Chiral Two-Body Currents and Neutrinoless Double-Beta Decay in the QRPA

Understand

We test the effects of an approximate treatment of two-body contributions to the axial-vector current on the QRPA matrix elements for neutrinoless double-beta decay in a range of isotopes.

• The form and strength of the two-body terms come from chiral effective-field theory.
• The two-body currents typically reduce the matrix elements by about 20%, not as much as in shell-model calculations.
• One reason for the difference is that standard practice in the QRPA is to adjust the strength of the isoscalar pairing interaction to reproduce two-neutrino double-beta decay lifetimes.