Closing in on $α$-attractors
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arXiv
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| Natura: | Preprint |
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2025
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| _version_ | 1866911274620682240 |
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| author | Iacconi, Laura Bhattacharya, Sukannya Fasiello, Matteo Wands, David |
| author_facet | Iacconi, Laura Bhattacharya, Sukannya Fasiello, Matteo Wands, David |
| contents | Recent observations of cosmic microwave background (CMB) anisotropies combined with large-scale structure may point towards higher values of the scalar spectral index, $n_s$. 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-$n_s$ 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 $(\bar w>1/3)$, which allows values for $n_s$ closer to unity. We employ constraints from P-ACT-LB-BK18 data to illustrate what large-$n_s$ observations might imply for T-models. We show that the $n_s$ measurement yields an upper limit on $α$ that is stronger than the one from the tensor-to-scalar ratio only. We find that $n_s$ is maximised for $α\sim1$, therefore the seven Poincaré models are well placed to deliver large $n_s$. However, the ability of a stiff reheating stage to increase the compatibility of T-models with large-$n_s$ measurements saturates as $\bar{w}\to1$. Thanks to this effect, we establish that the largest $n_s$ that T-models can produce is $n_s=0.9682$. T-models are therefore highly predictive in the large-$n_s$ 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. |
| format | Preprint |
| id |
arxiv_https___arxiv_org_abs_2511_14673 |
| institution | arXiv |
| publishDate | 2025 |
| record_format | arxiv |
| spellingShingle | Closing in on $α$-attractors Iacconi, Laura Bhattacharya, Sukannya Fasiello, Matteo Wands, David Cosmology and Nongalactic Astrophysics General Relativity and Quantum Cosmology High Energy Physics - Phenomenology High Energy Physics - Theory Recent observations of cosmic microwave background (CMB) anisotropies combined with large-scale structure may point towards higher values of the scalar spectral index, $n_s$. 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-$n_s$ 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 $(\bar w>1/3)$, which allows values for $n_s$ closer to unity. We employ constraints from P-ACT-LB-BK18 data to illustrate what large-$n_s$ observations might imply for T-models. We show that the $n_s$ measurement yields an upper limit on $α$ that is stronger than the one from the tensor-to-scalar ratio only. We find that $n_s$ is maximised for $α\sim1$, therefore the seven Poincaré models are well placed to deliver large $n_s$. However, the ability of a stiff reheating stage to increase the compatibility of T-models with large-$n_s$ measurements saturates as $\bar{w}\to1$. Thanks to this effect, we establish that the largest $n_s$ that T-models can produce is $n_s=0.9682$. T-models are therefore highly predictive in the large-$n_s$ 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. |
| title | Closing in on $α$-attractors |
| topic | Cosmology and Nongalactic Astrophysics General Relativity and Quantum Cosmology High Energy Physics - Phenomenology High Energy Physics - Theory |
| url | https://arxiv.org/abs/2511.14673 |