Abstract
Let \(G\) be a semi-simple simply connected group over \(\mathbb {C}\). Following Gerasimov et al. (Comm Math Phys 294:97–119, 2010) we use the \(q\)-Toda integrable system obtained by quantum group version of the Kostant–Whittaker reduction (cf. Etingof in Am Math Soc Trans Ser 2:9–25, 1999, Sevostyanov in Commun Math Phys 204:1–16, 1999) to define the notion of \(q\)-Whittaker functions \(\varPsi _{\check{\lambda }}(q,z)\). This is a family of invariant polynomials on the maximal torus \(T\subset G\) (here \(z\in T\)) depending on a dominant weight \(\check{\lambda }\) of \(G\) whose coefficients are rational functions in a variable \(q\in \mathbb {C}^*\). For a conjecturally the same (but a priori different) definition of the \(q\)-Toda system these functions were studied by Ion (Duke Math J 116:1–16, 2003) and by Cherednik (Int Math Res Notices 20:3793–3842, 2009) [we shall denote the \(q\)-Whittaker functions from Cherednik (Int Math Res Notices 20:3793–3842, 2009) by \(\varPsi '_{\check{\lambda }}(q,z)\)]. For \(G=SL(N)\) these functions were extensively studied in Gerasimov et al. (Comm Math Phys 294:97–119, 2010; Comm Math Phys 294:121–143, 2010; Lett Math Phys 97:1–24, 2011). We show that when \(G\) is simply laced, the function \(\hat{\varPsi }_{\check{\lambda }}(q,z)=\varPsi _{\check{\lambda }}(q,z)\cdot {\prod \nolimits _{i\in I}\prod \nolimits _{r=1}^{\langle \alpha _i,\check{\uplambda }\rangle }(1-q^r)}\) (here \(I\) denotes the set of vertices of the Dynkin diagram of \(G\)) is equal to the character of a certain finite-dimensional \(G[[{\mathsf {t}}]]\rtimes \mathbb {C}^*\)-module \(D(\check{\lambda })\) (the Demazure module). When \(G\) is not simply laced a twisted version of the above statement holds. This result is known for \(\varPsi _{\check{\lambda }}\) replaced by \(\varPsi '_{\check{\lambda }}\) (cf. Sanderson in J Algebraic Combin 11:269–275, 2000 and Ion in Duke Math J 116:1–16, 2003); however our proofs are algebro-geometric [and rely on our previous work (Braverman, Finkelberg in Semi-infinite Schubert varieties and quantum \(K\)-theory of flag manifolds, arXiv/1111.2266, 2011)] and thus they are completely different from Sanderson (J Algebraic Combin 11:269–275, 2000) and Ion (Duke Math J 116:1–16, 2003) [in particular, we give an apparently new algebro-geometric interpretation of the modules \(D(\check{\lambda })]\).
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In fact, as we are going to explain later, the results of this paper together with the results of [18] imply that \({\mathcal {M}}_f={\mathcal {M}}_f'\) for any \(G\), but we would like to have a more direct proof of this fact.
References
Braverman, A., Finkelberg, M.: Finite difference quantum Toda lattice via equivariant \(K\)-theory. Transform. Groups 10, 363–386 (2005)
Braverman, A., Finkelberg, M.: Semi-infinite Schubert varieties and quantum \(K\)-theory of flag manifolds. arXiv/1111.2266 (2011)
Chari, V., Fourier, G., Khandai, T.: A categorical approach to Weyl modules. Transform. Groups 15(3), 517–549 (2010)
Chari, V., Loktev, S.: Weyl, Demazure and fusion modules for the current algebra of \({\mathfrak{sl}}_{r+1}\). Adv. Math. 207(2), 928–960 (2006)
Cherednik, I.: Whittaker limits of difference spherical functions. Int. Math. Res. Notices 20, 3793–3842 (2009)
Drinfeld, V.: On the Grinberg–Kazhdan formal arc theorem. arXiv:math/0203263
Etingof, P.: Whittaker functions on quantum groups and \(q\)-deformed Toda operators. Am. Math. Soc. Trans. Ser. 2(194), 9–25 (1999)
Feigin, B., Finkelberg, M., Mirković, I., Kuznetsov, A.: Semi-infinite flags. II. Local and global Intersection Cohomology of Quasimaps’ spaces. In: Differential topology, infinite-dimensional Lie algebras, and applications. American Mathematical Society Translations Series 2, vol. 194, pp. 113–148. American Mathemathical Society, Providence, RI (1999)
Feigin, B., Feigin, E., Jimbo, M., Miwa, T., Mukhin, E.: Fermionic formulas for eigenfunctions of the difference Toda Hamiltonian. Lett. Math. Phys. 88, 39–77 (2009)
Finkelberg, M., Kuznetsov, A.: Global intersection cohomology of quasimaps’ spaces. Int. Math. Res. Notices 7, 301–328 (1997)
Fourier, G., Kus, D.: Demazure and Weyl modules: the twisted current case. Trans. Am. Math. Soc. 365(11), 6037–6064 (2013)
Fourier, G., Littelmann, P.: Weyl modules, Demazure modules, KR-modules, crystals, fusion products and limit constructions. Adv. Math. 211(2), 566–593 (2007)
Gerasimov, A., Lebedev, D., Oblezin, S.: On \(q\)-deformed \({\mathfrak{gl}}_{l+1}\)-Whittaker function. I. Comm. Math. Phys. 294, 97–119 (2010)
Gerasimov, A., Lebedev, D., Oblezin, S.: On \(q\)-deformed \({\mathfrak{gl}}_{l+1}\)-Whittaker function. II. Comm. Math. Phys. 294, 121–143 (2010)
Gerasimov, A., Lebedev, D., Oblezin, S.: On \(q\)-deformed \({\mathfrak{gl}}_{l+1}\)-Whittaker function. III. Lett. Math. Phys. 97(1), 1–24 (2011)
Givental, A., Lee, Y.-P.: Quantum K-theory on flag manifolds, finite-difference Toda lattices and quantum groups. Invent. Math. 151, 193–219 (2003)
Grinberg, M., Kazhdan, D.: Versal deformations of formal arcs. Geom. Funct. Anal. 10, 543–555 (2000)
Ion, B.: Nonsymmetric Macdonald polynomials and Demazure characters. Duke Math. J. 116(2), 299–318 (2003)
Lenart, C., Naito, S., Sagaki, D., Schilling, A., Shimozono, M.: A uniform model for Kirillov-Reshetikhin crystals. Extended abstract. arXiv:1211.6019 (2011)
Sanderson, Y.: On the connection between Macdonald polynomials and Demazure characters. J. Algebraic Combin. 11(3), 269–275 (2000)
Sevostyanov, A.: Regular nilpotent elements and quantum groups. Commun. Math. Phys. 204, 1–16 (1999)
Acknowledgments
This paper emerged as a result of numerous conversations held between the first author and Borodin in IHES in June 2011. In particular, A. Borodin has introduced the first author to the notion of \(q\)-Whittaker functions and brought to his attention the papers [13–15]. The first author wishes also to thank IHES staff for exceptionally pleasant working conditions and hospitality. We are grateful to B. Feigin and S. Loktev for their numerous patient explanations about Weyl modules. The observation that \(\varGamma (G[[{\mathsf {t}}]]/T\cdot U_-[[{\mathsf {t}}]],{\mathcal {O}}(\check{\uplambda }))\) is a dual Weyl module is essentially due to them. We would like to thank K. Schwede and other mathoverflowers for their explanations about Kodaira vanishing. The first author is also deeply indebted to Patrick Clark for his patient explanations about Macdonald polynomials and to Etingof and Cherednik for explanations about the \(q\)-Toda system. M.F. was partially supported by the RFBR grants 12-01-00944, 12-01-33101, 13-01-12401/13, the National Research University Higher School of Economics’ Academic Fund award No.12-09-0062 and the AG Laboratory HSE, RF government grant, ag. 11.G34.31.0023. This study comprises research findings from the “Representation Theory in Geometry and in Mathematical Physics” carried out within The National Research University Higher School of Economics’ Academic Fund Program in 2012, grant No 12-05-0014.
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To the memory of Andrei Zelevinsky who taught us the beauty of symmetric functions.
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Braverman, A., Finkelberg, M. Weyl modules and \(q\)-Whittaker functions. Math. Ann. 359, 45–59 (2014). https://doi.org/10.1007/s00208-013-0985-3
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DOI: https://doi.org/10.1007/s00208-013-0985-3