This title appears in the Scientific Report : 2014 

Pion production in nucleon-nucleon collisions in chiral effective field theory with Δ(1232) degrees of freedomm
Filin, A. (Corresponding Author)
Baru, V. / Epelbaum, E. / Krebs, H. / Hanhart, C. / Myhrer, F.
Theorie der starken Wechselwirkung; IKP-3
Theorie der Starken Wechselwirkung; IAS-4
Physical review / C, 88 (2013) 6, S. 064003
Woodbury, NY Inst. 2013
10.1103/PhysRevC.88.064003
Journal Article
Hadron Structure and Dynamics (HSD)
OpenAccess
Please use the identifier: http://dx.doi.org/10.1103/PhysRevC.88.064003 in citations.
Please use the identifier: http://hdl.handle.net/2128/8367 in citations.
A calculation of the pion-production operator up to next-to-next-to-leading order for s-wave pions is performed within chiral effective field theory. In the previous study [Phys. Rev. C 85, 054001 (2012)] we discussed the contribution of the pion-nucleon loops at the same order. Here we extend that study to include explicit Delta degrees of freedom and the 1/m_N^2 corrections to the pion-production amplitude. Using the power counting scheme where the Delta-nucleon mass difference is of the order of the characteristic momentum scale in the production process, we calculate all tree-level and loop diagrams involving Delta up to next-to-next-to-leading order. The long-range part of the Delta loop contributions is found to be of similar size to that from the pion-nucleon loops which supports the counting scheme. The net effect of pion-nucleon and Delta loops is expected to play a crucial role in understanding of the neutral pion production data.