Shell-Model Calculations of Two-Nucleon Tansfer Related to Double Beta Decay*

I will discuss theoretical results for two-nucleon transfer cross sections for nuclei in the regions of $^{48}$Ca, $^{76}$Ge and $^{136}$Xe of interest for testing the wavefuntions used for the nuclear matrix elements in double-beta decay. Various reaction models are used. A simple cluster transfer model gives relative cross sections. Thompson's code Fresco with direct and sequential transfer is used for absolute cross sections. Wavefunctions are obtained in large-basis proton-neutron coupled model spaces with the code NuShellX with realistic effecive Hamiltonians such as those used for the recent results for $^{136}$Xe [M. Horoi and B. A. Brown, Phys. Rev. Lett. 110, 222502 (2013)].