Maximal Ancillarity, Semiparametric Efficiency, and the Elimination of Nuisances

This paper resolves the non-uniqueness of maximal ancillary σ\sigma-fields by introducing a sequence-based asymptotic framework that enables semiparametrically efficient inference through finite-sample nuisance elimination, specifically utilizing center-outward residual ranks and signs to construct distribution-free restrictions of locally asymptotically normal experiments without requiring nuisance parameter estimation.

Marc Hallin, Bas J. M. Werker, Bo Zhou2026-03-10🔢 math

A note on diffusive/random-walk behaviour in Metropolis--Hastings algorithms

This paper establishes that Metropolis–Hastings algorithms with non-geometrically ergodic proposals and high acceptance rates at large states fail to be geometrically ergodic, while further demonstrating that guided walk variants converge twice as fast as random walk versions for polynomial-tailed targets but exhibit similar ballistic speeds to random walks for strictly convex potentials.

Yuxin Liu, Peiyi Zhou, Samuel Livingstone2026-03-10🔢 math

Unconditional structure of Banach spaces with few operators

This paper demonstrates that the pp-convexification of Gowers' space G\mathbb{G} yields Banach spaces with unique unconditional bases containing block bases with spreading models distinct from 1\ell_1, 2\ell_2, and c0c_0, thereby resolving a long-standing open problem by Bourgain et al. and disproving the conjecture that such spaces must be isomorphic to their squares.

Fernando Albiac, Jose L. Ansorena2026-03-10🔢 math