Alpha-alpha scattering in the Multiverse

Abstract

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.

Probing nuclear observables via primordial nucleosynthesis

“…A similar treatment of other reactions is the subject of current research, see e.g. the discussion of α − α scattering in [38]. A first application of the insight obtained here will be a reassessment of the dependence of primordial abundances on the electromagnetic fine-structure constant [39].…”

Axions in Baryon Chiral Perturbation Theory

“…While this instanton solution was the starting point for the resolution of the U(1) 𝐴 problem proposed by t'Hooft [4,5], it at the same time lead to a new, still unresolved issue in QCD: the strong CP-problem. QCD with the 𝜃-term is not CP-invariant as a non-vanishing 𝜃 angle leads to a contribution to the neutron electric dipole moment (nEDM) ∝ θ = 𝜃 + Arg det M [6] and affects meson and nucleon masses, as well as nuclear interactions and stellar and Big Bang nucleosynthesis [7,8]. However, theoretical estimations of the nEDM, which roughly vary between |𝑑 𝑛 | ≈ 10 −16 θ 𝑒 cm and |𝑑 𝑛 | ≈ 10 −15 θ 𝑒 cm [9,10], and recent measurements yielding |𝑑 exp 𝑛 | < 1.8 × 10 −26 𝑒 cm (90 % C.L.)…”

“…it is clear from Eqs. ( 4), (8), and ( 11) that any axion-baryon coupling can be organized in terms of inverse powers of the expectedly large parameter 𝑓 𝑎 , because…”

Constructing Inverse Scattering Potentials for α-α System using Physics Informed Machine Learning

“…To solve this crucial issue, we focused on α − α scattering in our article. This particular reaction has great importance in stellar astrophysics [2] and also in understanding the Hoyle state in 1 2C [3]. Current research on α − α scattering involves NLEFT alongside lattice QCD calculations [3,4].…”

“…This particular reaction has great importance in stellar astrophysics [2] and also in understanding the Hoyle state in 1 2C [3]. Current research on α − α scattering involves NLEFT alongside lattice QCD calculations [3,4]. To account for long range Coulomb interaction in alpha-alpha scattering [2], a Coulomb-modified effective range expansion from NLO onwards is utilized and lattice calculations are performed in a box of (100-120 fm) 3 [2,3], by assuming that it is far beyond the strong interaction range.…”