{"status":"ok","message-type":"work","message-version":"1.0.0","message":{"indexed":{"date-parts":[[2026,1,24]],"date-time":"2026-01-24T09:59:47Z","timestamp":1769248787620,"version":"3.49.0"},"reference-count":47,"publisher":"MDPI AG","issue":"4","license":[{"start":{"date-parts":[[2023,4,11]],"date-time":"2023-04-11T00:00:00Z","timestamp":1681171200000},"content-version":"vor","delay-in-days":0,"URL":"https:\/\/creativecommons.org\/licenses\/by\/4.0\/"}],"funder":[{"name":"Funda\u00e7\u00e3o para a Ci\u00eancia e a Tecnologia (FCT)","award":["UIDB\/04434\/2020"],"award-info":[{"award-number":["UIDB\/04434\/2020"]}]},{"name":"Funda\u00e7\u00e3o para a Ci\u00eancia e a Tecnologia (FCT)","award":["UIDP\/04434\/2020"],"award-info":[{"award-number":["UIDP\/04434\/2020"]}]},{"name":"Funda\u00e7\u00e3o para a Ci\u00eancia e a Tecnologia (FCT)","award":["CERN\/FIS-PAR\/0037\/2019"],"award-info":[{"award-number":["CERN\/FIS-PAR\/0037\/2019"]}]},{"name":"Funda\u00e7\u00e3o para a Ci\u00eancia e a Tecnologia (FCT)","award":["PTDC\/FIS-AST\/0054\/2021"],"award-info":[{"award-number":["PTDC\/FIS-AST\/0054\/2021"]}]}],"content-domain":{"domain":[],"crossmark-restriction":false},"short-container-title":["Universe"],"abstract":"<jats:p>General Relativity is an extremely successful theory, at least for weak gravitational fields; however, it breaks down at very high energies, such as in correspondence to the initial singularity. Quantum Gravity is expected to provide more physical insights in relation to this open question. Indeed, one alternative scenario to the Big Bang, that manages to completely avoid the singularity, is offered by Loop Quantum Cosmology (LQC), which predicts that the Universe undergoes a collapse to an expansion through a bounce. In this work, we use metric f(R) gravity to reproduce the modified Friedmann equations which have been obtained in the context of modified loop quantum cosmologies. To achieve this, we apply an order reduction method to the f(R) field equations, and obtain covariant effective actions that lead to a bounce, for specific models of modified LQC, considering a massless scalar field.<\/jats:p>","DOI":"10.3390\/universe9040181","type":"journal-article","created":{"date-parts":[[2023,4,12]],"date-time":"2023-04-12T01:35:08Z","timestamp":1681263308000},"page":"181","update-policy":"https:\/\/doi.org\/10.3390\/mdpi_crossmark_policy","source":"Crossref","is-referenced-by-count":6,"title":["Effective f(R) Actions for Modified Loop Quantum Cosmologies via Order Reduction"],"prefix":"10.3390","volume":"9","author":[{"ORCID":"https:\/\/orcid.org\/0000-0003-3205-5711","authenticated-orcid":false,"given":"Ana Rita","family":"Ribeiro","sequence":"first","affiliation":[{"name":"Instituto de Astrof\u00edsica e Ci\u00eancias do Espa\u00e7o, Faculdade de Ci\u00eancias da Universidade de Lisboa, Edif\u00edcio C8, Campo Grande, 1749-016 Lisbon, Portugal"}]},{"ORCID":"https:\/\/orcid.org\/0000-0003-4379-2549","authenticated-orcid":false,"given":"Daniele","family":"Vernieri","sequence":"additional","affiliation":[{"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":"Istituto Nazionale di Fisica Nucleare (INFN) Sezione di Napoli, Complesso Universitario di Monte Sant\u2019Angelo, Edificio G, Via Cinthia, 80126 Napoli, Italy"},{"name":"Scuola Superiore Meridionale, Largo San Marcellino 10, 80138 Napoli, Italy"}]},{"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 Espa\u00e7o, 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":[[2023,4,11]]},"reference":[{"key":"ref_1","first-page":"1","article-title":"Quantum-Spacetime Phenomenology","volume":"16","year":"2013","journal-title":"Living Rev. Relativ."},{"key":"ref_2","doi-asserted-by":"crossref","first-page":"885","DOI":"10.1088\/0034-4885\/64\/8\/301","article-title":"Quantum gravity: A Progress report","volume":"64","author":"Carlip","year":"2001","journal-title":"Rep. Prog. 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