  Higgs modes in condensed matter physics have drawn attention because of
analogies to the Higgs bosons of particle physics. Here we use a microscopic
time-dependent mean-field theory to study the collective mode spectra of
two-dimensional spatially indirect exciton (electron-hole pair) condensates,
focusing on the Higgs modes, i.e., those that have a large weight in
electron-hole pair amplitude response functions. We find that in the low
exciton density (BEC) limit, the dominant Higgs modes of spatially indirect
exciton condensates correspond to adding electron-hole pairs that are
orthogonal to the condensed pair state. We comment on the previously studied
Higgs-like collective excitations of superconductors in light of this finding.
