Can Pions and Weak Magnetism in 2νββ Tell Us Something About BSM Physics?

With experiments improving their 2𝜈𝛽𝛽 measurements, there is growing demand for precision in its theoretical calculation. A correction that has been applied to single 𝛽-decay and 0𝜈𝛽𝛽, but not yet to 2𝜈𝛽𝛽, is the chiral correction. This correction includes the chiral potential generated by pion exchange, and the addition of weak nuclear magnetism. We show that the chiral potential reduces the half life by a few percent, which may be experimentally determined once NME uncertainties have sufficiently decreased. We also show that the weak magnetic correction modifies the spectral shape at the sub-percent level. Which ought to be included in future high-precision measurements of 𝜉31 and 𝜉51, as well as in certain BSM scenarios, such as those involving sterile neutrinos.