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EFT beyond the horizon: stochastic inflation and how primordial quantum fluctuations go classical

C. P. Burgess, R. Holman, G. Tasinato, M. Williams, Gianmassimo Tasinato Orcid Logo

Journal of High Energy Physics, Volume: 2015, Issue: 3

Swansea University Author: Gianmassimo Tasinato Orcid Logo

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DOI (Published version): 10.1007/JHEP03(2015)090

Abstract

We identify the effective theory describing inflationary super-Hubble scales and show it to be a special case of effective field theories appropriate to open systems. Open systems allow information to be exchanged between the degrees of freedom of interest and those that are integrated out, such as...

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Published in: Journal of High Energy Physics
ISSN: 1029-8479
Published: 2015
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URI: https://cronfa.swan.ac.uk/Record/cronfa21641
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first_indexed 2015-05-22T02:03:42Z
last_indexed 2018-05-12T12:49:33Z
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spelling 2018-05-12T07:22:52.9041109 v2 21641 2015-05-21 EFT beyond the horizon: stochastic inflation and how primordial quantum fluctuations go classical cb754b073d1e4949c5e3db97744d3301 0000-0002-9835-4864 Gianmassimo Tasinato Gianmassimo Tasinato true false 2015-05-21 SPH We identify the effective theory describing inflationary super-Hubble scales and show it to be a special case of effective field theories appropriate to open systems. Open systems allow information to be exchanged between the degrees of freedom of interest and those that are integrated out, such as for particles moving through a fluid. Strictly speaking they cannot in general be described by an effective lagrangian; rather the appropriate `low-energy' limit is instead a Lindblad equation describing the evolution of the density matrix of the slow degrees of freedom. We derive the equation relevant to super-Hubble modes of quantum fields in near-de Sitter spacetimes and derive two implications. We show the evolution of the diagonal density-matrix elements quickly approaches the Fokker-Planck equation of Starobinsky's stochastic inflationary picture. This provides an alternative first-principles derivation of this picture's stochastic noise and drift, as well as its leading corrections. (An application computes the noise for systems with a sub-luminal sound speed.) We argue that the presence of interactions drives the off-diagonal density-matrix elements to zero in the field basis. This shows why the field basis is the `pointer basis' for the decoherence of primordial quantum fluctuations while they are outside the horizon, thus allowing them to re-enter as classical fluctuations, as assumed when analyzing CMB data. The decoherence process is efficient, occurring after several Hubble times even for interactions as weak as gravitational-strength. Crucially, the details of the interactions largely control only the decoherence time and not the nature of the final late-time stochastic state, much as interactions can control the equilibration time for thermal systems but are largely irrelevant to the properties of the resulting equilibrium state. Journal Article Journal of High Energy Physics 2015 3 1029-8479 31 3 2015 2015-03-31 10.1007/JHEP03(2015)090 COLLEGE NANME Physics COLLEGE CODE SPH Swansea University 2018-05-12T07:22:52.9041109 2015-05-21T20:16:33.1347240 Faculty of Science and Engineering School of Biosciences, Geography and Physics - Physics C. P. Burgess 1 R. Holman 2 G. Tasinato 3 M. Williams 4 Gianmassimo Tasinato 0000-0002-9835-4864 5 0021641-25072016163504.pdf EFT_beyond_the_horizon.pdf 2016-07-25T16:35:04.5670000 Output 676413 application/pdf Version of Record true 2016-07-25T00:00:00.0000000 Open access funded by SCOAP true
title EFT beyond the horizon: stochastic inflation and how primordial quantum fluctuations go classical
spellingShingle EFT beyond the horizon: stochastic inflation and how primordial quantum fluctuations go classical
Gianmassimo Tasinato
title_short EFT beyond the horizon: stochastic inflation and how primordial quantum fluctuations go classical
title_full EFT beyond the horizon: stochastic inflation and how primordial quantum fluctuations go classical
title_fullStr EFT beyond the horizon: stochastic inflation and how primordial quantum fluctuations go classical
title_full_unstemmed EFT beyond the horizon: stochastic inflation and how primordial quantum fluctuations go classical
title_sort EFT beyond the horizon: stochastic inflation and how primordial quantum fluctuations go classical
author_id_str_mv cb754b073d1e4949c5e3db97744d3301
author_id_fullname_str_mv cb754b073d1e4949c5e3db97744d3301_***_Gianmassimo Tasinato
author Gianmassimo Tasinato
author2 C. P. Burgess
R. Holman
G. Tasinato
M. Williams
Gianmassimo Tasinato
format Journal article
container_title Journal of High Energy Physics
container_volume 2015
container_issue 3
publishDate 2015
institution Swansea University
issn 1029-8479
doi_str_mv 10.1007/JHEP03(2015)090
college_str Faculty of Science and Engineering
hierarchytype
hierarchy_top_id facultyofscienceandengineering
hierarchy_top_title Faculty of Science and Engineering
hierarchy_parent_id facultyofscienceandengineering
hierarchy_parent_title Faculty of Science and Engineering
department_str School of Biosciences, Geography and Physics - Physics{{{_:::_}}}Faculty of Science and Engineering{{{_:::_}}}School of Biosciences, Geography and Physics - Physics
document_store_str 1
active_str 0
description We identify the effective theory describing inflationary super-Hubble scales and show it to be a special case of effective field theories appropriate to open systems. Open systems allow information to be exchanged between the degrees of freedom of interest and those that are integrated out, such as for particles moving through a fluid. Strictly speaking they cannot in general be described by an effective lagrangian; rather the appropriate `low-energy' limit is instead a Lindblad equation describing the evolution of the density matrix of the slow degrees of freedom. We derive the equation relevant to super-Hubble modes of quantum fields in near-de Sitter spacetimes and derive two implications. We show the evolution of the diagonal density-matrix elements quickly approaches the Fokker-Planck equation of Starobinsky's stochastic inflationary picture. This provides an alternative first-principles derivation of this picture's stochastic noise and drift, as well as its leading corrections. (An application computes the noise for systems with a sub-luminal sound speed.) We argue that the presence of interactions drives the off-diagonal density-matrix elements to zero in the field basis. This shows why the field basis is the `pointer basis' for the decoherence of primordial quantum fluctuations while they are outside the horizon, thus allowing them to re-enter as classical fluctuations, as assumed when analyzing CMB data. The decoherence process is efficient, occurring after several Hubble times even for interactions as weak as gravitational-strength. Crucially, the details of the interactions largely control only the decoherence time and not the nature of the final late-time stochastic state, much as interactions can control the equilibration time for thermal systems but are largely irrelevant to the properties of the resulting equilibrium state.
published_date 2015-03-31T03:25:42Z
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score 11.035634

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