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Yuki Kanakubo

Publications and source records attributed to Yuki Kanakubo.

At least 19 recordsLinked to original sources
arXiv2025

Products of Kirillov-Reshetikhin modules and maximal green sequences

We show that a $q$-character of a Kirillov-Reshetikhin module (KR modules) for untwisted quantum affine algebras of simply laced types $A_n^{(1)}$, $D_n^{(1)}$, $E_6^{(1)}$, $E_7^{(1)}$, $E_8^{(1)}$ might be obtained from a specific cluster variable of a seed obtained by applying a maximal green sequence to the initial (infinite) quiver of the Hernandez-Leclerc cluster algebra. For a collection of KR-modules with nested supports, we show an explicit construction of a cluster seed, which has cluster variables corresponding to the $q$-characters of KR-modules of such a collection. We prove that the product of KR-modules of such a collection is a simple module. We also construct cluster seeds with cluster variables corresponding to $q$-characters of KR-modules of some non-nested collections. We make a conjecture that tensor products of KR-modules for such non-nested collections are simple. We show that the cluster Donaldson-Thomas transformations for double Bruhat cells for $ADE$ types can be computed using $q$-characters of KR-modules.

math.RT↗
arXiv2025

A conjecture on monomial realizations and polyhedral realizations for crystal bases

Crystal bases are powerful combinatorial tools in the representation theory of quantum groups $U_q(\mathfrak{g})$ for a symmetrizable Kac-Moody algebras $\mathfrak{g}$. The polyhedral realizations are combinatorial descriptions of the crystal base $B(\infty)$ for Verma modules in terms of the set of integer points of a polyhedral cone, which equals the string cone when $\mathfrak{g}$ is finite dimensional simple. It is a fundamental and natural problem to find explicit forms of the polyhedral cone. The monomial realization expresses crystal bases $B(λ)$ of integrable highest weight representations as Laurent monomials with double indexed variables. In this paper, we give a conjecture between explicit forms of the polyhedral cones and monomial realizations. We prove the conjecture is true when $\mathfrak{g}$ is a classical Lie algebra, a rank $2$ Kac-Moody algebra or a classical affine Lie algebra.

math.QA↗
arXiv2024

Polyhedral realizations for crystal bases and Young walls of classical affine types

For affine Lie algebra $\mathfrak{g}$ of type $A^{(1)}_{n-1}$, $B^{(1)}_{n-1}$, $C^{(1)}_{n-1}$, $D^{(1)}_{n-1}$, $A^{(2)}_{2n-2}$, $A^{(2)}_{2n-3}$ or $D^{(2)}_{n}$, let $B(λ)$ and $B(\infty)$ be the crystal bases of integrable highest weight representation $V(λ)$ and negative part $U_q^-(\mathfrak{g})$ of quantum group $U_q(\mathfrak{g})$. We consider the polyhedral realizations of crystal bases, which realize $B(λ)$ and $B(\infty)$ as sets of integer points of some polytopes and cones in $\mathbb{R}^{\infty}$. It is a natural problem to find explicit forms of the polytopes and cones. In this paper, we introduce pairs of truncated walls, which are defined as modifications of level $2$-Young walls and describe inequalities defining the polytopes and cones in terms of level $1$-proper Young walls and pairs of truncated walls. As an application, we also give combinatorial descriptions of $\varepsilon_k^*$-functions on $B(\infty)$ in terms of Young walls and truncated walls.

math.QA↗
arXiv2023

Polyhedral realizations for crystal bases of integrable highest weight modules and combinatorial objects of type ${\rm A}^{(1)}_{n-1}$, ${\rm C}^{(1)}_{n-1}$, ${\rm A}^{(2)}_{2n-2}$, ${\rm D}^{(2)}_{n}$

In this paper, we consider polyhedral realizations for crystal bases $B(λ)$ of irreducible integrable highest weight modules of a quantized enveloping algebra $U_q(\mathfrak{g})$, where $\mathfrak{g}$ is a classical affine Lie algebra of type ${\rm A}^{(1)}_{n-1}$, ${\rm C}^{(1)}_{n-1}$, ${\rm A}^{(2)}_{2n-2}$ or ${\rm D}^{(2)}_{n}$. We will give explicit forms of polyhedral realizations in terms of extended Young diagrams or Young walls that appear in the representation theory of quantized enveloping algebras of classical affine type. As an application, a combinatorial description of $\varepsilon_k^*$ functions on $B(\infty)$ will be given.

math.QA↗
arXiv2023

Cell-sized confinements alter molecular diffusion in concentrated polymer solutions due to length-dependent wetting of polymers

Living cells are characterized by the micrometric confinement of various macromolecules at high concentrations. Using droplets containing binary polymer blends as artificial cells, we previously showed that cell-sized confinement causes phase separation of the binary polymer solutions because of the length-dependent wetting of the polymers. Here we demonstrate that the wetting-induced heterogeneity of polymers also emerges in single-component polymer solutions. The resulting heterogeneity leads to a slower transport of small molecules at the center of cell-sized droplets than that in bulk solutions. This heterogeneous distribution is observed when longer polymers with lower wettability are localized at the droplet center. Molecular simulations support this wetting-induced heterogeneous distribution by polymer length. Our results suggest that cell-sized confinement functions as a structural regulator for polydisperse polymer solutions that specifically manipulate the diffusion of molecules, particularly those with sizes close to the correlation length of the polymer chains.

cond-mat.soft↗
arXiv2022

An algorithm for Berenstein-Kazhdan decoration functions and trails for classical Lie algebras

For a simply connected connected simple algebraic group $G$, it is known that a variety $B_{w_0}^-:=B^-\cap U\overline{w_0}U$ has a geometric crystal structure with a positive structure $θ^-_{\mathbf{i}}:(\mathbb{C}^{\times})^{l(w_0)}\rightarrow B_{w_0}^-$ for each reduced word $\mathbf{i}$ of the longest element $w_0$ of Weyl group. A rational function $Φ^h_{BK}=\sum_{i\in I}Δ_{w_0Λ_i,s_iΛ_i}$ on $B_{w_0}^-$ is called a half-potential, where $Δ_{w_0Λ_i,s_iΛ_i}$ is a generalized minor. Computing $Φ^h_{BK}\circ θ^-_{\mathbf{i}}$ explicitly, we get an explicit form of string cone or polyhedral realization of $B(\infty)$ for the finite dimensional simple Lie algebra $\mathfrak{g}={\rm Lie}(G)$. In this paper, for an arbitrary reduced word $\mathbf{i}$, we give an algorithm to compute the summand $Δ_{w_0Λ_i,s_iΛ_i}\circ θ^-_{\mathbf{i}}$ of $Φ^h_{BK}\circ θ^-_{\mathbf{i}}$ in the case $i\in I$ satisfies that for any weight $μ$ of $V(-w_0Λ_i)$ and $t\in I$, it holds $\langle h_t,μ\rangle\in\{2,1,0,-1,-2\}$. In particular, if $\mathfrak{g}$ is of type ${\rm A}_n$, ${\rm B}_n$, ${\rm C}_n$ or ${\rm D}_n$ then all $i\in I$ satisfy this condition so that one can completely calculate $Φ^h_{BK}\circ θ^-_{\mathbf{i}}$. We will also prove that our algorithm works in the case $\mathfrak{g}$ is of type ${\rm G}_2$.

math.QA↗
arXiv2022

Half Potential on Geometric Crystals and Connectedness of Cellular Crystals

For any simple complex algebraic group, we define upper/lower half-decorated geometric crystals and show that their tropicalization will be upper/lower normal Kashiwara's crystals. In particular, we show that the tropicalization of the half-decorated geometric crystal on the big Bruhat cell(=$B^-_{w_0}:=B^-\cap U\bar w_0 U$) is isomorphic to the crystal $B(\infty)$ of the nilpotent subalgebra of quantum group $U_q^-(\mathfrak g)$. As an application, we shall show that any cellular crystal associated with a reduced word is connected in the sense of a crystal graph.

math.QA↗
arXiv2021

Adapted Sequences and Polyhedral Realizations of Crystal Bases for highest weight modules

The polyhedral realizations for crystal bases of the integrable highest weight modules of $U_q(\mathfrak{g})$ have been introduced in ([T.Nakashima, J. Algebra, vol.219, no. 2, (1999)]), which describe the crystal bases as sets of lattice points in the infinite $\mathbb{Z}$-lattice $\mathbb{Z}^{\infty}$ given by some system of linear inequalities, where $\mathfrak{g}$ is a symmetrizable Kac-Moody Lie algebra. To construct the polyhedral realization, we need to fix an infinite sequence $ι$ from the indices of the simple roots. If the pair ($ι$,$λ$) ($λ$: a dominant integral weight) satisfies the `ample' condition then there are some procedure to calculate the sets of linear inequalities. In this article, we show that if $ι$ is an adapted sequence (defined in our paper [Y.Kanakubo, T.Nakashima, arXiv:1904.10919]) then the pair ($ι$, $λ$) satisfies the ample condition for any dominant integral weight $λ$ in the case $\mathfrak{g}$ is a classical Lie algebra. Furthermore, we reveal the explicit forms of the polyhedral realizations of the crystal bases $B(λ)$ associated with arbitrary adapted sequences $ι$ in terms of column tableaux. As an application, we will give a combinatorial description of the function $\varepsilon_i^*$ on the crystal base $B(\infty)$.

math.QA↗
arXiv2021

Polyhedral realizations for $B(\infty)$ and extended Young diagrams, Young walls of type ${\rm A}^{(1)}_{n-1}$, ${\rm C}^{(1)}_{n-1}$, ${\rm A}^{(2)}_{2n-2}$, ${\rm D}^{(2)}_{n}$

The crystal bases are quite useful combinatorial tools to study the representations of quantized universal enveloping algebras $U_q(\mathfrak{g})$. The polyhedral realization for $B(\infty)$ is a combinatorial description of the crystal base, which is defined as an image of embedding $Ψ_ι:B(\infty)\hookrightarrow \mathbb{Z}^{\infty}_ι$, where $ι$ is an infinite sequence of indices and $\mathbb{Z}^{\infty}_ι$ is an infinite $\mathbb{Z}$-lattice with a crystal structure associated with $ι$. It is a natural problem to find an explicit form of the polyhedral realization ${\rm Im}(Ψ_ι)$. In this article, supposing that $\mathfrak{g}$ is of affine type ${\rm A}^{(1)}_{n-1}$, ${\rm C}^{(1)}_{n-1}$, ${\rm A}^{(2)}_{2n-2}$ or ${\rm D}^{(2)}_{n}$ and $ι$ satisfies the condition of `adaptedness', we describe ${\rm Im}(Ψ_ι)$ by using several combinatorial objects such as extended Young diagrams and Young walls.

math.QA↗
arXiv2021

An algorithm for Berenstein-Kazhdan decoration functions and trails for minuscule representations

For a simply connected connected simple algebraic group $G$, a cell $B_{w_0}^-=B^-\cap U\overline{w_0}U$ is a geometric crystal with a positive structure $θ_{\textbf{i}}^-:(\mathbb{C}^{\times})^{l(w_0)}\rightarrow B_{w_0}^-$. Applying the tropicalization functor to a rational function $Φ^h_{BK}=\sum_{i\in I}Δ_{w_0Λ_i,s_iΛ_i}$ called the half decoration on $B_{w_0}^-$, one can realize the crystal $B(\infty)$ in $\mathbb{Z}^{l(w_0)}$. By computing $Φ^h_{BK}$, we get an explicit form of $B(\infty)$ in $\mathbb{Z}^{l(w_0)}$. In this paper, we give an algorithm to compute $Δ_{w_0Λ_i,s_iΛ_i}\circ θ_{\textbf{i}}^-$ explicitly for $i\in I$ such that $V(Λ_i)$ is a minuscule representation of $\mathfrak{g}={\rm Lie}(G)$. In particular, the algorithm works for all $i\in I$ if $\mathfrak{g}$ is of type ${\rm A}_n$. The algorithm computes a directed graph $DG$, called a decoration graph, whose vertices are labelled by all monomials in $Δ_{w_0Λ_i,s_iΛ_i}\circ θ_{\textbf{i}}^-(t_1,\cdots,t_{l(w_0)})$. The decoration graph has some properties similar to crystal graphs of minuscule representations. We also verify that the algorithm works in some other cases, for example, the case $\mathfrak{g}$ is of type ${\rm G}_2$ though $V(Λ_i)$ is non-minuscule.

math.QA↗
arXiv2021

Adapted Sequence for Polyhedral Realization of Crystal Bases

The polyhedral realization of crystal base has been introduced by A.Zelevinsky and the second author([T.Nakashima, A.Zelevinsky, Adv. Math. 131, no. 1 (1997)]), which describe the crystal base $B(\infty)$ as a polyhedral convex cone in the infinite $\mathbb{Z}$-lattice $\mathbb{Z}^{\infty}$. To construct the polyhedral realization, we need to fix an infinite sequence $ι$ from the indices of the simple roots. According to this $ι$, one has certain set of linear functions defining a polyhedral convex cone and under the `positivity condition' on $ι$, it has been shown that the polyhedral convex cone is isomorphic to the crystal base $B(\infty)$. To confirm the positivity condition for a given $ι$, we need to obtain the whole feature of the set of linear functions, which requires, in general, a bunch of explicit calculations. In this article, we introduce the notion of the adapted sequence and show that if $ι$ is an adapted sequence then the positivity condition holds for classical Lie algebras. Furthermore, we reveal the explicit forms of the polyhedral realizations associated with arbitrary adapted sequences $ι$ in terms of column tableaux.

math.QA↗
arXiv2020

Cluster algebras of finite type via a Coxeter element and Demazure Crystals of type B,C,D

For a classical group $G$ and a Coxeter element $c$ of the Weyl group, it is known that the coordinate ring $\mathbb{C}[G^{e,c^2}]$ of the double Bruhat cell $G^{e,c^2}:=B\cap B_-c^2B_-$ has a structure of cluster algebra of finite type, where $B$ and $B_-$ are opposite Borel subgroups. In this article, we consider the case $G$ is of type ${\rm B}_r$, ${\rm C}_r$ or ${\rm D}_r$ and describe all the cluster variables in $\mathbb{C}[G^{e,c^2}]$ as monomial realizations of certain Demazure crystals.

math.QA↗
arXiv2018

Geometric crystals and Cluster ensembles in Kac-Moody setting

For a Kac-Moody group $G$, double Bruhat cells $G^{u,e}$ ($u$ is a Weyl group element) have positive geometric crystal structures. In arXiv:1210.2533, it is shown that there exist birational maps between `cluster tori' $\mathcal{X}_Σ$ (resp. $\mathcal{A}_Σ$) and $G_{\rm Ad}^{u,e}$ (resp. $G^{u,e}$), and they are extended to regular maps from cluster $\mathcal{X}$ (resp. $\mathcal{A}$) -varieties to $G_{\rm Ad}^{u,e}$ (resp. $G^{u,e}$). The aim of this article is to construct certain positive geometric crystal structures on the cluster tori $\mathcal{X}_Σ$ and $\mathcal{A}_Σ$ by presenting their explicit formulae. In particular, the geometric crystal structures on the tori $\mathcal{A}_Σ$ are obtained by applying the twist map. As a corollary, we see the sets of $\mathbb{Z}^T$-valued points of the cluster varieties have plural structures of crystals.

math.QA↗
arXiv2017

Explicit Forms of Cluster Variables on Double Bruhat Cells G^{u,e} of type C

Let $G=Sp_{2r}({\mathbb C})$ be a simply connected simple algebraic group over $\mathbb{C}$ of type $C_r$, $B$ and $B_-$ be its two opposite Borel subgroups, and $W$ be the associated Weyl group. For $u$, $v\in W$, it is known that the coordinate ring ${\mathbb C}[G^{u,v}]$ of the double Bruhat cell $G^{u,v}=BuB\cap B_-vB_-$ is isomorphic to an upper cluster algebra $\overline{\mathcal{A}}(\textbf{i})_{\mathbb C}$ and the generalized minors $Δ(k;\textbf{i})$ are the cluster variables of ${\mathbb C}[G^{u,v}]$[Berenstein A., Fomin S., Zelevinsky A., Duke Math. J. 126 (2005), 1-52, math.RT/0305434]. In the case $v=e$, we shall describe the generalized minor $Δ(k;\textbf{i})$ explicitly.

math.QA↗
arXiv2017

Explicit Forms of Cluster Variables on Double Bruhat Cells G^{u,e} of type B

Let $G$ be a simply connected simple algebraic group over $\mathbb{C}$ of type $B_r$, $B$ and $B_-$ be its two opposite Borel subgroups, and $W$ be the associated Weyl group. For $u$, $v\in W$, it is known that the coordinate ring ${\mathbb C}[G^{u,v}]$ of the double Bruhat cell $G^{u,v}=BuB\cap B_-vB_-$ is isomorphic to an upper cluster algebra $\overline{\mathcal{A}}(\textbf{i})_{\mathbb C}$ and the generalized minors $Δ(k;\textbf{i})$ are the cluster variables of ${\mathbb C}[G^{u,v}]$[A.Berenstein, S.Fomin, A.Zelevinsky, Duke Math. J. 126 (2005), 1-52, arxiv:math.RT/0305434]. Recently, it is also shown that ${\mathbb C}[G^{u,v}]$ have structure of cluster algebra [K. R. Goodearl, M. T. Yakimov, arxiv:1602.00498 (2016)]. In the case $v=e$, we shall describe the generalized minor $Δ(k;\textbf{i})$ explicitly.

math.QA↗
arXiv2017

Cluster algebras of finite type via a Coxeter element and Demazure Crystals of type A

Let $G$ be a simply connected simple algebraic group over $\mathbb{C}$, $B$ and $B_-$ be its two opposite Borel subgroups. For two elements $u$, $v$ of the Weyl group $W$, it is known that the coordinate ring ${\mathbb C}[G^{u,v}]$ of the double Bruhat cell $G^{u,v}=BuB\cap B_-vB_-$ is isomorphic to a cluster algebra $\mathcal{A}(\textbf{i})_{\mathbb C}$ [arXiv:math/0305434, arXiv:1602.00498]. In the case $u=e$, $v=c^2$ ($c$ is a Coxeter element), the algebra ${\mathbb C}[G^{e,c^2}]$ has only finitely many cluster variables. In this article, for $G={\rm SL}_{r+1}(\mathbb{C})$, we obtain explicit forms of all the cluster variables in $\mathbb{C}[G^{e,c^2}]$ by considering its additive categorification via preprojective algebras, and describe them in terms of monomial realizations of Demazure crystals.

math.QA↗
arXiv2017

Cluster Variables on Double Bruhat Cells $G^{u,e}$ of Classical Groups and Monomial Realizations of Demazure Crystals

Let $G$ be a simply connected simple algebraic group over $\mathbb{C}$, $B$ and $B_-$ its two opposite Borel subgroups, and $W$ the associated Weyl group. It is shown that the coordinate ring ${\mathbb C}[G^{u,v}]$ ($u$, $v\in W$) of the double Bruhat cell $G^{u,v}=BuB\cap B_-vB_-$ is isomorphic to the cluster algebra ${\mathcal{A}}(\textbf{i})_{\mathbb C}$ and the initial cluster variables of ${\mathbb C}[G^{u,v}]$ are the generalized minors $Δ(k;\textbf{i})$ by Berenstein, Fomin, Zelevinsky, Goodearl and Yakimov. In the case that a classical group $G$ is of type ${\rm B}_r$, ${\rm C}_r$ or ${\rm D}_r$, we shall describe the non-trivial last $r$ initial cluster variables $\{Δ(k;\textbf{i})\}_{(m-2)r<k\leq (m-1)r}$ ($m$ is some positive integer) of the cluster algebra $\mathbb{C}[L^{u,e}]$ in terms of monomial realization of Demazure crystals, where $L^{u,e}$ is the reduced double Bruhat cell of type $(u,e)$. The relation between $Δ(k;\textbf{i})$ on $G^{u,e}$ and on $L^{u,e}$ is described as well. We also present the corresponding results for type ${\rm A}_r$ though the results for all initial cluster variables have been obtained by ourselves.

math.QA↗