152174 20251017144550.0 doi 10.1103/PhysRevD.111.064020 sideral 143445 ART-2025-143445 eng Asorey, Manuel Universidad de Zaragoza (orcid)0000-0003-3669-6241 Stability of cosmological singularity-free solutions in quadratic gravity 2025 We introduce a large family of homogeneous and isotropic cosmological solutions in quadratic gravity which are singularity-free at early and late times. This kind of smooth solutions only emerge beyond the nonstandard de Sitter branch 3⁢ <, and being the couplings of the 2 and −2 ⁢ terms. We have analyzed the stability of these singularity-free solutions by computing the second-order variation of the action. We show that the expected instability is similar to that of the standard Λ Cold Dark Matter (Λ CDM) scenario. Thus, they provide cosmological background scenarios as legitimate as that of the Standard Model. The complete analysis shows that a singular big bang scenario can emerge from a singularity-free cosmological scenario when the parameters of the theory are slightly modified, which provides a bridge between the two very different cosmological scenarios with similar instabilities. info:eu-repo/grantAgreement/ES/DGA-FSE/E21-17R info:eu-repo/grantAgreement/ES/DGIID-DGA/2020-E21-17R info:eu-repo/grantAgreement/ES/MICINN/PGC2022-126078NB-C21 info:eu-repo/grantAgreement/ES/NextGenerationEU/PRTR info:eu-repo/semantics/closedAccess by https://creativecommons.org/licenses/by/4.0/deed.es info:eu-repo/semantics/article info:eu-repo/semantics/acceptedVersion Ezquerro, Fernando Universidad de Zaragoza Pardina, Miguel Universidad de Zaragoza 2004 X Universidad de Zaragoza Dpto. Física Teórica Área Administrativa 2004 405 Universidad de Zaragoza Dpto. Física Teórica Área Física Teórica 111, 6 (2025), 9 pp. Phys. rev. D Physical Review D 2470-0010 1235357 http://zaguan.unizar.es/record/152174/files/texto_completo.pdf Postprint 2841556 http://zaguan.unizar.es/record/152174/files/texto_completo.jpg?subformat=icon icon Postprint oai:zaguan.unizar.es:152174 articulos driver 2025-10-17-14:11:35 ARTICLE