arXiv subjects

Kohei Yamaguchi

Publications and source records attributed to Kohei Yamaguchi.

7 recordsLinked to original sources

arXiv2026

Relativistic Toda lattice of type B and quantum $K$-theory of type C flag variety

We introduce a classical integrable system associated with the torus-equivariant quantum $K$-theory of type C flag variety. We prove that its conserved quantities coincide with the generators of the defining ideal of the Borel presentation of the quantum $K$-ring obtained by Kouno and Naito. In particular, the Hamiltonian of the system is naturally regarded as a type B analogue of the relativistic Toda lattice introduced by Ruijsenaars. We also construct B\"acklund transformations describing the discrete time evolution of the system. This construction makes explicit the integrable structure underlying the quantum $K$-theory and provides a framework for further studies of the $K$-theoretic Peterson isomorphism.

math.RT↗

arXiv2025

Relativistic Toda Lattice and Equivariant $K$-Homology of Affine Grassmannian

We investigate the phenomenon known as ''quantum equals affine'' in the setting of $T$-equivariant quantum $K$-theory of the flag variety $G/B$, as established by Kato for any semisimple algebraic group $G$. In particular, we focus on the $K$-Peterson isomorphism between the $T$-equivariant quantum $K$-ring $QK_T(\mathrm{SL}_n(\mathbb{C})/B)$ and the $T$-equivariant $K$-homology ring $K_*^T(\mathrm{Gr}_{\mathrm{SL}_n})$ of the affine Grassmannian, after suitable localizations on both sides. Building on an earlier work by Ikeda, Iwao, and Maeno, we present an explicit algebraic realization of the $K$-Peterson map via a rational substitution that sends the generators of the quantum $K$-theory ring to explicit rational expressions in the fundamental generators of $K_*^T(\mathrm{Gr}_{\mathrm{SL}_n})$, thereby matching the Schubert bases on both sides. Our approach builds on recent developments in the theory of $QK_T(\mathrm{SL}_n(\mathbb{C})/B)$ by Maeno, Naito, and Sagaki, as well as the theory of $K$-theoretic double $k$-Schur functions introduced by Ikeda, Shimozono, and Yamaguchi. This concrete formulation provides new insight into the combinatorial structure of the $K$-Peterson isomorphism in the equivariant setting. As an application, we establish a factorization formula for the $K$-theoretic double $k$-Schur function associated with the maximal $k$-irreducible $k$-bounded partition.

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arXiv2024

Equivariant $K$-homology of affine Grassmannian and $K$-theoretic double $k$-Schur functions

We study the torus equivariant K-homology ring of the affine Grassmannian $\mathrm{Gr}_G$ where $G$ is a connected reductive linear algebraic group. In type $A$, we introduce equivariantly deformed symmetric functions called the K-theoretic double $k$-Schur functions as the Schubert bases. The functions are constructed by Demazure operators acting on equivariant parameters. As an application, we provide a Ginzburg-Peterson type realization of the torus-equivariant K-homology ring of $\mathrm{Gr}_{{SL}_n}$ as the coordinate ring of a centralizer family for $PGL_n(\mathbb{C})$.

math.RT↗

arXiv2024

Quantum $K$-theory of Lagrangian Grassmannian via parabolic Peterson isomorphism

We study Schubert calculus in the torus-equivariant quantum $K$-ring of the Lagrangian Grassmannian $\mathrm{LG}(n)$. Our main tool is the $K$-theoretic Peterson map due to Kato. The map is from the (localized) equivariant $K$-homology ring $K_{*}^{T}(\mathrm{Gr}_{G})$ of the affine Grassmannian $\mathrm{Gr}_{G}$ of the symplectic group $G=\mathrm{Sp}_{2n}(\mathbb{C})$ to the (localized) torus-equivariant quantum $K$-ring $QK_{T}(\mathrm{LG}(n))$. We determine explicitly the kernel of this map.

math.AG↗

arXiv2023

A review of rank one bispectral correspondence of quantum affine KZ equations and Macdonald-type eigenvalue problems

This note consists of two parts. The first part (§1 and §2) is a partial review of the works by van Meer and Stokman (2010), van Meer (2011) and Stokman (2014) which established a bispectral analogue of the Cherednik correspondence between quantum affine Knizhnik-Zamolodchikov equations and the eigenvalue problems of Macdonald type. In this review we focus on the rank one cases, i.e., on the reduced type $A_1$ and the non-reduced type $(C_1^\vee,C_1)$, to which the associated Macdonald-Koornwinder polynomials are the Rogers polynomials and the Askey-Wilson polynomials, respectively. We give detailed computations and formulas that may be difficult to find in the literature. The second part (§3) is a complement of the first part, and is also a continuation of our previous study (Y.-Y., 2022) on the parameter specialization of Macdonald-Koornwinder polynomials, where we found four types of specialization of the type $(C_1^\vee,C_1)$ parameters (which could be called the Askey-Wilson parameters) to recover the type $A_1$. In this note, we show that among the four specializations there is only one which is compatible with the bispectral correspondence discussed in the first part.

math.QA↗

arXiv2021

Specializing Koornwinder polynomials to Macdonald polynomials of type $B,C,D$ and $B C$

We study the specializations of parameters in Koornwinder polynomials to obtain Macdonald polynomials associated to the subsystems of the affine root system of type $(C_n^\vee,C_n)$ in the sense of Macdonald (2003), and summarize them in what we call the specialization table. As a verification of our argument, we check the specializations to type $B,C$ and $D$ via Ram-Yip type formulas of non-symmetric Koornwinder and Macdonald polynomials.

math.QA↗

arXiv2020

A Littlewood-Richardson rule for Koornwinder polynomials

Koornwinder polynomials are $q$-orthogonal polynomials equipped with extra five parameters and the $B C_n$-type Weyl group symmetry, which were introduced by Koornwinder (1992) as multivariate analogue of Askey-Wilson polynomials. They are now understood as the Macdonald polynomials associated to the affine root system of type $(C^\vee_n,C_n)$ via the Macdonald-Cherednik theory of double affine Hecke algebras. In this paper we give explicit formulas of Littlewood-Richardson coefficients for Koornwinder polynomials, i.e., the structure constants of the product as invariant polynomials. Our formulas are natural $(C^\vee_n,C_n)$-analogue of Yip's alcove-walk formulas (2012) which were given in the case of reduced affine root systems.

math.RT↗