The first part of this thesis concerns intersection cohomology sheaves on a smooth projective variety with a torus action that has finitely many fixed points. Under some additional assumptions, we consider tensor products of intersection cohomology sheaves on a Bialynicki-Birula stratification of the variety. We give a formula for the hypercohomology of the tensor product in terms of the tensor products of the individual sheaves, as well as the cohomology of the variety. We prove a similar result in the setting of equivariant cohomology.;In the second part of this thesis, we study the Bernstein-Sato polynomial, or the b-function, which is an invariant of singularities of hypersurfaces. We are interested in the b-function of hyperplane arrangements of Weyl arrangements, which are the arrangements of root systems of semi-simple Lie algebras. It has been conjectured that the poles of the local topological zeta function, which is another invariant of hypersurface singularities, are all roots of the b-function. Using the work of Opdam and Budur-Mustata-Teitler, we prove this conjecture for all Weyl arrangements. We also give an upper bound for the b-function of the Vandermonde determinant, which cuts out the Weyl arrangement in type A..
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