Higgs inflation still alive (1403.5043v2)

Abstract: The observed value of the Higgs mass indicates that the Higgs potential becomes small and flat at the scale around $10^{17}$GeV. Having this fact in mind, we reconsider the Higgs inflation scenario proposed by Bezrukov and Shaposhnikov. It turns out that the non-minimal coupling $\xi$ of the Higgs-squared to the Ricci scalar can be smaller than ten. For example, $\xi=7$ corresponds to the tensor-to-scalar ratio $r\simeq0.2$, which is consistent with the recent observation by BICEP2.

• The paper shows that tuning the Higgs and top quark masses flattens the potential near 10^17 GeV to support inflation.
• The analysis demonstrates that a low non-minimal coupling, potentially as small as ξ=7, facilitates a successful inflection point inflation with ~60 e-folds.
• The study suggests that adjusting ξ alleviates unitarity constraints and aligns the Higgs inflation model with observational data like BICEP2.

Overview of "Higgs Inflation Still Alive"

The paper "Higgs Inflation Still Alive" by Hamada et al. revisits the Higgs inflation scenario in light of the observed Higgs mass, which suggests that the Higgs potential becomes small and flat near a scale of approximately $10^{17}\,\text{GeV}$. This finding provides a basis to reconsider the original Higgs inflation model introduced by Bezrukov and Shaposhnikov. A crucial insight from the paper is that the non-minimal coupling $\xi$ between the Higgs squared and the Ricci scalar can be much smaller than previously thought, potentially as low as $\xi=7$, which aligns with the tensor-to-scalar ratio $r\approx0.2$ reported by BICEP2.

Detailed Analysis

1. Higgs Potential and Scale Matching: The paper underscores the significance of using the Higgs mass value $125.9\pm0.4$ GeV to infer a remarkably small and flat Higgs potential around a high-energy scale. The research addresses the implications of tuning the top quark mass to achieve desirable features in the Higgs potential. This tuning enhances the potential for inflationary scenarios compatible with cosmological observations.
2. Inflection Point Analysis: The authors analyze the possibility of using the inflection point in the Higgs potential for inflation. However, they assert that due to slow-roll conditions and the requirement for sufficient e-folds ($N_*\approx60$), it is challenging for this feature alone to drive successful inflation without fine-tuning of the top quark mass.
3. Role of Non-Minimal Coupling $\xi$: A primary contribution of the paper is the hypothesis that adjusting the non-minimal coupling $\xi$ could facilitate an effective inflection point inflation. By incorporating $\xi$, the Higgs field's contribution to the Ricci scalar can be optimized to accommodate realistic inflationary dynamics without requiring exceedingly high values of $\xi$.
4. Cosmological Compatibility: The paper presents examples where different $\xi$ values (0, 3, 10, 100, 1000) are toyed with under various parameter setups. The results illustrate the potential’s evolution and its ability to meet cosmological data requirements when $\xi$ is optimally chosen.
5. Implications for Other Inflationary Models: The authors contrast their findings with earlier models of Higgs inflation, highlighting that the particular settings allowing for smaller $\xi$ values could also resolve issues seen in chaotic or simpler quadratic inflation models.

Theoretical and Practical Implications

The findings of this paper have significant implications for both theoretical physics and cosmology. The potential to lower $\xi$ challenges previous assumptions about the necessity of large non-minimal couplings for Higgs inflation, which could ease theoretical constraints related to unitarity and the need for new physics at high energy scales. This adjustment also makes the Higgs inflation model more feasible within the Standard Model framework, avoiding the introduction of an artificial Planck-scale cutoff.

Furthermore, the paper suggests potential directions for future research, particularly in exploring the Higgs potential's alterations due to physics beyond the Standard Model, such as string theory. Investigating how these modifications influence inflationary parameters could bridge the predictive power of the model with observational results like those from the Planck satellite or other upcoming cosmic microwave background (CMB) experiments.

In conclusion, "Higgs Inflation Still Alive" revitalizes the Higgs inflation landscape by proposing a model with reduced $\xi$ alignment to cosmological observations, thereby enhancing its theoretical robustness and empirical compatibility. Future research in this area may further refine these predictions and unravel complexities associated with quantum corrections and higher-energy physics effects.