The explicit ghost conjecture for U5U_5

For a=0,,3a=0,\dots,3, define the ghost series

G(a)(w,t)=1+n=1gn(a)(w)tnZ5[w][[t]],G^{(a)}(w,t)=1+\sum_{n=1}^{\infty}g_n^{(a)}(w)t^n\in\mathbb{Z}_5[w][[t]],

where

gn(a)(w)=l2\lamod4(wwl)mn(a)(l)g_n^{(a)}(w)=\prod_{\substack{l\geq 2\l\equiv a\bmod 4}}(w-w_l)^{m_n^{(a)}(l)}

with the exponents mn(a)(l)m_n^{(a)}(l) prescribed by the source. Set

wk=exp(5(k2))1w_k=\exp(5(k-2))-1

and let Char(U5,w,a)Z5[[w]][[t]]\operatorname{Char}(U_5,w,a)\in\mathbb{Z}_5[[w]][[t]] satisfy

Char(U5,wk,a)=Char(U5,k,a)\operatorname{Char}(U_5,w_k,a)=\operatorname{Char}(U_5,k,a)

for every weight kk. The explicit ghost conjecture. For every weight kk congruent to aa modulo 44, Char(U5,wk,a)\operatorname{Char}(U_5,w_k,a) and G(a)(wk,t)G^{(a)}(w_k,t) have the same Newton polygon. This conjecture asserts that the explicitly constructed ghost series reproduces the Newton polygons governing the U5U_5 slopes; the source does not state a resolution.

Sources & referencesView supporting material

Primary source

Nha Xuan Truong, “An explicit computation of the Hecke operator and the ghost conjecture”, arXiv:2011.07708 (2023).

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