  Wilson-Fisher expansion near upper critical dimension has proven to be an
invaluable conceptual and computational tool in our understanding of the
universal critical behavior in the $\phi ^4$ field theories that describe
low-energy physics of the canonical models such as Ising, XY, and Heisenberg.
Here I review its application to a class of the Gross-Neveu-Yukawa (GNY) field
theories, which emerge as possible universal description of a number of quantum
phase transitions in electronic two-dimensional systems such as graphene and
d-wave superconductors. GNY field theories may be viewed as minimal
modifications of the $\phi^4$ field theories in which the order parameter is
coupled to relativistic Dirac fermions through Yukawa term, and which still
exhibit critical fixed points in the suitably formulated Wilson-Fisher
$\epsilon$-expansion. I discuss the unified GNY field theory for a set of
different symmetry-breaking patterns, with focus on the
semimetal-N\'eel-ordered-Mott insulator quantum phase transition in the
half-filled Hubbard model on the honeycomb lattice, for which a comparison
between the state-of-the-art $\epsilon$-expansion, quantum Monte Carlo,
large-N, and functional renormalization group calculations can be made.
