  We analyze a two-dimensional Pomeranchuk-Nematic instability, trigger by the
Landau parameter $F_2<0$, in the presence of a small magnetic field. Using
Landau Fermi liquid theory in the isotropic phase, we analyze the collective
modes near the quantum critical point $F_2=-1,\omega_c=0$ (where $\omega_c$ is
the cyclotron frequency). We focus on the effects of parity symmetry breaking
on the Fermi surface deformation. We show that, for studying the critical
regime, the linear response approximation of the Landau-Silin equation is not
sufficient and it is necessary to compute corrections at least of order
$\omega_c^2$. Identifying the slowest oscillation mode in the disordered phase,
we compute the phase diagram for the isotropic/nematic phase transition in
terms of $F_2$ and $\omega_c$.
