Electroweak baryogenesis and gravitational waves from a real scalar singlet (1611.02073v5)

Abstract: We consider a real scalar singlet field which provides a strong first-order electroweak phase transition via its coupling to the Higgs boson, and gives a $CP$ violating contribution on the top quark mass via a dimension-6 operator. We study the correlation between the baryon-to-entropy ratio produced by electroweak baryogenesis, and the gravitational wave signal from the electroweak phase transition. We show that future gravitational wave experiments can test, in particular, the region of the model parameter space where the observed baryon-to-entropy ratio can be obtained even if the new physics scale, which is explicit in the dimension-6 operator, is high.

• The paper introduces a model where a real scalar singlet couples with the Higgs to enable a strong first-order electroweak phase transition essential for baryogenesis.
• It details bubble nucleation dynamics and supercooling effects, linking them to gravitational wave signals potentially observable by detectors like LISA.
• The study solves transport equations for baryon asymmetry, suggesting that high new physics scales yield measurable signatures in future experiments.

Electroweak Baryogenesis and Gravitational Waves from a Real Scalar Singlet

The paper authored by Ville Vaskonen provides an in-depth exploration of a theoretical model elucidating the potential mechanisms behind electroweak baryogenesis and the production of gravitational waves, achieved by extending the Standard Model with a real scalar singlet field. The paper advances the understanding of phase transitions in the early Universe, highlighting notable implications for experimental physics.

Overview of the Model and Mechanisms

The model introduces a real scalar singlet field interacting with the Standard Model Higgs boson via a portal coupling. This interaction allows for a strong first-order electroweak phase transition, a necessity for electroweak baryogenesis. Beyond this, a dimension-6 operator is introduced to provide a source of $CP$ violation by influencing the top quark's mass during the phase transition. This $CP$ violation is crucial for generating the observed baryon asymmetry in the Universe.

First-Order Phase Transition and Bubble Dynamics

For electroweak baryogenesis to be effective, the electroweak phase transition must be of the first order. The paper details conditions under which the scalar potential in the model induces such a transition. Key parameters include the scalar's mass and the portal coupling strength, which determine not just the nature of the phase transition but also the bubble nucleation temperature—a significant factor due to its impact on the potential gravitational wave signal.

The phase transition's dynamics are captured by the action $S_3$, which underpins the calculation of bubble nucleation rates necessary for the transition analysis. The results indicate substantial supercooling effects, where nucleation occurs at temperatures significantly below the critical temperature.

Baryon Asymmetry and New Physics Scale

Calculating the baryon-to-entropy ratio involves solving a set of transport equations to account for diffusion processes across the bubble wall during the phase transition. The real scalar singlet model demonstrates adequate flexibility to produce the observed baryon asymmetry even for relatively high scales of new physics ($\Lambda$), suggesting that this model is a viable candidate for scenarios lying beyond the current Standard Model.

Correlation with Gravitational Wave Production

A significant aspect of this paper is linking the first-order electroweak phase transition to potential gravitational wave signals observable by space-based interferometers such as LISA and BBO. The model predicts gravitational wave spectra with amplitudes and frequencies that align with the sensitivity ranges of these future detectors. The strength of the gravitational wave signal, which correlates with the scale of new physics and the parameter $\alpha$, holds promise for indirect detection or constraint of the scalar singlet model through gravitational wave observatories.

Implications and Future Work

The results illuminate a testable prediction: models with high $\Lambda$ scales yielding successful baryogenesis should generate strong detectable gravitational wave signals. This correlation provides a promising approach to experimentally probing the validity of theoretical extensions to the Standard Model. Future advancements in determining the bubble wall velocity and precise dynamics could refine these predictions and address remaining uncertainties, such as the precise wall thickness estimate potentially affecting baryogenesis outcomes.

In conclusion, the paper presents a comprehensive analysis of an extended Standard Model proposing mechanisms for both electroweak baryogenesis and gravitational wave production through a real scalar singlet field. The model not only aligns theoretical predictions with potential experimental observations but also provides a framework for guiding future paper and validation of new physics beyond the Standard Model.