Particle production and classical condensates in de Sitter space

Milan Mijic

doi:10.1103/PhysRevD.57.2138

paper

Particle production and classical condensates in de Sitter space

arXiv:gr-qc/9801094 · doi:10.1103/PhysRevD.57.2138

Abstract

The cosmological particle production in a $k = 0$ expanding de Sitter universe with a Hubble parameter $H_{0}$ is considered for various values of mass or conformal coupling of a free, scalar field. One finds that, for a minimally coupled field with mass $0 \leq m^{2} < 9 H_{0}^{2} /4$ (except for $m^{2} = 2 H_{0}^{2}$ ), the one-mode occupation number grows to unity soon after the physical wavelength of the mode becomes larger than the Hubble radius, and afterwards diverges as $n (t) \sim O (1) (λ_{p h y s} (t) / H_{0}^{- 1})^{2 ν}$ , where $ν \equiv [9/4 - m^{2} / H_{0}^{2}]^{1/2}$ . However, for a field with $m^{2} > 9 H_{0}^{2} /4$ , the occupation number of a mode outside the Hubble radius is rapidly oscillating and bounded and does not exceed unity. These results, readily generalized for cases of a nonminimal coupling, provide a clear argument that the long-wavelength vacuum fluctuations of low-mass fields in an inflationary universe do show classical behavior, while those of heavy fields do not. The interaction or self-interaction does not appear necessary for the emergence of classical features, which are entirely due to the rapid expansion of the de Sitter background and the upside-down nature of quantum oscillators for modes outside the Hubble radius.

Revtex + 5 postscript figures. Accepted for Phys Rev D15. Revision of Aug 1996 preprint limited to the inclusion and discussion of references suggested by the referees

Particle production and classical condensates in de Sitter space

Abstract

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