Ultrahigh frequency primordial gravitational waves beyond the kHz: The case of cosmic strings

Abstract

We investigate gravitational-wave backgrounds (GWBs) of primordial origin that would manifest only at ultrahigh frequencies, from kilohertz to 100 gigahertz, and leave no signal at LIGO, the Einstein Telescope, the Cosmic Explorer, LISA, or pulsar-timing arrays. We focus on GWBs produced by cosmic strings and make predictions for the GW spectra scanning over high-energy scale (beyond 1010 GeV) particle physics parameters. Signals from local string networks can easily be as large as the big bang nucleosynthesis/cosmic microwave background bounds, with a characteristic strain as high as 10−26 in the 10 kHz band, offering prospects to probe grand unification physics in the 1014–1017 GeV energy range. In comparison, GWB from axionic strings is suppressed (with maximal characteristic strain ∼10−31) due to the early matter era induced by the associated heavy axions. We estimate the needed reach of hypothetical futuristic GW detectors to probe such GWB and, therefore, the corresponding high-energy physics processes. Beyond the information of the symmetry-breaking scale, the high-frequency spectrum encodes the microscopic structure of the strings through the position of the UV cutoffs associated with cusps and kinks, as well as potential information about friction forces on the string. The IR slope, on the other hand, reflects the physics responsible for the decay of the string network. We discuss possible strategies for reconstructing the scalar potential, particularly the scalar self-coupling, from the measurement of the UV cutoff of the GW spectrum. Published by the American Physical Society 2024

Quantum tunneling in the early universe: stable magnetic monopoles from metastable cosmic strings

“…In figure 5 we display the spectrum for two values of the metastability factor, namely √ κ = 5 and 6 respectively. For √ κ around 5, the monopole abundance from the string network decay is in the observable range but the gravitational wave spectrum would be hard to detect in the near future [96][97][98]. With √ κ ≈ 6, the monopole abundance is quite suppressed, but the gravitational wave spectrum shows a peak in the frequency range that will be tested by HLVK [88] in the near future, and hopefully by the Einstein Telescope (ET) [89] and Cosmic Explorer (CE) [90] in the foreseeable future.…”

Cosmic Strings’ Imprints in High-Frequency Gravitational Waves

“…But higher frequencies offer a detection window clean of astrophysical signals (such as those from black hole binaries) and dominated by signals coming from early-Universe processes (inflation, primordial phase transitions, and more). Now Géraldine Servant of Hamburg University, Germany, and the German Electron Synchrotron DESY and Peera Simakachorn of the University of Valencia, Spain, compute the spectrum of one possible source of primordial signals-cosmic strings [1]. The results suggest that cosmic strings might be the dominant source of ultrahigh-frequency signals.…”