TY - JOUR
T1 - Manifestly causal in-in perturbation theory about the interacting vacuum
AU - Baumgart, Matthew
AU - Sundrum, Raman
N1 - Publisher Copyright:
© 2021, The Author(s).
PY - 2021/3
Y1 - 2021/3
N2 - In-In perturbation theory is a vital tool for cosmology and nonequilibrium physics. Here, we reconcile an apparent conflict between two of its important aspects with particular relevance to De Sitter/inflationary contexts: (i) the need to slightly deform unitary time evolution with an iϵ prescription that projects the free (“Bunch-Davies”) vacuum onto the interacting vacuum and renders vertex integrals well-defined, and (ii) Weinberg’s “nested commutator” reformulation of in-in perturbation theory which makes manifest the constraints of causality within expectation values of local operators, assuming exact unitarity. We show that a modified iϵ prescription maintains the exact unitarity on which the derivation of (ii) rests, while nontrivially agreeing with (i) to all orders of perturbation theory.
AB - In-In perturbation theory is a vital tool for cosmology and nonequilibrium physics. Here, we reconcile an apparent conflict between two of its important aspects with particular relevance to De Sitter/inflationary contexts: (i) the need to slightly deform unitary time evolution with an iϵ prescription that projects the free (“Bunch-Davies”) vacuum onto the interacting vacuum and renders vertex integrals well-defined, and (ii) Weinberg’s “nested commutator” reformulation of in-in perturbation theory which makes manifest the constraints of causality within expectation values of local operators, assuming exact unitarity. We show that a modified iϵ prescription maintains the exact unitarity on which the derivation of (ii) rests, while nontrivially agreeing with (i) to all orders of perturbation theory.
KW - Beyond Standard Model
KW - Cosmology of Theories beyond the SM
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U2 - 10.1007/JHEP03(2021)080
DO - 10.1007/JHEP03(2021)080
M3 - Article
AN - SCOPUS:85102172147
SN - 1029-8479
VL - 2021
JO - Journal of High Energy Physics
JF - Journal of High Energy Physics
IS - 3
M1 - 80
ER -