Adiabaticity and gravity theory independent conservation laws for cosmological perturbations
Author
dc.contributor.author
Romano, Antonio
Author
dc.contributor.author
Mooij, Sander
Author
dc.contributor.author
Sasaki, Misao
Admission date
dc.date.accessioned
2016-11-18T18:40:50Z
Available date
dc.date.available
2016-11-18T18:40:50Z
Publication date
dc.date.issued
2016
Cita de ítem
dc.identifier.citation
Physics Letters B 755 (2016) 464–468
es_ES
Identifier
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10.1016/j.physletb.2016.02.054
Identifier
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https://repositorio.uchile.cl/handle/2250/141276
Abstract
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We carefully study the implications of adiabaticity for the behavior of cosmological perturbations. There are essentially three similar but different definitions of non-adiabaticity: one is appropriate for a thermodynamic fluid delta P-nad, another is for a general matter field delta P-c,(nad), and the last one is valid only on superhorizon scales. The first two definitions coincide if c(s)(2) = c(w)(2) where c(s) is the propagation speed of the perturbation, while c(w)(2) = P (over dot) / rho (over dot). Assuming the adiabaticity in the general sense, delta P-c,(nad) = 0, we derive a relation between the lapse function in the comoving slicing A(c) and delta P-nad valid for arbitrary matter field in any theory of gravity, by using only momentum conservation. The relation implies that as long as c(s) not equal c(w), the uniform density, comoving and the proper-time slicings coincide approximately for any gravity theory and for any matter field if delta P-nad = 0 approximately. In the case of general relativity this gives the equivalence between the comoving curvature perturbation R-c and the uniform density curvature perturbation zeta on superhorizon scales, and their conservation. This is realized on superhorizon scales in standard slow-roll inflation.
We then consider an example in which c(w) = c(s), where delta P-nad = delta P-c,(nad) = 0 exactly, but the equivalence between R-c and zeta no longer holds. Namely we consider the so-called ultra slow-roll inflation. In this case both R-c and are not conserved. In particular, as for zeta, we find that it is crucial to take into account the next-to-leading order term in zeta's spatial gradient expansion to show its non-conservation, even on superhorizon scales. This is an example of the fact that adiabaticity (in the thermodynamic sense) is not always enough to ensure the conservation of R-c or zeta.
es_ES
Patrocinador
dc.description.sponsorship
FONDECYT Postdoctoral Grant
3150126
"Anillo" project - "Programa de Investigacion Asociativa"
ACT1122
Greek national funds under the "ARISTEIA" Action
Dedicacion exclusica and Sostenibilidad programs at UDEA
UDEA CODI project
IN10219CE
2015-4044
COLCIENCIAS mobility project
483-2015
MEXT KAKENHI Grant
15H05888