Unit cyclotomic multiple zeta values for $\mu_2,\mu_3$ and $\mu_4$

Abstract

Denote by $\epsilon$ a primitive root of $N^{th}$-unity. In this paper, we show that the unit cyclotomic multiple zeta values for $\mu_N$ generate all the cyclotomic multiple zeta values for $\mu_N$ in cases $N=2,3,4$. Moreover, the unit cyclotomic multiple zeta values for $\mu_N$ can be written as $\mathbb{Q}$-linear combinations of $\left(\zeta\binom{1}{\epsilon}\right)^n, \left(\zeta\binom{1}{\epsilon^{-1}}\right)^n$ and lower depth terms in each weight $n$ in case of $N=2,3$ and $4$. By detailed analysis of the motivic Galois action, we compute the coefficients of $\left(\zeta\binom{1}{\epsilon}\right)^n, \left(\zeta\binom{1}{\epsilon^{-1}}\right)^n$ in the above expressions of unit cyclotomic multiple zeta values.