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The conjectures of Alday, Gaiotto and Tachikawa and its generalizations have been mathematically formulated as the existence of an action of a $W$-algebra on the cohomology or $K$-theory of the instanton moduli space, together with a Whitakker vector. However, the original conjectures also predict intertwining properties with the natural higher rank version of the $Ext^1$ operator which was previously studied by Okounkov and the author in [CO], a result which is now sometimes referred to as AGT in rank one [Alb,PSS]. Physically, this corresponds to incorporating matter in the Nekrasov partition functions, an obviously important feature in the physical theory. It is therefore of interest to study how the $Ext^1$ operator relates to the aforementioned structures on cohomology in higher rank, and if possible to find a formulation from which the AGT conjectures follow as a corollary. In this paper, we carry out something analogous using a modified Segal-Sugawara construction for the $hat{mathfrak{sl}}_2mathbb{C}$ structure that appears in Okounkov and Nekrasovs proof of Nekrasovs conjecture [NO] for rank two. This immediately implies the AGT identities when the central charge is one, a case which is of particular interest for string theorists, and because of the natural appearance of the Seiberg-Witten curve in this setup, see for instance Dijkgraaf and Vafa [DV], as well as [IKV].
We consider the centers of the affine vertex algebras at the critical level associated with simple Lie algebras. We derive new formulas for generators of the centers in the classical types. We also give a new formula for the Capelli-type determinant
For every simple Lie algebra $mathfrak{g}$ we consider the associated Takiff algebra $mathfrak{g}^{}_{ell}$ defined as the truncated polynomial current Lie algebra with coefficients in $mathfrak{g}$. We use a matrix presentation of $mathfrak{g}^{}_{e
It is known by results of Dyckerhoff-Kapranov and of Galvez--Carrillo-Kock-Tonks that the output of the Waldhausen S.-construction has a unital 2-Segal structure. Here, we prove that a certain S.-functor defines an equivalence between the category of
In a previous paper, we showed that a discrete version of the $S_bullet$-construction gives an equivalence of categories between unital 2-Segal sets and augmented stable double categories. Here, we generalize this result to the homotopical setting, b
Using the twisted denominator identity, we derive a closed form root multiplicity formula for all symmetrizable Borcherds-Bozec algebras and discuss its applications including the case of Monster Borcherds-Bozec algebra. In the second half of the pap