  Generation of high harmonics in a monolayer graphene initiated by strong
coherent radiation field, taking into account electron-electron Coulomb
interaction is investigated. A microscopic theory describing the nonlinear
optical response of graphene is developed. The Coulomb interaction of electrons
is treated in the scope of dynamic Hartree-Fock approximation. The closed set
of integrodifferential equations for the single-particle density matrix of a
graphene quantum structure is solved numerically. The obtained solutions show
the significance of many-body Coulomb interaction on the high harmonic
generation process in graphene.
