Bhargava–Cremona–Fisher–Gajović density functional-equation conjecture

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Let nn be a positive integer and let σ\sigma be a splitting type of degree nn. For a prime pp, let ρ(n,σ;p)\rho(n,\sigma;p) be the Haar measure of the pp-adic polynomials of degree at most nn with splitting type σ\sigma, let α(n,σ;p)\alpha(n,\sigma;p) be the measure of those that are monic, and let β(n,σ;p)\beta(n,\sigma;p) be the measure of those that are monic and congruent to xnx^n modulo pp. Bhargava–Cremona–Fisher–Gajović conjecture. The densities ρ(n,σ;p)\rho(n,\sigma;p), α(n,σ;p)\alpha(n,\sigma;p), and β(n,σ;p)\beta(n,\sigma;p) are rational functions in pp and satisfy

ρ(n,σ;p−1)=ρ(n,σ;p),\rho(n,\sigma;p^{-1})=\rho(n,\sigma;p), α(n,σ;p−1)=β(n,σ;p).\alpha(n,\sigma;p^{-1})=\beta(n,\sigma;p).

The paper proves rationality in the tamely ramified case and notes that the conjecture predicts rationality beyond the gcd condition on the residue characteristic and ramification indices; the full assertion is not proved there.

References

Primary source

John Yin, “Density of p-adic polynomials generating extensions with fixed splitting type”, arXiv:2211.10425 (2022).

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