Faber–Voloch conjecture on Newton approximation

Let gg be a polynomial of degree d2d\geq 2 with coefficients in a number field KK, and let y0Ky_0\in K. Define the Newton map

N(z)=zg(z)g(z)N(z)=z-\frac{g(z)}{g'(z)}

and, for each n0n\geq 0, set yn+1=N(yn)y_{n+1}=N(y_n). Assume that the Newton approximation sequence (yn)(y_n) is not eventually periodic. Let C(K,g,y0)C(K,g,y_0) be the set of primes \fP\fP of KK for which (yn)(y_n) converges in the completion K\fPK_{\fP} to a root of ff. Faber–Voloch's conjecture. The natural density of the set C(K,g,y0)C(K,g,y_0) is zero. This conjecture predicts that, outside the eventually periodic case, Newton approximation converges \fP\fP-adically to a root for a density-zero set of primes. The source presents it as a conjecture motivating the choice of polynomial, and no resolution is supplied here.

Sources & referencesView supporting material

Primary source

Robert L. Benedetto, Xander Faber, Benjamin Hutz, Jamie Juul and Yu Yasufuku, “A large arboreal Galois representation for a cubic postcritically finite polynomial”, arXiv:1612.03358 (2017).

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