### Abstract

We constrain the thermal evolution of the universe with a decaying cosmological term by using the method of the analysis for the Wilkinson Microwave Anisotropy Probe (WMAP) observation data. The cosmological term is assumed to be a function of the scale factor that increases toward the early universe, and the radiation energy density is lower compared to that in the model with the standard cosmological constant (ΛCDM). The decrease in the radiation density affects the thermal history of the universe; e.g. the photon decoupling occurs at higher-z compared to the case of the standard ΛCDM model. As a consequence, a decaying cosmological term affects the cosmic microwave background (CMB) anisotropy. Thanks to the Markov-Chain Monte Carlo method, we compare the angular power spectrum in the decaying ΛCDM model with the CMB data, and we get severe constraints on parameters of the model.

Original language | English |
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Article number | 123511 |

Journal | Physical Review D - Particles, Fields, Gravitation and Cosmology |

Volume | 77 |

Issue number | 12 |

DOIs | |

Publication status | Published - Jun 10 2008 |

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### All Science Journal Classification (ASJC) codes

- Nuclear and High Energy Physics
- Physics and Astronomy (miscellaneous)

### Cite this

*Physical Review D - Particles, Fields, Gravitation and Cosmology*,

*77*(12), [123511]. https://doi.org/10.1103/PhysRevD.77.123511

**Cosmic microwave background constraints on a decaying cosmological term related to the thermal evolution.** / Nakamura, Riou; Hashimoto, Masa Aki; Ichiki, Kiyotomo.

Research output: Contribution to journal › Article

*Physical Review D - Particles, Fields, Gravitation and Cosmology*, vol. 77, no. 12, 123511. https://doi.org/10.1103/PhysRevD.77.123511

}

TY - JOUR

T1 - Cosmic microwave background constraints on a decaying cosmological term related to the thermal evolution

AU - Nakamura, Riou

AU - Hashimoto, Masa Aki

AU - Ichiki, Kiyotomo

PY - 2008/6/10

Y1 - 2008/6/10

N2 - We constrain the thermal evolution of the universe with a decaying cosmological term by using the method of the analysis for the Wilkinson Microwave Anisotropy Probe (WMAP) observation data. The cosmological term is assumed to be a function of the scale factor that increases toward the early universe, and the radiation energy density is lower compared to that in the model with the standard cosmological constant (ΛCDM). The decrease in the radiation density affects the thermal history of the universe; e.g. the photon decoupling occurs at higher-z compared to the case of the standard ΛCDM model. As a consequence, a decaying cosmological term affects the cosmic microwave background (CMB) anisotropy. Thanks to the Markov-Chain Monte Carlo method, we compare the angular power spectrum in the decaying ΛCDM model with the CMB data, and we get severe constraints on parameters of the model.

AB - We constrain the thermal evolution of the universe with a decaying cosmological term by using the method of the analysis for the Wilkinson Microwave Anisotropy Probe (WMAP) observation data. The cosmological term is assumed to be a function of the scale factor that increases toward the early universe, and the radiation energy density is lower compared to that in the model with the standard cosmological constant (ΛCDM). The decrease in the radiation density affects the thermal history of the universe; e.g. the photon decoupling occurs at higher-z compared to the case of the standard ΛCDM model. As a consequence, a decaying cosmological term affects the cosmic microwave background (CMB) anisotropy. Thanks to the Markov-Chain Monte Carlo method, we compare the angular power spectrum in the decaying ΛCDM model with the CMB data, and we get severe constraints on parameters of the model.

UR - http://www.scopus.com/inward/record.url?scp=45149101985&partnerID=8YFLogxK

UR - http://www.scopus.com/inward/citedby.url?scp=45149101985&partnerID=8YFLogxK

U2 - 10.1103/PhysRevD.77.123511

DO - 10.1103/PhysRevD.77.123511

M3 - Article

AN - SCOPUS:45149101985

VL - 77

JO - Physical Review D - Particles, Fields, Gravitation and Cosmology

JF - Physical Review D - Particles, Fields, Gravitation and Cosmology

SN - 1550-7998

IS - 12

M1 - 123511

ER -