Hilbert’s 16th problem on a period annulus and Nash space of arcs

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This paper introduces an algebro-geometric setting for the space of bifurcation functions involved in the local Hilbert’s 16th problem on a period annulus. Each possible bifurcation function is in one-to-one correspondence with a point in the exceptional divisorEof the canonical blow-upBIℂnof the Bautin idealI. In this setting, the notion of essential perturbation, first proposed by Iliev, is defined via irreducible components of the Nash space of arcsArc(BIℂn,E). The example of planar quadratic vector fields in the Kapteyn normal form is further discussed.