Bhargava's ramification-density conjecture for SnS_n-number fields

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Let nn be a positive integer and let B>0B>0. Let Gn(B)\mathcal{G}_{n}(B) be the collection of SnS_n-number fields KK with ∣DK∣≤B|D_K|\leq B. For a prime pp, let Gn(B;p)\mathcal{G}_{n}(B;p) be the collection of degree-nn number fields satisfying: (p)(p) is unramified in KK, ∣DK∣≤B|D_K|\leq B, and the normal closure of K/QK/\mathbb{Q} has Galois group SnS_n. Let q(k,n)q(k,n) denote the number of partitions of kk into at most nn parts, with q(0,n)=1q(0,n)=1 for n≥1n\geq 1, and define

ρn(p):=∑k=1n−1q(k,n−k)pn−1−k∑k=0n−1q(k,n−k)pn−1−k.\rho_n(p):=\frac{\sum_{k=1}^{n-1}q(k,n-k)p^{n-1-k}}{\sum_{k=0}^{n-1}q(k,n-k)p^{n-1-k}}.

Bhargava's ramification-density conjecture. For every prime pp and positive integer nn,

lim⁡B→∞#{K∈Gn(B;p)}#{K∈Gn(B)}=1−ρn(p).\lim_{B\rightarrow\infty}\frac{\#\{K\in\mathcal{G}_n(B;p)\}}{\#\{K\in\mathcal{G}_n(B)\}}=1-\rho_n(p).

Here ρn(p)\rho_n(p) is the predicted probability of ramification at pp. Bhargava proves the conjecture for n≤5n\leq 5; the assertion remains conjectural for general nn.

References

Primary source

Jeffrey C. Lagarias and Benjamin L. Weiss, “Splitting Behavior of S_n-Polynomials”, arXiv:1408.6251 (2015).

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