ISW效应对Yukawa引力势的检验

Testing Yukawa-Like Gravitational Potential Against the ISW Effect

该文利用Integrated Sachs-Wolfe(ISW)效应探测宇宙大尺度引力势随时间的变化速率,从而能够在宇宙学尺度上检验引力的性质。以Yukawa引力势为例,探讨了利用ISW效应检验引力性质的能力。计算表明,ISW效应对引力的性质很敏感,通过与宇宙微波背景辐射实验WMAP五年的观测结果相比较,发现相对于牛顿常数,等效牛顿常数在宇宙学尺度上最多只有约2%的改变。

The late time integrated Sachs-Wolfe （ISW） effect measures the net energy gain or loss in CMB photons when passing through a time varying gravitational potential. The ISW effect has been detected through the induced correlation between the CMB and the large scale structure from the year 2003. The detection of the ISW effect has profound impact on the understanding of the dark universe. At large scales relevant to the ISW effect, if the universe is flat with only matter and if gravity is described by the general relativity （GR）, the gravitational potential is nonvolving and the ISW effect vanishes. Thus the detection of the ISW effect implies three possibilities, （1）the universe is curved, （2）there is dark energy, or （3）gravity at cosmological scales deviates from GR. Current CMB observations has basically ruled out the first possibility. Thus the detection of the ISW effect leads to either the existence of dark energy or modified gravity. In this paper we explore the potential of the ISW effect to constrain the nature of gravity. Our fiducial gravity theory is Yukawa-like, in which the effective Newton＇s constant deviates from the local one at scales above a transition scale. Since this modified gravity model is not general covariant, we are not able to calculate the expansion rate self-consistently. Thus we adopt a common assumption that the expansion rate in this model is the same as that in standard cosmology. Given this assumption, we are able to calculate the linear structure growth in this modified gravity model. We find that the time variation in gravitational potential, especially at redshift around 10, is strongly sensitive to the nature of gravity. As a consequence, the ISW contribution from redshifts above 10 is often non-negligible or even dominant, contrast to the case of the standard cosmology. This makes the ISW effect a sensitive indicator of gravity. We compare the model prediction against the WMAP 5 year result. We find that, for the transition scale 10 Mpc/h, the WMAP result has already ruled out any 2% or larger deviations in the effective Newton＇s constant from the local one. This constraint is much more stringent comparing to constraints from other observations such as galaxy clustering.