Alpha-alpha scattering in the Multiverse
Serdar Elhatisari (Faculty of Natural Sciences and Engineering, Gaziantep Islam Science and Technology University, Gaziantep, 27010, Turkey); Timo Lähde (Institute for Advanced Simulation, Institut für Kernphysik, Center for Advanced Simulation and Analytics, and Jülich Center for Hadron Physics, Forschungszentrum Jülich, Jülich, D-52425, Germany); Dean Lee (Facility for Rare Isotope Beams and Department of Physics and Astronomy, Michigan State University, East Lansing, MI, 48824, USA); Ulf-G. Meißner (Tbilisi State University, Tbilisi, 0186, Georgia, Helmholtz-Institut für Strahlen- und Kernphysik and Bethe Center for Theoretical Physics, Universität Bonn, Bonn, D-53115, Germany, Institute for Advanced Simulation, Institut für Kernphysik, Center for Advanced Simulation and Analytics, and Jülich Center for Hadron Physics, Forschungszentrum Jülich, Jülich, D-52425, Germany); Thomas Vonk (Helmholtz-Institut für Strahlen- und Kernphysik and Bethe Center for Theoretical Physics, Universität Bonn, Bonn, D-53115, Germany)
We investigate the phase shifts of low-energy α-α scattering under variations of the fundamental parameters of the Standard Model, namely the light quark mass, the electromagnetic fine-structure constant as well as the QCD θ-angle. As a first step, we recalculate α-α scattering in our Universe utilizing various improvements in the adiabatic projection method, which leads to an improved, parameter-free prediction of the S- and D-wave phase shifts for laboratory energies below 10 MeV. We find that positive shifts in the pion mass have a small effect on the S-wave phase shift, whereas lowering the pion mass adds some repulsion in the two-alpha system. The effect on the D-wave phase shift turns out to be more pronounced as signaled by the D-wave resonance parameters. Variations of the fine-structure constant have almost no effect on the low-energy α-α phase shifts. We further show that up-to-and-including next-to-leading order in the chiral expansion, variations of these phase shifts with respect to the QCD θ-angle can be expressed in terms of the θ-dependent pion mass.
