k-inflation: Non-separable case meets ACT measurements
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| Format: | Preprint |
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2025
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| author | Serish, Tahere Fallahi Mansoori, Seyed Ali Hosseini Felegary, Fereshteh Akarsu, Özgür Sami, Mohamad |
| author_facet | Serish, Tahere Fallahi Mansoori, Seyed Ali Hosseini Felegary, Fereshteh Akarsu, Özgür Sami, Mohamad |
| contents | We investigate a non-separable subset of $k$-essence in which the kinetic and potential sectors interact through an $X^ρV(ϕ)$ coupling, implemented via a potential-dependent prefactor $f(ϕ)=1+2\mathcal{K}V$. In slow roll, this structure preserves a constant sound speed $c_s^2=1/(2ρ-1)$ while modifying the Hubble flow in a controlled way, thereby shifting the inflationary observables relative to the separable template. For monomial potentials $V=Aϕ^n$ (with $n=2$ and $n=2/3$ as representative cases) we derive closed analytic expressions for $n_s(N_\ast)$ and $r(N_\ast)$ to $\mathcal{O}(ε_{\rm mix}^2)$, where $ε_{\rm mix}\propto\mathcal{K}$ encodes the non-separable $X^ρV$ mixing, and we validate them against exact background integrations. The analytic and numerical predictions agree at the sub-per-mille level for $n_s$ and at the percent level for $r$, confirming the accuracy of the small-mixing expansion. For $\mathcal{K}<0$ the mixing systematically lowers both $n_s$ and $r$ at fixed $N_\ast$, allowing otherwise marginal monomials to fall within the region favored by recent ACT+{\it Planck}+BAO constraints (P--ACT--LB). All solutions shown satisfy the health conditions $f(ϕ)>0$, $ρ>\tfrac12$, and the positivity bound $V<1/(2|\mathcal K|)$ (from $f>0$). We also discuss parameter dependence and the expected equilateral-type non-Gaussianity, which remains comfortably within current bounds for the benchmarks considered. |
| format | Preprint |
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arxiv_https___arxiv_org_abs_2511_16621 |
| institution | arXiv |
| publishDate | 2025 |
| record_format | arxiv |
| spellingShingle | k-inflation: Non-separable case meets ACT measurements Serish, Tahere Fallahi Mansoori, Seyed Ali Hosseini Felegary, Fereshteh Akarsu, Özgür Sami, Mohamad General Relativity and Quantum Cosmology Cosmology and Nongalactic Astrophysics High Energy Physics - Theory We investigate a non-separable subset of $k$-essence in which the kinetic and potential sectors interact through an $X^ρV(ϕ)$ coupling, implemented via a potential-dependent prefactor $f(ϕ)=1+2\mathcal{K}V$. In slow roll, this structure preserves a constant sound speed $c_s^2=1/(2ρ-1)$ while modifying the Hubble flow in a controlled way, thereby shifting the inflationary observables relative to the separable template. For monomial potentials $V=Aϕ^n$ (with $n=2$ and $n=2/3$ as representative cases) we derive closed analytic expressions for $n_s(N_\ast)$ and $r(N_\ast)$ to $\mathcal{O}(ε_{\rm mix}^2)$, where $ε_{\rm mix}\propto\mathcal{K}$ encodes the non-separable $X^ρV$ mixing, and we validate them against exact background integrations. The analytic and numerical predictions agree at the sub-per-mille level for $n_s$ and at the percent level for $r$, confirming the accuracy of the small-mixing expansion. For $\mathcal{K}<0$ the mixing systematically lowers both $n_s$ and $r$ at fixed $N_\ast$, allowing otherwise marginal monomials to fall within the region favored by recent ACT+{\it Planck}+BAO constraints (P--ACT--LB). All solutions shown satisfy the health conditions $f(ϕ)>0$, $ρ>\tfrac12$, and the positivity bound $V<1/(2|\mathcal K|)$ (from $f>0$). We also discuss parameter dependence and the expected equilateral-type non-Gaussianity, which remains comfortably within current bounds for the benchmarks considered. |
| title | k-inflation: Non-separable case meets ACT measurements |
| topic | General Relativity and Quantum Cosmology Cosmology and Nongalactic Astrophysics High Energy Physics - Theory |
| url | https://arxiv.org/abs/2511.16621 |