Fractal Cosmos

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Published March 16, 2026 | Version 3.0.0
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Transient Domain-Wall Networks from Spontaneous Symmetry Breaking: A Unified Solution to the Hubble Tension and Nanohertz Gravitational Waves

Authors/Creators

  • 1. Independent Researcher

Description

Version 3 Update:

This version represents a major update to the manuscript, incorporating comprehensive technical refinements and supplementary materials for full reproducibility. Key updates include:

  • Numerical Implementation & Source Code: For the first time, the complete Python source code used for numerical simulations, background evolution solver, and figure generation (Figures 6, 7, and 8) is included as a supplementary archive.

  • Enhanced Theoretical Framework: Detailed derivations in the Appendices have been expanded to clarify the domain-wall tension calculation from the scalar field theory and the horizon scaling regime.

  • Bibliographic Refinement: The reference list has been thoroughly updated to include the latest 2024-2025 results from PTA collaborations (NANOGrav, EPTA) and current developments in modified Friedmann cosmologies.

  • Structural Improvements: Technical consistency checks regarding the Effective Field Theory (EFT) cutoff and vacuum bias mechanisms have been integrated to address potential referee inquiries.

Abstract:

We present a cosmological model where an initially symmetric two-field scalar sector undergoes spontaneous symmetry breaking, leading to the formation of a transient domain-wall network. Starting from a fundamental action, we derive the full background dynamics and show that the coarse-grained energy density of the network scales as $\rho_{DW} \propto H$ during a metastable scaling regime. This introduces a linear correction term in the Friedmann equation, generating a late-time enhancement of the expansion rate that can alleviate the Hubble tension. The same physical mechanism produces a stochastic gravitational-wave background during network decay, with a peak frequency in the nanohertz band accessible to pulsar timing arrays. We perform a covariant second-order perturbation analysis using the ADM formalism and demonstrate that isocurvature modes decay exponentially, ensuring consistency with cosmic microwave background constraints. The model contains $\Lambda$CDM as a continuous limit and predicts a correlated observational signature: a percent-level shift in $H_0$ implies a gravitational-wave amplitude $\Omega_{GW} \sim 10^{-9}-10^{-8}$ in the nHz band.

Files

Transient_Domain_Wall_Networks_from_Spontaneous_Symmetry_Breaking__A_Unified_Solution_to_the_Hubble_Tension_and_Nanohertz_Gravitational_Waves__22_.pdf

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Additional details

Related works

Is new version of
Preprint: 10.5281/zenodo.19007990 (DOI)

Dates

Updated
2026-03-16

Software

Programming language
Python
Development Status
Active

References

  • [1] P. Collaboration (Planck), Astron. Astrophys. 641, A6 (2020). [2] A. G. Riess et al. (SH0ES), Astrophys. J. Lett. 934, L7 (2022). [3] L. Verde, T. Treu, and A. G. Riess, Nature Astron. 3, 891 (2019). [4] V. Poulin, T. L. Smith, T. Karwal, and M. Kamionkowski, Phys. Rev. Lett. 122, 221301 (2019). [5] E. Di Valentino et al., Class. Quant. Grav. 38, 153001 (2021). [6] T. W. B. Kibble, J. Phys. A 9, 1387 (1976). [7] A. Vilenkin, Phys. Rept. 121, 263 (1985). [8] Y. B. Zeldovich, I. Y. Kobzarev, and L. B. Okun, Zh. Eksp. Teor. Fiz. 67, 3 (1974). [9] A. Vilenkin and E. P. S. Shellard, Cosmic Strings and Other Topological Defects (Cambridge University Press, 2000). [10] T. Hiramatsu, M. Kawasaki, and K. Saikawa, JCAP 02, 031. [11] K. Saikawa, Universe 3, 40 (2017). [12] G. Agazie et al. (NANOGrav), Astrophys. J. Lett. 951, L8 (2023). [13] J. Antoniadis et al. (EPTA), Astron. Astrophys. 678, A50 (2023). [14] D. J. Reardon et al., Astrophys. J. Lett. 951, L6 (2023). [15] C. J. A. P. Martins and E. P. S. Shellard, Phys. Rev. D 62, 023504 (2000). [16] P. P. Avelino, C. J. A. P. Martins, and J. C. R. E. Oliveira, Phys. Rev. D 72, 083506 (2005). [17] T. L. Smith, V. Poulin, and M. A. Amin, Phys. Rev. D 101, 063523 (2020). [18] J. Ellis et al., Phys. Rev. D 108, 103511 (2023). [19] C. Caprini and D. G. Figueroa, Class. Quant. Grav. 35, 163001 (2018). [20] C. Gordon, D. Wands, B. A. Bassett, and R. Maartens, Phys. Rev. D 63, 023506 (2000). [21] D. Wands, N. Bartolo, S. Matarrese, and A. Riotto, Phys. Rev. D 66, 043520 (2002). [22] A. A. Starobinsky, Lect. Notes Phys. 246, 107 (1986). [23] M. Sasaki, T. Tanaka, and K. Yamamoto, Phys. Rev. D 78, 083522 (2008). [24] R. D. Peccei and H. R. Quinn, Phys. Rev. Lett. 38, 1440 (1977). [25] J. E. Kim, Phys. Rev. Lett. 43, 103 (1979). [26] M. A. Shifman, A. I. Vainshtein, and V. I. Zakharov, Nucl. Phys. B 166, 493 (1980). [27] M. Dine, W. Fischler, and M. Srednicki, Phys. Lett. B 104, 199 (1981). [28] S. Alexander, Phys. Rev. D 65, 023507 (2001). [29] Z. Berezhiani, Int. J. Mod. Phys. A 19, 3775 (2004). [30] E. Witten, Phys. Lett. B 149, 351 (1984). [31] P. Svrcek and E. Witten, JHEP 06, 051. [32] A. Arvanitaki, S. Dimopoulos, S. Dubovsky, N. Kaloper, and J. March-Russell, Phys. Rev. D 81, 123530 (2010)