Abstract
A standard expectation of primordial cosmological inflation is that it dilutes all relics created before its onset to unobservable levels. We present a counterexample to this expectation by demonstrating that a network of cosmic strings diluted by inflation can regrow to a level that is potentially observable today in gravitational waves (GWs). In contrast to undiluted cosmic strings, whose primary GW signals are typically in the form of a stochastic GW background, the leading signal from a diluted cosmic string network can be distinctive bursts of GWs within the sensitivity reach of current and future GW observatories.
Highlights
Introduction.—Cosmological observations provide strong support for initial conditions of the form expected from inflation followed by reheating: a hot thermal plasma that is very uniform with small, approximately adiabatic and scale-invariant density fluctuations over distances that are much larger than the Hubble length in that era [1,2]
We present a counterexample to this expectation by demonstrating that a network of cosmic strings diluted by inflation can regrow to a level that is potentially observable today in gravitational waves (GWs)
In this work we investigate cosmic strings as a counterexample to these expectations, and we study the distinctive gravitational wave (GW) signals they produce in this scenario
Summary
(Received 30 January 2020; revised 30 September 2020; accepted 5 October 2020; published 20 November 2020). Introduction.—Cosmological observations provide strong support for initial conditions of the form expected from inflation followed by reheating: a hot thermal plasma that is very uniform with small, approximately adiabatic and scale-invariant density fluctuations over distances that are much larger than the Hubble length in that era [1,2] In addition to these features, inflation is expected to have diluted any relics created prior to its beginning, such as superheavy massive particles or most types of topological defects, to negligible levels [3,4,5]. Following inflation the energy density in long cosmic strings only falls off as a−2, where aðtÞ is cosmological scale factor, which is much slower than the a−4 dilution of radiation and a−3 of matter that are expected to dominate the energy budget of the cosmos until close to the present This difference in dilution rates implies that a network of
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