String-inspired Gauss-Bonnet Gravity Inflation and ACT
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arXiv
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| Auteurs principaux: | , , , , |
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| Format: | Preprint |
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2026
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| _version_ | 1866913050669350912 |
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| author | Odintsov, S. D. Oikonomou, V. K. Tsyba, Pyotr Razina, Olga Rakhatov, Dauren |
| author_facet | Odintsov, S. D. Oikonomou, V. K. Tsyba, Pyotr Razina, Olga Rakhatov, Dauren |
| contents | In this article we present a systematic observational verification of the ghost-free string-inspired $f(R,\mathcal{G})$ model, where the Gauss-Bonnet invariant is non-minimally coupled to an auxiliary scalar field $χ$ through the coupling function $h(χ)$. Previous studies confirmed the theoretical viability of this framework using phenomenological parameter choices. In this work, for the first time, a systematic comparison with observational data from Planck 2018 and the Atacama Comsology Telescope is carried out via a Bayesian MCMC analysis using the Cobaya code. We explore an extended set of sixteen models constructed from four types of the Hubble parameter combined with power-law, exponential, hybrid, and inverse logarithmic coupling functions $h(χ)$. The hybrid coupling $h(χ) = γe^{b_1χ}χ^{b_2}$, introduced in this context, allows for interpolation between the power-law and exponential forms, providing additional flexibility in controlling the Gauss-Bonnet contribution at different stages of inflation. All sixteen models reproduce the red spectral tilt of scalar perturbations consistent with CMB observations, yielding $n_s \approx 0.97$ at $N = 60$ e-folds. We find that the preference for the dataset is systematically determined by the choice of Hubble parametrization rather than by the coupling function. The parameter $μ\approx0.1$ remains stable in all configurations, suggesting its fundamental role within the ghost-free formalism. |
| format | Preprint |
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arxiv_https___arxiv_org_abs_2604_18861 |
| institution | arXiv |
| publishDate | 2026 |
| record_format | arxiv |
| spellingShingle | String-inspired Gauss-Bonnet Gravity Inflation and ACT Odintsov, S. D. Oikonomou, V. K. Tsyba, Pyotr Razina, Olga Rakhatov, Dauren General Relativity and Quantum Cosmology Cosmology and Nongalactic Astrophysics High Energy Physics - Theory In this article we present a systematic observational verification of the ghost-free string-inspired $f(R,\mathcal{G})$ model, where the Gauss-Bonnet invariant is non-minimally coupled to an auxiliary scalar field $χ$ through the coupling function $h(χ)$. Previous studies confirmed the theoretical viability of this framework using phenomenological parameter choices. In this work, for the first time, a systematic comparison with observational data from Planck 2018 and the Atacama Comsology Telescope is carried out via a Bayesian MCMC analysis using the Cobaya code. We explore an extended set of sixteen models constructed from four types of the Hubble parameter combined with power-law, exponential, hybrid, and inverse logarithmic coupling functions $h(χ)$. The hybrid coupling $h(χ) = γe^{b_1χ}χ^{b_2}$, introduced in this context, allows for interpolation between the power-law and exponential forms, providing additional flexibility in controlling the Gauss-Bonnet contribution at different stages of inflation. All sixteen models reproduce the red spectral tilt of scalar perturbations consistent with CMB observations, yielding $n_s \approx 0.97$ at $N = 60$ e-folds. We find that the preference for the dataset is systematically determined by the choice of Hubble parametrization rather than by the coupling function. The parameter $μ\approx0.1$ remains stable in all configurations, suggesting its fundamental role within the ghost-free formalism. |
| title | String-inspired Gauss-Bonnet Gravity Inflation and ACT |
| topic | General Relativity and Quantum Cosmology Cosmology and Nongalactic Astrophysics High Energy Physics - Theory |
| url | https://arxiv.org/abs/2604.18861 |