Stability bounds on inflationary initial states from UV–IR reflection on a trans-Planckian band

Abstract We derive model-independent constraints on finite-time inflationary initial states by combining an EFT with physical cutoff $$\Lambda $$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mi>Λ</mml:mi> </mml:math> , backreaction control at the initialization time, and a UV–IR reflection principle imposed only on a logarithmic “trans-Planckian band” about the cutoff pivot. For Gaussian, homogeneous and isotropic states, Bogoliubov data $$\beta _k$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:msub> <mml:mi>β</mml:mi> <mml:mi>k</mml:mi> </mml:msub> </mml:math> determine the excitation energy density, and backreaction finiteness selects a natural weighted Hilbert norm on this data. We introduce a windowed symmetry defect on the band and an explicit local completion map that enforces the reflection without constraining modes outside the band. Requiring that completion does not move admissible data by an order-one amount in the backreaction norm yields a parametric lower bound on the excitation energy density in terms of cutoff-scale Bogoliubov jets. In the narrow-band regime the defect admits a universal jet expansion, so generic non–Bunch–Davies data require tuned cancellations among cutoff derivatives or a nonzero excitation floor.