The strangeness-changing $(\mathrm{<ruby><rb>\Delta </rb><rt>でるた</rt></ruby>}S=1)$ weak baryon-baryon interaction is studied through the nonmesonic weak decay (NMD) of double-Λらむだ hypernuclei. Besides the usual nucleon-induced decay $\mathrm{<ruby><rb>\Lambda </rb><rt>らむだ</rt></ruby>}N\to \mathrm{NN}$ we discuss novel hyperon-induced decay modes $\mathrm{<ruby><rb>\Lambda </rb><rt>らむだ</rt></ruby>}\mathrm{<ruby><rb>\Lambda </rb><rt>らむだ</rt></ruby>}\to \mathrm{<ruby><rb>\Lambda </rb><rt>らむだ</rt></ruby>}N$ and $\mathrm{<ruby><rb>\Lambda </rb><rt>らむだ</rt></ruby>}\mathrm{<ruby><rb>\Lambda </rb><rt>らむだ</rt></ruby>}\to \mathrm{<ruby><rb>\Sigma </rb><rt>しぐま</rt></ruby>}N.\mathrm{}$ These reactions provide unique access to the exotic $\mathrm{<ruby><rb>\Lambda </rb><rt>らむだ</rt></ruby>}\mathrm{<ruby><rb>\Lambda </rb><rt>らむだ</rt></ruby>}K$ and $\mathrm{<ruby><rb>\Lambda </rb><rt>らむだ</rt></ruby>}\mathrm{<ruby><rb>\Sigma </rb><rt>しぐま</rt></ruby>}K$ vertices that place new constraints on chiral pertubation theory $\left(\mathrm{<ruby><rb>\chi </rb><rt>かい</rt></ruby>}\mathrm{PT}\right)\mathrm{}$ in the weak SU(3) sector. Within a meson-exchange framework, we use the pseudoscalar $\mathrm{<ruby><rb>\pi </rb><rt>ぱい</rt></ruby>},\mathrm{<ruby><rb>\eta </rb><rt>いーた</rt></ruby>},K$ octet for the long-range part while parametrizing the short-range part through the vector mesons $\mathrm{<ruby><rb>\rho </rb><rt>ろー</rt></ruby>},\mathrm{<ruby><rb>\omega </rb><rt>おめが</rt></ruby>}{,K}^{*}.$ Realistic baryon-baryon forces for the $S=0,$ -1, and -2 sectors account for the strong interaction in the initial and final states. For ${}_{\mathrm{<ruby><rb>\Lambda </rb><rt>らむだ</rt></ruby>}\mathrm{<ruby><rb>\Lambda </rb><rt>らむだ</rt></ruby>}}^6\mathrm{He}$ the new hyperon-induced decay modes account for up to 4% of the total nonmesonic decay rate. Predictions are made for all possible nonmesonic decay modes.

• Received 22 June 2001

DOI:https://doi.org/10.1103/PhysRevC.65.015205