Science with the space-based interferometer eLISA. II: Gravitational waves from cosmological phase transitions (1512.06239v2)

Abstract: We investigate the potential for the eLISA space-based interferometer to detect the stochastic gravitational wave background produced by strong first-order cosmological phase transitions. We discuss the resulting contributions from bubble collisions, magnetohydrodynamic turbulence, and sound waves to the stochastic background, and estimate the total corresponding signal predicted in gravitational waves. The projected sensitivity of eLISA to cosmological phase transitions is computed in a model-independent way for various detector designs and configurations. By applying these results to several specific models, we demonstrate that eLISA is able to probe many well-motivated scenarios beyond the Standard Model of particle physics predicting strong first-order cosmological phase transitions in the early Universe.

• The paper demonstrates that gravitational waves from cosmological phase transitions arise through bubble collisions, sound waves, and MHD turbulence with detailed insights into bubble dynamics.
• It employs a model-independent analysis to assess various eLISA configurations, using signal-to-noise ratios and parameters like α, β/H*, and T* for detection criteria.
• The research highlights opportunities to probe extensions of the Standard Model, underscoring eLISA’s potential to reveal new physics beyond traditional collider experiments.

Overview of "Science with the space-based interferometer eLISA II: Gravitational waves from cosmological phase transitions"

This paper provides a comprehensive examination of the potential for the eLISA (Evolved Laser Interferometer Space Antenna) space-based interferometer to detect gravitational waves (GWs) created during cosmological phase transitions in the early Universe. Specifically, it investigates signals arising from strong first-order phase transitions, characterized by significant changes in phase states, like bubble collisions and magnetohydrodynamic (MHD) turbulence. The authors employ a model-independent approach to assess eLISA's sensitivity across a range of detector configurations.

Key Contributions and Findings

1. Phase Transition Dynamics and GW Sources:
   • The paper identifies the production of gravitational waves through three primary processes: bubble wall collisions, sound waves in the plasma, and MHD turbulence. These processes each contribute to a stochastic background of GWs.
   • For a phase transition to contribute substantially to the GW background, a detailed understanding of bubble dynamics, especially wall velocities, is necessary. The paper identifies cases of non-runaway and runaway bubbles, where the potential implications for GW detection vary significantly.
2. Sensitivity of eLISA Configurations:
   • Four potential configurations of eLISA are analyzed, characterized by different numbers of laser links, arm lengths, mission durations, and noise levels.
   • Detection capabilities are assessed using a signal-to-noise ratio (SNR) analysis, accounting for variations in detector sensitivity to different GW backgrounds.
   • The analysis specifies conditions (e.g., values of $\alpha$, $\beta/H_*$, and $T_*$) under which eLISA can detect GW signals from phase transitions.
3. Model-Specific Benchmarks:
   • The paper evaluates several theoretical models that predict strong first-order phase transitions, including models with supersymmetric extensions of the Standard Model (MSSM), those with additional scalar fields, and theories involving higher-dimensional operators.
   • Each model presents a set of parameters that can be mapped onto eLISA's detection sensitivity, underscoring scenarios where eLISA could positively identify phase transitions.
4. Implications for Theoretical and Experimental Physics:
   • The successful detection of GWs from early-universe phase transitions could provide crucial insights into the structure of new physics beyond the Standard Model.
   • Scenarios involving singlet scalar extensions and models with a dilaton or dark matter-related sectors highlight the potential for eLISA to probe new physics inaccessible to traditional collider experiments.

Future Prospects

The paper speculates on the broader implications of detecting GWs from cosmological phase transitions, emphasizing their significance for understanding electroweak symmetry breaking and possible connections to dark matter sectors. The authors assert the importance of refined models that more accurately describe these transitions to better predict GW signals.

The research highlights the technical challenges in configuring the eLISA mission to optimize GW detection, encouraging further analysis into possible design improvements. The exploration of model possibilities that furnish strong transitions, even beyond the electroweak scale, suggests fertile ground for future theoretical work, especially in developing models that predict significant supercooling or nonlinear effects in the early Universe.

Overall, the paper positions eLISA as a promising tool for cosmological GW astronomy, with the potential to unlock previously unattainable data on the early universe's dynamical processes and fundamental physics through gravitational wave observations.