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Paper IPM / Physic / 15677  


Abstract:  
Most of the inflationary scenarios that try to explain the origin of Primordial Black Holes (PBHs) from the enhancements of the power spectrum to values of order one at the relevant scales, run into clashes with the Effective Field Theory (EFT) criteria or fail to enhance the power spectrum to such large amplitudes. In this paper, we unravel a mechanism of enhancing the power spectrum during inflation without flattening the potential or reducing the sound speed of scalar perturbations. The mechanism is based on this observation in the formalism of Extended EFT of inflation (EEFToI) with the sixth order polynomial dispersion relation for scalar perturbations, that if the quartic coefficient in the dispersion relation is negative and smaller than a certain threshold, the amplitude of power spectrum can be enhanced substantially. The instability mechanism needs to be arranged to kick in at the scales of interest which is related to the mass of the PBHs one would like to produce, which can be ten(s) of solar mass PBHs, suitable for LIGO events, or 10^{−13}−10^{−17} solar mass PBHs, which can comprise the whole dark matter energy density. This can be accommodated within the EEFToI by endowing timedependence to the coefficients of the dispersion relation, or in turn, to the couplings in the unitary gauge action. We argue that for the range of parameters that the mechanisms enhance the power spectrum to the required amount, the strong coupling is avoided.
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