11.07.2015 Views

International Congress of Mathematicians

International Congress of Mathematicians

International Congress of Mathematicians

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606 A. KlyachkoUnitary spectral problem. Find possible spectra <strong>of</strong> product X(UV), when spectra<strong>of</strong> the factors X(U), X(V) are given.To state the result we need in quantum cohomology H*(Gp <strong>of</strong> GrassmannianGp <strong>of</strong> linear subspaces <strong>of</strong> dimension p and codimension r. This is an algebra overpolynomial ring C[q] generated by Schubert cycles 07, J C {1,2,... ,n}, |J| = p,n = p + r with multiplication given by the formulaO-I * O-J = ^2K,dC fj( d ) ( Ì d(T Kwhere structure constants cfj(d) are defined as follows. Let G| < L -¥ W(f\ p C n )Pliicker imbedding andbetp : P 1 -• G r pbe a rational curve <strong>of</strong> degree d in Gressmanian G| C W(f\ p C n ). One can checkthat Lp depends on dimG| + nd parameters. For fixed point x £ P 1 the conditionifi(x) £ a 1 imposes codim 07 constraints on ip. Hence forthe numberscodim a 1 + codim a j + codim OK = dim G r p + nd(a 1, a j, a K )d = #{

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