Abstract
An appealing explanation for the Planck data is provided by inflationary models with a singular non-canonical kinetic term: a Laurent expansion of the kinetic function translates into a potential with a nearly shift-symmetric plateau in canonical fields. The shift symmetry can be broken at large field values by including higher-order poles, which need to be hierarchically suppressed in order not to spoil the inflationary plateau. The herefrom resulting corrections to the inflationary dynamics and predictions are shown to be universal at lowest order and possibly to induce power loss at large angular scales. At lowest order there are no corrections from a pole of just one order higher and we argue that this phenomenon is related to the well-known extended no-scale structure arising in string theory scenarios. Finally, we outline which other corrections may arise from string loop effects.
Highlights
An appealing explanation for the Planck data is provided by inflationary models with a singular non-canonical kinetic term: a Laurent expansion of the kinetic function translates into a potential with a nearly shift-symmetric plateau in canonical fields
At lowest order there are no corrections from a pole of just one order higher and we argue that this phenomenon is related to the well-known extended no-scale structure arising in string theory scenarios
Assuming the corrections to follow the pattern of shift-symmetry in an effective field theory (EFT) sense, we study an infinite tower of corrections and demonstrate that the leading order corrections coincide with the structure obtained before
Summary
A scalar potential arising from a weakly broken shift symmetry is known to provide for controlled trans-Planckian field excursion during slow-roll inflation. The shift symmetry is said to be weakly broken, if the inflaton scalar potential V (φ) 1 itself provides the leading source of symmetry breaking. Which amounts to a shift symmetry φ → φ + c weakly broken by V0(φ). The same shift symmetry requirement is evident in the structure of f (R)-gravity versions producing inflation models close to the Starobinsky model. The condition eq (2.7) again marks the pattern of an effective weakly broken shift symmetry. One of the main aims of this paper is to provide the analogue formulation of this shift symmetry for non-canonical models of inflation, to which we turn
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