Smith Tristan L, Pierpaoli Elena, Kamionkowski Marc
California Institute of Technology, Mail Code 130-33, Pasadena, 91125, USA.
Phys Rev Lett. 2006 Jul 14;97(2):021301. doi: 10.1103/PhysRevLett.97.021301.
Primordial gravitational waves (GWs) with frequencies > or approximately equal to 10(-15) Hz contribute to the radiation density of the Universe at the time of decoupling of the cosmic microwave background (CMB). This affects the CMB and matter power spectra in a manner identical to massless neutrinos, unless the initial density perturbation for the GWs is nonadiabatic, as may occur if such GWs are produced during inflation or some post-inflation phase transition. In either case, current observations provide a constraint to the GW amplitude that competes with that from big-bang nucleosynthesis (BBN), although it extends to much lower frequencies (approximately 10(-15) Hz rather than the approximately 10(-10) Hz from BBN): at 95% confidence level, omega(gw)h(2) <or approximately = 8.4 x 10(-6) for homogeneous (i.e., nonadiabatic) initial conditions. Future CMB experiments, like Planck and CMBPol, should allow sensitivities to omega(gw)h(2) <or approximately = 1.4 x 10(-6) and omega(gw)h(2) < or approximately 5 x 10(-7), respectively.
频率大于或约等于10^(-15)赫兹的原初引力波（GWs）在宇宙微波背景（CMB）解耦时对宇宙的辐射密度有贡献。这以与无质量中微子相同的方式影响CMB和物质功率谱，除非GWs的初始密度扰动是非绝热的，例如在暴胀期间或某些暴胀后相变过程中产生此类GWs时可能发生的情况。在任何一种情况下，当前的观测都对GW振幅提供了一个与大爆炸核合成（BBN）相竞争的限制，尽管它延伸到低得多的频率（约10^(-15)赫兹，而不是BBN的约10^(-10)赫兹）：在95%置信水平下，对于均匀（即非绝热）初始条件，Ω(gw)h²≤8.4×10^(-6)。未来的CMB实验，如普朗克卫星和CMBPol，应该分别能够探测到Ω(gw)h²≤1.4×10^(-6)和Ω(gw)h²≤5×10^(-7)。
