RT Book, Whole DB /z-wcorg/ DS http://worldcat.org ID 61309399 LA English T1 Convexity properties of Hamiltonian group actions A1 Guillemin, Victor,, Sjamaar, Reyer,, PB American Mathematical Society PP Providence, R.I. YR 2005 SN 0821839187 9780821839188 AB "This is a monograph on convexity properties of moment mappings in symplectic geometry. The fundamental result in this subject is the Kirwan convexity theorem, which describes the image of a moment map in terms of linear inequalities. This theorem bears a close relationship to perplexing old puzzles from linear algebra, such as the Horn problem on sums of Hermitian matrices, on which considerable progress has been made in recent years following a breakthrough by Klyachko. The book presents a simple local model for the moment polytope, valid in the "generic" case, and an elementary Morse-theoretic argument deriving the Klyachko inequalities and some of their generalizations. It reviews various infinite-dimensional manifestations of moment convexity, such as the Kostant type theorems for orbits of a loop group (due to Atiyah and Pressley) or a symplectomorphism group (due to Bloch, Flaschka and Ratiu). Finally, it gives an account of a new convexity theorem for moment map images of orbits of a Borel subgroup of a complex reductive group acing on a Kahler manifold, based on potential-theoretic methods in several complex variables."--BOOK JACKET.