TY - JOUR T1 - Virasoro Symmetries of the Extended Toda Hierarchy JF - Comm. Math.\\nPhys. 250 (2004) 161-193. Y1 - 2004 A1 - Boris Dubrovin A1 - Zhang Youjin AB - We prove that the extended Toda hierarchy of \\\\cite{CDZ} admits nonabelian Lie algebra of infinitesimal symmetries isomorphic to the half of the Virasoro algebra. The generators $L_m$, $m\\\\geq -1$ of the Lie algebra act by linear differential operators onto the tau function of the hierarchy. We also prove that the tau function of a generic solution to the extended Toda hierarchy is annihilated by a combination of the Virasoro operators and the flows of the hierarchy. As an application we show that the validity of the Virasoro constraints for the $CP^1$ Gromov-Witten invariants and their descendents implies that their generating function is the logarithm of a particular tau function of the extended Toda hierarchy. UR - http://hdl.handle.net/1963/2544 U1 - 1575 U2 - Mathematics U3 - Mathematical Physics ER -