Kac Moody Research Articles

Darboux Transforms for the $${\hat{B}}_n^{(1)}$$-Hierarchy

The $${\hat{B}}_n^{(1)}$$ -hierarchy is constructed from the standard splitting of the affine Kac–Moody algebra $${\hat{B}}_n^{(1)}$$ , the Drinfeld–Sokolov $${\hat{B}}_n^{(1)}$$ –KdV hierarchy is obtained by pushing down the $${\hat{B}}_n^{(1)}$$ -flows along certain gauge orbit to a cross section of the gauge action. In this paper, we

A SERRE PRESENTATION FOR THE ıQUANTUM GROUPS

Let (U, ) be a quasi-split quantum symmetric pair of arbitrary Kac–Moody type, where “quasi-split” means the corresponding Satake diagram contains no black node. We give a presentation of the group with explicit relations. The verification of new relations is reduced to some new q-binomial identities. Consequently, is shown to admit a bar involution under suitable conditions on the parameters.

Unified Characterizations of Minuscule Kac–Moody Representations Built from Colored Posets

R.M. Green described structural properties that "doubly infinite" colored posets should possess so that they can be used to construct representations of most affine Kac–Moody algebras. These representations are analogs of the minuscule representations of the semisimple Lie algebras, and his posets ("full heaps") are analogs of the finite minuscule posets. Here only simply laced Kac–Moody algebras are considered. Working with their derived subalgebras, we provide a converse to Green's theorem. Smaller collections of colored structural properties are also shown to be necessary and sufficient for such poset-built representations to be produced for smaller subalgebras, especially the "Borel derived" subalgebra. These developments lead to the formulation of unified definitions of finite and infinite colored minuscule and $d$-complete posets. This paper launches a program that seeks to extend the notion of "minuscule representation" to Kac–Moody algebras, and to classify such representations.

Timelike minimal Lagrangian surfaces in the indefinite complex hyperbolic two-space

It has been known for some time that there exist 5 essentially different real forms of the complex affine Kac–Moody algebra of type \(A_2^{(2)}\) and that one can associate 4 of these real forms with certain classes of “integrable surfaces,” such as minimal Lagrangian surfaces in \(\mathbb {CP}^2\) and \(\mathbb {CH}^2\), as well as definite and indefinite affine spheres in \({\mathbb {R}}^3\). In this paper, we consider the class of timelike minimal Lagrangian surfaces in the indefinite complex hyperbolic two-space \(\mathbb {CH}^{2}_1\). We show that this class of surfaces corresponds to the fifth real form. Moreover, for each timelike Lagrangian surface in \(\mathbb {CH}^{2}_1\) we define natural Gauss maps into certain homogeneous spaces and prove a Ruh–Vilms-type theorem, characterizing timelike minimal Lagrangian surfaces among all timelike Lagrangian surfaces in terms of the harmonicity of these Gauss maps.

Double Extensions of Restricted Lie (Super)Algebras

A double extension ( $${\mathscr {D}}$$ -extension) of a Lie (super)algebra $${\mathfrak {a}}$$ with a non-degenerate invariant symmetric bilinear form $${\mathscr {B}}$$ , briefly, a NIS-(super)algebra, is an enlargement of $${\mathfrak {a}}$$ by means of a central extension and a derivation; the affine Kac–Moody algebras are the best known examples of double extensions of loops algebras. Let $${\mathfrak {a}}$$ be a restricted Lie (super)algebra with a NIS $${\mathscr {B}}$$ . Suppose $${\mathfrak {a}}$$ has a restricted derivation $${\mathscr {D}}$$ such that $${\mathscr {B}}$$ is $${\mathscr {D}}$$ -invariant. We show that the double extension of $${\mathfrak {a}}$$ constructed by means of $${\mathscr {B}}$$ and $${\mathscr {D}}$$ is restricted. We show that, the other way round, any restricted NIS-(super)algebra with non-trivial center can be obtained as a $${\mathscr {D}}$$ -extension of another restricted NIS-(super)algebra subject to an extra condition on the central element. We give new examples of $${\mathscr {D}}$$ -extensions of restricted Lie (super)algebras, and pre-Lie superalgebras indigenous to characteristic 3.

Classical Lie symmetries and similarity reductions of the (2 + 1)-dimensional dispersive long wave system

In the present work, classical Lie symmetry method is adopted to obtain the Lie symmetries and similarity reductions of the [Formula: see text]-dimensional dispersive long wave equation. We also demonstrate that the symmetry algebra of this equation is an infinte dimensional, together with Kac–Moody–Virasoro type subalgebras.

On the structure of Kac–Moody algebras

AbstractLet A be a symmetrisable generalised Cartan matrix, and let $\mathfrak {g}(A)$ be the corresponding Kac–Moody algebra. In this paper, we address the following fundamental question on the structure of $\mathfrak {g}(A)$ : given two homogeneous elements $x,y\in \mathfrak {g}(A)$ , when is their bracket $[x,y]$ a nonzero element? As an application of our results, we give a description of the solvable and nilpotent graded subalgebras of $\mathfrak {g}(A)$ .

The rational cohomology Hopf algebra of a generic Kac–Moody group

In this paper we determine the rational homotopy type of the classifying space of a generic Kac-Moody group by computing its rational cohomology ring. As an application we determine the rational homology Hopf algebra of the generic Kac-Moody group.

Symmetric pairs for Nichols algebras of diagonal type via star products

We construct symmetric pairs for Drinfeld doubles of pre-Nichols algebras of diagonal type and determine when they possess an Iwasawa decomposition. This extends G. Letzter's theory of quantum symmetric pairs. Our results can be uniformly applied to Kac–Moody quantum groups for a generic quantum parameter, for roots of unity in respect to both big and small quantum groups, to quantum supergroups and to exotic quantum groups of ufo type. We give a second construction of symmetric pairs for Heisenberg doubles in the above generality and prove that they always admit an Iwasawa decomposition.For symmetric pair coideal subalgebras with Iwasawa decomposition in the above generality we then address two problems which are fundamental already in the setting of quantum groups. Firstly, we show that the symmetric pair coideal subalgebras are isomorphic to intrinsically defined deformations of partial bosonizations of the corresponding pre-Nichols algebras. To this end we develop a general notion of star products on N-graded connected algebras which provides an efficient tool to prove that two deformations of the partial bosonization are isomorphic. The new perspective also provides an effective algorithm for determining the defining relations of the coideal subalgebras.Secondly, for Nichols algebras of diagonal type, we use the linear isomorphism between the coideal subalgebra and the partial bosonization to give an explicit construction of quasi K-matrices as sums over dual bases. We show that the resulting quasi K-matrices give rise to weakly universal K-matrices in the above generality.

The [formula omitted]-tower of weak Jacobi forms and applications

We construct the tower of arithmetic generators of the bigraded polynomial ring J∗,∗w,O(Dn) of the weak Jacobi modular forms invariant with respect to the full orthogonal group O(Dn) of the root lattice Dn for 2≤n≤8. This tower corresponds to the tower of strongly reflective modular forms on the orthogonal groups of signature (2,n) which determine the Lorentzian Kac–Moody algebras related to the BCOV (Bershadsky–Cecotti–Ooguri–Vafa)-analytic torsions. We prove that the main three generators of index one of the graded ring satisfy a special system of modular differential equations. We found also a general modular differential equation of the generator of weight 0 and index 1 which generates the automorphic discriminant of the moduli space of Enriques surfaces.

Quantization of continuum Kac–Moody algebras

Continuum Kac-Moody algebras have been recently introduced by the authors and O. Schiffmann. These are Lie algebras governed by a continuum root system, which can be realized as uncountable colimits of Borcherds-Kac-Moody algebras. In this paper, we prove that any continuum Kac-Moody algebra is canonically endowed with a non-degenerate invariant bilinear form. The positive and negative Borel subalgebras form a Manin triple with respect to this pairing, inducing on the continuum Kac-Moody algebra a topological quasi-triangular Lie bialgebra structure. We then construct an explicit quantization, which we refer to as a continuum quantum group, and we show that the latter is similarly realized as an uncountable colimit of Drinfeld-Jimbo quantum groups.

Nilmanifolds and their associated non-local fields

For six dimensional nilmanifolds we build a module $\mathcal{H}$ of an affine Kac Moody vertex algebras. Then, we associate some logarithmic fields for the module $\mathcal{H}$ and we study their singularities. We also presented a physics motivation behind this construction. We study a particular case, we show that when the nilmanifold $N$ is a $k$ degree $S^1$--fibration over the two torus and a choice of $l \in \mathbb{Z} \simeq H^3(N, \mathbb{Z})$ the fields associated to the space $\mathcal{H}$ have tri-logarithm singularities whenever $kl \neq 0$.

Conformal bootstrap in dS/CFT and topological quantum gravity

We show that the correspondence among [Formula: see text], the 1D Schwarzian Model, Sachdev–Ye–Kitaev model and [Formula: see text] Topological Quantum Gravity can be extended to the case of [Formula: see text]. The [Formula: see text]-matrix, related to the gravitational scattering amplitude near the horizon of [Formula: see text] black hole, corresponds (on the side of the holographic projection) to a crossing kernel in the Schwarzian Model. The [Formula: see text]-matrix is related to the 6j-symbol of SU[Formula: see text]. We also find that in the Euclidean [Formula: see text] a new Kac–Moody symmetry of instantons emerges out. We dub these new solutions Kac–Moodions. A one-to-one correspondence of Kac–Moodion levels and SU[Formula: see text] spin representations is established. Every instanton then corresponds to spin representations deployed in Topological Quantum Gravity. The instantons are directly connected to the Black Hole entropy as punctures on its horizon. This strongly supports the recent proposal, in arXiv:1707.00347, that a Kac–Moody symmetry of gravitational instantons is related to the black hole information processing. We also comment on a further correspondence that can be established between the Schwarzian Model and noncommutative spacetimes in [Formula: see text]D, passing through the equivalence with Topological Quantum Gravity with cosmological constant, in the limit when the latter vanishes.

Geometric crystals and cluster ensembles in Kac–Moody setting

For a Kac–Moody group G, double Bruhat cells Gu,e (u is a Weyl group element) have positive geometric crystal structures. In Williams (2013), it is shown that there exist birational maps between ‘cluster tori’ XΣ (resp. AΣ) and GAdu,e (resp. Gu,e), and they are extended to regular maps from cluster X (resp. A) -varieties to GAdu,e (resp. Gu,e). The aim of this article is to compute explicit formulae for the induced geometric crystal structures on these cluster tori. As a corollary, the sets of ZT-valued points of these cluster varieties have crystal structures.

Fock Space Representation of the Circle Quantum Group

Abstract In [12] we have defined quantum groups $\mathbf{U}_{\upsilon }(\mathfrak{sl}(\mathbb{R}))$ and $\mathbf{U}_{\upsilon }(\mathfrak{sl}(S^1))$, which can be interpreted as continuum generalizations of the quantum groups of the Kac–Moody Lie algebras of finite, respectively affine type $A$. In the present paper, we define the Fock space representation $\mathcal{F}_{\mathbb{R}}$ of the quantum group $\mathbf{U}_{\upsilon }(\mathfrak{sl}(\mathbb{R}))$ as the vector space generated by real pyramids (a continuum generalization of the notion of partition). In addition, by using a variant version of the “folding procedure” of Hayashi–Misra–Miwa, we define an action of $\mathbf{U}_{\upsilon }(\mathfrak{sl}(S^1))$ on $\mathcal{F}_{\mathbb{R}}$.

A note on toric degeneration of a Bott–Samelson–Demazure–Hansen variety

In this paper, we study the geometry of toric degeneration of a Bott–Samelson–Demazure–Hansen (BSDH) variety, which was algebraically constructed by Pasquier (J Algebra 323(10):2834–2847, 2010). We give some applications to BSDH varieties. Precisely, we classify Fano, weak Fano and log Fano BSDH varieties and their toric limits in Kac–Moody setting. We prove some vanishing theorems for the cohomology of tangent bundle (and line bundles) on BSDH varieties. We also recover the results in (Parameswaran and Karuppuchamy, Toric degeneration of Bott–Samelson–Demazure–Hansen varieties. arXiv:1604.01998 , 2016) and extend them to the Kac-Moody setting, by toric methods.

Drinfeld–Sokolov Hierarchies and Diagram Automorphisms of Affine Kac–Moody Algebras

For a diagram automorphism of an affine Kac-Moody algebra such that the folded diagram is still an affine Dynkin diagram, we show that the associated Drinfeld-Sokolov hierarchy also admits an induced automorphism. Then we show how to obtain the Drinfeld-Sokolov hierarchy associated to the affine Kac-Moody algebra that corresponds to the folded Dynkin diagram from the invariant sub-hierarchy of the original Drinfeld-Sokolov hierarchy.

Gravitational edge modes: from Kac–Moody charges to Poincaré networks

We revisit the canonical framework for general relativity in its connection-vierbein formulation, recasting the Gauss law, the Bianchi identity and the space diffeomorphism bulk constraints as conservation laws for boundary surface charges, respectively electric, magnetic and momentum charges. Partitioning the space manifold into 3D regions glued together through their interfaces, we focus on a single domain and its punctured 2D boundary. The punctures carry a ladder of Kac–Moody edge modes, whose 0-modes represent the electric and momentum charges while the higher modes describe the stringy vibration modes of the 1D-boundary around each puncture. In particular, this allows to identify missing observables in the discretization scheme used in loop quantum gravity (LQG) and leads to an enhanced theory upgrading spin networks to tube networks carrying Virasoro representations. In the limit where the tubes are contracted to 1D links and the string modes neglected, we do not just recover LQG but obtain a more general structure: Poincaré charge networks, which carry a representation of the 3D diffeomorphism boundary charges on top of the fluxes and gauge transformations.

Generalized Casimir operators

Let [Formula: see text] be symmetrizable Kac–Moody Lie algebra. In this paper, we describe a new class of central operators generalizing the Casimir operator. We also prove some properties of these operators and show that these operators move highest weight vectors to new highest weight vectors.

Discrete exponential type systems on a quad graph, corresponding to the affine Lie algebras

The article deals with the problem of the integrable discretization of the well-known Drinfeld–Sokolov hierarchies related to the Kac–Moody algebras. A class of discrete exponential systems connected with the Cartan matrices has been suggested earlier in Garifullin et al (2012 SIGMA 8 33) which coincide with the corresponding Drinfeld–Sokolov systems in the continuum limit. It was conjectured that the systems in this class are all integrable and the conjecture has been proven by numerous examples. In the present article we study those systems from this class which are related to the algebras . We found the Lax pair for arbitrary N, briefly discussed the possibility of using the method of formal diagonalization of Lax operators for describing a series of local conservation laws and illustrated the technique using the example of N = 3. Higher symmetries of the system are presented in both characteristic directions. The recursion operator for the case N = 3 is found. It is interesting to note that this operator is not weakly nonlocal.