Adiabatic and isocurvature perturbations for multifield generalized Einstein models

By F. Marco, F. Finelli, Robert Brandenberger. 2002

149 citations recorded by the source corpus.

Low energy effective field theories motivated by string theory will likely contain several scalar moduli fields which will be relevant to early Universe cosmology. Some of these fields are expected to couple with non-standard kinetic terms to gravity. In this paper, we study the splitting into adiabatic and isocurvature perturbations for a model with two scalar fields, one of which has a non-standard kinetic term in the Einstein-frame action. Such actions can arise, e.g., in the Pre-Big-Bang and Ekpyrotic scenarios. The presence of a non-standard kinetic term induces a new coupling between adiabatic and isocurvature perturbations which is non-vanishing when the potential for the matter fields is nonzero. This coupling is un-suppressed in the long wavelength limit and thus can lead to an important transfer of power from the entropy to the adiabatic mode on super-Hubble scales. We apply the formalism to the case of a previously found exact solution with an exponential potential and study the resulting mixing of adiabatic and isocurvature fluctuations in this example. We also discuss the possible relevance of the extra coupling in the perturbation equations for the process of generating an adiabatic component of the fluctuations spectrum from isocurvature perturbations without considering a later decay of the isocurvature component.

Subfields: Astronomy and Astrophysics, Nuclear and High Energy Physics

View Paper: https://www.semanticscholar.org/paper/f114a32a3a06a7d1ae93789ff2c78dd4492028a9

How researchers see this paper

The researchers whose trusted networks rank it highest, strongest advocate first. Every researcher gets a different order.

In Astronomy and Astrophysics

In Nuclear and High Energy Physics

Citations in the corpus

Cosmology and Fundamental Physics with the Euclid Satellite (2012, unknown): “If the two fields φ and χ are coupled through the kinetic term exp(−bφ)g∂μ∂νχ [416] then nearly scale invariant perturbations are generated when b ∼ c and χ has no potential [484].”
Primordial bispectrum from multifield inflation with nonminimal couplings (2012, methodology): “In this paper we work in the Einstein frame, following the approach established in [6–9, 25, 30, 32–34].”
Generating PBHs and small-scale GWs in two-field models of inflation (2020, methodology): “[52, 53] we define f(φ) ≡ e2b(φ).”
New Ekpyrotic Cosmology (2007, unknown): “earlier and closely related work, see [26, 27, 28, 29 ].”