Starobinsky-type inflation from α′-corrections

Abstract

Working in the Large Volume Scenario (LVS) of IIB Calabi-Yau flux compactifications, we construct inflationary models from recently computed higher derivative (α ) 3 -corrections. Inflation is driven by a Kähler modulus whose potential arises from the aforementioned corrections, while we use the inclusion of string loop effects just to ensure the existence of a graceful exit when necessary. The effective inflaton potential takes a Starobinsky-type form V = V 0 (1 − e −νφ ) 2 , where we obtain one set-up with ν = −1/ √ 3 and one with ν = 2/ √ 3 corresponding to inflation occurring for increasing or decreasing φ respectively. The inflationary observables are thus in perfect agreement with PLANCK, while the two scenarios remain observationally distinguishable via slightly varying predictions for the tensor-to-scalar ratio r. Both set-ups yield r (2 . . . 7) × 10 −3 . They hence realise inflation with moderately large fields (∆φ ∼ 6 M P l ) without saturating the Lyth bound. Control over higher corrections relies in part on tuning underlying microscopic parameters, and in part on intrinsic suppressions. The intrinsic part of control arises as a leftover from an approximate effective shift symmetry at parametrically large volume.ArXiv ePrint: 1509.00024 arXiv:1509.00024v2 [hep-th]

Global embedding of fibre inflation models

“…On the other hand, inflation to the left has f = 1/k, and so, from the typical r-n s relation of generalised fibre inflation models, it predicts a tensor-to-scalar ratio smaller by a factor of 4. Hence for 50-60 e-foldings and a spectral index compatible with observations, the final predictions for tensor modes are: r R 0.006 and r L r R /4 0.0015 [55].…”

“…Ref. [55] considered the same CY geometry and included F 4 higher derivative corrections but neglected winding loops. The resulting inflationary potential contains four terms: two positive KK corrections and two F 4 terms whose sign is undetermined.…”

“…smaller than the other by a factor at least of order 10 −4 [55]. The typical prediction of these generalised fibre inflation models is a relation between the tensor-to-scalar ratio r and the spectral index n s of the form r = 2f 2 (n s − 1) 2 where f is an effective decay constant controlling the strength of the inflationary plateau generated by the term e −φ/f [30].…”

“…Note that in the original fibre inflation model f = 2/k [32]. The two inflationary potentials proposed in [55] look like:…”

On four-derivative terms in IIB Calabi-Yau orientifold reductions

“…It is an old approach in the context of string theory to drive slow roll inflation by a Kähler modulus [52][53][54][55][56]. It would be interesting to analyze the consequences of the derived novel couplings to such inflationary models and their relevance due to their α ′3 -suppression [57][58][59]. Finally, let us discuss the coupling G µν ∇ ν ∇ µ L a .…”