# Approximate KMS states for scalar and spinor fields in Friedmann-Robertson-Walker spacetimes

September 27, 2010

We construct and discuss Hadamard states for both scalar and Dirac spinor
fields in a large class of spatially flat Friedmann-Robertson-Walker spacetimes
characterised by an initial phase either of exponential or of power-law
expansion. The states we obtain can be interpreted as being in thermal
equilibrium at the time when the scale factor a has a specific value a=a_0. In
the case a_0=0, these states fulfil a strict KMS condition on the boundary of
the spacetime, which is either a cosmological horizon, or a Big Bang
hypersurface. Furthermore, in the conformally invariant case, they are
conformal KMS states on the full spacetime. However, they provide a natural
notion of an approximate KMS state also in the remaining cases, especially for
massive fields. On the technical side, our results are based on a
bulk-to-boundary reconstruction technique already successfully applied in the
scalar case and here proven to be suitable also for spinor fields. The
potential applications of the states we find range over a broad spectrum, but
they appear to be suited to discuss in particular thermal phenomena such as the
cosmic neutrino background or the quantum state of dark matter.

open access link
Annales Henri Poincare 12 (2011) 1449-1489

@article{Dappiaggi:2010gt,
author = "Dappiaggi, Claudio and Hack, Thomas-Paul and Pinamonti,
Nicola",
title = "{Approximate KMS states for scalar and spinor fields in
Friedmann-Robertson-Walker spacetimes}",
journal = "Annales Henri Poincare",
volume = "12",
year = "2011",
pages = "1449-1489",
doi = "10.1007/s00023-011-0111-6",
eprint = "1009.5179",
archivePrefix = "arXiv",
primaryClass = "gr-qc",
reportNumber = "DESY-10-160, ESI-2266, ZMP-HH-10-19",
SLACcitation = "%%CITATION = ARXIV:1009.5179;%%"
}

Keywords:

*none*