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Gauge Fields and Inflation (1212.2921v3)

Published 12 Dec 2012 in hep-th, astro-ph.CO, and hep-ph

Abstract: The isotropy and homogeneity of the cosmic microwave background (CMB) favors "scalar driven" early Universe inflationary models. Non-scalar fields, and in particular gauge fields, are on the other hand commonplace in all high energy particle physics models proposed to be at work at the upper bound on energy scale of inflation set by the current CMB observations. In this review we consider the role and consequences, theoretical and observational, that gauge fields can have during inflationary era. Gauge fields may be turned on in the background during inflation, or may become relevant at the level of cosmic perturbations. There have been two main class of models with gauge fields in the background, models which show violation of cosmic no-hair theorem and those which lead to isotropic FLRW cosmology, respecting the cosmic no-hair theorem. Models in which gauge fields are only turned on at the cosmic perturbation level, may source primordial magnetic fields. We also review specific observational features of these models on the CMB and/or the primordial cosmic magnetic fields. Our discussions will be mainly focused on the inflation period, with only a brief discussion on the post inflationary (p)reheating era.

Citations (316)

Summary

  • The paper introduces inflation models where gauge fields challenge the conventional scalar field approach.
  • It analyzes scenarios in which gauge fields either minimally affect or dominate the inflationary energy, preserving cosmic isotropy.
  • Findings include quantitative predictions on perturbations and non-Gaussianities that could serve as observable signatures in the CMB.

An Overview of Gauge Fields and Inflation

This paper explores an alternative approach to conventional scalar field-driven models of inflation by incorporating gauge fields. While the standard inflationary paradigm relies on scalar fields to drive the exponential expansion of the early universe, this paper investigates the potential role of non-scalar fields, specifically gauge fields, during the inflationary era.

The isotropy and homogeneity observed in the cosmic microwave background radiation (CMB) typically favor scalar field inflation models. However, this paper proposes considering gauge fields, which are more commonly associated with high energy scales. The authors identify two main classes of inflationary models that incorporate gauge fields: those that violate the cosmic no-hair theorem and those that achieve isotropic Friedmann-LemaƮtre-Robertson-Walker (FLRW) cosmology, which respects the cosmic no-hair theorem.

Key Findings and Models

The paper provides an in-depth review of different inflationary models where gauge fields play a critical role. In one class of models, gauge fields are turned on during inflation, contributing to the energy budget, albeit remaining a subdominant component. These models are designed to minimally impact the isotropy of the universe, yet they introduce potentially detectable anisotropy in cosmic perturbations.

Another class of models includes gauge-flation and chromo-natural inflation, where the gauge fields play a dominant role in the inflationary dynamics. Here, the potential energy from non-Abelian gauge fields becomes the primary driver for inflation, resulting in a more significant modification to the standard inflationary picture.

Methodology and Approach

The authors explore the theoretical implications of gauge field-dominated inflation. By examining models where vector gauge fields are either minimally or dominantly contributing to the inflationary energy density, they debate the circumstances under which these models can exist while maintaining consistency with the observable isotropy of the universe.

A significant focus of the paper is on the quantitative effects these gauge fields have on the CMB and potential observational signatures, such as the generation of primordial magnetic fields and the statistical anisotropy in the CMB. The paper methodically computes the perturbations within these models and offers a contrasting viewpoint to purely scalar field-based wave spectra.

Theoretical Predictions and Observations

The authors confront the predictions of these gauge field inflationary models with existing observational constraints from the CMB data. They explore potential signatures that might distinguish these models from conventional scalar field inflation, emphasizing the gauge fields' ability to provide potentially significant non-Gaussianities in the CMB, something typically suppressed in scalar-driven inflation models.

Implications and Future Directions

The paper suggests that the inclusion of non-scalar fields, such as gauge fields in the inflationary framework, might be theoretically relevant and provide observationally distinguishable features. By integrating gauge fields into inflation models, the primordial universe's dynamics and its isotropic expansion could acquire new dimensions, potentially addressing unresolved questions of the early universe.

Conclusion

While these models offer new pathways for understanding inflation, deriving strong, distinguishable observational signatures remains challenging. The choice of parameters, such as the gauge coupling and the form of the interaction terms, crucially affects the inflationary trajectory and the feasibility of these models. Further exploration of these models, particularly concerning their stability and compatibility with high-energy physics theories, remains a promising direction for future research on their fundamental impact on cosmology.