Revisiting small-scale fluctuations in α-attractor models of inflation

Laura Iacconi, Hooshyar Assadullahi, Matteo Fasiello, David Wands

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Cosmological alpha-attractors stand out as particularly compelling models to describe inflation in the very early universe, naturally meeting tight observational bounds from cosmic microwave background (CMB) experiments. We investigate alpha-attractor potentials in the presence of an inflection point, leading to enhanced curvature perturbations on small scales. We study both single- and multi-field models, driven by scalar fields living on a hyperbolic field space. In the single-field case, ultra-slow-roll dynamics at the inflection point is responsible for the growth of the power spectrum, while in the multi-field set-up we study the effect of geometrical destabilisation and non geodesic motion in field space. The two mechanisms can in principle be distinguished through the spectral shape of the resulting scalar power spectrum on small scales. These enhanced scalar perturbations can lead to primordial black hole (PBH) production and second-order gravitational wave (GW) generation. Due to the existence of universal predictions in alpha-attractors, consistency with current CMB constraints on the large-scale spectral tilt implies that PBHs can only be produced with masses smaller than 10^8g and are accompanied by ultra-high frequency GWs, with a peak expected to be at frequencies of order 10kHz or above.
Original languageEnglish
Article number007
Number of pages71
JournalJournal of Cosmology and Astroparticle Physics
Issue number06
Publication statusPublished - 9 Jun 2022


  • inflation
  • primordial black holes
  • primordial gravitational waves (theory)
  • cosmological parameters from CMBR
  • UKRI
  • STFC
  • ST/R505018/1
  • ST/S505651/1
  • ST/S000550/1
  • TC_highlight


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