[Paper Review] New Ideas in Baryogenesis: A Snowmass White Paper

Gilly Elor, Julia Harz+22 more|arXiv (Cornell University)|Mar 9, 2022

Cosmology and Gravitation Theories4 citations

TL;DR

This Snowmass white paper reviews recent theoretical advances in baryogenesis, emphasizing low-scale new physics models that satisfy Sakharov's conditions—baryon number violation, CP violation, and departure from thermal equilibrium—offering experimentally testable signals. It highlights how these models, particularly those involving electroweak phase transitions with modified Higgs potentials, can generate the observed baryon asymmetry and be probed via collider measurements of triple Higgs couplings and gravitational wave detectors.

ABSTRACT

The Standard Model of Particle Physics cannot explain the observed baryon asymmetry of the Universe. This observation is a clear sign of new physics beyond the Standard Model. There have been many recent theoretical developments to address this question. Critically, many new physics models that generate the baryon asymmetry have a wide range of repercussions for many areas of theoretical and experimental particle physics. This white paper provides an overview of such recent theoretical developments with an emphasis on experimental testability.

Motivation & Objective

• To survey recent theoretical developments in baryogenesis that go beyond the Standard Model and are experimentally testable.
• To identify low-scale new physics models satisfying Sakharov's conditions for generating the baryon asymmetry of the Universe (BAU).
• To connect theoretical mechanisms to observable signatures in colliders and gravitational wave detectors.
• To assess the viability of electroweak baryogenesis with strong first-order phase transitions and modified Higgs potentials.
• To provide a roadmap for multi-pronged experimental searches targeting new physics responsible for the BAU.

Proposed method

• Analyzes new physics models that introduce B-violating interactions, CP-violating phases, and out-of-equilibrium dynamics at low energy scales.
• Examines extensions of the Standard Model, such as scalar singlets, two-Higgs doublet models, and composite Higgs scenarios, to generate a strong first-order electroweak phase transition.
• Evaluates the role of heavy fermions in modifying the Higgs effective potential and enabling a first-order transition at accessible temperatures.
• Assesses the impact of new interactions on the Higgs potential, particularly through temperature-dependent corrections that can trigger electroweak symmetry breaking.
• Considers gravitational wave signals from bubble collisions during a first-order phase transition as a probe of the electroweak scale physics.
• Reviews collider observables, especially the triple Higgs coupling, as a direct probe of new physics in the Higgs sector.

Experimental results

Research questions

• RQ1 Can low-scale new physics models satisfy the Sakharov conditions and generate the observed baryon asymmetry?
• RQ2 How do modified Higgs potentials from new scalar or fermionic states affect the strength and nature of the electroweak phase transition?
• RQ3 What are the detectable signatures of such models in collider experiments, particularly in Higgs self-coupling measurements?
• RQ4 To what extent can gravitational wave detectors probe the dynamics of the electroweak phase transition in these models?
• RQ5 What constraints do existing limits on the Higgs mass and stop squark searches place on the viability of electroweak baryogenesis in models like the MSSM?

Key findings

• Many new baryogenesis models generate the baryon asymmetry at low energy scales, making them experimentally accessible via collider and gravitational wave searches.
• Extensions of the Standard Model with additional scalar or fermionic states can induce a strong first-order electroweak phase transition, enabling efficient baryogenesis.
• The triple Higgs coupling is a key observable at colliders that can test the presence of new physics in the Higgs sector affecting the phase transition.
• Gravitational wave detectors, especially space-based interferometers, are sensitive to the stochastic background from colliding bubble walls during a first-order phase transition.
• Fermions with masses much higher than the critical temperature can contribute to the Higgs effective potential similarly to scalars, enabling a strong phase transition.
• Recent simulations suggest that the parameter space for successful electroweak baryogenesis and efficient gravitational wave production is limited, but alternative mechanisms involving relativistic bubble walls may still be detectable.