- The paper introduces a novel single field double inflation model that uses non-minimal coupling and an exact solution of the inflaton dynamics beyond the slow-roll approximation.
- The study reveals that the transition between inflationary phases generates large curvature perturbations, which can seed primordial black holes as dark matter candidates.
- The model aligns with CMB observations by predicting key parameters such as a tensor-to-scalar ratio of approximately 0.05 and a spectral index near 0.96.
Single Field Double Inflation and Primordial Black Holes
The paper "Single Field Double Inflation and Primordial Black Holes" by K. Kannike, L. Marzola, M. Raidal, and H. Veermäe presents a detailed analysis of a single field double inflation model within scalar-tensor theories framework, aiming to explain both observable cosmic microwave background (CMB) data and the potential origin of dark matter via primordial black holes (PBHs). This research explores the conditions necessary to produce a double inflation scenario where a single scalar field undergoes two distinct inflationary phases, separated by a non-inflationary period.
The authors innovate within single-field inflation by emphasizing the impact of the inflaton's non-minimal coupling to gravity and its self-coupling undergoing radiative corrections. A haLLMark of their approach is the transition from a regime dominated by a non-minimal coupling at large field values to a polynomial-dominated hilltop inflation at smaller field values. This shift allows the model to comply with CMB perturbation measurements and simultaneously predict substantial primordial curvature fluctuations, potentially seeding PBHs.
A key contribution of the paper is the departure from the slow-roll approximation in modeling inflationary dynamics. By solving the inflaton's equation of motion exactly, the authors reveal that between the two phases of inflation, slow-roll conditions often break down, justifying the need for an exact treatment. This precise computation is pivotal, especially for predicting the spectrum of density perturbations that can lead to PBH formation, which are hypothesized to constitute a significant fraction of dark matter.
The results demonstrate that a local minimum in the inflaton potential plays a crucial role, facilitating the creation of large perturbations. Additionally, the paper argues that such a potential intrinsically results in a power spectrum deviating from lognormal without assuming specific ad hoc conditions, as commonly seen in other works.
The authors propose a particle physics-motivated model where the inflaton undergoes two distinct inflationary stages: initially influenced by a non-minimal coupling and logarithmic corrections and later transitioning into hilltop inflation with the aid of a specific polynomial potential. The findings suggest that this framework accommodates both the inflation dynamics and the required density fluctuations for PBH production. The research aligns with CMB data and proposes observationally distinguished inflationary parameters: a tensor-to-scalar ratio (r) approximately 0.05 and a spectral index compatible with current observations (n_s ≈ 0.96).
The implications of this work span both theoretical insights into inflationary dynamics and practical considerations for PBH-generated dark matter. If feasible and further supported by observations, such a model might address the elusive nature of dark matter without extending the Standard Model of particle physics by introducing additional dark sectors.
Future avenues explored in the paper include further empirical support for the predicted PBH mass functions and potential signatures in upcoming cosmological surveys. As PBH constraints continue tightening with improved observational capabilities, models like this one, which provide a consistent narrative aligning cosmological inflation and dark matter origins, might gain increased relevance.
In summary, the research provides a rigorous examination of double inflation facilitated by single fields and elucidates its potential to generate PBHs as dark matter candidates, enriched by a technically robust approach transcending typical slow-roll approximations.