Heavy-to-light chromomagentic matrix element

TL;DR

This paper computes the chromomagnetic matrix element relevant to flavor-changing neutral currents in B and D mesons using light-cone sum rules, revealing a large strong phase and discussing complex analytic structures.

Contribution

It introduces a novel LCSR-based calculation of the chromomagnetic matrix element, including the analysis of complex anomalous thresholds and comparison with QCD factorization.

Findings

Large strong phase observed in the matrix element

Complex anomalous threshold affects the sum rule analysis

Comparison shows differences with QCD factorization at endpoint divergences

Abstract

We report the computation of the matrix element of the chromomagnetic operator of the flavour changing neutral current (FCNC)-type between a $B$- or $D$-meson state and a light hadron and off-shell photon. The computation is carried out by using the method of light-cone sum rules (LCSR). It is found that the matrix element exhibits a large strong phase for which we give a long distance interpretation. The analytic structure of the correlation function in use admits a complex anomalous threshold on the physical sheet, the meaning and handling of which within the sum rule approach is discussed. We compare our results to QCD factorisation for which spectator photon emission is end-point divergent.