  The Weyl semimetals are topologically protected from a gap opening against
weak disorder in three dimensions. However, a strong disorder drives this
relativistic semimetal through a quantum transition towards a diffusive
metallic phase characterized by a finite density of states at the band
crossing. This transition is usually described by a perturbative
renormalization group in $d=2+\varepsilon$ of a $U(N)$ Gross-Neveu model in the
limit $N \to 0$. Unfortunately, this model is not multiplicatively
renormalizable in $2+\varepsilon$ dimensions: An infinite number of relevant
operators are required to describe the critical behavior. Hence its use in a
quantitative description of the transition beyond one-loop is at least
questionable. We propose an alternative route, building on the correspondence
between the Gross-Neveu and Gross-Neveu-Yukawa models developed in the context
of high energy physics. It results in a model of Weyl fermions with a random
non-Gaussian imaginary potential which allows one to study the critical
properties of the transition within a $d=4-\varepsilon$ expansion. We also
discuss the characterization of the transition by the multifractal spectrum of
wave functions.
