Induced gravitational waves, metastable cosmic strings and primordial black holes in GUTs

TL;DR

This paper investigates a flipped SU(5) hybrid inflation model predicting metastable cosmic strings, scalar-induced gravitational waves, and primordial black holes, which could explain recent PTA data and be tested by future experiments.

Contribution

It introduces a realistic GUT-based hybrid inflation model with metastable cosmic strings and scalar-induced gravitational waves, linking these phenomena to observable signals and primordial black holes.

Findings

Gravitational wave spectrum compatible with PTA measurements.

Primordial black holes with mass ~10^{29} g from waterfall transition.

Potential for future experimental detection of predicted signals.

Abstract

We explore the cosmological and astrophysical implications of a realistic hybrid inflation model based on flipped $SU(5)$. The model contains superheavy metastable cosmic strings arising from a waterfall field that encounters a limited number of $e$-foldings during the inflationary phase. In addition to the gravitational waves emitted by the metastable strings, there also appear scalar induced gravitational waves linked to the waterfall phase transition. These two independent sources of gravitational waves can yield a combined spectrum that is compatible with the recent PTA measurements, and with additional features that can be probed in future experiments. We also show the appearance of primordial black holes with mass on the order of $10^{29}$ g from the waterfall phase transition, and with an abundance that can be tested in the gravitational lensing experiments.