2002/11/19 by Fabrizio Di Marco, F. Finelli⋆, Fabio Finelli +1 · 7 citations
Physics and Astronomy · #Adiabatic process #Black Holes and Theoretical Physics #Classical mechanics #Cosmology #Cosmology and Gravitation Theories #Dark energy #Ekpyrotic universe #Galaxies: Formation, Evolution, Phenomena #Kinetic term #Metric expansion of space #Physics #Quantum electrodynamics #Quantum mechanics #Scalar field #Theoretical physics #astro-ph #gr-qc #hep-ph #hep-th
paper · pdf · doi:10.1103/physrevd.67.063512
published as Phys.Rev. D67 (2003) 063512 · 11 pages, 3 figures, one equation corrected, typos fixed, conclusions unchanged
arxiv created 2002/11/19 · openalex publication_date 2003/03/26 · arxiv updated 2009/11/30 · openalex created_date 2025/10/10 · openalex updated_date 2026/08/05
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 nonstandard kinetic terms to other fields. In this paper, we study the splitting into adiabatic and isocurvature perturbations for a model with two scalar fields, one of which has a nonstandard 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 coupling through a nonstandard kinetic term induces a novel coupling between adiabatic and isocurvature perturbations which is nonvanishing when the potential for the matter fields is nonzero. This coupling is unsuppressed 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 fluctuation spectrum from isocurvature perturbations without considering a later decay of the isocurvature component.