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تسجيل مستخدم جديدTopological comparison theorems for Bredon motivic cohomology
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In this paper we study the topological invariant ${sf {TC}}(X)$ reflecting the complexity of algorithms for autonomous robot motion. Here, $X$ stands for the configuration space of a system and ${sf {TC}}(X)$ is, roughly, the minimal number of contin
uous rules which are needed to construct a motion planning algorithm in $X$. We focus on the case when the space $X$ is aspherical; then the number ${sf TC}(X)$ depends only on the fundamental group $pi=pi_1(X)$ and we denote it ${sf TC}(pi)$. We prove that ${sf TC}(pi)$ can be characterised as the smallest integer $k$ such that the canonical $pitimespi$-equivariant map of classifying spaces $$E(pitimespi) to E_{mathcal D}(pitimespi)$$ can be equivariantly deformed into the $k$-dimensional skeleton of $E_{mathcal D}(pitimespi)$. The symbol $E(pitimespi)$ denotes the classifying space for free actions and $E_{mathcal D}(pitimespi)$ denotes the classifying space for actions with isotropy in a certain family $mathcal D$ of subgroups of $pitimespi$. Using this result we show how one can estimate ${sf TC}(pi)$ in terms of the equivariant Bredon cohomology theory. We prove that ${sf TC}(pi) le max{3, {rm cd}_{mathcal D}(pitimespi)},$ where ${rm cd}_{mathcal D}(pitimespi)$ denotes the cohomological dimension of $pitimespi$ with respect to the family of subgroups $mathcal D$. We also introduce a Bredon cohomology refinement of the canonical class and prove its universality. Finally we show that for a large class of principal groups (which includes all torsion free hyperbolic groups as well as all torsion free nilpotent groups) the essential cohomology classes in the sense of Farber and Mescher are exactly the classes having Bredon cohomology extensions with respect to the family $mathcal D$.
We show that the analogue of the Peterson conjecture on the action of Steenrod squares does not hold in motivic cohomology.
We provide a complete analysis of the motivic Adams spectral sequences converging to the bigraded coefficients of the 2-complete algebraic Johnson-Wilson spectra BPGL<n> over p-adic fields. These spectra interpolate between integral motivic cohomolog
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