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Dark bubble cosmology and the equivalence principle

Ivano Basile1,*, Alessandro Borys2,†, and Joaquin Masias1,‡

  • *Contact author: ibasile@mpp.mpg.de
  • †Contact author: alessandro.borys@dfa.unict.it
  • ‡Contact author: jmasias@mpp.mpg.de
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Phys. Rev. D 113, 026009 – Published 13 January, 2026

DOI: https://doi.org/10.1103/qm3b-kpm8

Abstract

The main goal of string phenomenology is to find realistic models of particle physics and cosmology within string theory. Dark bubble cosmology is an alternative to string compactifications, where our Universe lives on a bubble expanding in a higher-dimensional spacetime. This construction is inherently nonsupersymmetric and can yield a four-dimensional realistic cosmology, where radiation behaves as expected due to its coupling to higher-dimensional fields. We study the coupling of the electroweak and strong sectors to the induced braneworld gravity via the same mechanism. While the electroweak sector is unaffected, the gravitational and inertial masses of the proton differ significantly, severely violating measurements of the equivalence principle.

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Phys. Rev. D 113, 026009– Published 13 January, 2026
  • Received 26 August 2025
  • Accepted 9 December 2025
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