An Explicit Construction of Commuting Quantum KdV Hamiltonians in the Universal Virasoro Vertex Algebra

Abstract

We give an explicit formula for elements $H_{2k}$ of conformal weight $2k$, $k\ge 1$, in the universal Virasoro vertex operator algebra $V$ at every central charge, such that $H_{2k}(0)H_{2l}\in TV$ for all $k,l\ge 1$. Modulo translation, the kernel of $H_4(0)$ is generated by $[H_{2k}]$ in each positive even weight and is zero in positive odd weights. The formula uses a realization on differential polynomials by possibly infinite-order differential operators in a completion of the Weyl algebra, together with the inverse of the identity plus a nilpotent operator on each weight space. A Koszul-type exactness argument for the classical KdV flows proves conservation; uniqueness and the Jacobi identity give commutativity. The classical limit recovers the normalized Gelfand--Dickey densities. Explicit low-weight elements and exact symbolic verifications illustrate the construction.