Effective <i>f</i>(<i>R</i>) Actions for Modified Loop Quantum Cosmologies via Order Reduction
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,...
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| Format: | Article |
| Language: | English |
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MDPI AG
2023-04-01
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| Series: | Universe |
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| Online Access: | https://www.mdpi.com/2218-1997/9/4/181 |
| _version_ | 1797603315942424576 |
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| author | Ana Rita Ribeiro Daniele Vernieri Francisco S. N. Lobo |
| author_facet | Ana Rita Ribeiro Daniele Vernieri Francisco S. N. Lobo |
| author_sort | Ana Rita Ribeiro |
| collection | DOAJ |
| description | 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 <inline-formula><math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><semantics><mrow><mi>f</mi><mo>(</mo><mi>R</mi><mo>)</mo></mrow></semantics></math></inline-formula> 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 <inline-formula><math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><semantics><mrow><mi>f</mi><mo>(</mo><mi>R</mi><mo>)</mo></mrow></semantics></math></inline-formula> field equations, and obtain covariant effective actions that lead to a bounce, for specific models of modified LQC, considering a massless scalar field. |
| first_indexed | 2024-03-11T04:28:27Z |
| format | Article |
| id | doaj.art-cea4509215954d279fe4966d68797a2c |
| institution | Directory Open Access Journal |
| issn | 2218-1997 |
| language | English |
| last_indexed | 2024-03-11T04:28:27Z |
| publishDate | 2023-04-01 |
| publisher | MDPI AG |
| record_format | Article |
| series | Universe |
| spelling | doaj.art-cea4509215954d279fe4966d68797a2c2023-11-17T21:40:24ZengMDPI AGUniverse2218-19972023-04-019418110.3390/universe9040181Effective <i>f</i>(<i>R</i>) Actions for Modified Loop Quantum Cosmologies via Order ReductionAna Rita Ribeiro0Daniele Vernieri1Francisco S. N. Lobo2Instituto de Astrofísica e Ciências do Espaço, Faculdade de Ciências da Universidade de Lisboa, Edifício C8, Campo Grande, 1749-016 Lisbon, PortugalDipartimento di Fisica “E. Pancini”, Università di Napoli “Federico II”, Complesso Universitario di Monte Sant’Angelo, Edificio G, Via Cinthia, 80126 Napoli, ItalyInstituto de Astrofísica e Ciências do Espaço, Faculdade de Ciências da Universidade de Lisboa, Edifício C8, Campo Grande, 1749-016 Lisbon, PortugalGeneral 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 <inline-formula><math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><semantics><mrow><mi>f</mi><mo>(</mo><mi>R</mi><mo>)</mo></mrow></semantics></math></inline-formula> 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 <inline-formula><math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><semantics><mrow><mi>f</mi><mo>(</mo><mi>R</mi><mo>)</mo></mrow></semantics></math></inline-formula> field equations, and obtain covariant effective actions that lead to a bounce, for specific models of modified LQC, considering a massless scalar field.https://www.mdpi.com/2218-1997/9/4/181modified gravityloop quantum cosmologybouncing cosmologies |
| spellingShingle | Ana Rita Ribeiro Daniele Vernieri Francisco S. N. Lobo Effective <i>f</i>(<i>R</i>) Actions for Modified Loop Quantum Cosmologies via Order Reduction Universe modified gravity loop quantum cosmology bouncing cosmologies |
| title | Effective <i>f</i>(<i>R</i>) Actions for Modified Loop Quantum Cosmologies via Order Reduction |
| title_full | Effective <i>f</i>(<i>R</i>) Actions for Modified Loop Quantum Cosmologies via Order Reduction |
| title_fullStr | Effective <i>f</i>(<i>R</i>) Actions for Modified Loop Quantum Cosmologies via Order Reduction |
| title_full_unstemmed | Effective <i>f</i>(<i>R</i>) Actions for Modified Loop Quantum Cosmologies via Order Reduction |
| title_short | Effective <i>f</i>(<i>R</i>) Actions for Modified Loop Quantum Cosmologies via Order Reduction |
| title_sort | effective i f i i r i actions for modified loop quantum cosmologies via order reduction |
| topic | modified gravity loop quantum cosmology bouncing cosmologies |
| url | https://www.mdpi.com/2218-1997/9/4/181 |
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