Sustaining Quasi De-Sitter Inflation with Bulk Viscosity
The de-Sitter spacetime is a maximally symmetric Lorentzian manifold with constant positive scalar curvature that plays a fundamental role in modern cosmology. Here, we investigate bulk-viscosity-assisted quasi de-Sitter inflation, that is the period of accelerated expansion in the early universe du...
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| Format: | Article |
| Language: | English |
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MDPI AG
2024-02-01
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| Series: | Symmetry |
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| Online Access: | https://www.mdpi.com/2073-8994/16/2/194 |
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| author | Sayantani Lahiri Luciano Rezzolla |
| author_facet | Sayantani Lahiri Luciano Rezzolla |
| author_sort | Sayantani Lahiri |
| collection | DOAJ |
| description | The de-Sitter spacetime is a maximally symmetric Lorentzian manifold with constant positive scalar curvature that plays a fundamental role in modern cosmology. Here, we investigate bulk-viscosity-assisted quasi de-Sitter inflation, that is the period of accelerated expansion in the early universe during which <inline-formula><math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><semantics><mrow><mo>−</mo><mover accent="true"><mi>H</mi><mo>˙</mo></mover><mo>≪</mo><msup><mi>H</mi><mn>2</mn></msup></mrow></semantics></math></inline-formula>, with <inline-formula><math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><semantics><mrow><mi>H</mi><mo>(</mo><mi>t</mi><mo>)</mo></mrow></semantics></math></inline-formula> being the Hubble expansion rate. We do so in the framework of a causal theory of relativistic hydrodynamics, which takes into account non-equilibrium effects associated with bulk viscosity, which may have been present as the early universe underwent an accelerated expansion. In this framework, the existence of a quasi de-Sitter universe emerges as a natural consequence of the presence of bulk viscosity, without requiring introducing additional scalar fields. As a result, the equation of state, determined by numerically solving the generalized momentum-conservation equation involving bulk viscosity pressure turns out to be time dependent. The transition timescale characterising its departure from an exact de-Sitter phase is intricately related to the magnitude of the bulk viscosity. We examine the properties of the new equation of state, as well as the transition timescale in the presence of bulk viscosity pressure. In addition, we construct a fluid description of inflation and demonstrate that, in the context of the causal formalism, it is equivalent to the scalar field theory of inflation. Our analysis also shows that the slow-roll conditions are realised in the bulk-viscosity-supported model of inflation. Finally, we examine the viability of our model by computing the inflationary observables, namely the spectral index and the tensor-to-scalar ratio of the curvature perturbations, and compare them with a number of different observations, finding good agreement in most cases. |
| first_indexed | 2024-03-07T22:12:10Z |
| format | Article |
| id | doaj.art-86f9e63ca74b49c0b592f871c1a98c80 |
| institution | Directory Open Access Journal |
| issn | 2073-8994 |
| language | English |
| last_indexed | 2024-03-07T22:12:10Z |
| publishDate | 2024-02-01 |
| publisher | MDPI AG |
| record_format | Article |
| series | Symmetry |
| spelling | doaj.art-86f9e63ca74b49c0b592f871c1a98c802024-02-23T15:35:58ZengMDPI AGSymmetry2073-89942024-02-0116219410.3390/sym16020194Sustaining Quasi De-Sitter Inflation with Bulk ViscositySayantani Lahiri0Luciano Rezzolla1Center of Applied Space Technology and Microgravity (ZARM), University of Bremen, 28359 Bremen, GermanyInstitut für Theoretische Physik, Goethe Universität Frankfurt, Max-von-Laue-Str.1, 60438 Frankfurt am Main, GermanyThe de-Sitter spacetime is a maximally symmetric Lorentzian manifold with constant positive scalar curvature that plays a fundamental role in modern cosmology. Here, we investigate bulk-viscosity-assisted quasi de-Sitter inflation, that is the period of accelerated expansion in the early universe during which <inline-formula><math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><semantics><mrow><mo>−</mo><mover accent="true"><mi>H</mi><mo>˙</mo></mover><mo>≪</mo><msup><mi>H</mi><mn>2</mn></msup></mrow></semantics></math></inline-formula>, with <inline-formula><math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><semantics><mrow><mi>H</mi><mo>(</mo><mi>t</mi><mo>)</mo></mrow></semantics></math></inline-formula> being the Hubble expansion rate. We do so in the framework of a causal theory of relativistic hydrodynamics, which takes into account non-equilibrium effects associated with bulk viscosity, which may have been present as the early universe underwent an accelerated expansion. In this framework, the existence of a quasi de-Sitter universe emerges as a natural consequence of the presence of bulk viscosity, without requiring introducing additional scalar fields. As a result, the equation of state, determined by numerically solving the generalized momentum-conservation equation involving bulk viscosity pressure turns out to be time dependent. The transition timescale characterising its departure from an exact de-Sitter phase is intricately related to the magnitude of the bulk viscosity. We examine the properties of the new equation of state, as well as the transition timescale in the presence of bulk viscosity pressure. In addition, we construct a fluid description of inflation and demonstrate that, in the context of the causal formalism, it is equivalent to the scalar field theory of inflation. Our analysis also shows that the slow-roll conditions are realised in the bulk-viscosity-supported model of inflation. Finally, we examine the viability of our model by computing the inflationary observables, namely the spectral index and the tensor-to-scalar ratio of the curvature perturbations, and compare them with a number of different observations, finding good agreement in most cases.https://www.mdpi.com/2073-8994/16/2/194quasi de-Sitter inflationbulk viscositygeneralized Israel-Stewart theory |
| spellingShingle | Sayantani Lahiri Luciano Rezzolla Sustaining Quasi De-Sitter Inflation with Bulk Viscosity Symmetry quasi de-Sitter inflation bulk viscosity generalized Israel-Stewart theory |
| title | Sustaining Quasi De-Sitter Inflation with Bulk Viscosity |
| title_full | Sustaining Quasi De-Sitter Inflation with Bulk Viscosity |
| title_fullStr | Sustaining Quasi De-Sitter Inflation with Bulk Viscosity |
| title_full_unstemmed | Sustaining Quasi De-Sitter Inflation with Bulk Viscosity |
| title_short | Sustaining Quasi De-Sitter Inflation with Bulk Viscosity |
| title_sort | sustaining quasi de sitter inflation with bulk viscosity |
| topic | quasi de-Sitter inflation bulk viscosity generalized Israel-Stewart theory |
| url | https://www.mdpi.com/2073-8994/16/2/194 |
| work_keys_str_mv | AT sayantanilahiri sustainingquasidesitterinflationwithbulkviscosity AT lucianorezzolla sustainingquasidesitterinflationwithbulkviscosity |