Kaplansky's zero divisor and unit conjectures on elements with supports of size $3$

Kaplansky's zero divisor conjecture (unit conjecture, respectively) states that for a torsion-free group $G$ and a field $\mathbb{F}$, the group ring $\mathbb{F}[G]$ has no zero divisors (has no unit with support of size greater than $1$). In this paper, we study possible zero divisors and units in $\mathbb{F}[G]$ whose supports have size $3$. For any field $\mathbb{F}$ and all torsion-free groups $G$, we prove that if $αβ=0$ for some non-zero $α, β\in \mathbb{F}[G]$ such that $|supp(α)|=3$, then $|supp(β)|\geq 10$. If $\mathbb{F}=\mathbb{F}_2$ is the field with 2 elements, the latter result can be improved so that $|supp(β)|\geq 20$. This improves a result in [J. Group Theory, 16 (2013), no. 5, 667-693]. Concerning the unit conjecture, we prove that if $αβ=1$ for some $α, β\in \mathbb{F}[G]$ such that $|supp(α)|=3$, then $|supp(β)|\geq 9$. The latter improves a part of a result in [Exp. Math., 24 (2015), 326-338] to arbitrary fields.

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