Reconciling threshold and subthreshold expansions for pion-nucleon scattering
| Autor: | Siemens, D., de Elvira, J. Ruiz, Epelbaum, E., Hoferichter, M., Krebs, H., Kubis, B., Meißner, U. -G. |
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| Rok vydání: | 2016 |
| Předmět: | |
| Zdroj: | Phys.Lett. B770: 27-34, 2017 |
| Druh dokumentu: | Working Paper |
| DOI: | 10.1016/j.physletb.2017.04.039 |
| Popis: | Heavy-baryon chiral perturbation theory (ChPT) at one loop fails in relating the pion-nucleon amplitude in the physical region and for subthreshold kinematics due to loop effects enhanced by large low-energy constants. Studying the chiral convergence of threshold and subthreshold parameters up to fourth order in the small-scale expansion, we address the question to what extent this tension can be mitigated by including the $\Delta(1232)$ as an explicit degree of freedom and/or using a covariant formulation of baryon ChPT. We find that the inclusion of the $\Delta$ indeed reduces the low-energy constants to more natural values and thereby improves consistency between threshold and subthreshold kinematics. In addition, even in the $\Delta$-less theory the resummation of $1/m_N$ corrections in the covariant scheme improves the results markedly over the heavy-baryon formulation, in line with previous observations in the single-baryon sector of ChPT that so far have evaded a profound theoretical explanation. Comment: 10 pages, 4 tables, Mathematica notebook with the analytic expressions for threshold and subthreshold parameters included as supplementary material; journal version |
| Databáze: | arXiv |
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