# Observational constraints on cosmic neutrinos and dark energy revisited

## Abstract

Using several cosmological observations, i.e. the cosmic microwave background anisotropies (WMAP), the weak gravitational lensing (CFHTLS), the measurements of baryon acoustic oscillations (SDSS+WiggleZ), the most recent observational Hubble parameter data, the Union2.1 compilation of type Ia supernovae, and the HST prior, we impose constraints on the sum of neutrino masses (m{sub ν}), the effective number of neutrino species (N{sub eff}) and dark energy equation of state (w), individually and collectively. We find that a tight upper limit on m{sub ν} can be extracted from the full data combination, if N{sub eff} and w are fixed. However this upper bound is severely weakened if N{sub eff} and w are allowed to vary. This result naturally raises questions on the robustness of previous strict upper bounds on m{sub ν}, ever reported in the literature. The best-fit values from our most generalized constraint read m{sub ν} = 0.556{sup +0.231}{sub −0.288} eV, N{sub eff} = 3.839±0.452, and w = −1.058±0.088 at 68% confidence level, which shows a firm lower limit on total neutrino mass, favors an extra light degree of freedom, and supports the cosmological constant model. The current weak lensing data are already helpful in constraining cosmological model parameters for fixed w. Themore »

- Authors:

- Department of Astronomy, Beijing Normal University, Beijing 100875 (China)
- Department of Physics and Tsinghua Center for Astrophysics, Tsinghua University, Beijing, 100084 (China)
- Department of Physics and Astronomy, University of California, Irvine, CA 92697 (United States)
- National Astronomical Observatories, Chinese Academy of Sciences, Beijing 100012 (China)
- School of Astronomy and Space Science, Nanjing University, Nanjing, 210093 (China)

- Publication Date:

- OSTI Identifier:
- 22279687

- Resource Type:
- Journal Article

- Journal Name:
- Journal of Cosmology and Astroparticle Physics

- Additional Journal Information:
- Journal Volume: 2012; Journal Issue: 11; Other Information: Country of input: International Atomic Energy Agency (IAEA); Journal ID: ISSN 1475-7516

- Country of Publication:
- United States

- Language:
- English

- Subject:
- 79 ASTROPHYSICS, COSMOLOGY AND ASTRONOMY; ANISOTROPY; BARYONS; COSMOLOGICAL CONSTANT; COSMOLOGICAL MODELS; DEGREES OF FREEDOM; EQUATIONS OF STATE; GRAVITATIONAL LENSES; MASS; NONLUMINOUS MATTER; OSCILLATIONS; RELICT RADIATION; SUPERNOVAE; VISIBLE RADIATION

### Citation Formats

```
Wang, Xin, Meng, Xiao-Lei, Zhang, Tong-Jie, Shan, HuanYuan, Tao, Charling, Gong, Yan, Chen, Xuelei, and Huang, Y.F., E-mail: albertfxwang@gmail.com, E-mail: mlwx@mail.bnu.edu.cn, E-mail: tjzhang@bnu.edu.cn, E-mail: shanhuany@gmail.com, E-mail: ygong1@uci.edu, E-mail: tao@cppm.in2p3.fr, E-mail: xuelei@cosmology.bao.ac.cn, E-mail: hyf@nju.edu.cn.
```*Observational constraints on cosmic neutrinos and dark energy revisited*. United States: N. p., 2012.
Web. doi:10.1088/1475-7516/2012/11/018.

```
Wang, Xin, Meng, Xiao-Lei, Zhang, Tong-Jie, Shan, HuanYuan, Tao, Charling, Gong, Yan, Chen, Xuelei, & Huang, Y.F., E-mail: albertfxwang@gmail.com, E-mail: mlwx@mail.bnu.edu.cn, E-mail: tjzhang@bnu.edu.cn, E-mail: shanhuany@gmail.com, E-mail: ygong1@uci.edu, E-mail: tao@cppm.in2p3.fr, E-mail: xuelei@cosmology.bao.ac.cn, E-mail: hyf@nju.edu.cn.
```*Observational constraints on cosmic neutrinos and dark energy revisited*. United States. doi:10.1088/1475-7516/2012/11/018.

```
Wang, Xin, Meng, Xiao-Lei, Zhang, Tong-Jie, Shan, HuanYuan, Tao, Charling, Gong, Yan, Chen, Xuelei, and Huang, Y.F., E-mail: albertfxwang@gmail.com, E-mail: mlwx@mail.bnu.edu.cn, E-mail: tjzhang@bnu.edu.cn, E-mail: shanhuany@gmail.com, E-mail: ygong1@uci.edu, E-mail: tao@cppm.in2p3.fr, E-mail: xuelei@cosmology.bao.ac.cn, E-mail: hyf@nju.edu.cn. Thu .
"Observational constraints on cosmic neutrinos and dark energy revisited". United States. doi:10.1088/1475-7516/2012/11/018.
```

```
@article{osti_22279687,
```

title = {Observational constraints on cosmic neutrinos and dark energy revisited},

author = {Wang, Xin and Meng, Xiao-Lei and Zhang, Tong-Jie and Shan, HuanYuan and Tao, Charling and Gong, Yan and Chen, Xuelei and Huang, Y.F., E-mail: albertfxwang@gmail.com, E-mail: mlwx@mail.bnu.edu.cn, E-mail: tjzhang@bnu.edu.cn, E-mail: shanhuany@gmail.com, E-mail: ygong1@uci.edu, E-mail: tao@cppm.in2p3.fr, E-mail: xuelei@cosmology.bao.ac.cn, E-mail: hyf@nju.edu.cn},

abstractNote = {Using several cosmological observations, i.e. the cosmic microwave background anisotropies (WMAP), the weak gravitational lensing (CFHTLS), the measurements of baryon acoustic oscillations (SDSS+WiggleZ), the most recent observational Hubble parameter data, the Union2.1 compilation of type Ia supernovae, and the HST prior, we impose constraints on the sum of neutrino masses (m{sub ν}), the effective number of neutrino species (N{sub eff}) and dark energy equation of state (w), individually and collectively. We find that a tight upper limit on m{sub ν} can be extracted from the full data combination, if N{sub eff} and w are fixed. However this upper bound is severely weakened if N{sub eff} and w are allowed to vary. This result naturally raises questions on the robustness of previous strict upper bounds on m{sub ν}, ever reported in the literature. The best-fit values from our most generalized constraint read m{sub ν} = 0.556{sup +0.231}{sub −0.288} eV, N{sub eff} = 3.839±0.452, and w = −1.058±0.088 at 68% confidence level, which shows a firm lower limit on total neutrino mass, favors an extra light degree of freedom, and supports the cosmological constant model. The current weak lensing data are already helpful in constraining cosmological model parameters for fixed w. The dataset of Hubble parameter gains numerous advantages over supernovae when w = −1, particularly its illuminating power in constraining N{sub eff}. As long as w is included as a free parameter, it is still the standardizable candles of type Ia supernovae that play the most dominant role in the parameter constraints.},

doi = {10.1088/1475-7516/2012/11/018},

journal = {Journal of Cosmology and Astroparticle Physics},

issn = {1475-7516},

number = 11,

volume = 2012,

place = {United States},

year = {2012},

month = {11}

}