The completion conjecture for plus test ideals

Let XX be a normal integral scheme of finite type over a complete local ring (R,m)(R,\mathfrak{m}) such that R/mR/\mathfrak{m} has positive characteristic. Let B0B\geq 0 be a Q\mathbb{Q}-divisor on XX such that KX+BK_X+B is Q\mathbb{Q}-Cartier. Fix a point xXx\in X with residual characteristic p>0p>0, and let S=OX,xS=\mathcal{O}_{X,x} be the stalk at xx. The completion conjecture. One has

τ+(OX,B)xS^=τ+(S^,B^)=τR+^(S^,B^)\tau_+(\mathcal{O}_{X},B)_x\cdot\widehat{S}=\tau_+(\widehat{S},\widehat{B})=\tau_{\widehat{R^+}}(\widehat{S},\widehat{B})

and

τ+(OX,B)x=τ+(S^,B^)S.\tau_+(\mathcal{O}_{X},B)_x=\tau_+(\widehat{S},\widehat{B})\cap S.

This asks whether plus test ideals commute with completion and contract back from the completed local ring. The source presents it as an open question in mixed characteristic.

Sources & referencesView supporting material

Primary source

Christopher Hacon, Alicia Lamarche and Karl Schwede, “Global generation of test ideals in mixed characteristic and applications”, arXiv:2106.14329 (2022).

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