ABSTRACT. We consider dynamical systems with two degrees of freedom whose configuration space is a torus and which admit first integrals polynomial in velocity. We obtain constructive criteria for the existence of conditional linear and quadratic integrals on the two-dimensional torus. Moreover, we show that under some additional conditions the degree of an ~irreducible ~ integral of the geodesic flow on the torus does not exceed 2.KgY WORDS: dynamical systems on the torus, polynomial first integrals, complete integrability.
w IntroductionWe consider dynamical systems with two degrees of freedom whose configuration space is the twodimensional toms T 2 and which admit first integrals polynomial in the velocity. This is equivalent to the complete integrability of the system. Polynomial integrals can be represented as polynomials in the velocity with smooth single-valued coefficients on the configuration space. A least-order nontrivial polynomial F independent of energy is called irredncible. Polynomials in the velocity which are integrals only for some given values of the total energy are said to be conditional polynomial integrals.In [1] Birldaoff studied the local existence of conditional integrals polynomial of order <_ 2 in the velocity. It turned out that the presence of a conditional linear integral is related to "hidden" cyclic coordinates and the presence of a conditional quadratic integral permits one to separate the canonical variables. In w and w of this paper, we present the global versions of these statements for the case in which the configuration space of the system is the two-dimensional toms.In w we extend the result of [2] to polynomial integrals of degree _> 2 for geodesic flows on the two-dimensional toms.The problem for polynomial integrals of degree _< 2 was considered in [3,4]. It was shown in [5] that the natural mechanical system on the two-dimensional torus with kinetic energy 1 -2 has no irreducible integrals of degrees 3 and 4; in this case there necessarily exist integrals of degrees 1 and 2, respectively.In [6] the problem of the existence of a complete set of independent polynomial integrals was considered for a system with configuration space T n = {Zl,..., zn rood 27r}, kinetic energy