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Title: Analytical approximation of primordial black hole formation by an ultra slow-roll period †Speaker: Jason Kristiano †Primordial quantum fluctuations that are stretched by cosmic inflation can explain the anisotropy of cosmic microwave background (CMB). Such fluctuations have a long wavelength and the amplitude of the power spectrum is constrained to be around 10^(-9) by observation. However, at small scales, fluctuations with wavelength much smaller than CMB scales, the observational constraints are very loose. Theoretically, if there is a peak with order of 10^(-2) in the amplitude of the power spectrum at small scales, it can collapse into primordial black hole (PBH). In this seminar, I will show how to form this peak at small scales analytically. I will explain the formation of PBH generated by a short ultra slow-roll (USR) period right before the end of inflation. [1] J. Liu, et. al., Analytical approximation of the scalar spectrum in the ultraslow-roll inflationary models, Phys. Rev. D 101, 083535 (2020), arXiv:2003.02075. |