Conversations in the Dark: Using Cross-Correlation of Cosmic Birefringence and Large-Scale Structure to Constrain Axion-Like Particles

Core Concepts

Cross-correlating cosmic birefringence with galaxy distribution data offers a novel and potentially powerful method for constraining the properties of ultralight axion-like particles, particularly in the mass range where they could contribute to dark energy.

Abstract

Bibliographic Information:

Arcari, S., Bartolo, N., Greco, A., Gruppuso, A., Lattanzi, M., & Natoli, P. (2024). Conversations in the dark: cross-correlating birefringence and LSS to constrain axions. Journal of Cosmology and Astroparticle Physics. Retrieved from https://arxiv.org/abs/2407.02144v2

Research Objective:

This research paper investigates the potential of using the cross-correlation between cosmic birefringence and galaxy number counts to constrain the properties of ultralight axion-like particles (ALPs).

Methodology:

The authors utilize a modified version of the Boltzmann code CLASS, incorporating an early dark energy model for ALPs with a cosine-like potential. They calculate the cross-correlation signal between anisotropic birefringence and galaxy counts, considering various ALP masses, initial misalignment angles, and axion-photon couplings. The study focuses on ultralight ALPs with masses between 10^-33 eV and 10^-28 eV, exploring their potential impact on cosmic birefringence and its correlation with the large-scale structure traced by galaxies.

Key Findings:

• The cross-correlation signal is particularly sensitive to ultralight ALPs, with masses around 10^-32 eV, as their late-time evolution aligns with the epoch of galaxy formation.
• The amplitude of the cross-correlation increases with larger initial misalignment angles and stronger axion-photon couplings.
• For specific ALP parameters, the signal-to-noise ratio of the cross-correlation can exceed that of the birefringence auto-correlation, highlighting its potential as a powerful probe.

Main Conclusions:

The study demonstrates that cross-correlating cosmic birefringence with galaxy distribution data from future surveys like Euclid, combined with CMB polarization data from missions like CMB-S4, Simons Observatory, and LiteBIRD, offers a promising avenue for constraining the properties of ultralight ALPs and probing their potential role as dark energy candidates.

Significance:

This research introduces a novel approach to constrain axion-like particles, which are strong candidates for dark matter and dark energy, by combining two independent cosmological probes: cosmic birefringence and galaxy clustering. This method has the potential to significantly enhance our understanding of fundamental physics and the nature of dark energy.

Limitations and Future Research:

The study primarily focuses on a specific type of ALP potential and a simplified, non-tomographic approach for galaxy distribution. Future research could explore the impact of different ALP potentials, incorporate redshift tomography for a more detailed analysis, and investigate the potential synergy with other cosmological probes to further refine constraints on ALP parameters.

Stats

The study focuses on ultralight axions with masses (mϕ) in the range of 10^-33 eV to 10^-28 eV.
The upper bound for the axion-photon coupling (gγ) considered is 10^-12 GeV^-1.
The analysis utilizes a single redshift bin extending up to z = 2.5 for the galaxy distribution.
The forecast sky fraction for Euclid's DR3 used in the analysis is 36%.
The average number of galaxies per angular volume projected for Euclid is assumed to be 30 arcmin^-2.

Quotes

Key Insights Distilled From

Conversations in the dark: cross-correlating birefringence and LSS to constrain axions

by S. Arcari, N... at arxiv.org 11-05-2024

https://arxiv.org/pdf/2407.02144.pdf

Deeper Inquiries

How might the inclusion of data from other upcoming galaxy surveys, such as DESI or SPHEREx, further enhance the constraints on ALP parameters obtained through this cross-correlation technique?

Including data from upcoming galaxy surveys like DESI and SPHEREx could significantly enhance the constraints on ALP parameters obtained through this cross-correlation technique. Here's how:

Increased Sky Coverage and Redshift Range: DESI and SPHEREx will map a larger fraction of the sky and probe a wider redshift range compared to Euclid alone. This broader coverage would allow for a more comprehensive exploration of the cross-correlation signal across different cosmic epochs, potentially revealing subtle variations that could be linked to ALP properties.

Complementary Redshift Tomography: Each survey has a unique redshift distribution of observed galaxies. Combining data from multiple surveys would enable a more refined tomographic analysis, effectively slicing the Universe into finer redshift bins. This would enhance our ability to disentangle the evolution of the birefringence signal and its correlation with galaxy clustering across cosmic time, leading to tighter constraints on ALP parameters like mass ($m_{\phi}$) and initial misalignment angle ($\theta_i$).

Improved Statistical Power: The combination of data from multiple surveys would significantly increase the statistical power of the analysis. This would be particularly beneficial for constraining ALP models that produce weak cross-correlation signals, as the increased signal-to-noise ratio would make it easier to distinguish these faint signatures from statistical fluctuations.

Cross-Validation and Systematic Error Mitigation: Comparing results obtained from independent surveys can help cross-validate the findings and mitigate systematic errors inherent to each individual survey. This cross-validation would strengthen the robustness of the constraints on ALP parameters derived from the cross-correlation analysis.
In essence, the complementary strengths of DESI, SPHEREx, and Euclid would provide a more comprehensive and robust dataset for probing ALP-induced cosmic birefringence. This synergy would be instrumental in pushing the boundaries of our understanding of axion-like particles and their role in the Universe.

Could interactions between ALPs and other hypothetical particles, beyond the standard model of particle physics, potentially alter the predicted cross-correlation signal and complicate the interpretation of the results?

Yes, interactions between ALPs and other hypothetical particles beyond the Standard Model could indeed alter the predicted cross-correlation signal and introduce complexities in interpreting the results. Here's why:

Modified ALP Dynamics: Interactions with new particles could modify the equations of motion governing the ALP field. This could lead to changes in the ALP's background evolution, its perturbations, and consequently, its impact on cosmic birefringence. For instance, new interactions could influence the onset of ALP oscillations, their effective mass, or introduce additional damping effects, all of which would leave distinct imprints on the birefringence signal.

Additional Cosmological Effects: These hypothetical particles, if they couple to other sectors like dark matter or dark energy, could induce additional cosmological effects that might be correlated with the ALP-induced birefringence. Disentangling these intertwined signals would be challenging and require careful modeling of the interplay between ALPs and these new particles.

Degeneracies in Parameter Space: Interactions with new particles could introduce degeneracies in the ALP parameter space. This means that different combinations of ALP parameters and the coupling strengths of these new interactions could potentially produce similar cross-correlation signals. Resolving such degeneracies would necessitate complementary probes and a deeper understanding of the underlying particle physics model.

Energy Injection and Thermal History: Interactions between ALPs and other particles could lead to energy injection into the early Universe, potentially altering the thermal history and affecting cosmological observables like the Cosmic Microwave Background. These modifications could complicate the interpretation of the cross-correlation signal, as they might mimic or mask the effects of ALPs.
Therefore, while the cross-correlation technique offers a promising avenue for constraining ALPs, it's crucial to acknowledge that the presence of new physics beyond the Standard Model could significantly impact the signal. Careful analysis, robust modeling, and complementary probes will be essential to disentangle the effects of ALPs from those of other hypothetical particles and gain a clearer understanding of their role in the Universe.

If this method successfully identifies the presence of ALPs and constrains their properties, what broader implications might this discovery have for our understanding of the early universe and the fundamental laws of physics?

If this cross-correlation method successfully identifies the presence of ALPs and constrains their properties, it would have profound implications for our understanding of the early Universe and fundamental physics:

New Physics Beyond the Standard Model: The discovery of ALPs would be a definitive confirmation of physics beyond the Standard Model, opening up new avenues of research in particle physics. It would necessitate extensions to our current theoretical frameworks and could provide crucial insights into the nature of dark matter, dark energy, and the unification of fundamental forces.

Insights into the Strong CP Problem: ALPs, particularly those arising from the Peccei-Quinn mechanism, offer a compelling solution to the strong CP problem in quantum chromodynamics. Constraining their properties would provide valuable clues about the validity of this solution and the nature of CP violation in the early Universe.

Probing Cosmic Inflation and Early Dark Energy: The presence of ALPs and their potential role as early dark energy could offer new ways to probe the physics of cosmic inflation. Their interactions and evolution during this epoch could leave imprints on cosmological observables, providing a unique window into the very first moments of the Universe.

Understanding the Nature of Dark Matter: ALPs are well-motivated dark matter candidates. If their presence is confirmed and their properties constrained, it would significantly impact our understanding of dark matter's production mechanisms, abundance, and distribution in the Universe.

Testing Fundamental Symmetries: The parity-violating nature of ALP-photon interactions, leading to cosmic birefringence, provides a unique opportunity to test fundamental symmetries in the early Universe. Precise measurements of birefringence could reveal subtle violations of parity, offering insights into the fundamental laws governing particle interactions.

Constraining String Theory and the Axiverse: ALPs are a generic prediction of string theory. Their discovery would lend credence to string theory and the existence of a vast landscape of axion-like particles, known as the "axiverse." Constraining their properties would provide valuable input for string theory model building and our understanding of the fundamental building blocks of nature.
In conclusion, the successful identification and characterization of ALPs through this cross-correlation technique would be a groundbreaking achievement. It would not only deepen our understanding of the early Universe and fundamental physics but also pave the way for new discoveries and a more complete picture of the cosmos.