Non-minimal unimodular inflation revisited: Swampland diagnostics and CMB constraints
Abstract
We study non-minimal unimodular inflation in the Einstein frame; the effective potential takes the form U(φ)=U0(1+ξφ2/mpl2)−2. We consider the canonical field map and the inflationary observables directly from the Einstein-frame action. The exact potential slow-roll parameters, the leading scalar running, the scalar-amplitude normalization, the e-fold relation, and the end-of-inflation condition are obtained analytically. The model has a nontrivial structural tension: an εV=1 exit requires ξ>1/2, whereas the near-origin slow-roll regime requires ξ≪1 and gives ns≃1−8ξ. We next test three distinct swampland diagnostics. The further-refined de Sitter conjecture (FRDSSC) introduces the independent conjectural parameters a, b, and q, while the scalar weak gravity conjecture (SWGC) and its strong form (SSWGC) contain no analogous tunable conjecture parameter in the single-field realization adopted here. All three criteria are evaluated using the canonically normalized Einstein-frame scalar. Analytic limits show that the SWGC is violated at the stationary point for every nonzero ξ, whereas the SSWGC at that point requires ξ≳0.0643. In the large-field limit both scalar weak-gravity diagnostics reduce to the same threshold ξ≥0.1. Numerical scans then show that the observationally relevant ACT/P-ACT region does not satisfy either scalar weak-gravity criterion, while the FRDSSC can be satisfied for a close to unity. Consequently, the minimal model can reproduce acceptable (ns,r) at isolated field values, but this does not constitute a complete 50-60 e-fold inflationary history or simultaneous satisfaction of all three conjectures.
Related
- Evading the Swampland de Sitter Obstruction via Thermodynamic Duality-Induced Horizon Corrections in Unimodular Gravity
- Observational constraints on Diffusion Cosmologies in Unimodular Gravity from DESI DR2
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- Revisiting the Lyth bound constraints on inflation from ACT DR6 results
- General Spin-1 Dynamics During Inflation: Microcausality Constraints and Cosmological Collider Signals
BibTeX
@misc{gashti2026nonminimal,
title = {{Non-minimal unimodular inflation revisited: Swampland diagnostics and CMB constraints}},
author = {Saeed Noori Gashti and Mohammad Reza Alipour and Mohammad Ali S. Afshar and Behnam Pourhassan and İzzet Sakallı and Phongpichit Channuie},
howpublished = {arXiv},
year = {2026},
month = oct,
doi = {10.48550/arxiv.2610.27991},
eprint = {2610.27991},
archivePrefix = {arXiv},
url = {https://arxiv.org/abs/2610.27991},
note = {CC BY 4.0},
}
RIS
TY - UNPB
TI - Non-minimal unimodular inflation revisited: Swampland diagnostics and CMB constraints
AU - Saeed Noori Gashti
AU - Mohammad Reza Alipour
AU - Mohammad Ali S. Afshar
AU - Behnam Pourhassan
AU - İzzet Sakallı
AU - Phongpichit Channuie
PY - 2026
DA - 2026/10/20
PB - arXiv
DO - 10.48550/arxiv.2610.27991
UR - https://arxiv.org/abs/2610.27991
AB - We study non-minimal unimodular inflation in the Einstein frame; the effective potential takes the form U(φ)=U_0(1+ξφ^2/mpl^2)^−2. We consider the canonical field map and the inflationary observables directly from the Einstein-frame action. The exact potential slow-roll parameters, the leading scalar running, the scalar-amplitude normalization, the e-fold relation, and the end-of-inflation condition are obtained analytically. The model has a nontrivial structural tension: an ε_V=1 exit requires ξ>1/2, whereas the near-origin slow-roll regime requires ξ≪1 and gives n_s≃1−8ξ. We next test three distinct swampland diagnostics. The further-refined de Sitter conjecture (FRDSSC) introduces the independent conjectural parameters a, b, and q, while the scalar weak gravity conjecture (SWGC) and its strong form (SSWGC) contain no analogous tunable conjecture parameter in the single-field realization adopted here. All three criteria are evaluated using the canonically normalized Einstein-frame scalar. Analytic limits show that the SWGC is violated at the stationary point for every nonzero ξ, whereas the SSWGC at that point requires ξ≳0.0643. In the large-field limit both scalar weak-gravity diagnostics reduce to the same threshold ξ≥0.1. Numerical scans then show that the observationally relevant ACT/P-ACT region does not satisfy either scalar weak-gravity criterion, while the FRDSSC can be satisfied for a close to unity. Consequently, the minimal model can reproduce acceptable (n_s,r) at isolated field values, but this does not constitute a complete 50-60 e-fold inflationary history or simultaneous satisfaction of all three conjectures.
ER -