Journal
CLASSICAL AND QUANTUM GRAVITY
Volume 30, Issue 21, Pages -Publisher
IOP Publishing Ltd
DOI: 10.1088/0264-9381/30/21/214002
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Funding
- KITP at UCSB (NSF grant) [NSF PHY11-25915]
- Department of Energy [DE-FG02-91ER-40671]
- DOE [DE-FG02-94ER-40823]
- University of Padova
- INFN
- Sezione di Padova
- Cosmology Group at the Department of Theoretical Physics of the University of Geneva
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Because the inflationary mechanism is extremely sensitive to UV-physics, the construction of theoretically robust models of inflation provides a unique window on Planck scale physics. We review efforts to use an axion with a shift symmetry to ensure a prolonged slow-roll background evolution. The symmetry dictates which operators are allowed, and these in turn determine the observational predictions of this class of models, which include observable gravitationalwaves (potentially chiral), oscillations in all primordial correlators, specific deviations from scale invariance and Gaussianity and primordial black holes. We discuss the constraints on this class of models in light of the recent Planck results and comment on future perspectives. The shift symmetry is very useful in models of large-field inflation, which typically have monomial potentials, but it cannot explain why two or more terms in the potential are fine-tuned against each other, as needed for typical models of small-field inflation. Therefore some additional symmetries or fine tuning will be needed if forthcoming experiments will constrain the tensor-to-scalar ratio to be r less than or similar to 0.01.
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