QCD Axion Dark Matter in String Theory: Haloscopes and Helioscopes as Probes of the Landscape (2407.07143v2)

Abstract: Laboratory experiments have the capacity to detect the QCD axion in the next decade, and precisely measure its mass, if it composes the majority of the dark matter. In type IIB string theory on Calabi-Yau threefolds in the geometric regime, the QCD axion mass, $m_a$, is strongly correlated with the topological Hodge number $h^{1,1}$. We compute $m_a$ in a scan of $185{,}965$ compactifications of type IIB string theory on toric hypersurface Calabi-Yau threefolds. We compute the range of $h^{1,1}$ probed by different experiments under the condition that the QCD axion can provide the observed dark matter density with minimal fine-tuning. Taking the experiments DMRadio, ADMX, MADMAX, and BREAD as indicative on different mass ranges, the $h^{1,1}$ distributions peak near $h^{1,1}=24.9, \ 65.4, \ 196.8,$ and $310.9,$ respectively. We furthermore conclude that, without severe fine tuning, detection of the QCD axion as dark matter \emph{at any mass} disfavours 80% of models with $h^{1,1} =491$, which is thought to have the most known Calabi-Yau threefolds. Measurement of the solar axion mass with IAXO is the dominant probe of all models with $h^{1,1}\gtrsim 250$. This study demonstrates the immense importance of axion detection in experimentally constraining the string landscape.

• The paper establishes a strong correlation between QCD axion mass and Calabi-Yau topology by analyzing 185,965 compactifications.
• The paper evaluates axion detection experiments (DMRadio, ADMX, MADMAX, BREAD, IAXO) to determine their mass sensitivity ranges.
• The paper shows that detecting QCD axions can constrain the string landscape, potentially disfavoring about 80% of models with h^(1,1)=491.

Overview of "QCD Axion Dark Matter in String Theory: Haloscopes and Helioscopes as Probes of the Landscape"

The paper at hand explores exploring the role of the quantum chromodynamics (QCD) axion within the framework of string theory, specifically focusing on its detection potential by various experimental setups and its implications for the string theory landscape. It systematically evaluates the QCD axion's properties in the context of type IIB string theory compactifications on Calabi-Yau threefolds and examines how these theoretical constructs could be constrained by current and future axion detection experiments.

Key Contributions

The paper presents several notable contributions that are critical for researchers interested in the intersection of string theory, particle physics, and cosmology:

1. Correlation between Axion Mass and Calabi-Yau Topology: The authors compute the QCD axion mass across a substantial set of 185,965 compactifications, establishing a strong correlation between the axion mass and the topological Hodge number $h^{1,1}$ of the Calabi-Yau threefolds. This correlation is pivotal in predicting the mass range of axions based on string theory models.
2. Experimental Probes and Axion Detection: The paper evaluates several axion detection experiments (DMRadio, ADMX, MADMAX, BREAD, and IAXO) within the theoretical framework. It identifies the mass sensitivity range of these experiments and associates them with the probability distribution of $h^{1,1}$, demonstrating how these experiments could significantly narrow down the viable string theory models.
3. Constraints on the String Landscape: A critical conclusion is that the detection of QCD axions would significantly constrain the string theory landscape. Notably, the paper finds that if no severe fine-tuning is allowed, the detection at a given mass disfavors about 80% of the models with $h^{1,1} = 491$, a value indicative of the most populous Calabi-Yau threefolds in the landscape.

Implications and Future Directions

The implications of this research extend both theoretically and practically. On a theoretical level, it provides a framework for understanding how string theory compactifications might be limited by experimental findings, thereby bridging high-energy physics with cosmological observations. Specifically, it highlights the ability of axion experiments to function as probes into the extra-dimensional spaces postulated by string theory.

Practically, the findings underscore the significance of the ongoing and future axion search experiments. For instance, resonant cavity experiments like ADMX that succeeded in reaching sensitivity needed to test models from the 1980s highlight the evolving nature of the experimental landscape. Other experiments, such as IAXO, which focuses on solar axions, offer complementary avenues of probing these theoretical predictions with different interaction mechanisms.

The research also points to potential future developments in theoretical physics. The possibility of post-inflation scenarios, where axion physics allows for phenomena like cosmic string decays to explain dark matter, hints at a rich tapestry of astrophysical signatures. Such avenues suggest further investigation into open and closed string sectors to validate or refute these scenarios.

Conclusion

This paper constitutes a comprehensive effort to link the theoretical predictions of string theory with tangible outcomes in experimental axion physics. Its integration of complex multi-dimensional calculations with practical experimental constraints affords a refined understanding of how high-energy theoretical models could be realized or refuted through disciplined experimental inquiry. As the experimental frontier advances, this research serves as a crucial reference point for interpreting potential findings in the search for axions, further informing the dialogue between theory and experiment in the quest to understand dark matter and fundamental physics.