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Sihao Ma

Publications and source records attributed to Sihao Ma.

5 recordsLinked to original sources
arXiv2026

Generating hypotheses along the motivic deformation

At every prime $p$, we disprove the algebraic generating hypothesis for compact objects in Hovey's stable category of $BP_*BP$-comodules and its local analog at every positive height, answering questions of Barthel and Heard. In both settings, for every $r,n\geq1$, we construct a ghost whose first $n$ composition powers are all nonzero and have exact additive order $p^r$. The same construction applies to the stable category of $E_*E$-comodules for even $p$-local Landweber exact theories $E$ that are not rational. Through the motivic deformation of Gheorghe--Wang--Xu, these examples give $Cτ$-linear counterexamples to the cellular $\mathbb{C}$-motivic generating hypothesis, with the same order and composition properties. We also construct nonzero non-$Cτ$-linear ghosts between $Cτ$-modules and a nonzero ghost on a motivic spectrum with noncontractible Betti realization.

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arXiv2026

Equivariant generating hypotheses for finite groups

We disprove Bohmann's equivariant generating hypothesis for every nontrivial finite group $G$, even when all $\RO(H)$-graded homotopy groups at every subgroup $H$ are tested. For each fixed $G$ and prime $p$ dividing $|G|$, we construct ghosts on finite $G$-spectra with arbitrarily long nonzero composition powers. We also prove that the homotopy-module functors are nonfull and construct non-equivalent finite $G$-spectra with isomorphic full homotopy modules. Our constructions use circle power maps and cyclic permutations of products of projective spaces, and are motivated by Ma--Xu's categorical method in the motivic setting and the projective-space power maps.

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arXiv2026

A Hurewicz Theorem for $RO(C_2)$-graded Equivariant Homology Governed by Vector Fields on Spheres

We determine the $RO(C_2)$-graded Hurewicz images of the $C_2$-equivariant Eilenberg--MacLane spectra $H\underline{\mathbb F_2}$, $H\underline{\mathbb Z}$ and $H\underline{A}$, where $\underline{\mathbb F_2}$ and $\underline{\mathbb Z}$ denote the constant Mackey functors with values in $\mathbb F_2$ and $\mathbb Z$, respectively, and $\underline A$ denotes the Burnside Mackey functor. Surprisingly, the answer is closely tied to the problem of vector fields on spheres: the element $\fracθ{ρ^kτ^n}$ in the negative cone of the homotopy groups of $H\underline{\mathbb F_2}$ lies in the Hurewicz image if and only if $S^n$ admits $k$ linearly independent vector fields. Moreover, using the Generalized Leibniz Rule and the Generalized Mahowald Trick introduced by arXiv:2412.10879, we show that there are nonzero Adams differentials of arbitrary length supported by filtration-$0$ elements in the genuine $C_2$-equivariant Adams spectral sequence.

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arXiv2025

The Borel and genuine $C_2$-equivariant Adams spectral sequences

We find out some relations between the classical Adams spectral sequences for stunted real projective spectra, the Borel $C_2$-equivariant Adams spectral sequence for the 2-completed sphere, and the genuine $C_2$-equivariant Adams spectral sequence for the 2-completed sphere. This allows us to understand the genuine $C_2$-equivariant Adams spectral sequence from the Borel Adams spectral sequences. We show that the Borel Adams spectral sequence is computable as a classical Adams spectral sequence.

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