Domains of analyticity for response solutions in strongly dissipative forced systems

We study the ordinary differential equation $\varepsilon\ddot x + \dot x + \varepsilon g(x) = \e f(\omega t)$,where$g$and$f$ are real-analytic functions, with $f$ quasi-periodic in $t$ with frequency vector $\omega$. If $c_0\in \mathbb{R}$ is such that $g(c_0)$ equals the average of $f$ and $g^{\mathrm{\prime }}(c_0)\mathrm{\ne }0$, under very mild assumptions on $\omega$ there exists a quasi-periodic solution close to $c_0$. We show that such a solution depends analytically on $\epsilon$ in a domain of the complex plane tangent more than quadratically to the imaginary axis at the origin.