China
This paper investigates the number of limit cycles in a hyperelliptic gourd-shaped Hamiltonian system under polynomial perturbations. Specifically, we consider the perturbed system ˙ x = y, ˙y = x − 5 4 x3 + 1 4 x5 + ε f (x, δ)y, where 0 < |ε| 1 and f (x, δ) = 6 i=0 ai xi is a polynomial of degree six. By studying limit cycles bifurcating near the elementary centers, the double homoclinic loop and the heteroclinic loop, we obtain lower bounds for the number of limit cycles and their corresponding configurations. Furthermore, under the assumption that some parameters ai vanish, we derive sharp upper bounds for the number of limit cycles by constructing ECT-systems and using geometric methods.
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