The analogue of the string equation which specifies the partition function of c = 1 string with a compactification radius β ∈ Z ≥1 is described in the framework of the Toda lattice hierarchy.
1Recently much attention has been paid to the understanding of c = 1 string theory from the view of integrable hierarchy. In paticular the tachyon dynamics of the theory has been described in the framework of the (dispersionless) Toda lattice hierarchy [1],[2], [3]. In spite of these developments our understanding of the nonperturbative aspects for c = 1 string still has a gap from that of non-critical string theory. In the non-critical string theory the full partition function is the τ function of Kadomtsev-Petriashivil (KP) hierarchy specified by the solution of string equation [4] : [ P, Q ] = 1 where P, Q are differential operators. These pairs can be given in terms of the Lax and Orlov operators of KP hierarchy [5]. On the other hand, even in the framework of the Toda lattice (TL) hierarchy, the analogue of the string equation at c = 1 has not been clarified yet. In this letter, by utilizing the concepts of these integrable hierarchies, we try to obtain this nonperturbative counterpart which characterizes the generating function for the tachyon correlation functions of c = 1 string with a compactification radius β ∈ Z ≥1 .