  Recently, the existence of Dirac/Weyl cones in three dimensional systems has
been demonstrated experimentally. While in high energy physics the isotropy of
the Dirac/Weyl cones is guaranteed by relativistic invariance, in condensed
matter systems corrections to this can occur, one possible type being a tilt.
In this paper we study the effect of of tilted Weyl cones in collective
effects. We study both the opticql conductivity as well as the polarization
function. We also investigate the perturbative effect of long-range Coulomb
interactions using a renormalization group calculation. We find that the tilt
is perturbatively renormalized towards zero and at low energies the system
flows to an effectively untilted theory.
