Heavy pseudoscalar twist-3 distribution amplitudes within QCD theory in background fields Tao Zhong, Xing-Gang Wu, Tao Huang and Hai-Bing Fu Eur. Phys. J. C, 76 9 (2016) 509 Published online: 17 September 2016 DOI: 10.1140/epjc/s10052-016-4350-z