The Standard Model Higgs boson as the inflaton (0710.3755v2)

Abstract: We argue that the Higgs boson of the Standard Model can lead to inflation and produce cosmological perturbations in accordance with observations. An essential requirement is the non-minimal coupling of the Higgs scalar field to gravity; no new particle besides already present in the electroweak theory is required.

• The paper demonstrates that inflation can be driven by the SM Higgs field through a non-minimal gravitational coupling.
• The study employs a transition from the Jordan to Einstein frame to derive a flat inflationary potential that matches cosmological data.
• Results indicate that the model remains robust against quantum corrections and supports efficient post-inflationary reheating.

The Standard Model Higgs Boson as the Inflaton

The paper "The Standard Model Higgs boson as the inflaton" by Fedor Bezrukov and Mikhail Shaposhnikov explores the intriguing prospect of utilizing the Higgs boson from the Standard Model (SM) as the inflaton responsible for cosmic inflation. This notion challenges the conventional approach, where inflation is typically driven by a hypothetical scalar field distinct from the Higgs boson. The authors argue for a model where inflationary dynamics are naturally integrated into the SM framework with minimal extensions, specifically through a non-minimal coupling of the Higgs field to gravity.

Conceptual Framework

The traditional viewpoint posits that the SM of particle physics, while remarkably successful, does not account for cosmological inflation due to its requirement of nearly flat, homogeneous, and isotropic initial conditions. Inflationary models typically introduce an additional scalar, termed the inflaton, potentially arising from theories such as Grand Unified Theories (GUTs) or string theory, to drive the exponential expansion of the early universe and generate the observed perturbations.

In this paper, the authors propose that the Higgs field itself could serve as the inflaton if it is non-minimally coupled to gravity. This approach does not necessitate the introduction of new particles beyond those already present in the electroweak sector of the SM. The crucial element here is the coupling constant, ξ, which characterizes the strength of the interaction between the Higgs scalar and the gravitational sector.

Theoretical Examination

The authors analyze a Lagrangian for the SM that incorporates this non-minimal coupling. They show that standard inflationary predictions, particularly those concerning the spectral index and amplitude of tensor perturbations, align with empirical observations, such as those from the WMAP-3 dataset, within the $1\sigma$ confidence intervals.

The mathematical framework necessitates the transition between the Jordan frame and the Einstein frame to effectively paper the inflationary potential. In the Einstein frame, the Higgs field gains properties that are conducive to inflation, notably the flattening of the potential for large field values. This behavior facilitates a successful inflationary phase without invoking additional fields or scales between the electroweak scale and the Planck scale.

Implications and Future Directions

From a theoretical perspective, this proposal elegantly integrates the inflationary phase into the SM, potentially offering a new paradigm for understanding the early universe. This integration suggests that the cosmological parameters could be intrinsically linked to the Higgs sector, establishing a novel interdependency between particle physics and cosmological observations. Practically, this model suggests post-inflationary reheating is highly efficient due to the strong coupling of the Higgs field to the other SM fields.

The paper also touches upon the robustness of the potential against quantum corrections, both from quantum gravity and SM field interactions. The authors provide a scenario where these radiative corrections do not disrupt the essential flatness of the inflationary potential, preserving the model's predictions.

Conclusion

This work opens up a channel for further investigation into the viability of SM-driven inflation and calls for more precise cosmological measurements that could validate or challenge the predictions stemming from using the Higgs boson as the inflaton. The exploration of non-minimal couplings in the context of established particle models could also provide insights into the unification of fundamental forces and the role of gravity in early universe cosmology. Future studies may explore parameter spaces and alternative scenarios within this framework, potentially extending its implications to models that attempt to bridge the electroweak and quantum gravity scales without introducing extraneous elements, a principle underscored by this paper's conclusions.