A New Class of Chiral U(1)X Symmetries and Their Phenomenological Implications

Core Concepts

This paper proposes a new class of chiral U(1)X symmetries, dubbed "Dark Hypercharge" symmetries, to address the limitations of the Standard Model in explaining phenomena like dark matter.

Abstract

Bibliographic Information:

Prajapati, H., & Srivastava, R. (2024). The Dark HyperCharge Symmetry. arXiv preprint arXiv:2411.02512v1.

Research Objective:

This paper explores new chiral solutions for U(1)X extensions of the Standard Model (SM) to address the shortcomings of the SM in explaining phenomena like dark matter. The research aims to introduce and analyze a new class of U(1)X symmetries, termed "Dark Hypercharge" (DHC) symmetries, and investigate their phenomenological implications.

Methodology:

The authors systematically investigate potential chiral solutions for gauge anomaly cancellation in U(1)X extensions of the SM. They consider scenarios where one, two, or all three generations of SM fermions are charged under the U(1)X symmetry. Anomaly cancellation conditions are used to determine the U(1)X charges of both SM and new dark fermions. The study analyzes the viability of the lightest dark fermion as a dark matter candidate and explores collider constraints on the Z′ gauge boson associated with the DHC symmetry.

Key Findings:

• The study introduces a new class of chiral U(1)X symmetries, termed "Dark Hypercharge" (DHC) symmetries, where SM fermions have different left- and right-handed charges.
• Anomaly cancellation under DHC symmetries necessitates the introduction of three SM gauge singlet dark fermions.
• The U(1)X charges of these dark fermions are uniquely determined by anomaly cancellation conditions.
• The lightest dark fermion is identified as a potential dark matter candidate.
• The Z′ gauge boson mediates interactions between the dark and visible sectors.
• Analysis of a benchmark DHC model demonstrates that the lightest dark fermion satisfies current dark matter constraints over a wide mass range.

Main Conclusions:

The research proposes that DHC symmetries offer a viable extension to the SM, potentially addressing the limitations of the SM in explaining dark matter. The study highlights the connection between the dark and visible sectors through the Z′ gauge boson and demonstrates the viability of the lightest dark fermion as a dark matter candidate.

Significance:

This research contributes significantly to the field of particle physics by proposing a new class of chiral U(1)X symmetries and exploring their potential to address the limitations of the Standard Model. The study's findings on dark matter candidates and their interactions with the visible sector have significant implications for understanding the nature of dark matter and its role in the universe.

Limitations and Future Research:

The study focuses on a specific benchmark DHC model. Further research could explore a wider range of DHC models and their phenomenological implications. Additionally, investigating the potential signatures of DHC symmetries at future collider experiments would be valuable.

Stats

Quotes

"In this study, we systematically investigate potential chiral solutions and introduce entirely new classes of solutions for (a) one, (b) two, and (c) three generations of SM fermions that are charged under the U(1)X symmetry."
"These new fermions belong to the dark sector, with the lightest of them being a good dark matter candidate."
"Additionally, the Z′ gauge boson mediates interactions between the dark and visible sectors, and we call this U(1)X symmetry as the “Dark HyperCharge” symmetry."

Key Insights Distilled From

The Dark HyperCharge Symmetry

by Hemant Praja... at arxiv.org 11-06-2024

https://arxiv.org/pdf/2411.02512.pdf

Deeper Inquiries

How do the proposed Dark Hypercharge symmetries compare to other proposed extensions of the Standard Model, such as supersymmetry or extra dimensions, in terms of their potential to explain dark matter and other unexplained phenomena?

Dark Hypercharge (DHC) symmetries, as described in the context, offer a compelling avenue for extending the Standard Model (SM) and addressing some of its limitations, particularly concerning dark matter. Here's a comparative analysis of DHC symmetries against other popular SM extensions:
DHC Symmetries:

Strengths:

Simplicity: DHC extensions are conceptually straightforward, introducing a new U(1)X gauge symmetry with relatively minimal additions to the particle content.
Dark Matter Candidate: The lightest dark fermion (DF) naturally arises as a potential dark matter candidate, stabilized by the DHC symmetry.
Testable Predictions: DHC models predict a new gauge boson, Z', which mediates interactions between the dark and visible sectors. This Z' boson, along with the DFs, could be observed in collider experiments like the LHC.

Limitations:

Specifics Depend on Model Parameters: The exact nature of dark matter, its interactions, and potential observational signatures are highly dependent on the specific choice of DHC charges and the masses of the new particles.
Other SM Issues: DHC symmetries primarily address dark matter and may not directly solve other SM shortcomings like the hierarchy problem or neutrino masses, although they could potentially be incorporated into larger frameworks that do.
Supersymmetry (SUSY):

Strengths:

Elegant Framework: SUSY offers an elegant solution to the hierarchy problem by introducing supersymmetric partners for all SM particles.
Dark Matter Candidate: The lightest supersymmetric particle (LSP) is often stable and can serve as a dark matter candidate.

Limitations:

Complexity: SUSY significantly expands the particle content and introduces many new parameters, making it challenging to test experimentally.
Lack of Definitive Evidence: Despite extensive searches, no supersymmetric particles have been observed so far, putting constraints on SUSY models.
Extra Dimensions:

Strengths:

Novel Approach: Extra dimensions provide a fundamentally different perspective on space-time and can address the hierarchy problem.
Variety of Models: Extra-dimensional models offer a rich phenomenology, with potential implications for dark matter, gravity, and other fundamental forces.

Limitations:

Difficult to Test: Direct experimental verification of extra dimensions is extremely challenging due to the high energies involved.
Theoretical Challenges: Constructing consistent and stable extra-dimensional models can be theoretically demanding.
Comparison:
DHC symmetries, compared to SUSY or extra dimensions, offer a more focused approach to explaining dark matter. They are relatively simpler and provide more direct testable predictions at colliders. However, they may not address other SM issues as comprehensively as SUSY or extra dimensions. The choice of the "best" extension ultimately depends on which experimental signatures are observed and the theoretical elegance one prioritizes.

Could the DHC symmetries and the associated dark fermions have implications for other areas of cosmology or astrophysics, such as the formation of large-scale structures or the cosmic microwave background radiation?

Yes, DHC symmetries and their associated dark fermions could potentially have significant implications for various cosmological and astrophysical phenomena beyond just explaining dark matter. Here are some possible avenues:

Large-Scale Structure Formation: The presence of dark fermions, especially if they interact with each other through a new force mediated by the Z' boson, could influence the formation of large-scale structures in the universe. These interactions could lead to:

Modified Dark Matter Halos: DFs might form halos around galaxies with different density profiles compared to standard cold dark matter scenarios.
Impact on Cosmic Web: The interactions between DFs could affect the formation and evolution of the cosmic web, the large-scale network of filaments and voids observed in the universe.

Cosmic Microwave Background (CMB): The CMB provides a snapshot of the early universe, and any new physics interacting at that time could leave its imprint on the CMB:

DF Annihilations: If DFs were abundant in the early universe and could annihilate into SM particles, the energy released could modify the CMB temperature and polarization power spectra.
Z' Interactions: Interactions mediated by the Z' boson in the early universe could also potentially affect the CMB, although the details would depend on the specific DHC model.

Other Potential Implications:

Early Universe Phase Transitions: DHC symmetry breaking could have driven phase transitions in the early universe, potentially leaving observable relics.
Dark Matter Self-Interactions: Self-interacting dark matter models, where DFs interact with each other, are of significant interest, and DHC symmetries could provide a framework for such scenarios.
Observational Constraints and Future Prospects:
Current cosmological observations, particularly from the CMB, already place stringent constraints on new physics beyond the SM. Any DHC model must be consistent with these observations. However, future cosmological surveys with increased sensitivity, such as those mapping the large-scale structure in more detail, could potentially detect the subtle effects of DHC symmetries and their associated dark fermions.

If the lightest dark fermion is indeed a good dark matter candidate, what would be the implications for the search for dark matter through direct and indirect detection experiments?

If the lightest dark fermion (DF) within a DHC model is indeed the dominant component of dark matter, it would have profound implications for both direct and indirect detection experiments:
Direct Detection:

Z' Mediated Interactions: The Z' boson, mediating interactions between DFs and SM particles, becomes crucial. The strength of these interactions, determined by the DHC charges and the Z' mass, dictates the direct detection prospects.

Enhanced Signals: If the Z' is relatively light and the couplings are not too suppressed, DHC models could predict significantly enhanced direct detection signals compared to scenarios with only weakly interacting massive particles (WIMPs).
New Detection Channels: Depending on the DHC model, the Z' could facilitate interactions with quarks, potentially leading to observable signals in experiments like XENONnT and LUX-ZEPLIN.

Nuclear Recoil Signatures: Direct detection experiments typically search for nuclear recoils resulting from dark matter particles scattering off atomic nuclei. The mass of the lightest DF and its interaction cross-section with nucleons would determine the energy range and event rate expected in these experiments.
Indirect Detection:

DF Annihilations: Indirect detection experiments look for the annihilation products of dark matter particles. DHC models could lead to distinctive signatures:

Z' Resonance: If kinematically allowed, DFs could annihilate into Z' bosons, which would subsequently decay into SM particles. This could produce a characteristic spectral feature at the Z' mass in indirect detection experiments like Fermi-LAT and CTA.
SM Particle Final States: DFs could also annihilate directly into SM particles, such as quarks, leptons, or gauge bosons, leading to excesses in cosmic rays, gamma rays, or neutrinos.

Astrophysical Targets: The distribution of dark matter in the Milky Way and other galaxies would influence the expected signals in indirect detection experiments.
Challenges and Opportunities:

Model Dependence: The specific predictions for direct and indirect detection depend heavily on the chosen DHC charges, the masses of the Z' and DFs, and the details of the dark sector.
Complementarity of Searches: Combining results from direct and indirect detection experiments, along with collider searches for the Z', would be crucial for constraining or discovering DHC dark matter.
The potential for enhanced signals and new detection channels makes DHC models an exciting prospect for the ongoing search for dark matter. These models highlight the importance of exploring a wide range of dark matter candidates and interaction types beyond the traditional WIMP paradigm.