COT2 - Inhomogeneous Cosmologies Averaging and Back Reaction |
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Speaker |
Subramaniam, Shankaranarayanan |
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Co-autors |
Corrado Appignani, Roberto Casadio |
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Talk Title |
Ambiguities in second-order cosmological perturbations for non-canonical scalar fields |
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Abstract |
The problem of propagation of cosmological perturbations can be treated in linear theory as a first approximation, although the exact problem is fundamentally nonlinear. The linear perturbations, due to the general non-canonical scalar fields, in the early and late universe can effect the background geometry and energy density in which they propagate which is known as non-linear feed back or back-reaction effect. However, it is still unclear which quantities are gauge-invariant in second-order and hence, physical understanding of the various second-order physical quantities is not transparent. As an attempt to understand these quantities, we consider a general non-canonical scalar field, minimally coupled to gravity, on the unperturbed FRW background, where metric fluctuations are neglected a priori. In this simplified set-up, we show that there arise ambiguities in the expressions of physically relevant quantities, such as the effective speed of the perturbations. Further, the stress tensor and energy density display a potential instability which is not present at linear order. |
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