Black Holes and Gravitational Waves from Slow First-Order Phase Transitions

Area of Science:

• Cosmology
• Particle Physics
• Astrophysics

Background:

• First-order phase transitions in the early universe can generate significant density fluctuations.
• These inhomogeneities are a potential source for the formation of primordial black holes.
• Gravitational waves are a key probe of early universe phenomena.

Purpose of the Study:

• To analyze the gravitational wave spectrum produced by slow first-order phase transitions.
• To investigate the impact of these gravitational waves on primordial black hole formation.
• To assess the implications for interpreting pulsar timing array data.

Main Methods:

• Simulating the dynamics of slow first-order phase transitions.
• Calculating the resulting gravitational wave spectrum, including contributions from bubble collisions and perturbations.
• Analyzing the characteristics of the gravitational wave signal, such as spectral shape and peak dominance.
• Considering the role of negative non-Gaussianity in enhancing the gravitational wave signal.

Main Results:

• The gravitational wave spectrum is characterized by a primary component from bubble collisions and a secondary component from large perturbations.
• The secondary component can dominate the spectrum if β/H_{0}<12.
• This scenario impacts the interpretation of current pulsar timing array data.
• The gravitational wave signal is enhanced due to negative non-Gaussianity, leading to a distinguishable two-peak shape.

Conclusions:

• Slow first-order phase transitions provide a viable mechanism for generating primordial black holes and a unique gravitational wave signature.
• The secondary gravitational wave component offers a new avenue for probing early universe physics.
• The predicted signal's characteristics, including its two-peak structure and potential dominance, warrant further observational investigation, particularly with pulsar timing arrays.