On the determination of the Singer transfer

Abstract

Let $P_k$ be the graded polynomial algebra $\mathbb F_2[x_1,x_2,\ldots ,x_k]$ with the degree of each generator $x_i$ being 1, where $\mathbb F_2$ denote the prime field of two elements, and let $GL_k$ be the general linear group over $\mathbb F_2$ which acts regularly on $P_k$. We study the algebraic transfer $Tr_k^*$ constructed by Singer using the technique of the Peterson hit problem. This transfer is a homomorphism from the homology of the mod-2 Steenrod algebra $\mathcal A$, $\text{Tor}^{\mathcal A}_{k,k+d} (\mathbb F_2,\mathbb F_2)$, to the subspace of $\mathbb F_2{\otimes}_{\mathcal A}P_k$ consisting of all the $GL_k$-invariant classes of degree $d$. In this paper, by using the results on the Peterson hit problem we present the proof of the fact that the Singer algebraic transfer is an isomorphism for $k \leqslant 3$. We also explicitly determine the fourth Singer algebraic transfer in some degrees. The new results in the paper are different from the ones of Bruner, Ha and Hung [5], Chon and Ha [6,7,8], Ha [9], Hung and Quynh [12], Nam [16]. To illustrate the fact that $d_0 \in \mbox{Im}(Tr_4)$, we present the computations of Ha [9, Page 102] for this result. We can easily verify that these computations are correct. So, it is possible the algorithm in Phuc [29] is flawed.