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Particle-hole continuum (PHC) for massive Dirac fermions in presence of shortrange interactions, provides an unprecedented opportunity for formation of twocollective split-off states, one in the singlet and the other in the triplet(spin-1) channel in undoped system. Both poles are close in energy and areseparated from thec continuum of free particle-hole excitations by an energyscale of the order of gap parameter $\Delta$. They both disperse linearly withtwo different velocities reminiscent of spin-charge separation in Luttingerliquids. When the strength of Hubbard interactions is stronger than a criticalvalue, the velocity of singlet excitation which we interpret as a charge bosoncomposite becomes zero, and renders the system a Mott insulator. Beyond thiscritical point, the low-energy sector is left with a linearly dispersingtriplet mode -- a characteristic of a Mott insulator. The velocity of tripletmode at the Mott criticality is twice the velocity of underlying Diracfermions. The phase transition line in the space of $U$ and $\Delta$ is inqualitative agreement with a more involved dynamical mean field theory (DMFT)calculation.

Collective excitations and the nature of Mott transition in undoped gapped graphene