  The Berezinskii-Kosterlitz-Thouless transition in 2D dipolar systems has been
studied recently by path integral Monte Carlo (PIMC) simulations [A. Filinov et
al., PRL 105, 070401 (2010)]. Here, we complement this analysis and study
temperature-coupling strength dependence of the density (particle-hole) and
single-particle (SP) excitation spectra both in superfluid and normal phases.
The dynamic structure factor, S(q,omega), of the longitudinal excitations is
rigorously reconstructed with full information on damping. The SP spectral
function, A(q,omega), is worked out from the one-particle Matsubara Green's
function. A stochastic optimization method is applied for reconstruction from
imaginary times. In the superfluid regime sharp energy resonances are observed
both in the density and SP excitations. The involved hybridization of both
spectra is discussed. In contrast, in the normal phase, when there is no
coupling, the density modes, beyond acoustic phonons, are significantly damped.
Our results generalize previous zero temperature analyses based on variational
many-body wavefunctions [F. Mazzanti et al., PRL 102, 110405 (2009), D. Hufnagl
et al., PRL 107, 065303 (2011)], where the underlying physics of the excitation
spectrum and the role of the condensate has not been addressed.
