We consider neutralino annihilation in dense extragalactic systems known to be dominated by dark matter, in particular M87 and several local dwarf spheroidal galaxies. These annihilations can produce energetic gamma rays which may be visible to atmosphericČerenkov telescopes. We explore the supersymmetric parameter space, and compute the expected flux of gamma-rays coming from these objects. It is shown that some parts of the parameter space lead to a signal observable with the next generation ofČerenkov telescopes, provided the supersymmetric dark matter has a clumpy structure, as may be expected in a hierarchical scenario for structure formation. 95.35.+d, 14.80.Ly, 95.85.Pw, 98.70.Rz

We construct a wide class of finite W-algebras as truncations of Yangians. These truncations correspond to algebra homomorphisms and allow to construct the Walgebras as exchange algebras, the R-matrix being the Yangian's one.As an application, we classify all irreducible finite dimensional representations of these W-algebras and determine their center.

We show that some finite W-superalgebras based on gl(M |N ) are truncation of the super-Yangian Y (gl(M |N )). In the same way, we prove that finite W-superalgebras based on osp(M |2n) are truncation of the twisted super-Yangians Y (gl(M |2n)) + . Using this homomorphism, we present these W-superalgebras in an R-matrix formalism, and we classify their finite-dimensional irreducible representations.math.QA/0209339

Starting with the super-Yangian Y(M|N) based on gl(M|N), we define twisted super-Yangians Y(M|N)±. Only Y+(M|2n) and Y−(2m|N) can be defined, and appear to be isomorphic one with each other. We study their finite-dimensional irreducible highest weight representations.