  We study the role of finite size effects on a metallic critical behavior near
a q = 0 critical point and compare the results with the recent extensive
quantum Monte-Carlo (QMC) study [Y. Schattner et al, PRX 6, 0231028]. This
study found several features in both bosonic and fermionic responses, in
disagreement with the expected critical behavior with dynamical exponent z = 3.
We show that finite size effects are particularly strong for z = 3 criticality
and give rise to a behavior different from that of an infinite system, over a
wide range of momenta and frequencies. We argue that by taking finite size
effects into account, the QMC results can be explained within z = 3 theory. Our
results also have implications for small interacting fermionic systems, such as
magnetic nanoparticles.
