#### Vol. 2, No. 7, 2008

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Quasimaps, straightening laws, and quantum cohomology for the Lagrangian Grassmannian

### James Ruffo

Vol. 2 (2008), No. 7, 819–858
##### Abstract

The Drinfel’d Lagrangian Grassmannian compactifies the space of algebraic maps of fixed degree from the projective line into the Lagrangian Grassmannian. It has a natural projective embedding arising from the canonical embedding of the Lagrangian Grassmannian. We show that the defining ideal of any Schubert subvariety of the Drinfel’d Lagrangian Grassmannian is generated by polynomials which give a straightening law on an ordered set. Consequentially, any such subvariety is Cohen–Macaulay and Koszul. The Hilbert function is computed from the straightening law, leading to a new derivation of certain intersection numbers in the quantum cohomology ring of the Lagrangian Grassmannian.

##### Keywords
algebra with straightening law, quasimap, Lagrangian Grassmannian, quantum cohomology
##### Mathematical Subject Classification 2000
Primary: 13F50
Secondary: 13P10, 14N35, 14N15