Drinfeld-type presentations of loop algebras

Let g\mathfrak {g} be the derived subalgebra of a Kac-Moody Lie algebra of finite-type or affine-type, let μ\mu be a diagram automorphism of g\mathfrak {g}, and let L(g,μ)\mathcal {L}(\mathfrak {g},\mu ) be the loop algebra of g\mathfrak {g} associated to μ\mu. In this paper, by using the vertex algebra technique, we provide a general construction of current-type presentations for the universal central extension g^[μ]\widehat {\mathfrak {g}}[\mu ] of L(g,μ)\mathcal {L}(\mathfrak {g},\mu ). The construction contains the classical limit of Drinfeld’s new realization for (twisted and untwisted) quantum affine algebras [Soviet Math. Dokl. 36 (1988), pp. 212–216] and the Moody-Rao-Yokonuma presentation for toroidal Lie algebras [Geom. Dedicata 35 (1990), pp. 283–307] as special examples. As an application, when g\mathfrak {g} is of simply-laced-type, we prove that the classical limit of the μ\mu-twisted quantum affinization of the quantum Kac-Moody algebra associated to g\mathfrak {g} introduced in [J. Math. Phys. 59 (2018), 081701] is the universal enveloping algebra of g^[μ]\widehat {\mathfrak {g}}[\mu ].