Quantum Grothendieck Polynomials

Quantum K-theory is a K-theoretic version of quantum cohomology, which was recently defined by Y.-P. Lee. Based on a presentation for the quantum K-theory of the classical flag variety Fl_n, we define and study quantum Grothendieck polynomials. We conjecture that they represent Schubert classes (i.e., the natural basis elements) in the quantum K-theory of Fl_n, and present strong evidence for this conjecture. We describe an efficient algorithm which, if the conjecture is true, computes the quantum K-invariants of Gromov-Witten type for Fl_n. Two explicit constructions for quantum Grothendieck polynomials are presented. The natural generalizations of several properties of Grothendieck polynomials and of the quantum Schubert polynomials due to Fomin, Gelfand, and Postnikov are proved for our quantum Grothendieck polynomials. For instance, we use a quantization map satisfying a factorization property similar to the cohomology quantization map, and we derive a Monk-type multiplication formula. We also define quantum double Grothendieck polynomials and derive a Cauchy identity. Our constructions are considerably more complex than those for quantum Schubert polynomials. In particular, a crucial ingredient in our work is the Pieri formula for Grothendieck polynomials due to the first author and Sottile.