Theoretical efforts to predict half-lives of double beta decay

Double beta decay ($2\nu\beta\beta$) is a very rare nuclear process. The reason of the rarity of such decay is the second order forbiddance in the Standard Model of electroweak interactions for this process. Over the last 80 years two-neutrino double beta decay have been observed in 12 nuclei and their half-lives range from $10^{19}$ to $10^{24}$ years. This article is concerned with methods of theoretical calculations of half-lives of double beta decay. Also some attempts to describe the experimental data using empirical formulas are under consideration.