In this article we prove two results concerning the motivic Milnor fibres $S^{ \epsilon}(f)$ associated to a map germ $f: (\mathbb{ R}^n,0)\to(\mathbb{ R},0)$, defined by G. Comte and G. Fichou. Firstly, we prove that if $f,g:(\mathbb{ R}^n,0)\to(\mathbb{ R},0)$ are arc-analytically equivalent germs of Nash functions then the virtual Poincar\'e polynomial of the corresponding motivic Milnor fibres are equal. This extends (and provides a new proof) of a result of G. Fichou. Secondly, let $T\subset\mathbb{ R}^m$ be a real algebraic set and $f: T\times(\mathbb{ R}^n,0)\to\mathbb{ R}$ a polynomial function of polynomial map germs such that $f(t,0)=0$ for any $t\in T$. Then we prove that there exists a locally finite real analytic stratification $\mathcal{ S}$ of $T$ such that if $S\in\mathcal{ S}$ is a stratum then $f_t\sim_a f_{ t'}$ are arc-analytically equivalent, for any $t,t'\in S$. Furthermore, if $T$ is compact then the stratification $\mathcal{ S}$ can be taken to be finite. These two results imply in particular that the virtual Poincar\'e polynomials of the respective zeta functions are equal i.e $\beta(S^{ \epsilon}(f_t))=\beta(S^{ \epsilon}(f_{ t'}))$.
Categories: math.AG