期刊
JOURNAL OF COSMOLOGY AND ASTROPARTICLE PHYSICS
卷 -, 期 11, 页码 -出版社
IOP PUBLISHING LTD
DOI: 10.1088/1475-7516/2016/11/047
关键词
alternatives to inflation; cosmic singularity; initial conditions and eternal universe; physics of the early universe
资金
- Swiss National Science Foundation [200020-150060]
- MIUR-FIRB [RBFR12H1MW]
- Swiss National Science Foundation (SNF) [200020_150060] Funding Source: Swiss National Science Foundation (SNF)
We study the stability of spatially flat FRW solutions which are geodesically complete, i.e. for which one can follow null (graviton) geodesics both in the past and in the future without ever encountering singularities. This is the case of NEC-violating cosmologies such as smooth bounces or solutions which approach Minkowski in the past. We study the EFT of linear perturbations around a solution of this kind, including the possibility of multiple fields and fluids. One generally faces a gradient instability which can be avoided only if the operator R-(3)delta N is present and its coefficient changes sign along the evolution. This operator (typical of beyond-Horndeski theories) does not lead to extra degrees of freedom, but cannot arise starting from any theory with second-order equations of motion. The change of sign of this operator prevents to set it to zero with a generalised disformal transformation.
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