Andrew R. Liddle coauthored an analysis of when observable perturbations were produced relative to the end of cosmic inflation. It shows why a single universal count of expansion factors is not an assumption-free link between an inflationary model and present observations.[ref]
How long before the end of inflation were observable perturbations produced? by Andrew R. Liddle and Samuel M. Leach. Abstract: standard and nonstandard expansion histories
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Andrew R. Liddle is a prominent theoretical physicist and cosmologist known for his work in the field of cosmology, particularly related to the early universe, inflation, and the nature of dark energy. He has contributed to various areas of research, including the dynamics of cosmic structures and the interaction of gravitational waves with matter. Liddle has been involved in both theoretical research and teaching, and he may have published numerous papers and books in his field.