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Ali Taghavi
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Flat Riemannian metrics adaptaded to quadratic vector fields with center

Assume that $P(x,y),Q(x,y)\in \mathbb{R}[x,y]$ are two polynomials of degree $2$ with $P(0,0)=Q(0,0)=0.$ Suppose that the vector field $$\begin{cases} x'=P(x,y)\\ y'=Q(x,y) \end{cases}$$ has a center singularity at the origin. This means that the origin is surounded by a band of closed orbits.

Is there a Riemannian metric on $\mathbb{R}^2 \setminus C$ with zero curvature such that all closed orbits of the vector field are closed geodesic? Here $C$ is the algebraic curve $$C=\{(x,y)\mid yP(x,y)-xQ(x,y)=0\}$$

The motivation comes from the idea of consideration of "Limit cycles" of polynomial vector fields as $Closed Geodesics" of a Riemannian meteic on the phase space. This situation is discussed in the following posts and prwprint.

Finding a 1-form adapted to a smooth flow

Limit cycles of quadratic systems and closed geodesics(Finitness of $H(2)$)

Limit cycles as closed geodesics (in negatively or positively curved space)

Ali Taghavi
  • 356
  • 8
  • 31
  • 123