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In quantum field theory in curved spacetime, there is a unique quantum state over a background de Sitter space which is invariant under all the isometries. This is a thermal state, which is at the de Sitter temperature of \( T = H/2\pi \) where H is the Hubble constant. This state is called the Bunch–Davies vacuum or Euclidean vacuum.[1]

The Bunch–Davies vacuum can also be described as being generated by an infinite time trace from the condition that the scale of quantum fluctuations is much smaller than the Hubble scale.[2] The state possesses no quanta at the asymptotic past infinity.[3]

The Bunch-Davies state is the zero-particle state as seen by a geodesic observer, that is, an observer who is in free fall in the expanding state.[4] The state explains the origin of cosmological perturbation fluctuations in inflationary models.

See also

Quantum field theory in curved spacetime
Unruh effect
Hawking radiation
Inflation (cosmology)

References

Bunch, Timothy Stephen; Davies, Paul (1978). "Quantum Field Theory In De Sitter Space: Renormalization By Point Splitting". Proceedings of the Royal Society of London. A 360: 117. Bibcode:1978RSPSA.360..117B. doi:10.1098/rspa.1978.0060.
Danielsson, Ulf H; Olsson, Martin E (15 March 2004). "On thermalization in de Sitter space". Journal of High Energy Physics 2004 (03): 036–036. arXiv:hep-th/0309163. Bibcode:2004JHEP...03..036D. doi:10.1088/1126-6708/2004/03/036.
Armendariz-Picon, C (26 February 2007). "Why should primordial perturbations be in a vacuum state?". Journal of Cosmology and Astroparticle Physics 2007 (02): 031–031. arXiv:astro-ph/0612288. Bibcode:2007JCAP...02..031A. doi:10.1088/1475-7516/2007/02/031.

Greene, Brian R; Parikh, Maulik K; Schaar, Jan Pieter van der (28 April 2006). "Universal correction to the inflationary vacuum". Journal of High Energy Physics 2006 (04): 057–057. arXiv:hep-th/0512243. Bibcode:2006JHEP...04..057G. doi:10.1088/1126-6708/2006/04/057.