ИСТИНА

It is well-known that anti-de Sitter Lie algebra o(2,3) has a standard Z_2-graded superextension. Recently it was shown that de Sitter Lie algebra o(1,4) admits a superextension based on the Z_2×Z_2-grading. A main aim of this talk is to show that there exits a nontrivial superextention of de Sitter and anti-de Sitter Lie algebras simultaneously. Using the standard contraction procedure for this superextension we obtain an Z_2×Z_2-graded superalgebra which contains simultaneously standard (Z_2-graded) and alternative (Z_2×Z_2-graded) super-Poincar´e algebras with N = 2,4, . . . supercharge multiplets.