scholarly journals A note on the modular representation on the $\mathbb Z/2$-homology groups of the fourth power of real projective space and its application

2021 ◽  
Author(s):  
Đặng Võ Phúc
Keyword(s):  
Homotopy Theory ◽  
Cartesian Product ◽  
Steenrod Algebra ◽  
Fourth Power ◽  
Real Projective Space ◽  
Divided Power ◽  
Classifying Space ◽  
Left Action ◽  
Homology Groups ◽  
Positive Integers

We write $BV_h$ for the classifying space of the elementary Abelian 2-group $V_h$ of rank $h,$ which is homotopy equivalent to the cartesian product of $h$ copies of $\mathbb RP^{\infty}.$ Its cohomology with $\mathbb Z/2$-coefficients can be identified with the graded unstable algebra $P^{\otimes h} = \mathbb Z/2[t_1, \ldots, t_h]= \bigoplus_{n\geq 0}P^{\otimes h}_n$ over the Steenrod ring $\mathcal A$, where grading is by the degree of the homogeneous terms $P^{\otimes h}_n$ of degree $n$ in $h$ generators with the degree of each $t_i$ being one. Let $GL_h$ be the usual general linear group of rank $h$ over $\mathbb Z/2.$ The algebra $P^{\otimes h}$ admits a left action of $\mathcal A$ as well as a right action of $GL_h.$ A central problem of homotopy theory is to determine the structure of the space of $GL_h$-coinvariants, $\mathbb Z/2\otimes_{GL_h}{\rm Ann}_{\overline{\mathcal A}}H_n(BV_h; \mathbb Z/2) ,$ where ${\rm Ann}_{\overline{\mathcal A}}H_n(BV_h; \mathbb Z/2) ={\rm Ann}_{\overline{\mathcal A}}[P^{\otimes h}_n]^{*}$ denotes the space of primitive homology classes, considered as a representation of $GL_h$ for all $n.$ Solving this problem is very difficult and still unresolved for $h\geq 4.$ The aim of this Note is of studying the dimension of $\mathbb Z/2\otimes_{GL_h}{\rm Ann}_{\overline{\mathcal A}}[P^{\otimes h}_n]^{*}$ for the case $h = 4$ and the "generic" degrees $n$ of the form $k(2^{s} - 1) + r.2^{s},$ where $k,\, r,\, s$ are positive integers. Applying the results, we investigate the behaviour of the Singer cohomological "transfer" of rank $4$, which is a homomorphism from a certain subquotient of the divided power algebra $\Gamma(a_1^{(1)}, \ldots, a_4^{(1)})$ to mod-2 cohomology groups ${\rm Ext}_{\mathcal A}^{4, 4+n}(\mathbb Z/2, \mathbb Z/2)$ of the algebra $\mathcal A.$ Singer's algebraic transfer is one of the relatively efficient tools in determining the cohomology of the Steenrod algebra.

The Morava K-theories of wreath products

1990 ◽  
Vol 107 (2) ◽  
pp. 309-318 ◽  
Author(s):  
John Hunton
Keyword(s):  
Homotopy Theory ◽  
Wreath Products ◽  
Stable Homotopy ◽  
Classifying Spaces ◽  
Classifying Space ◽  
Stable Homotopy Theory ◽  
Recent Developments ◽  
Positive Integers ◽  
Extended Power ◽  
A Current

In p-primary stable homotopy theory, recent developments have shown the importance of the Morava K-theory spectra K(n) for positive integers n. A current major problem concerns the behaviour of the K(n)-cohomologies on the classifying spaces of finite groups and on related spaces. In this paper we show how to compute the Morava K-theory of extended power constructions Here Xp is the p-fold product of some space X and Cp is the cyclic group of order p. In particular, if we take X as the classifying space BG for some group G, then Dp(X) forms the classifying space for , the wreath product of G by Cp.

General position properties of ANR's

1982 ◽  
Vol 92 (3) ◽  
pp. 451-466 ◽  
Author(s):  
W. J. R. Mitchell
Keyword(s):  
Real Line ◽  
General Position ◽  
Cartesian Product ◽  
Vital Role ◽  
The Real ◽  
Homology Groups ◽  
Local Homology

This paper investigates the ‘general position’ properties which ANR's may possess. The most important of these is the disjoint discs property of Cannon (5), which plays a vital role in recent striking characterizations of manifolds (5, 9, 12, 18, 19, 22). Also considered are the property Δ of Borsuk(2) (which ensures an abundance of dimension-preserving maps), and the vanishing of local homology groups up to a given dimension (cf. (9)). Our main results give relations between these properties, and clarify their behaviour under the stabilization operation of taking cartesian product with the real line. In the last section these results are applied to give partial solutions to questions about homogeneous ANR's.

scholarly journals One-relator groups and algebras related to polyhedral products

2021 ◽  
pp. 1-20
Author(s):  
Jelena Grbić ◽  
George Simmons ◽  
Marina Ilyasova ◽  
Taras Panov
Keyword(s):  
Homology Group ◽  
Homotopy Theory ◽  
Commutator Subgroup ◽  
Homology Groups ◽  
Homological Characterization ◽  
One Relator Groups ◽  
Combinatorial Condition ◽  
The Moment ◽  
Necessary And Sufficient

We link distinct concepts of geometric group theory and homotopy theory through underlying combinatorics. For a flag simplicial complex $K$ , we specify a necessary and sufficient combinatorial condition for the commutator subgroup $RC_K'$ of a right-angled Coxeter group, viewed as the fundamental group of the real moment-angle complex $\mathcal {R}_K$ , to be a one-relator group; and for the Pontryagin algebra $H_{*}(\Omega \mathcal {Z}_K)$ of the moment-angle complex to be a one-relator algebra. We also give a homological characterization of these properties. For $RC_K'$ , it is given by a condition on the homology group $H_2(\mathcal {R}_K)$ , whereas for $H_{*}(\Omega \mathcal {Z}_K)$ it is stated in terms of the bigrading of the homology groups of $\mathcal {Z}_K$ .

On the hit problem for the unstable $\mathscr A$-module $\mathcal P_5 = H^*((K(\mathbb F_2, 1))^{\times 5}, \mathbb F_2)$ and application

2021 ◽  
Author(s):  
Đặng Võ Phúc
Keyword(s):  
Algebraic Topology ◽  
Homotopy Theory ◽  
Polynomial Algebra ◽  
Steenrod Algebra ◽  
Minimal Set ◽  
Open Problems ◽  
Polynomial Algebras ◽  
Prime Field ◽  
Trivial Element ◽  
Hit Problem

Let us consider the prime field of two elements, $\mathbb F_2.$ One of the open problems in Algebraic topology is the hit problem for a module over the mod 2 Steenrod algebra $\mathscr A$. More specifically, this problem asks a minimal set of generators for the polynomial algebra $\mathcal P_m:=\mathbb F_2[x_1, x_2, \ldots, x_m]$ regarded as a connected unstable $\mathscr A$-module on $m$ variables $x_1, \ldots, x_m,$ each of degree one. The algebra $\mathcal P_m$ is the cohomology with $\mathbb F_2$-coefficients of the product of $m$ copies of the Eilenberg-MacLan space of type $(\mathbb F_2, 1).$ The hit problem has been thoroughly studied for 35 years in a variety of contexts by many authors and completely solved for $m\leq 4.$ Furthermore, it has been closely related to some classical problems in the homotopy theory and applied in studying the $m$-th Singer algebraic transfer $Tr^{\mathscr A}_m$ \cite{W.S1}. This transfer is one of the useful tools for studying the Adams $E^{2}$-term, ${\rm Ext}_{\mathscr A}^{*, *}(\mathbb F_2, \mathbb F_2) = H^{*, *}(\mathscr A, \mathbb F_2).$The aim of this work is to continue our study of the hit problem of five variables. At the same time, this result will be applied to the investigation of the fifth transfer of Singer and the modular representation of the general linear group of rank 5 over $\mathbb F_2.$ More precisely, we grew out of a previous result of us in \cite{D.P3} on the hit problem for $\mathscr A$-module $\mathcal P_5$ in the generic degree $5(2^t-1) + 18.2^t$ with $t$ an arbitrary non-negative integer. The result confirms Sum's conjecture \cite{N.S2} on the relation between the minimal set of $\mathscr A$-generators for the polynomial algebras $\mathcal P_{m-1}$ and $\mathcal P_{m}$ in the case $m=5$ and the above generic degree. Moreover, by using our result \cite{D.P3} and a presentation in the $\lambda$-algebra of $Tr_5^{\mathscr A}$, we show that the non-trivial element $h_1e_0 = h_0f_0\in {\rm Ext}_{\mathscr A}^{5, 5+(5(2^0-1) + 18.2^0)}(\mathbb F_2, \mathbb F_2)$ is in the image of the fifth transfer and that $Tr^{\mathscr A}_5$ is an isomorphism in the bidegree $(5, 5+(5(2^0-1) + 18.2^0)).$ In addition, the behavior of $Tr^{\mathscr A}_5$ in the bidegree $(5, 5+(5(2^t-1) + 18.2^t))$ when $t\geq 1$ was also discussed. This method is different from that of Singer in studying the image of the algebraic transfer.

A finiteness theorem in homological algebra

1961 ◽  
Vol 57 (1) ◽  
pp. 31-36 ◽  
Author(s):  
J. F. Adams
Keyword(s):  
Homotopy Theory ◽  
Homological Algebra ◽  
Steenrod Algebra ◽  
Stable Homotopy ◽  
Finiteness Theorem ◽  
Stable Homotopy Theory

In (1), (2), (3) and (4) it is shown that homological algebra (5) can be applied to stable homotopy-theory. In this application, we deal with A-modules, where A is the mod p Steenrod algebra. In the present paper, we shall prove a finiteness theorem for the cohomology of the Steenrod algebra. This theorem is stated as Corollary 2 below. It is purely algebraic, but it is not claimed that it has any algebraic interest; it is inspired solely by the application mentioned above. Here it has the following uses.

scholarly journals On the dimension of the "cohits" space $\mathbb Z_2\otimes_{\mathcal A_2} H^{*}((\mathbb RP(\infty))^{\times t}, \mathbb Z_2)$ and some applications

2021 ◽  
Author(s):  
Đặng Võ Phúc
Keyword(s):  
Vector Space ◽  
Homotopy Theory ◽  
Polynomial Algebra ◽  
Steenrod Algebra ◽  
Negative Integer ◽  
Central Problem ◽  
Minimal Set ◽  
Prime Field ◽  
Monomial Basis ◽  
Hit Problem

We denote by $\mathbb Z_2$ the prime field of two elements and by $P_t = \mathbb Z_2[x_1, \ldots, x_t]$ the polynomial algebra of $t$ generators $x_1, \ldots, x_t$ with the degree of each $x_i$ being one. Let $\mathcal A_2$ be the Steenrod algebra over $\mathbb Z_2.$ A central problem of homotopy theory is to determine a minimal set of generators for the $\mathbb Z_2$-graded vector space $\mathbb Z_2\otimes_{\mathcal A_2} P_t.$ This problem, which is called the "hit" problem for Steenrod algebra, has been systematically studied for $t\leq 4.$ The present paper is devoted to the investigation of the structure of the "cohits" space $\mathbb Z_2\otimes_{\mathcal A_2} P_t$ in some certain "generic" degrees. More specifically, we explicitly determine a monomial basis of $\mathbb Z_2\otimes_{\mathcal A_2} P_5$ in degree \mbox{$n_s=5(2^{s}-1) + 42.2^{s}$} for every non-negative integer $s.$ As a result, it confirms Sum's conjecture \cite{N.S2} for a relation between the minimal sets of $\mathcal A_2$-generators of the algebras $P_{t-1}$ and $P_{t}$ in the case $t=5$ and degree $n_s$. Based on Kameko's map \cite{M.K} and a previous result by Sum \cite{N.S1}, we obtain a inductive formula for the dimension of $\mathbb Z_2\otimes_{\mathcal A_2} P_t$ in a generic degree given. As an application, we obtain the dimension of $\mathbb Z_2\otimes_{\mathcal A_2} P_6$ in the generic degree $5(2^{s+5}-1) + n_0.2^{s+5}$ for all $s\geq 0,$ and show that the Singer's cohomological transfer \cite{W.S1} is an isomorphism in bidegree $(5, 5+n_s)$.

On Certain Stable Wedge Summands of B(𝓩/p)n+

1992 ◽  
Vol 44 (1) ◽  
pp. 104-118 ◽  
Author(s):  
John C. Harris
Keyword(s):  
Representation Theory ◽  
Group Ring ◽  
Steenrod Algebra ◽  
Classifying Space ◽  
Natural Decomposition

AbstractCampbell and Selick have given a natural decomposition of the cohomology of an elementary abelian p-group over the Steenrod algebra. We study the corresponding stable wedge summands of the classifying space B(𝓩/p)n+using representation theory and explicit idempotents in the group ring 𝓕p[GLn(𝓩/p)].

A Case When the Fiber of the Double Suspension is the Double Loops on Anick's Space

2010 ◽  
Vol 53 (4) ◽  
pp. 730-736 ◽  
Author(s):  
Stephen D. Theriault
Keyword(s):  
Homotopy Theory ◽  
Classifying Space ◽  
Moore Spaces

AbstractThe fiber Wn of the double suspension S2n–1 → Ω2S2n+1 is known to have a classifying space BWn. An important conjecture linking the EHP sequence to the homotopy theory of Moore spaces is that BWn ≃ ΩT2np+1(p), where T2np+1(p) is Anick's space. This is known if n = 1. We prove the n = p case and establish some related properties.

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