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Yusuke Ohkubo

Publications and source records attributed to Yusuke Ohkubo.

11 recordsLinked to original sources
arXiv2025

Direct Sum Structure of the Super Virasoro Algebra and a Fermion Algebra Arising from the Quantum Toroidal $\mathfrak{gl}_2$

It is known that the $q$-deformed Virasoro algebra can be constructed from a certain representation of the quantum toroidal $\mathfrak{gl}_1$ algebra. In this paper, we apply the same construction to the quantum toroidal algebra of type $\mathfrak{gl}_2$ and study the properties of resulting generators $W_i(z)$ ($i=1,2$). The algebra generated by $W_i(z)$ can be regarded as a $q$-deformation of the direct sum $\mathsf{F} \oplus \mathsf{SVir}$, where $\mathsf{F}$ denotes the free fermion algebra and $\mathsf{SVir}$ stands for the $N=1$ super Virasoro algebra, also referred to as the $N=1$ superconformal algebra or the Neveu-Schwarz-Ramond algebra. Moreover, the generators $W_i(z)$ admit two screening currents, and we show that their degeneration limits coincide with the screening currents of $\mathsf{SVir}$. We also establish quadratic relations satisfied by $W_i(z)$ and show that they generate a pair of commuting $q$-deformed Virasoro algebras, which degenerate into two nontrivial commuting Virasoro algebras included in $\mathsf{F} \oplus \mathsf{SVir}$.

math.QA↗
arXiv2021

Branching Formula for $q$-Toda Function of Type B

We present a proof of the explicit formula for the asymptotically free eigenfunctions of the $B_N$ $q$-Toda operator which was conjectured by the first and third authors. This formula can be regarded as a branching formula from the $B_N$ $q$-Toda eigenfunction restricted to the $A_{N-1}$ $q$-Toda eigenfunctions. The proof is given by a contigulation relation of the $A_{N-1}$ Toda eigenfunctions and a recursion relation of the branching coefficients.

math.QA↗
arXiv2020

Non-Stationary Ruijsenaars Functions for $κ=t^{-1/N}$ and Intertwining Operators of Ding-Iohara-Miki Algebra

We construct the non-stationary Ruijsenaars functions (affine analogue of the Macdonald functions) in the special case $κ=t^{-1/N}$, using the intertwining operators of the Ding-Iohara-Miki algebra (DIM algebra) associated with $N$-fold Fock tensor spaces. By the $S$-duality of the intertwiners, another expression is obtained for the non-stationary Ruijsenaars functions with $κ=t^{-1/N}$, which can be regarded as a natural elliptic lift of the asymptotic Macdonald functions to the multivariate elliptic hypergeometric series. We also investigate some properties of the vertex operator of the DIM algebra appearing in the present algebraic framework; an integral operator which commutes with the elliptic Ruijsenaars operator, and the degeneration of the vertex operators to the Virasoro primary fields in the conformal limit $q \rightarrow 1$.

math.QA↗
arXiv2019

Generalized Macdonald Functions on Fock Tensor Spaces and Duality Formula for Changing Preferred Direction

An explicit formula is obtained for the generalized Macdonald functions on the $N$-fold Fock tensor spaces, calculating a certain matrix element of a composition of several screened vertex operators. As an application, we prove the factorization property of the arbitrary matrix elements of the multi-valent intertwining operator (or refined topological vertex operator) associated with the Ding--Iohara--Miki algebra (DIM algebra) with respect to the generalized Macdonald functions, which was conjectured by Awata, Feigin, Hoshino, Kanai, Yanagida and one of the authors. Our proof is based on the combinatorial and analytic properties of the asymptotic eigenfunctions of the ordinary Macdonald operator of $A$-type, and the Euler transformation formula for Kajihara and Noumi's multiple basic hypergeometric series. That factorization formula provides us with a reasonable algebraic description of the 5D (K-theoretic) Alday-Gaiotto-Tachikawa (AGT) correspondence, and the interpretation of the invariance under the preferred direction from the point of view of the $SL(2,\mathbb{Z})$ duality of the DIM algebra.

math.QA↗
arXiv2017

(q,t)-KZ equation for Ding-Iohara-Miki algebra

We derive the generalization of the Knizhnik-Zamolodchikov equation (KZE) associated with the Ding-Iohara-Miki (DIM) algebra U_{q,t}(\widehat{\widehat{\mathfrak{gl}}}_1). We demonstrate that certain refined topological string amplitudes satisfy these equations and find that the braiding transformations are performed by the R-matrix of U_{q,t}(\widehat{\widehat{\mathfrak{gl}}}_1). The resulting syste is the uplifting of the \widehat{\mathfrak{u}}_1 Wess-Zumino-Witten model. The solutions to the (q,t)-KZE are identified with the (spectral dual of) building blocks of the Nekrasov partition function for 5d linear quiver gauge theories. We also construct an elliptic version of the KZE and discuss its modular and monodromy properties, the latter being related to a dual version of KZE.

hep-th↗
arXiv2017

Singular Vector of Ding-Iohara-Miki Algebra and Hall-Littlewood Limit of 5D AGT Conjecture

In this thesis, we obtain the formula for the Kac determinant of the algebra arising from the level $N$ representation of the Ding-Iohara-Miki algebra. This formula can be proved by decomposing the level $N$ representation into the deformed $W$-algebra part and the $U(1)$ boson part, and using the screening currents of the deformed $W$-algebra. It is also discovered that singular vectors obtained by its screening currents correspond to the generalized Macdonald functions. Moreover, we investigate the $q \rightarrow 0$ limit of five-dimensional AGT correspondence. In this limit, the simplest 5D AGT conjecture is proved, that is, the inner product of the Whittaker vector of the deformed Virasoro algebra coincides with the partition function of the 5D pure gauge theory. Furthermore, the R-Matrix of the Ding-Iohara-Miki algebra is explicitly calculated, and its general expression in terms of the generalized Macdonald functions is conjectured.

math-ph↗
arXiv2016

Explicit examples of DIM constraints for network matrix models

Dotsenko-Fateev and Chern-Simons matrix models, which describe Nekrasov functions for SYM theories in different dimensions, are all incorporated into network matrix models with the hidden Ding-Iohara-Miki (DIM) symmetry. This lifting is especially simple for what we call balanced networks. Then, the Ward identities (known under the names of Virasoro/W-constraints or loop equations or regularity condition for qq-characters) are also promoted to the DIM level, where they all become corollaries of a single identity.

hep-th↗
arXiv2016

Toric Calabi-Yau threefolds as quantum integrable systems. R-matrix and RTT relations

R-matrix is explicitly constructed for simplest representations of the Ding-Iohara-Miki algebra. The calculation is straightforward and significantly simpler than the one through the universal R-matrix used for a similar calculation in the Yangian case by A.~Smirnov but less general. We investigate the interplay between the R-matrix structure and the structure of DIM algebra intertwiners, i.e.\ of refined topological vertices and show that the R-matrix is diagonalized by the action of the spectral duality belonging to the SL(2,Z) group of DIM algebra automorphisms. We also construct the T-operators satisfying the RTT relations with the R-matrix from refined amplitudes on resolved conifold. We thus show that topological string theories on the toric Calabi-Yau threefolds can be naturally interpreted as lattice integrable models. Integrals of motion for these systems are related to q-deformation of the reflection matrices of the Liouville/Toda theories.

hep-th↗
arXiv2015

Crystallization of deformed Virasoro algebra, Ding-Iohara-Miki algebra and 5D AGT correspondence

In this paper, we consider the $q \rightarrow 0$ limit of the deformed Virasoro algebra and that of the level 1, 2 representation of Ding-Iohara-Miki algebra. Moreover, 5D AGT correspondence at this limit is discussed. This specialization corresponds to the limit from Macdonalds functions to Hall-Littlewood functions. Using the theory of Hall-Littlewood functions, some problems are solved. For example, the simplest case of 5D AGT conjectures is proven at this limit, and we obtain a formula for the 4-point correlation function of a certain operator.

math-ph↗