Testing spatial curvature and anisotropic expansion on top of the ΛCDM model

Özgür Akarsu; Eleonora Di Valentino; Suresh Kumar; Maya Özyiğit; Shivani Sharma

doi:10.1016/j.dark.2022.101162

Testing spatial curvature and anisotropic expansion on top of the ΛCDM model

Özgür Akarsu^*, Eleonora Di Valentino, Suresh Kumar, Maya Özyiğit, Shivani Sharma

^*Corresponding author for this work

Department of Physics Engineering

Research output: Contribution to journal › Article › peer-review

27 Citations (Scopus)

Abstract

We explore the possible advantages of extending the standard ΛCDM model by more realistic backgrounds compared to its spatially flat Robertson–Walker (RW) spacetime assumption, while preserving the underpinning physics; in particular, by simultaneously allowing non-zero spatial curvature and anisotropic expansion on top of ΛCDM, viz., the An-oΛCDM model. This is to test whether the latest observational data still support spatial flatness and/or isotropic expansion in this case, and, if not, to explore the roles of spatial curvature and expansion anisotropy (due to its stiff fluid-like behavior) in addressing some of the current cosmological tensions associated with ΛCDM. We first present the theoretical background and explicit mathematical construction of An-oΛCDM; in the simplest manner, combining the simplest anisotropic generalizations of the RW spacetime, viz., the Bianchi type I, V, and IX spacetimes, in one Friedmann equation. Then we constrain the parameters of this model and its particular cases, namely, An-ΛCDM, oΛCDM, and ΛCDM, by using the data sets from different observational probes, viz., Planck cosmic microwave background (CMB) with or without lensing (Lens), baryonic acoustic oscillations (BAO), type Ia Supernovae (SnIa) Pantheon, and cosmic chronometers (CC) data, and discuss the results in detail. Ultimately, we conclude that, within the setup under consideration, (i) the observational data confirm the spatial flatness and isotropic expansion assumptions of ΛCDM, though a very small amount of present-day expansion anisotropy (Ω_σ0) cannot be excluded, e.g., Ω_σ0≲10⁻¹⁸ (95% C.L.) for An-ΛCDM from CMB+Lens data, (ii) the introduction of spatial curvature or anisotropic expansion, or both, on top ΛCDM does not offer a possible relaxation to the H₀ tension, and (iii) the introduction of anisotropic expansion neither affects the closed space prediction from the CMB data nor does it improve the drastically reduced value of H₀ led by the closed space. We discuss why it is important and indispensable to maintain the geometric generalization work program, especially in models that offer solutions to cosmological tensions, even though our findings do not appear to favor the geometric generalizations of ΛCDM considered in this work.

Original language	English
Article number	101162
Journal	Physics of the Dark Universe
Volume	39
DOIs	https://doi.org/10.1016/j.dark.2022.101162
Publication status	Published - Feb 2023

Bibliographical note

Publisher Copyright:
© 2022 Elsevier B.V.

Funding

The authors thank the anonymous referee for their comments and suggestions that helped improve the paper. The authors also thank Shahin Sheikh-Jabbari for valuable comments. Ö.A. acknowledges the support by the Turkish Academy of Sciences in the scheme of the Outstanding Young Scientist Award (TÜBA-GEBİP). E.D.V. is supported by a Royal Society Dorothy Hodgkin Research Fellowship. S.K. gratefully acknowledges the support from Science and Engineering Research Board (SERB), Govt. of India (File No. CRG/2021/004658). This article is based upon work from COST Action CA21136 Addressing observational tensions in cosmology with systematics and fundamental physics (CosmoVerse) supported by COST (European Cooperation in Science and Technology). The authors thank the anonymous referee for their comments and suggestions that helped improve the paper. The authors also thank Shahin Sheikh-Jabbari for valuable comments. Ö.A. acknowledges the support by the Turkish Academy of Sciences in the scheme of the Outstanding Young Scientist Award (TÜBA-GEBİP) . E.D.V. is supported by a Royal Society Dorothy Hodgkin Research Fellowship . S.K. gratefully acknowledges the support from Science and Engineering Research Board (SERB), Govt. of India (File No. CRG/2021/004658 ). This article is based upon work from COST Action CA21136 Addressing observational tensions in cosmology with systematics and fundamental physics (CosmoVerse) supported by COST (European Cooperation in Science and Technology) .

Funders	Funder number
TÜBA-GEBİP
Royal Society
European Cooperation in Science and Technology
Science and Engineering Research Board	CRG/2021/004658
Türkiye Bilimler Akademisi

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title = "Testing spatial curvature and anisotropic expansion on top of the ΛCDM model",

abstract = "We explore the possible advantages of extending the standard ΛCDM model by more realistic backgrounds compared to its spatially flat Robertson–Walker (RW) spacetime assumption, while preserving the underpinning physics; in particular, by simultaneously allowing non-zero spatial curvature and anisotropic expansion on top of ΛCDM, viz., the An-oΛCDM model. This is to test whether the latest observational data still support spatial flatness and/or isotropic expansion in this case, and, if not, to explore the roles of spatial curvature and expansion anisotropy (due to its stiff fluid-like behavior) in addressing some of the current cosmological tensions associated with ΛCDM. We first present the theoretical background and explicit mathematical construction of An-oΛCDM; in the simplest manner, combining the simplest anisotropic generalizations of the RW spacetime, viz., the Bianchi type I, V, and IX spacetimes, in one Friedmann equation. Then we constrain the parameters of this model and its particular cases, namely, An-ΛCDM, oΛCDM, and ΛCDM, by using the data sets from different observational probes, viz., Planck cosmic microwave background (CMB) with or without lensing (Lens), baryonic acoustic oscillations (BAO), type Ia Supernovae (SnIa) Pantheon, and cosmic chronometers (CC) data, and discuss the results in detail. Ultimately, we conclude that, within the setup under consideration, (i) the observational data confirm the spatial flatness and isotropic expansion assumptions of ΛCDM, though a very small amount of present-day expansion anisotropy (Ωσ0) cannot be excluded, e.g., Ωσ0≲10−18 (95% C.L.) for An-ΛCDM from CMB+Lens data, (ii) the introduction of spatial curvature or anisotropic expansion, or both, on top ΛCDM does not offer a possible relaxation to the H0 tension, and (iii) the introduction of anisotropic expansion neither affects the closed space prediction from the CMB data nor does it improve the drastically reduced value of H0 led by the closed space. We discuss why it is important and indispensable to maintain the geometric generalization work program, especially in models that offer solutions to cosmological tensions, even though our findings do not appear to favor the geometric generalizations of ΛCDM considered in this work.",

author = "{\"O}zg{\"u}r Akarsu and {Di Valentino}, Eleonora and Suresh Kumar and Maya {\"O}zyiğit and Shivani Sharma",

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year = "2023",

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doi = "10.1016/j.dark.2022.101162",

language = "English",

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T1 - Testing spatial curvature and anisotropic expansion on top of the ΛCDM model

AU - Akarsu, Özgür

AU - Di Valentino, Eleonora

AU - Kumar, Suresh

AU - Özyiğit, Maya

AU - Sharma, Shivani

PY - 2023/2

Y1 - 2023/2

N2 - We explore the possible advantages of extending the standard ΛCDM model by more realistic backgrounds compared to its spatially flat Robertson–Walker (RW) spacetime assumption, while preserving the underpinning physics; in particular, by simultaneously allowing non-zero spatial curvature and anisotropic expansion on top of ΛCDM, viz., the An-oΛCDM model. This is to test whether the latest observational data still support spatial flatness and/or isotropic expansion in this case, and, if not, to explore the roles of spatial curvature and expansion anisotropy (due to its stiff fluid-like behavior) in addressing some of the current cosmological tensions associated with ΛCDM. We first present the theoretical background and explicit mathematical construction of An-oΛCDM; in the simplest manner, combining the simplest anisotropic generalizations of the RW spacetime, viz., the Bianchi type I, V, and IX spacetimes, in one Friedmann equation. Then we constrain the parameters of this model and its particular cases, namely, An-ΛCDM, oΛCDM, and ΛCDM, by using the data sets from different observational probes, viz., Planck cosmic microwave background (CMB) with or without lensing (Lens), baryonic acoustic oscillations (BAO), type Ia Supernovae (SnIa) Pantheon, and cosmic chronometers (CC) data, and discuss the results in detail. Ultimately, we conclude that, within the setup under consideration, (i) the observational data confirm the spatial flatness and isotropic expansion assumptions of ΛCDM, though a very small amount of present-day expansion anisotropy (Ωσ0) cannot be excluded, e.g., Ωσ0≲10−18 (95% C.L.) for An-ΛCDM from CMB+Lens data, (ii) the introduction of spatial curvature or anisotropic expansion, or both, on top ΛCDM does not offer a possible relaxation to the H0 tension, and (iii) the introduction of anisotropic expansion neither affects the closed space prediction from the CMB data nor does it improve the drastically reduced value of H0 led by the closed space. We discuss why it is important and indispensable to maintain the geometric generalization work program, especially in models that offer solutions to cosmological tensions, even though our findings do not appear to favor the geometric generalizations of ΛCDM considered in this work.

AB - We explore the possible advantages of extending the standard ΛCDM model by more realistic backgrounds compared to its spatially flat Robertson–Walker (RW) spacetime assumption, while preserving the underpinning physics; in particular, by simultaneously allowing non-zero spatial curvature and anisotropic expansion on top of ΛCDM, viz., the An-oΛCDM model. This is to test whether the latest observational data still support spatial flatness and/or isotropic expansion in this case, and, if not, to explore the roles of spatial curvature and expansion anisotropy (due to its stiff fluid-like behavior) in addressing some of the current cosmological tensions associated with ΛCDM. We first present the theoretical background and explicit mathematical construction of An-oΛCDM; in the simplest manner, combining the simplest anisotropic generalizations of the RW spacetime, viz., the Bianchi type I, V, and IX spacetimes, in one Friedmann equation. Then we constrain the parameters of this model and its particular cases, namely, An-ΛCDM, oΛCDM, and ΛCDM, by using the data sets from different observational probes, viz., Planck cosmic microwave background (CMB) with or without lensing (Lens), baryonic acoustic oscillations (BAO), type Ia Supernovae (SnIa) Pantheon, and cosmic chronometers (CC) data, and discuss the results in detail. Ultimately, we conclude that, within the setup under consideration, (i) the observational data confirm the spatial flatness and isotropic expansion assumptions of ΛCDM, though a very small amount of present-day expansion anisotropy (Ωσ0) cannot be excluded, e.g., Ωσ0≲10−18 (95% C.L.) for An-ΛCDM from CMB+Lens data, (ii) the introduction of spatial curvature or anisotropic expansion, or both, on top ΛCDM does not offer a possible relaxation to the H0 tension, and (iii) the introduction of anisotropic expansion neither affects the closed space prediction from the CMB data nor does it improve the drastically reduced value of H0 led by the closed space. We discuss why it is important and indispensable to maintain the geometric generalization work program, especially in models that offer solutions to cosmological tensions, even though our findings do not appear to favor the geometric generalizations of ΛCDM considered in this work.

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Testing spatial curvature and anisotropic expansion on top of the ΛCDM model

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