http://arxiv.org/abs/2112.09409
We investigate the phase shifts of low-energy $\alpha$-$\alpha$ 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 $\theta$-angle. As a first step, we recalculate $\alpha$-$\alpha$ 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 tends to unbind the two-alpha system, limiting such variations to less than 7%. 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 $\alpha$-$\alpha$ 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 $\theta$-angle can be expressed in terms of the $\theta$-dependent pion mass.
S. Elhatisari, T. Lähde, D. Lee, et. al.
Mon, 20 Dec 21
33/59
Comments: 22 pages, 8 figures