Eva Belmont, Bertrand J. Guillou, Daniel C. Isaksen
We show that the $C_2$-equivariant and $\mathbb{R}$-motivic stable homotopy groups are isomorphic in a range. This result supersedes previous work of Dugger and the third author.
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We establish, in the setting of equivariant motivic homotopy theory for a finite group, a version of tom Dieck's splitting theorem for the fixed points of a suspension spectrum. Along the way we establish structural results and constructions for equivariant motivic homotopy theory of independent interest. This includes geometric fixed point functors and the motivic Adams isomorphism.
In this paper, we produce a cellular motivic spectrum of motivic modular forms over $\R$ and $\C$, answering positively to a conjecture of Dan Isaksen. This spectrum is constructed to have the appropriate cohomology, as a module over the relevant motivic Steenrod algebra. We first produce a $\G$-equivariant version of this spectrum, and then use a machinery to construct a motivic spectrum from an equivariant one. We believe that this machinery will be of independent interest.
We establish an isomorphism between the stable homotopy groups of the 2-completed motivic sphere spectrum over the real numbers and the corresponding stable homotopy groups of the 2-completed Z/2-equivariant sphere spectrum, in a certain range of dimensions.
We generalize the Mahowald invariant to the $\mathbb{R}$-motivic and $C_2$-equivariant settings. For all $i>0$ with $i \equiv 2,3 \mod 4$, we show that the $\mathbb{R}$-motivic Mahowald invariant of $(2+ρη)^i \in π_{0,0}^{\mathbb{R}}(S^{0,0})$ contains a lift of a certain element in Adams' classical $v_1$-periodic families, and for all $i > 0$, we show that the $\mathbb{R}$-motivic Mahowald invariant of $η^i \in π_{i,i}^{\mathbb{R}}(S^{0,0})$ contains a lift of a certain element in Andrews' $\mathbb{C}$-motivic $w_1$-periodic families. We prove analogous results about the $C_2$-equivariant Mah…
We study thick ideals in the stable motivic homotopy category SH(k) and in its subcategories of compact and of finite cellular objects. If k is a subfield of the complex or even the real numbers, then using comparison functors we find thick ideals corresponding to thick ideals in classical or Z/2-equivariant stable homotopy theory, respectively. We also study motivic Morava K-theories AK(n), for which we prove the motivic analogue of the decomposition of the Bousfield class of E(n) into Bousfield classes of K(i)'s over the complex numbers if p>2. In that case we also prove that AK(n)-acyclicit…
We establish a differential $d_2(D_1)=h_0^2h_3g_2$ in the $51$-stem of the Adams spectral sequence at the prime $2$, which gives the first correct calculation of the stable 51 and 52 stems. This differential is remarkable since we know of no way to prove it without recourse to the motivic Adams spectral sequence. It is the last undetermined differential in the range of the first author's detailed calculations of the $n$-stems for $n<60$ [6]. This note advertises the use of the motivic Adams spectral sequence to obtain information about classical stable homotopy groups.
We compute some R-motivic stable homotopy groups. For $s - w \leq 11$, we describe the motivic stable homotopy groups $π_{s,w}$ of a completion of the R-motivic sphere spectrum. We apply the $ρ$-Bockstein spectral sequence to obtain R-motivic Ext groups from the C-motivic Ext groups, which are well-understood in a large range. These Ext groups are the input to the R-motivic Adams spectral sequence. We fully analyze the Adams differentials in a range, and we also analyze hidden extensions by $ρ$, 2, and $η$. As a consequence of our computations, we recover Mahowald invariants of many low-dimens…
In this paper we establish a formula for computing $d_2(sq^i(x))$ where $x$ is a permanent cycle in the $C_2$-equivariant Adams spectral sequence or the motivic Adams spectral sequence over $Spec(\mathbb{R})$. This requires establishing that the Adams towers have an $H_{\infty}$-structure as well as determining the attaching maps for $C_2$-equivariant projective spaces. The attaching maps of $C_2$-equivariant projective spaces can then be used to determine the coefficients of differentials in both the equivariant and motivic case. At the end some sample computations are given.
We give a method for computing the C_2-equivariant homotopy groups of the Betti realization of a p-complete cellular motivic spectrum over R in terms of its motivic homotopy groups. More generally, we show that Betti realization presents the C_2-equivariant p-complete stable homotopy category as a localization of the p-complete cellular real motivic stable homotopy category.
In this paper we study a model structure on a category of schemes with a group action and the resulting unstable and stable equivariant motivic homotopy theories. The new model structure introduced here samples a comparison to the one by Voevodsky and Hu-Kriz-Ormsby. We show that it allows to detect equivariant motivic weak equivalences on fixed points and how this property leads to a topologically convenient behavior of stable equivalences. We also prove a negative result concerning descent for equivariant algebraic K-theory.
Let $\ell$ be a prime and $q = p^ν$ where $p$ is a prime different from $\ell$. We show that the $\ell$-completion of the $n$th stable homotopy group of spheres is a summand of the $\ell$-completion of the $(n, 0)$ motivic stable homotopy group of spheres over the finite field with $q$ elements $F_q$. With this, and assisted by computer calculations, we are able to explicitly compute the two-complete stable motivic stems $π_{n, 0}(F_q)^{\wedge}_2$ for $0\leq n\leq 18$. Additionally, we compute $π_{19, 0}(F_q)^{\wedge}_2$ and $π_{20, 0}(F_q)^{\wedge}_2$ when $q \equiv 1 \bmod 4$ assuming Morel'…
We introduce a Bredon motivic cohomology theory for smooth schemes defined over a field and equipped with an action by a finite group. These cohomology groups are defined for finite dimensional representations as the hypercohomology of complexes of equivariant correspondences in the equivariant Nisnevich topology. We generalize the theory of presheaves with transfers to the equivariant setting and prove a Cancellation Theorem.
We present a detailed analysis of 2-complete stable homotopy groups, both in the classical context and in the motivic context over C. We use the motivic May spectral sequence to compute the cohomology of the motivic Steenrod algebra over C through the 70-stem. We then use the motivic Adams spectral sequence to obtain motivic stable homotopy groups through the 59-stem. In addition to finding all Adams differentials in this range, we also resolve all hidden extensions by 2, eta, and nu, except for a few carefully enumerated exceptions that remain unknown. The analogous classical stable homotopy …
Synthetic equivariant spectra for finite abelian groups and motivic homotopy theory
本文证明复数域上有限阿贝尔群等变动机谱范畴在素数完备化后等价于合成等变谱范畴的完备化，后者是等变谱的形变并范畴化等变完美偶滤过，其计算依赖于等变形式群律描述的等变代数配边同伦群。
The motivic Mahowald invariant was introduced in \cite{Qui19a} and \cite{Qui19b} to study periodicity in the $\mathbb{C}$- and $\mathbb{R}$-motivic stable stems. In this paper, we define the motivic Mahowald invariant over any field $F$ of characteristic not two and use it to study periodicity in the $F$-motivic stable stems. In particular, we construct lifts of some of Adams' classical $v_1$-periodic families \cite{Ada66} and identify them as the motivic Mahowald invariants of powers of $2+ρη$.
In this paper, we show that the finite subalgebra $\mathcal{A}^{\mathbb{R}}(1)$, generated by $\mathrm{Sq}^1$ and $\mathrm{Sq}^2$, of the $\mathbb{R}$-motivic Steenrod algebra $\mathcal{A}^{\mathbb{R}}$ can be given $128$ different $\mathcal{A}^{\mathbb{R}}$-module structures. We also show that all of these $\mathcal{A}^{\mathbb{R}}$-modules can be realized as the cohomology of a $2$-local finite $\mathbb{R}$-motivic spectrum. The realization results are obtained using an $\mathbb{R}$ -motivic analogue of the Toda realization theorem. We notice that each realization of $\mathcal{A}^{\mathbb{R}…
We identify the equivariant structure of the filtered pieces of the motivic filtration defined by Bhatt, Morrow and Scholze on the topological Hochschild cohomology spectrum of polynomial algebras over $\mathbb{F}_p$.
This article computes some motivic stable homotopy groups over R. For 0 <= p - q <= 3, we describe the motivic stable homotopy groups of a completion of the motivic sphere spectrum. These are the first four Milnor-Witt stems. We start with the known Ext groups over C and apply the rho-Bockstein spectral sequence to obtain Ext groups over R. This is the input to an Adams spectral sequence, which collapses in our low dimensional range.
In this paper, we develop the theory of equivariant motivic homotopy theory, both unstable and stable. While our original interest was in the case of profinite group actions on smooth schemes, we discuss our results in as broad a setting as possible so as to be applicable in a variety of contexts, for example to the case of smooth group scheme actions on schemes that are not necessarily smooth. We also discuss how ${\mathbb A}^1$-localization behaves with respect to mod-$\ell$-completion, where $\ell$ is a fixed prime.
Motivic stable stems and Galois approximations of cellular motivic categories
本文证明小上同调维数域上的胞腔动机谱范畴可由绝对 Galois 群刻画，并据此确定几乎所有域在特征外的动机稳定茎。
This document contains large-format Adams charts that compute 2-complete stable homotopy groups, both in the classical context and in the motivic context over C. The charts are essentially complete through the 61-stem and contain partial results to the 70-stem. In the classical context, we believe that these are the most accurate charts of their kind. We also include Adams charts for the motivic homotopy groups of the cofiber of tau.
Let $k$ be a field with a real embedding. We compare the motivic slice filtration of a motivic spectrum over $Spec(k)$ with the $C_2$-equivariant slice filtration of its equivariant Betti realization, giving conditions under which realization induces an equivalence between the associated slice towers. In particular, we show that, up to reindexing, the towers agree for all spectra obtained from localized quotients of $MGL$ and $MR$, and for motivic Landweber exact spectra and their realizations. As a consequence, we deduce that equivariant spectra obtained from localized quotients of $MR$ are e…
We compute the cohomology of the subalgebra $A^{C_2}(1)$ of the $C_2$-equivariant Steenrod algebra $A^{C_2}$. This serves as the input to the $C_2$-equivariant Adams spectral sequence converging to the $RO(C_2)$-graded homotopy groups of an equivariant spectrum $ko_{C_2}$. Our approach is to use simpler $\mathbb{C}$-motivic and $\mathbb{R}$-motivic calculations as stepping stones.
We prove equivariant versions of the Beilinson-Lichtenbaum conjecture for Bredon motivic cohomology of smooth complex and real varieties with an action of the group of order two. This identifies equivariant motivic and topological invariants in a large range of degrees.
We define an unstable equivariant motivic homotopy category for an algebraic group over a Noetherian base scheme. We show that equivariant algebraic $K$-theory is representable in the resulting homotopy category. Additionally, we establish homotopical purity and blow-up theorems for finite abelian groups.
The six operations in equivariant motivic homotopy theory
本文将母题同伦理论推广到商叠 [X/G] 的等变情形，证明纯度、粘合与双手性定理，并由此建立等变母题谱的六运算形式体系，进而得到绝对母题谱表示的上同调理论满足 cdh 下降。
We consider a nontrivial action of $\mathrm{C}_2$ on the type $1$ spectrum $\mathcal{Y} := \mathrm{M}_2(1) \wedge \mathrm{C}(η)$, which is well-known for admitting a $1$-periodic $v_1-$self-map. The resultant finite $\mathrm{C}_2$-equivariant spectrum $\mathcal{Y}^{\mathrm{C}_2}$ can also be viewed as the complex points of a finite $\mathbb{R}$-motivic spectrum $\mathcal{Y}^\mathbb{R}$. In this paper, we show that one of the $1$-periodic $v_1-$self-maps of $\mathcal{Y}$ can be lifted to a self-map of $\mathcal{Y}^{\mathrm{C}_2}$ as well as $\mathcal{Y}^{\mathbb{R}}$. Further, the cofiber of th…
Endomorphisms of Equivariant Algebraic $K$-theory
本文证明了有限常值群概形作用下等变代数K-理论由Grassmannian的余极限表示，并通过显式计算Grassmannian的等变K-理论，证明了等变动机空间与无限Grassmannian的自同态集一致。
Bredon motivic cohomology of the complex numbers
本文在复数域上计算了$C_2$-等变Bredon母题上同调环，并利用刚性将Suslin的经典结果推广到等变母题框架。
For groups of prime order, equivariant stable maps between equivariant representation spheres are investigated using the Borel cohomology Adams spectral sequence. Features of the equivariant stable homotopy category, such as stability and duality, are shown to lift to the category of modules over the associated Steenrod algebra. The dependence on the dimension functions of the representations is clarified.
For a finite Galois extension of fields L/k with Galois group G, we study a functor from the G-equivariant stable homotopy category to the stable motivic homotopy category over k induced by the classical Galois correspondence. We show that after completing at a prime and eta (the motivic Hopf map) this results in a full and faithful embedding whenever k is real closed and L = k[i]. It is a full and faithful embedding after eta-completion if a motivic version of Serre's finiteness theorem is valid. We produce strong necessary conditions on the field extension L/k for this functor to be full and…
Periods in equivariant and motivic contexts
该研究定义了稳定对称幺半∞-范畴的乘法特征“周期”，发展其性质并研究等变和 motive 同伦论等例子，还将结果应用于 motive tt-几何的各向同性点，含相关附录。
The zeroth stable homotopy groups of motivic spheres over the integers
本文确定了整数上动机球面谱的第零积分Milnor-Witt茎，并建立了多种动机谱的细胞性及混合特征Dedekind域上的绝对纯性结果。
We calculate the equivariant motivic Chern class for configuration space of a quasiprojective (maybe singular) variety and the space of vectors with different directions. We prove the formulas for generating series of these classes. We generalize the localization theorems results about Bialynicki-Birula decomposition to acquire some stability for the motivic Chern classes of configuration spaces.
In this short note, we compute the rational $C_{2^n}$-equivariant stable stems and give minimal presentations for the $RO(C_{2^n})$-graded Bredon cohomology of the equivariant classifying spaces $B_{C_{2^n}}S^1$ and $B_{C_{2^n}}Σ_2$ over the rational Burnside functor $A_{\mathbf Q}$. We also examine for which compact Lie groups $L$ the maximal torus inclusion $T\to L$ induces an isomorphism from $H^*_{C_{2^n}}(B_{C_{2^n}}L;A_{\mathbf Q})$ onto the fixed points of $H^*_{C_{2^n}}(B_{C_{2^n}}T;A_{\mathbf Q})$ under the Weyl group action. We prove that this holds for $L=U(m)$ and any $n,m\ge 1$ bu…
Equivariant localizing motives and multiplicative norms on algebraic K-theory
本文构建了有限群G的等变非连通代数K-理论的乘法规范，并构造了带有Dennis追踪映射的等变THH，证明规范保持等变动机等价。
The reduced ring of the $RO(C_2)$-graded $C_2$-equivariant stable stems
研究$RO(C_2)$-graded $C_2$-equivariant 稳定茎的环结构，通过生成元和关系描述，确定其在去除所有 nilpotent 元素后的结构，并记录有理 $C_2$-equivariant 球面的同调群结构。
We construct geometric models for classifying spaces of linear algebraic groups in G-equivariant motivic homotopy theory, where G is a tame group scheme. As a consequence, we show that the equivariant motivic spectrum representing the homotopy K-theory of G-schemes (which we construct as an E-infinity-ring) is stable under arbitrary base change, and we deduce that homotopy K-theory of G-schemes satisfies cdh descent.
C_2-Equivariant Stable Stems
本文计算了茎在0至25、余权在-1至7范围内的2-准素$C_2$-等变稳定同伦群，并结合周期性同构与$\mathbb{R}$-动机计算确定了茎至20的所有群，同时计算了到经典稳定同伦群的遗忘映射。
Let $kq$ denote the very effective cover of Hermitian K-theory. We apply the $kq$-based motivic Adams spectral sequence, or $kq$-resolution, to computational motivic stable homotopy theory. Over base fields of characteristic not two, we prove that the $n$-th stable homotopy group of motivic spheres is detected in the first $n$ lines of the $kq$-resolution, thereby reinterpreting results of Morel and R{ö}ndigs-Spitzweck-Østvær in terms of $kq$ and $kq$-cooperations. Over algebraically closed fields of characteristic 0, we compute the ring of $kq$-cooperations modulo $v_1$-torsion, establish a v…
Bredon motivic cohomology of the real numbers
本文在实数域上以 $\Z/2$-系数计算 $C_2$-等变 Borel 动机上同调环与 Bredon 动机上同调群，证明其为点空间 $RO(C_2\times C_2)$-分次 Bredon 上同调环的真子环，并推广至任意实闭域。
We use an Adams spectral sequence to calculate the R-motivic stable homotopy groups after inverting eta. The first step is to apply a Bockstein spectral sequence in order to obtain h_1-inverted R-motivic Ext groups, which serve as the input to the eta-inverted R-motivic Adams spectral sequence. The second step is to analyze Adams differentials. The final answer is that the Milnor-Witt (4k-1)-stem has order 2^{u+1}, where u is the 2-adic valuation of 4k. This answer is reminiscent of the classical image of J. We also explore some of the Toda bracket structure of the eta-inverted R-motivic stabl…
On the rational $C_2$-homotopy type of ${BSU_{\mathbb{R}}}_m$
本文通过等价Eilenberg-Maclane空间描述实数BSU_m的有理C_2等价同调类型，解决动机同调论中的相关问题。
$C_3$-equivariant stable stems
论文计算了$C_3$-equivariant稳定同调群$π_{i,j}^{C_3}$，针对茎小于25和权重范围-16到16的情况，并描述了几何固定点映射和底层映射。
The cohomology of $\mathbb{R}$-motivic $\mathcal{A}(2)$
通过$\rho$-Bockstein谱序列计算$\mathbb{R}$-动机对偶Steenrod代数的商代数$\mathcal{A}(2)$的上同调，为Adams谱序列提供输入以研究$\mathbb{R}$-动机模形式谱的同伦群。
Given a finite group G, we develop a theory of G-equivariant noncommutative motives. This theory provides a well-adapted framework for the study of G-schemes, Picard groups of schemes, G-algebras, 2-cocycles, equivariant algebraic K-theory, orbifold cohomology theory, etc. Among other results, we relate our theory with its commutative counterpart as well as with Panin's motivic theory. As a first application, we extend Panin's computations, concerning twisted projective homogeneous varieties, to a large class of invariants. As a second application, we prove that whenever the category of perfec…
Motivic homotopy theory and stable homotopy groups
本文综述域上的 Morel-Voevodsky 动机同伦论及其同伦层计算，并说明动机 Adams 谱序列在确定稳定茎和催生综合同伦论中的作用。
We show that if G is a finite constant group acting on a scheme X such that the order of G is invertible in the residue fields of X, then the G-equivariant motivic stable homotopy category of X is equivalent to the stabilization of the category of motivic G-spaces with finite étale transfers over X at the trivial representation sphere. Along the way we obtain several results of independent interest, among them: we construct and study norms in the motivic homotopy theory of stacks, and we extend the homotopy t-structure to DM-stacks and establish some favorable properties.
Galois reconstruction of Artin-Tate $\mathbb{R}$-motivic spectra
本文通过将Artin-Tate $\mathbb{R}$-动机谱范畴重构为$C_2$-等变稳定范畴的形变，推广了$τ$余纤维哲学，发现该子范畴含胞腔子范畴缺失的$τ$映射变体，更易研究。
We define a notion of colimit for diagrams in a motivic category indexed by a presheaf of spaces (e.g. an étale classifying space), and we study basic properties of this construction. As a case study, we construct the motivic analogs of the classical extended and generalized powers, which refine the categorical versions of these constructions as special cases. We also offer more computationally tractable models of these constructions using equivariant motivic homotopy theory. This is the first in a series of papers on power operations in motivic stable homotopy theory.
Motivic real topological Hochschild spectrum
定义带对合的分离对数方案的实拓扑Hochschild同调，证明其(ℙⁿ,ℙⁿ⁻¹)-不变性，从而构造动机实拓扑Hochschild谱，并探讨其性质及动机实拓扑循环谱。
Motivic Segre classes of Schubert cells and the connective formal group law
利用连接形式群律定义 d 步旗簇中 Schubert 胞腔的动机 Segre 类的单参数 β 形变，并给出 d=1 时的有理函数表示和组合公式。
A deformation of Borel equivariant homotopy
该研究描述了有限群G的Borel G-谱∞-范畴的形变，当G=C₂时为a-完备实Artin-Tate motivic稳定同伦范畴提供新表示，给出a-完备C₂-有效切片谱序列新解释，并提出修正的Adams-Novikov谱序列作为计算工具。
Monadic resolutions for generalized spaces
本文将 Bousfield–Kan 的单子分解方法推广到 ∞-拓扑斯，证明主纤维化引理，并据此建立不稳定等变与母题同伦理论中多类单子分解的收敛性，特别证明了代数闭域上不稳定 Adams–Novikov 谱序列对幂零连通 2-有效母题空间的收敛性。
$T$-equivariant motives of flag varieties
本文利用Khan-Ravi稳定同伦范畴构造，将旗簇的T-等变K-理论环谱分解为以Weyl群为指标的BT的K-理论谱直和，并由此推导出T-等变相交理论与K-理论的经典结果。
Generalized cohomology theories for algebraic stacks
本文扩展了Voevodsky的稳定motivic同调范畴至scalloped代数堆，展示其具备Grothendieck的六操作公理，为堆上的广义上同调理论提供框架，包括代数K理论和新的例子如motivic上同调和代数 bordism。
On normed $\mathbb{E}_\infty$-rings in genuine equivariant $C_p$-spectra
本文研究真等变 $C_p$-谱中的 $C_p$-$\mathbb{E}_\infty$-代数，证明其高阶一致性坍缩，可用赋范代数简化描述，并给出识别准则及对实动机不变量的应用。
The $RO(C_2)$-graded Hurewicz image of Atiyah's Real K-theory
本研究确定了$RO(C_2)$分次的阿蒂亚实K-理论的胡雷维茨像，得到四类等变稳定茎中的无限族，还构造了捕获相关周期现象的等变亚当斯周期算子。
Over any field of characteristic not 2, we establish a 2-term resolution of the $η$-periodic, 2-local motivic sphere spectrum by shifts of the connective 2-local Witt K-theory spectrum. This is curiously similar to the resolution of the K(1)-local sphere in classical stable homotopy theory. As applications we determine the $η$-periodized motivic stable stems and the $η$-periodized algebraic symplectic and SL-cobordism groups. Along the way we construct Adams operations on the motivic spectrum representing Hermitian K-theory and establish new completeness results for certain motivic spectra ove…
In previous work, the authors constructed and studied a lift of the Galois correspondence to stable homotopy categories. In particular, if $L/k$ is a finite Galois extension of fields with Galois group $G$, there is a functor $c_{L/k}^*$ from the $G$-equivariant stable homotopy category to the stable motivic homotopy category over $k$ such that $c_{L/k}^*(G/H_+) = Spec(L^H)_+$. We proved that when $k$ is a real closed field and $L=k[i]$, the restriction of $c_{L/k}^*$ to the $η$-complete subcategory is full and faithful. Here we "uncomplete" this theorem so that it applies to $c_{L/k}^*$ itsel…
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