Gauge-flation: Inflation From Non-Abelian Gauge Fields (1102.1513v4)

Abstract: Inflationary models are usually based on dynamics of one or more scalar fields coupled to gravity. In this work we present a new class of inflationary models, gauge-flation or non-Abelian gauge field inflation, where slow-roll inflation is driven by a non-Abelian gauge field. This class of models are based on a gauge field theory with a generic non-Abelian gauge group minimally coupled to gravity. We then focus on a particular gauge-flation model by specifying the action for the gauge theory which allows for a successful slow-roll inflation. This model has two parameters the value of which can be fixed using the CMB and other cosmological data. These values are within the natural range of parameters in generic grand unified theories of particle physics.

• The paper presents a gauge-flation model where non-Abelian SU(2) fields, with a higher-order (F~F)² term, drive slow-roll inflation while preserving isotropy.
• It constrains key parameters like the gauge coupling and κ within particle physics limits and aligns predictions with observed spectral tilt and tensor-to-scalar ratios.
• The model predicts unique features such as non-zero scalar anisotropic inertia and parity-violating tensor perturbations, offering clear avenues for empirical validation.

Overview of Gauge-Flation: Inflation from Non-Abelian Gauge Fields

The paper "Gauge-flation: Inflation From Non-Abelian Gauge Fields" by A. Maleknejad and M.M. Sheikh-Jabbari introduces an innovative class of inflationary models known as gauge-flation, wherein the driving mechanism for inflation is a non-Abelian gauge field rather than the traditional scalar field(s) commonly associated with inflationary theory. The study is motivated by the desire to explore alternatives to scalar-driven inflationary scenarios and provides a detailed theoretical framework for gauge-flation, examining its viability and implications in the context of cosmological observations.

Key Elements of the Research

1. Model Foundation: The gauge-flation model is built upon a gauge field with a non-Abelian structure minimally coupled to gravity, specifically utilizing $SU(2)$ gauge fields. The authors propose an inflationary scenario where isotropy is preserved through the intrinsic properties of the gauge field, allowing for a coherent expansion of the universe.
2. Action and Dynamics: The model employs a specific action consisting of the standard Yang-Mills action supplemented with a higher order term, proportional to the square of the Pontryagin density $(F\tilde{F})^2$. This term is pivotal for introducing a potential allowing slow-roll inflation, thereby playing the role typically reserved for the inflaton field in scalar-driven models.
3. Parameter Specification: The gauge-flation model is characterized by two primary parameters: the gauge coupling $g$ and the coefficient $\kappa$ associated with the $(F\tilde{F})^2$ term. These parameters are not arbitrarily set but are constrained within the allowable range of particle physics models, consistent with Grand Unified Theories (GUT).
4. Cosmological Perturbations and Observational Constraints: The paper explores the tensor perturbations induced by gauge-flation and their deviation from parity symmetry, a notable departure from scalar-driven models. It provides detailed calculations for the power spectra of metric perturbations, both scalar and tensor, in the course of cosmic inflation. Furthermore, the authors confront the theoretical model with observational data, suggesting its compatibility with constraints on the spectral tilt ($n_s$) and tensor-to-scalar ratio ($r$).
5. Potential Observational Signatures: The gauge-flation framework predicts a non-zero scalar anisotropic inertia, a feature not present in traditional inflation models. This distinctive characteristic enriches the landscape of inflationary cosmology and proposes empirical verification avenues.

Implications and Future Directions

The introduction of gauge-flation as a credible model for cosmic inflation opens new theoretical avenues in early universe cosmology. The reliance on non-Abelian gauge fields signifies a compelling link between high-energy physics and cosmological dynamics, which might have practical implications concerning quantum field stability and gauge invariance in an inflationary setting. The predictions made by the model on parameters such as the tensor-to-scalar ratio are poised for validation through forthcoming high-precision observational missions, such as the Planck satellite.

The paper suggests that future lines of inquiry might involve more comprehensive exploration into the physical origin of the $(F\tilde{F})^2$ term within fundamental physics frameworks, potentially through axion physics or other mechanisms within GUT. Additionally, further refinement in the treatment of cosmic perturbation theory within gauge-flation, alongside more robust numerical simulations, may provide deeper insights and consolidate its status alongside prevailing inflationary models.

In conclusion, the authors present a substantive theoretical proposal that integrates non-Abelian gauge fields into the inflationary narrative, underscoring the importance of bridging cosmological phenomena with the tenets of particle physics. The gauge-flation model, while intricate, offers an insightful and potentially fruitful extension to conventional understanding of the early universe and invites ongoing investigation to fully realize its theoretical and observational potential.