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Stochastic background of induced gravitational waves: recent developments †Shi Pi †Our universe is fulfilled by stochastic gravitational wave background (SGWB) with a large range of frequencies, which may have various astrophysical/cosmological origins in the early universe. In this talk I will briefly review the properties of SGWB induced by the scalar perturbation, as well as its connection to the primordial black holes (PBHs). Recently, NANOGrav reported the discovery of a common-spectrum process of the time residuals in their 12.5-yr data set of pulsar timing array, which might be the first detection of nano-hertz SGWB. Based on the recent developments on the spectral shape of SGWB, I will show that this signal could be connected to the planet-mass PBH candidates found by OGLE recently, if there is a dust-like stage prior to the radiation dominated era. |