Unramified Euler sums and Hoffman $\star$ basis

Abstract

When looking at how periods of $\pi_{1}^{\mathfrak{m}}(\mathbb{P}^{1}\diagdown \lbrace 0, 1, \infty \rbrace )$, i.e. multiple zeta values, embeds into periods of $\pi_{1}^{\mathfrak{m}}(\mathbb{P}^{1}\diagdown \lbrace 0, \pm 1, \infty \rbrace )$, i.e. Euler sums, an explicit criteria via the coaction $\Delta$ acting on their motivic versions comes out. In this paper, adopting this Galois descent approach, we present a new basis for the space $\mathcal{H}^{1}$ of motivic multiple zeta values via motivic Euler sums. Up to an analytic conjecture, we also prove that the motivic Hoffman star basis $\zeta^{\star, \mathfrak{m}} (2^{a_{1}},3,\cdots,3, 2^{a_{p}}, 3, 2^{b})$ is a basis of $\mathcal{H}^{1}$. Under a general motivic identity that we conjecture, these bases are identical. Other examples of unramified ES with alternating patterns of even and odds are also provided.