Higher-order tree-level amplitudes in the nonlinear sigma model

• Main Authors: Johan Bijnens, Karol Kampf, Mattias Sjö
• Format: Article
• Language: English
• Published: SpringerOpen 2019-11-01
• Series: Journal of High Energy Physics
• Subjects: Chiral Lagrangians; Effective Field Theories; Scattering Amplitudes; Spon- taneous Symmetry Breaking
• Online Access: http://link.springer.com/article/10.1007/JHEP11(2019)074

Abstract We present a generalisation of the flavour-ordering method applied to the chiral nonlinear sigma model with any number of flavours. We use an extended Lagrangian with terms containing any number of derivatives, organised in a power-counting hierarchy. The method allows diagrammatic computations at tree-level with any number of legs at any order in the power-counting. Using an automated implementation of the method, we calculate amplitudes ranging from 12 legs at leading order, O $$ \mathcal{O} $$ (p 2), to 6 legs at next-to- next-to-next-to-leading order, O $$ \mathcal{O} $$ (p 8). In addition to this, we generalise several properties of amplitudes in the nonlinear sigma model to higher orders. These include the double soft limit and the uniqueness of stripped amplitudes.