Leading SU(3) breaking in lightcone distribution amplitudes

The lightcone formalism including SU(3) breaking effects for the light pseudoscalar mesons is studied using soft-collinear effective theory (SCET), where the conformal symmetries needed for the expansion can be clearly implemented. The lightcone distribution amplitudes (LCDAs) are well-defined at each order in the SCET power counting, lambda. Relations between the LCDAs are reproduced using the SCET formalism. Treating the SU(3) breaking perturbatively, the leading breaking effects can be described in a simple manner. As a result, a new relationship among the LCDAs for the light mesons pi, K, and eta is developed, valid to leading order in the SU(3) breaking.