Pions as gluons in higher dimensions
Clifford Cheung (Walter Burke Institute for Theoretical Physics, California Institute of Technology, Pasadena, CA, 91125, U.S.A.); Grant Remmen (Theoretical Physics Group, Lawrence Berkeley National Laboratory, Berkeley, CA, 94720, U.S.A., Berkeley Center for Theoretical Physics, Department of Physics, University of California, Berkeley, CA, 94720, U.S.A.); Chia-Hsien Shen (Mani L. Bhaumik Institute for Theoretical Physics, Department of Physics and Astronomy, UCLA, Los Angeles, CA, 90095, U.S.A.); Congkao Wen (Walter Burke Institute for Theoretical Physics, California Institute of Technology, Pasadena, CA, 91125, U.S.A., Mani L. Bhaumik Institute for Theoretical Physics, Department of Physics and Astronomy, UCLA, Los Angeles, CA, 90095, U.S.A.)
We derive the nonlinear sigma model as a peculiar dimensional reduction of Yang-Mills theory. In this framework, pions are reformulated as higher-dimensional gluons arranged in a kinematic configuration that only probes cubic interactions. This procedure yields a purely cubic action for the nonlinear sigma model that exhibits a symmetry enforcing color-kinematics duality. Remarkably, the associated kinematic algebra originates directly from the Poincaré algebra in higher dimensions. Applying the same construction to gravity yields a new quartic action for Born-Infeld theory and, applied once more, a cubic action for the special Galileon theory. Since the nonlinear sigma model and special Galileon are subtly encoded in the cubic sectors of Yang-Mills theory and gravity, respectively, their double copy relationship is automatic.