8 Search Results

We calculate the S-factor for proton–proton fusion using chiral effective field theory interactions and currents. By performing order-by-order calculations with a variety of chiral interactions that are regularized and calibrated in different ways, we assess the uncertainty in the S-factor from the truncation of the effective field theory expansion and from the sensitivity of the S-factor to the short-distance axial current determined from three- and four-nucleon observables. We find that S(0) = (4.100 ± 0.024(syst) ± 0.013(stat) ± 0.008(g$$_{A}$$)) × 10$$^{−23}$$ MeV fm$$^{2}$$, where the three uncertainties arise, respectively, from the truncation of the effective field theory expansion, use ofmore » the two-nucleon axial current fit to few-nucleon observables and variation of the axial coupling constant within the recommended range. The increased value of S(0) compared to previous calculations is mainly driven by an increase in the recommended value for the axial coupling constant and is in agreement with a recent analysis based on pionless effective field theory.« less

Here, we consider the capture of a muon on a deuteron. An uncertainty analysis of the dominant channels is important for a careful analysis of forthcoming experimental data. We quantify the theoretical uncertainties of chiral effective-field-theory predictions of the muon-deuteron capture rate from the relevant neutron-neutron partial wave channels in the final state. We study the dependence on the cutoff used to regularize the interactions, low-energy constants calibrated using different fitting data and strategies, and truncation of the effective-field-theory expansion of the currents. Combining these approaches gives as an estimate of $$Γ^{1/2}_{μd}$$ = 399.1 ± 7.6 ± 4.4 s^–1 formore » capture from the atomic doublet state, and $$Γ^{3/2}_{μd}$$= 12.31 ± 0.47 ± 0.04 s^–1 for capture from the quartet state and the first and second uncertainties given here are due to the effective field theory truncation error and the uncertainty in the axial radius, respectively.« less

Pion exchange is the central ingredient to nucleon-nucleon interactions used in nuclear structure calculations, and one-pion exchange (OPE) enters at leading order in chiral effective field theory. In the ^2S+1L_J = ¹S₀ partial wave, however, OPE and a contact term needed for proper renormalization fail to produce the qualitative, and quantitative, features of the scattering phase shifts. Cutoff variation also revealed a surprisingly low breakdown momentum Λ_b ≈ 330 MeV in this partial wave. Here we show that potentials consisting of OPE, two-pion exchange (TPE), and a single contact address these problems and yield accurate and renormalization group (RG) invariantmore » phase shifts in the ¹S₀ partial wave. Here, we demonstrate that a leading-order potential with TPE can be systematically improved by adding a contact quadratic in momenta. For momentum cutoffs Λ ≲ 500 MeV, the removal of relevant physics from TPE loops needs to be compensated by additional contacts to keep RG invariance. Inclusion of the Δ isobar degree of freedom in the potential does not change the strong contributions of TPE.« less

We consider the system of three ⁴He atoms to assess whether a pure van der Waals potential can be used as a starting point for an effective field theory to describe three-body processes in ultracold atomic systems. Using a long-range van der Waals interaction in combination with short-distance two-body counterterms, we analyze the dependence of two- and three-body observables on the short-distance regulator that is required due to the singular nature of the van der Waals interaction. We benchmark our approach with results obtained with the realistic ⁴He-⁴He LM2M2 potential and find good agreement. We furthermore show that in thismore » effective field theory approach no three-body force is required at leading order and that universal van der Waals physics leads to a universal correlation between three-body observables in the absence of an Efimov three-body parameter.« less