Bc→ηc form factors at large recoil: Double logarithms and endpoint divergences in SCET

by Dennis Horstmann (Karlsruhe Institute of Technology)

Tuesday 27 Oct 2026, 10:45 → 11:45 Europe/Berlin

PH 3344, (5101.01.344) (TUM, Physics Department, Garching)

At next-to-leading power, Soft-Collinear Effective Theory suffers from endpoint-divergent convolution integrals. While this difficulty has been overcome for a number of processes by employing novel refactorization-based subtraction techniques, this method appears to be inapplicable for hard exclusive processes. We show that the double-logarithmic series of the soft-overlap contribution to the B_c → η_c transition form factors, assuming the scale hierarchy m_b >> m_c >> Λ_QCD, is given by a novel type of integral equations encoding a non-trivial interplay between soft-quark and soft-gluon corrections. Further, we perform an independent check of this result. With appropriate regulators in place, the corresponding bare factorization formula derived in Soft-Collinear Effective Theory can be used at fixed order. Based on the structure of the bare factorization formula, we formulate a pole-cancellation argument and identify the leading pole of the three-loop hard-collinear region as the only missing ingredient up to three-loop order. An explicit computation of this ingredient confirms our integral equations up to the three-loop level. Finally, we discuss a method that reproduces the double-logarithmic series by means of renormalization-group equations of cut-off inverse moments of B_c-meson light-cone distribution amplitudes.