UV Luminosity Functions from HST and JWST: A Possible Resolution to the High-Redshift Galaxy Abundance Puzzle and Implications for Cosmic Strings

UV Luminosity Functions from HST and JWST: A Possible Resolution to the High-Redshift Galaxy Abundance Puzzle and Implications for Cosmic Strings. Blamart, M., Liu, A., Brandenberger, R., Muñoz, J. B., & Cyr, B. December, 2025. arXiv:2512.09980 [astro-ph]

Paper doi abstract bibtex

Recent observations of high redshift galaxies by the James Webb Space Telescope suggest the presence of a bright population of galaxies that is more abundant than predicted by most galaxy formation models. These observations have led to a rethinking of these models, and numerous astrophysical and cosmological solutions have been proposed, including cosmic strings, topological defects that may be remnants of a specific phase transition in the very early moments of the Universe. In this paper, we integrate cosmic strings, a source of nonlinear and non-Gaussian perturbations, into the semi analytical code Zeus21, allowing us to efficiently predict the ultraviolet luminosity function (UVLF). We conduct a precise study of parameter degeneracies between star-formation astrophysics and cosmic-string phenomenology. Our results suggest that cosmic strings can boost the early-galaxy abundance enough to explain the measured UVLFs from the James Webb and Hubble Space Telescopes from redshift z = 4 to z = 17 without modifying the star-formation physics. In addition, we set a new upper bound on the string tension of $Gμ{\}lessapprox 10{\textasciicircum}\{-8\}$ ($95{\}%$ credibility), improving upon previous limits from the cosmic microwave background. Although with current data there is some level of model and prior dependence to this limit, it suggests that UVLFs are a promising avenue for future observational constraints on cosmic-string physics.

@misc{blamart_uv_2025,
	title = {{UV} {Luminosity} {Functions} from {HST} and {JWST}: {A} {Possible} {Resolution} to the {High}-{Redshift} {Galaxy} {Abundance} {Puzzle} and {Implications} for {Cosmic} {Strings}},
	shorttitle = {{UV} {Luminosity} {Functions} from {HST} and {JWST}},
	url = {http://arxiv.org/abs/2512.09980},
	doi = {10.48550/arXiv.2512.09980},
	abstract = {Recent observations of high redshift galaxies by the James Webb Space Telescope suggest the presence of a bright population of galaxies that is more abundant than predicted by most galaxy formation models. These observations have led to a rethinking of these models, and numerous astrophysical and cosmological solutions have been proposed, including cosmic strings, topological defects that may be remnants of a specific phase transition in the very early moments of the Universe. In this paper, we integrate cosmic strings, a source of nonlinear and non-Gaussian perturbations, into the semi analytical code Zeus21, allowing us to efficiently predict the ultraviolet luminosity function (UVLF). We conduct a precise study of parameter degeneracies between star-formation astrophysics and cosmic-string phenomenology. Our results suggest that cosmic strings can boost the early-galaxy abundance enough to explain the measured UVLFs from the James Webb and Hubble Space Telescopes from redshift z = 4 to z = 17 without modifying the star-formation physics. In addition, we set a new upper bound on the string tension of \$Gμ{\textbackslash}lessapprox 10{\textasciicircum}\{-8\}\$ (\$95{\textbackslash}\%\$ credibility), improving upon previous limits from the cosmic microwave background. Although with current data there is some level of model and prior dependence to this limit, it suggests that UVLFs are a promising avenue for future observational constraints on cosmic-string physics.},
	language = {en},
	urldate = {2025-12-18},
	publisher = {arXiv},
	author = {Blamart, Mattéo and Liu, Adrian and Brandenberger, Robert and Muñoz, Julian B. and Cyr, Bryce},
	month = dec,
	year = {2025},
	note = {arXiv:2512.09980 [astro-ph]},
	keywords = {Astrophysics - Astrophysics of Galaxies, Astrophysics - Cosmology and Nongalactic Astrophysics, General Relativity and Quantum Cosmology, High Energy Physics - Phenomenology, High Energy Physics - Theory},
}

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