Abstract:
We derive the response function for a comoving, pointlike Unruh-DeWitt particle detector coupled
to a complex scalar field φ, in the (3 + 1)-dimensional cosmological de Sitter spacetime. The fielddetector coupling is taken to be proportional to φ
†φ. We address both conformally invariant and massless
minimally coupled scalar field theories, respectively in the conformal and the Bunch-Davies vacuum. The
response function integral for the massless minimal complex scalar, not surprisingly, shows divergences
and accordingly we use suitable regularisation scheme to find out well behaved results. The regularised
result also contains a de Sitter symmetry breaking logarithm, growing with the cosmological time.
Possibility of extension of these results with the so called de Sitter α-vacua is discussed. While we find
no apparent problem in computing the response function for a real scalar in these vacua, a complex
scalar field is shown to contain some possible ambiguities in the detector response. The case of the
minimal and nearly massless scalar field theory is also briefly discussed.
