Stochastic gravitational-wave (GW) background (SGWB) contains information
about the early Universe and astrophysical processes. The recent evidence of
SGWB by pulsar timing arrays in the nanohertz band is a breakthrough in the GW
astronomy. For ground-based GW detectors, while unfortunately in data analysis
the SGWB can be masked by loud GW events from compact binary coalescences
(CBCs). Assuming a next-generation ground-based GW detector network, we
investigate the potential for detecting the astrophysical and cosmological SGWB
with non-CBC origins by subtracting recovered foreground signals of loud CBC
events. As an extension of the studies by Sachdev et al. (2020) and Zhou et al.
(2023), we incorporate aligned spin parameters in our waveform model. Because
of the inclusion of spins, we obtain significantly more pessimistic results
than the previous work, where the residual energy density of foreground is even
larger than the original background. The degeneracy between the spin parameters
and symmetric mass ratio is strong in the parameter estimation process and it
contributes most to the imperfect foreground subtraction. Our results have
important implications for assessing the detectability of SGWB from non-CBC
origins for ground-based GW detectors.
Stochastic gravitational-wave (GW) background (SGWB) research has made significant progress with the recent evidence of SGWB by pulsar timing arrays in the nanohertz band. However, ground-based GW detectors face challenges in detecting the SGWB due to loud GW events from compact binary coalescences (CBCs) that can mask the background signals. In this study, we explore the potential of detecting the astrophysical and cosmological SGWB with non-CBC origins by subtracting foreground signals of loud CBC events, building on previous studies by Sachdev et al. (2020) and Zhou et al. (2023).
Incorporating Aligned Spin Parameters
A significant contribution of our study is the inclusion of aligned spin parameters in our waveform model. By incorporating spins, we obtain more pessimistic results compared to previous work. In fact, the residual energy density of the foreground after subtraction is found to be even larger than the original background. This indicates a strong degeneracy between the spin parameters and symmetric mass ratio in the parameter estimation process, which hampers the effectiveness of foreground subtraction.
Implications for Detectability
The results of our study have important implications for the detectability of SGWB from non-CBC origins for ground-based GW detectors. The imperfect foreground subtraction due to the degeneracy between spin parameters and symmetric mass ratio challenges the accurate determination of the background signal. This suggests that future efforts in detecting the astrophysical and cosmological SGWB will require careful consideration of these challenges.
Roadmap for Future Research
Based on our findings, a roadmap for future research in the field of SGWB detection can be outlined:
- Investigating Improved Foreground Subtraction Techniques: Addressing the degeneracy between spin parameters and symmetric mass ratio is crucial in improving the accuracy of foreground subtraction. Research should focus on developing techniques that can effectively disentangle these parameters to enhance the detectability of the SGWB.
- Refining Waveform Models: Further refinement of waveform models is necessary to account for the impact of spins on the foreground subtraction process. Incorporating more accurate and comprehensive models will help in obtaining realistic estimates of the residual energy density after foreground subtraction.
- Experimental Validation: The effectiveness of improved foreground subtraction techniques and refined waveform models should be experimentally validated using next-generation ground-based GW detectors. Extensive tests and comparisons with simulated data can provide valuable insights into their performance and limitations.
- Expanding Data Analysis Methods: Exploring alternative data analysis methods that can mitigate the challenges posed by loud GW events from CBCs is another avenue for future research. Investigating novel approaches and algorithms may enable more accurate discrimination between foreground signals and the SGWB.
Conclusion
The incorporation of aligned spin parameters in our study highlights the challenges of detecting the astrophysical and cosmological SGWB with non-CBC origins using ground-based GW detectors. The degeneracy between spin parameters and symmetric mass ratio poses a significant hurdle in achieving accurate foreground subtraction. Nevertheless, future research focusing on improving foreground subtraction techniques, refining waveform models, experimental validation, and exploring alternative data analysis methods is expected to pave the way for enhanced detectability of the SGWB.