BibTex format
@article{Trotta:2004:10.1103/PhysRevD.69.023509,
author = {Trotta, R and Hansen, SH},
doi = {10.1103/PhysRevD.69.023509},
journal = {Physical Review D},
title = {Constraining the helium abundance with CMB data},
url = {http://dx.doi.org/10.1103/PhysRevD.69.023509},
volume = {69},
year = {2004}
}