Abstract. We study the preprojective cohomological Hall algebra (CoHA) introduced by the authors in [YZ1] for any quiver Q and any one-parameter formal group G. In this paper, we construct a comultiplication on the CoHA, making it a bialgebra. We also construct the Drinfeld double of the CoHA. The Drinfeld double is a quantum affine algebra of the Lie algebra gQ associated to Q, whose quantization comes from the formal group G. We prove, when the group G is the additive group, the Drinfeld double of the CoHA is isomorphic to the Yangian.
IntroductionIn this paper, we construct comultiplications on certain cohomological Hall algebras, making them bialgebras. We also construct the Drinfeld double of these bialgebras. This gives a uniform way to construct both old and new affine-type quantum groups.The cohomological Hall algebra involved, called the preprojective cohomological Hall algebra (CoHA for short) and denoted by P(Q, A) or simply P, is associated to a quiver Q and an algebraic oriented cohomology theory A. The construction of the preprojective CoHA is given in [YZ1], as a generalization of the K-theoretic Hall algebra of commuting varieties studied by SchiffmannVasserot in [SV12]. The preprojective CoHA is defined to be the A-homology of the moduli of representations of the preprojective algebra of Q. It has the same flavor as the cohomological Hall algebra associated to quiver with potential defined by . The authors also construct an action of P(Q, A) on the A-homology of Nakajima quiver varieties associated toLet g Q be the corresponding symmetric Kac-Moody Lie algebra of Q and b Q ⊂ g Q be the Borel subalgebra. As is shown in [YZ1], a certain spherical subalgebra in an extension of P(Q, A), denoted by P s,e (Q, A) or P s,e , is a quantization of (a central extension of), where the quantization depends on the underlying formal group law of A. As in the case of quantized enveloping algebra of g Q , the Drinfeld double of the Borel subalgebra should be the entire quantum group. This is the subject of the present paper. We construct a coproduct on P(Q, A), and define the Drinfeld double, which is a quantization offor some 1-dimensional algebraic group or formal group G. When G is an affine algebraic group, the Drinfeld double of P(Q, A) recovers the Drinfeld realization of the quantization of the Manin triple associated to P 1 as described in [D86, § 4]. When G is a formal group which does not come from an algebraic group, this gives new affine quantum groups which have not been studied in literature. In the case when G is the elliptic curve, the method here gives a Drinfeld realization of the elliptic quantum group of [Fed94] which is previously unknown.In this paper, we focus on the purely algebraic description of P(Q, A) in terms of shuffle algebra without explicit reference to Nakajima quiver varieties. The shuffle algebra is reviewed in detail in § 1. The algebra P s,e has two deformation parameters t 1 , t 2 , coming from a 2-dimensional torus action. Let P s,e be the quotient of P s,e by the torsion...