New constraint on the cosmological background of relativistic particles.pdfVIP

下载本文档

2
0
约1.97万字
约 10页
2017-04-06 发布于江苏
举报
版权申诉

New constraint on the cosmological background of relativistic particles.pdf

1、有哪些信誉好的足球投注网站（book118）网站文档一经付费（服务费），不意味着购买了该文档的版权，仅供个人/单位学习、研究之用，不得用于商业用途，未经授权，严禁复制、发行、汇编、翻译或者网络传播等，侵权必究。。
2、本站所有内容均由合作方或网友上传，本站不对文档的完整性、权威性及其观点立场正确性做任何保证或承诺！文档内容仅供研究参考，付费前请自行鉴别。如您付费，意味着您自己接受本站规则且自行承担风险，本站不退款、不进行额外附加服务；查看《如何避免下载的几个坑》。如果您已付费下载过本站文档，您可以点击这里二次下载。
3、如文档侵犯商业秘密、侵犯著作权、侵犯人身权等，请点击“版权申诉”（推荐），也可以打举报电话：400-050-0827(电话支持时间：9:00-18:30)。
4、该文档为VIP文档，如果想要下载，成为VIP会员后，下载免费。
5、成为VIP后，下载本文档将扣除1次下载权益。下载后，不支持退款、换文档。如有疑问请联系我们。
6、成为VIP后，您将拥有八大权益，权益包括：VIP文档下载权益、阅读免打扰、文档格式转换、高级专利检索、专属身份标志、高级客服、多端互通、版权登记。
7、VIP文档为合作方或网友上传，每下载1次，网站将根据用户上传文档的质量评分、类型等，对文档贡献者给予高额补贴、流量扶持。如果你也想贡献VIP文档。上传文档

New constraint on the cosmological background of relativistic particles

a r X i v : a s t r o - p h / 0 5 1 0 5 8 2 v 2 2 5 O c t 2 0 0 5 New constraint on the cosmological background of relativistic particles Steen Hannestad Department of Physics and Astronomy, University of Aarhus, Ny Munkegade, DK-8000 Aarhus C, Denmark Abstract. We have derived new bounds on the relativistic energy density in the Universe from cosmic microwave background (CMB), large scale structure (LSS), and type Ia supernova (SNI-a) observations. In terms of the effective number of neutrino species a bound of Nν = 4.2 +1.2 ?1.7 is derived at 95% confidence. This bound is significantly stronger than previous determinations, mainly due to inclusion of new CMB and SNI-a observations. The absence of a cosmological neutrino background (Nν = 0) is now excluded at 5.4σ. The value of Nν is compatible with the value derived from big bang nucleosynthesis considerations, marking one of the most remarkable successes of the standard cosmological model. In terms of the cosmological helium abundance, the CMB, LSS, and SNI-a observations predict a value of 0.240 Y 0.281. New constraint on the cosmological background of relativistic particles 2 1. Introduction From detailed observations of the cosmic microwave background (CMB) [1–8], the large scale structure (LSS) of galaxies [9–11], and distant type Ia supernovae (SNI-a) [12– 14] many of the fundamental cosmological parameters are known quite precisely. Very interestingly the precision of the data is now also at a level where particle physics beyond the standard model can be probed. One of the prime examples of this is the total cosmological energy density in relativistic particles. In the standard model photons and neutrinos are by far the largest source of entropy in the Universe (and consequently also of energy density in the early Universe), and neutrinos are therefore the largest source of entropy in non-electromagnetically interacting species. In the early Universe neutrinos decouple at a temperature of roughly 2-3