Bifurcations and distribution of limit cycles which appear from two nests of periodic orbits

In this paper, we study the distribution and simultaneous bifurcation of limit cycles bifurcated from the two periodic annuli of the holomorphic differential equation (z) over dot = iz+z(3), after a small polynomial perturbation. We first show that, under small perturbations of the form epsilon P(2m-1)(z, (z) over barz), where P(2m-1)(z, (z) over bar) is a polynomial of degree 2 m - 1 in which the power of z is odd and the power of (z) over bar is even, the only possible distribution of limit cycles is (u, u) for all values of u = 0, 1, 2, ... , m - 3. Hence, the sharp upper bound for the number of limit cycles bifurcated from each two period annuli of (z) over dot = iz + z(3) is m - 3, for m >= 4. Then we consider a perturbation of the form epsilon P(m)(z, (z) over bar), where P(m) (z, (z) over bar) is a polynomial of degree m in which the power of z is odd and obtain the upper bound m - 5, for m >= 6. Moreover, we show that the distribution. (u, v) of limit cycles is possible for 0 <= u <= m - 5, 0 <= v <= m - 5 with u + v <= m - 2 and m >= 9. (c) 2010 Elsevier Ltd. All rights reserved.