  We consider the finite-size corrections in the Dicke model and determine the
scaling exponents at the critical point for several quantities such as the
ground state energy or the gap. Therefore, we use the Holstein-Primakoff
representation of the angular momentum and introduce a nonlinear transformation
to diagonalize the Hamiltonian in the normal phase. As already observed in
several systems, these corrections turn out to be singular at the transition
point and thus lead to nontrivial exponents. We show that for the atomic
observables, these exponents are the same as in the Lipkin-Meshkov-Glick model,
in agreement with numerical results. We also investigate the behavior of the
order parameter related to the radiation mode and show that it is driven by the
same scaling variable as the atomic one.
