algebra / Algebraic K-theory of regular local rings

Gersten's conjecture for integral K-theory of arbitrary regular local rings (Quillen's form), in ramified mixed characteristic

Theorem 1.1 (degree five): with VV the integers of the unramified degree-eight extension of Q5\mathbb Q_5 and A=(V[x,y]/(5+x4+y4))(5,x,y)A=(V[x,y]/(5+x^4+y^4))_{(5,x,y)}, AA is a two-dimensional regular local domain and ker⁡(K5(A)→K5(Frac A))≠0\ker(K_5(A)\to K_5(\mathrm{Frac}\,A))\ne0; the class also gives generic noninjectivity with Z/5\mathbb Z/5 coefficients. Companion Theorem 1.1 (degree three): the local ring of a cyclotomic quintic model over Z5[ζ5]\mathbb Z_5[\zeta_5] at a special point has a nonzero class in ker⁡(K3(A)→K3(Frac A))\ker(K_3(A)\to K_3(\mathrm{Frac}\,A)) not divisible by 5. Not shown: the order of these classes, whether they survive rationally (the rational Gersten conjecture is untouched), anything about unramified or smooth-over-DVR rings, or the least degree of failure.

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algebraSep 25, 2026Significance 30/100Registry: contested

Gersten's conjecture for integral K-theory of arbitrary regular local rings (Quillen's form), in ramified mixed characteristic

Prior state unknown→disproved

Theorem 1.1 (degree five): with VV the integers of the unramified degree-eight extension of Q5\mathbb Q_5 and A=(V[x,y]/(5+x4+y4))(5,x,y)A=(V[x,y]/(5+x^4+y^4))_{(5,x,y)}, AA is a two-dimensional regular local domain and ker⁡(K5(A)→K5(Frac A))≠0\ker(K_5(A)\to K_5(\mathrm{Frac}\,A))\ne0; the class also gives generic noninjectivity with Z/5\mathbb Z/5 coefficients. Companion Theorem 1.1 (degree three): the local ring of a cyclotomic quintic model over…

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Theorem 1.1 (degree five): with VV the integers of the unramified degree-eight extension of Q5\mathbb Q_5 and A=(V[x,y]/(5+x4+y4))(5,x,y)A=(V[x,y]/(5+x^4+y^4))_{(5,x,y)}, AA is a two-dimensional regular local domain and ker⁡(K5(A)→K5(Frac A))≠0\ker(K_5(A)\to K_5(\mathrm{Frac}\,A))\ne0; the class also gives generic noninjectivity with Z/5\mathbb Z/5 coefficients. Companion Theorem 1.1 (degree three): the local ring of a cyclotomic quintic model over Z5[ζ5]\mathbb Z_5[\zeta_5] at a special point has a nonzero class in ker⁡(K3(A)→K3(Frac A))\ker(K_3(A)\to K_3(\mathrm{Frac}\,A)) not divisible by 5. Not shown: the order of these classes, whether they survive rationally (the rational Gersten conjecture is untouched), anything about unramified or smooth-over-DVR rings, or the least degree of failure.

S. Mochizuki, Local Gersten's conjecture for regular system of parameters (arXiv:1503.07966v8, 2020), abstract: 'we show local Gersten's conjecture for regular system of parameters. As its consequence we obtain Gersten's conjecture for a commutative regular local ring and smooth over a commutative discrete valuation ring.' The release's degree-five paper says: 'Mochizuki's Theorem 5 in version 8 ... asserts that, for a commutative Noetherian local ring B and a nonzerodivisor g, the inclusion from finitely generated projective B/gB-modules to finitely generated B-modules of projective dimension at most one induces zero on K-theory. This statement reaches the exact support in the present paper', so it 'would annihilate' the class constructed. The release gives a counterexample to Lemma 13(III) used in that proof, and says this 'by itself does not refute its theorem statement'. Mochizuki's headline corollary (rings smooth over a DVR) does not cover the ring used here. Theorem 1.1 (degree five): with VV the integers of the unramified degree-eight extension of Q5\mathbb Q_5 and A=(V[x,y]/(5+x4+y4))(5,x,y)A=(V[x,y]/(5+x^4+y^4))_{(5,x,y)}, AA is a two-dimensional regular local domain and ker⁡(K5(A)→K5(Frac A))≠0\ker(K_5(A)\to K_5(\mathrm{Frac}\,A))\ne0; the class also gives generic noninjectivity with Z/5\mathbb Z/5 coefficients. Companion Theorem 1.1 (degree three): the local ring of a cyclotomic quintic model over Z5[ζ5]\mathbb Z_5[\zeta_5] at a special point has a nonzero class in ker⁡(K3(A)→K3(Frac A))\ker(K_3(A)\to K_3(\mathrm{Frac}\,A)) not divisible by 5. Not shown: the order of these classes, whether they survive rationally (the rational Gersten conjecture is untouched), anything about unramified or smooth-over-DVR rings, or the least degree of failure.

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Gersten's conjecture for integral K-theory of arbitrary regular local rings (Quillen's form), in ramified mixed characteristic — Mathematical Frontier Network