Some Recent Bounds on Neff in the Literature

[1] [2] [3] [4] [5] [6] [7] [8] [9] [10] [11] [12] [13]
BBN < 3.9 (95%) 2.4 +/- 0.4
CMB 3.9 +/- 0.6 4.3 +/- 0.9 3.9 +/- 0.7 3.62 +/ 0.48
CMB+ 3.9 +/- 0.4 4.1 +/- 0.7 (95%) 4.2 +/- 0.7 4.5 +/- 0.8 4.1 +/- 0.6 3.58 +/- 0.54 (95%) 3.7+/- 0.7 (95%) 3.26 +/ 0.35 3.71 +/ 0.35

References

1. Mangano & Serpico 2011
2. Benson et al 2011
3. Keisler et al 2011
4. Archidiacono et al 2011
5. Riess et al 2011
6. Simha & Steigman 2008
7. Guo & Zhang 2012
8. Komatsu et al 2011
9. Mehta et al 2012
10. Riemer-Sorensen et al 2012
11. Giusarma et al 2012
12. Hinshaw et al 2012 (WMAP9)
13. Hou et al 2012 (SPT)