New chiral structures for baryon number violating nucleon decays

Abstract

We examine the most general nucleon decay interactions that involve three light quarks without being acted upon by a derivative. We identify four generic operator structures that correspond to the irreducible representations in the chiral group ${\rm SU(3)}_{\tt L}\otimes {\rm SU(3)}_{\tt R}$ of QCD, \{$\pmb{8}_{\tt L}\otimes \pmb{1}_{\tt R}$, $\bar{\pmb{3}}_{\tt L}\otimes \pmb{3}_{\tt R}$, $\pmb{6}_{\tt L}\otimes \pmb{3}_{\tt R}$, $\pmb{10}_{\tt L}\otimes \pmb{1}_{\tt R}$\}, plus their chirality partners under the interchange of chiralities ${\tt L}\leftrightarrow {\tt R}$. While half of them have been extensively discussed in the literature, the other half, $\pmb{6}_{\tt L(R)}\otimes \pmb{3}_{\tt R(L)}$ and $\bar{\pmb{10}}_{\tt L(R)}\otimes \pmb{1}_{\tt R(L)}$, are identified for the first time. We perform chiral matching for these interactions at the leading chiral order and find that each has a unique chiral realization in terms of the octet baryons and pseudoscalars. Notably, the chiral interaction in the $\pmb{6}_{\tt L(R)}\otimes \pmb{3}_{\tt R(L)}$ representation appears at the same chiral order as those of the known ones, while the one in the $\pmb{10}_{\tt L(R)}\otimes \pmb{1}_{\tt R(L)}$ representation appears at a higher chiral order. These new structures are prevalent in effective field theories and ultraviolet models, and they offer novel experimental avenues to search for baryon number violating nucleon decays.