→pℓν[over ¯]_{ℓ}. This channel provides a clean, theoretically controlled avenue for extracting the Cabibbo-Kobayashi-Maskawa 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-to-electron decay rates, an observable sensitive to possible nonstandard scalar and tensor interactions. We compare our nonperturbative 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 nonperturbative form factor inputs for achieving the subpercent precision targets of upcoming experimental programs.