{"status":"ok","message-type":"work","message-version":"1.0.0","message":{"indexed":{"date-parts":[[2025,10,11]],"date-time":"2025-10-11T02:56:52Z","timestamp":1760151412543,"version":"build-2065373602"},"reference-count":21,"publisher":"MDPI AG","issue":"3","license":[{"start":{"date-parts":[[2022,3,4]],"date-time":"2022-03-04T00:00:00Z","timestamp":1646352000000},"content-version":"vor","delay-in-days":0,"URL":"https:\/\/creativecommons.org\/licenses\/by\/4.0\/"}],"content-domain":{"domain":[],"crossmark-restriction":false},"short-container-title":["Universe"],"abstract":"<jats:p>The Big Bang initial singularity problem can be solved by means of bouncing solutions. In the context of extended theories of gravity, we will look for covariant effective actions whose field equations contain up to fourth-order derivatives of the metric tensor. In finding such bouncing solutions, we will make use of an order reduction technique based on a perturbative approach. Reducing the order of the field equations to second-order, we are able to find solutions which are perturbatively close to General Relativity. We will build the covariant effective actions of the resulting order reduced theories.<\/jats:p>","DOI":"10.3390\/universe8030161","type":"journal-article","created":{"date-parts":[[2022,3,6]],"date-time":"2022-03-06T20:40:38Z","timestamp":1646599238000},"page":"161","update-policy":"https:\/\/doi.org\/10.3390\/mdpi_crossmark_policy","source":"Crossref","is-referenced-by-count":5,"title":["Bouncing Cosmology in Fourth-Order Gravity"],"prefix":"10.3390","volume":"8","author":[{"ORCID":"https:\/\/orcid.org\/0000-0003-0397-2705","authenticated-orcid":false,"given":"Marcello","family":"Miranda","sequence":"first","affiliation":[{"name":"Scuola Superiore Meridionale, Largo San Marcellino 10, 80138 Napoli, Italy"},{"name":"INFN Sez. di Napoli, Complesso Universitario di Monte Sant\u2019Angelo, Edificio G, Via Cinthia, 80126 Napoli, Italy"}]},{"ORCID":"https:\/\/orcid.org\/0000-0003-4379-2549","authenticated-orcid":false,"given":"Daniele","family":"Vernieri","sequence":"additional","affiliation":[{"name":"INFN Sez. di Napoli, Complesso Universitario di Monte Sant\u2019Angelo, Edificio G, Via Cinthia, 80126 Napoli, Italy"},{"name":"Dipartimento di Fisica \u201cE. Pancini\u201d, Universit\u00e0 di Napoli \u201cFederico II\u201d, Complesso Universitario di Monte Sant\u2019Angelo, Edificio G, Via Cinthia, 80126 Napoli, Italy"}]},{"given":"Salvatore","family":"Capozziello","sequence":"additional","affiliation":[{"name":"Scuola Superiore Meridionale, Largo San Marcellino 10, 80138 Napoli, Italy"},{"name":"INFN Sez. di Napoli, Complesso Universitario di Monte Sant\u2019Angelo, Edificio G, Via Cinthia, 80126 Napoli, Italy"},{"name":"Dipartimento di Fisica \u201cE. Pancini\u201d, Universit\u00e0 di Napoli \u201cFederico II\u201d, Complesso Universitario di Monte Sant\u2019Angelo, Edificio G, Via Cinthia, 80126 Napoli, Italy"},{"name":"Laboratory of Theoretical Cosmology, International Centre of Gravity and Cosmos, Tomsk State University of Control Systems and Radioelectronics (TUSUR), 634050 Tomsk, Russia"}]},{"ORCID":"https:\/\/orcid.org\/0000-0002-9388-8373","authenticated-orcid":false,"given":"Francisco S. N.","family":"Lobo","sequence":"additional","affiliation":[{"name":"Instituto de Astrof\u00edsica e Ci\u00eancias do Espaco, Faculdade de Ci\u00eancias da Universidade de Lisboa, Edif\u00edcio C8, Campo Grande, 1749-016 Lisbon, Portugal"},{"name":"Departamento de F\u00edsica, Faculdade de Ci\u00eancias, Universidade de Lisboa, Edif\u00edcio C8, Campo Grande, 1749-016 Lisbon, Portugal"}]}],"member":"1968","published-online":{"date-parts":[[2022,3,4]]},"reference":[{"key":"ref_1","doi-asserted-by":"crossref","first-page":"213001","DOI":"10.1088\/0264-9381\/28\/21\/213001","article-title":"Loop Quantum Cosmology: A Status Report","volume":"28","author":"Ashtekar","year":"2011","journal-title":"Class. Quant. Grav."},{"key":"ref_2","doi-asserted-by":"crossref","first-page":"213001","DOI":"10.1088\/0264-9381\/29\/21\/213001","article-title":"Quantum Cosmology: Effective Theory","volume":"29","author":"Bojowald","year":"2012","journal-title":"Class. Quant. 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