Challenges and Opportunities of Gravitational Wave Searches above 10 kHz

Abstract

The first direct measurement of gravitational waves by the LIGO and Virgo collaborations has opened up new avenues to explore our Universe. This white paper outlines the challenges and gains expected in gravitational-wave searches at frequencies above the LIGO/Virgo band. The scarcity of possible astrophysical sources in most of this frequency range provides a unique opportunity to discover physics beyond the Standard Model operating both in the early and late Universe, and we highlight some of the most promising of these sources. We review several detector concepts that have been proposed to take up this challenge, and compare their expected sensitivity with the signal strength predicted in various models. This report is the summary of a series of workshops on the topic of high-frequency gravitational wave detection, held in 2019 (ICTP, Trieste, Italy), 2021 (online) and 2023 (CERN, Geneva, Switzerland).

Figures (13)

• Figure 1: Overview of achieved and projected strain sensitivities of high-frequency gravitational wave detectors up to 100GHz. Solid (dashed) lines indicate broadband (resonant) detectors. The color coding (see text for details) indicates the development stage ranging from published GW results (orange) to active R&D efforts (purple) and proposed concepts (cyan). Details on the different proposals are given in \ref{['sec:exp']}.
• Figure 2: Overview of projected strain sensitivities of gravitational wave detectors above 100GHz. The color coding is the same as in \ref{['fig:sens_HF']}, with orange, purple and cyan curves indicating published GW results, active R&D efforts, and proposed concepts, respectively. Details on the different proposals are given in \ref{['sec:exp']}.
• Figure 3: Distance reach of different broad-band high-frequency GW detectors for equal-mass PBH binaries with chirp mass $M_c$. The color code matches the one used in \ref{['fig:sens_HF', 'fig:sens_VHF']}, with orange, purple and cyan curves indicating published GW results, active R&D efforts, and proposed concepts, respectively. The upper shaded region corresponds to distances within which $\geq 1$ event/yr is expected, assuming PBHs to account for all of the dark matter in the Universe (solid) or 0.1% of it (dashed).
• Figure 4: Sensitivity of high-frequency gravitational wave detectors to stochastic gravitational wave backgrounds assuming one year of integration time. The solid curves (broadband instruments) are power-law-integrated sensitivity curves, the dashed lines (resonant instruments) indicate the reach when running at fixed frequency for $t_\text{int} = 1year$. See text for details and caveats. In blue we indicate astrophysical constraints as discussed in \ref{['sec:AstroDetectors']}, where integration time varies dependent on observations Hill:2018trh. The horizontal dashed blue line indicates the upper bound from BBN on cosmological sources, see \ref{['sec:earlyU']}. The remainder of the color coding is as in \ref{['fig:sens_HF', 'fig:sens_VHF']}, with orange, purple and cyan curves indicating published GW results, active R&D efforts, and proposed concepts, respectively.
• Figure 5: Left: GW spectrum of slowly rotating core-collapse supernovae from several different simulations compared to the sensitivities of interferometric detectors. Right: Frequency of the signal from a core-collapse supernova of a $25 M_\odot$ progenitor star as a function of time and of the proto-neutron star's oscillatory modes. The white dots denote the eigenfrequencies associated with the quadrupolar f- and g-modes of the PNS. Asymmetric accretion produces an early subdominant peak around 100Hz and excites the proto-neutron star oscillations which emit the dominant peak around 1kHz. Figures taken from Vartanyan:2023sxmRadice:2018usf.