Closing in on α-attractors
2025-11-20 05:00 - 07:00 UTC | B447-1 (CTPU-CGA)
Speakers: David Wands (U. of Portsmouth (ICG))

Recent observations of cosmic microwave background (CMB) anisotropies combined with large-scale structure may point towards higher values of the scalar spectral index, ns. This puts previously preferred inflationary models, such as α-attractors, in tension with the new measurements. Pending a resolution of the tension between BAO parameters as determined by CMB datasets and those determined by DESI, we explore in this work the large-ns regime of α-attractor T-models. We show that some T-models can self-consistently produce an extended reheating stage with a stiff equation of state (w¯>1/3), which allows values for ns closer to unity. We employ constraints from P-ACT-LB-BK18 data to illustrate what large-ns observations might imply for T-models. We show that the ns measurement yields an upper limit on α that is stronger than the one from the tensor-to-scalar ratio only. We find that ns is maximised for α∼1, therefore the seven Poincaré models are well placed to deliver large ns. However, the ability of a stiff reheating stage to increase the compatibility of T-models with large-ns measurements saturates as w¯→1. Thanks to this effect, we establish that the largest ns that T-models can produce is ns=0.9682. T-models are therefore highly predictive in the large-ns regime and our result provides, under the assumption of perturbative reheating, a benchmark which could be used in the future to rule out T-models. [Based on arXiv:2511.14673]

https://indico.ibs.re.kr/event/1105/
