  In this article, we discuss strong coupling limits of topological quantum
critical points (TQCPs) where quantum phase transitions between two topological
distinct superconducting states take place. We illustrate that while
superconducting phases on both sides of TQCPs spontaneously break same
symmetries, universality classes of critical states can be identified only when
global symmetries in topological states are further specified. In dimensions
$d=2,3$, we find that continuous $(d+1)$th order transitions at weakly
interacting TQCPs that were pointed out previously in the presence of emergent
Lorentz symmetry can be terminated by strongly interacting fixed points of
majorana fields. For $2d$ time reversal symmetry breaking TQCPs, termination
points are supersymmetric with ${\mathcal N}=4N_f={1}$ (where $N_f$ is the
number of four-component Dirac fermions and ${\mathcal N}$ is the number of
two-component real fermions) beyond which transitions are discontinuous first
order ones. For $2d$ time reversal symmetric TQCPs without other global
symmetries, termination points of $(d+1)$th order continuous transition lines
are generically conformal invariant without supersymmetry. Beyond these strong
coupling fixed points, there are first-order discontinuous transitions as far
as the protecting symmetry is not spontaneously broken but no direct
transitions if the protecting symmetry is spontaneously broken in the presence
of strong interactions. In $3d$, strong coupling termination points can be
further effectively represented by new emergent gapless real bosons weakly
coupled with free gapless majorana fermions. However, in $1d$, time reversal
symmetric $(d+1)$th continuous transition lines of TQCPs are terminated by
simple free majorana fermion fixed points.
