Particle Physics and Gravitational Waves as complementary windows on the Universe

Abstract

Particle physics and gravitational waves provide complementary probes of the deep structure of the Universe. Gravitational waves from the mergers of neutron stars and black holes are sensitive to the structure of dense quark matter and to different dark matter scenarios. Measurements of stochastic gravitational waves backgrounds can teach us about possible first order phase transitions in the early Universe, including providing sensitivity to the TeV scale which is of key interest to future particle collider experiments. Gravitational waves measurements will also give new probes of the evolution and expansion of the Universe, complementary to measurements with electromagnetic radiation. This Perspectives article explores the physics synergies between the science opportunities provided by next generation gravitational waves measurements and particle physics experiments. Gravitational waves can also probe deep into the early Universe reaching physics much above possible collider energies if the signals can be detected.

Figures (4)

• Figure 1: The gravitational waves spectrum showing phenomena that appear at different frequencies and the different types of GW detectors. Figure credit: ESA.
• Figure 2: Left: Upper limits on the spin-independent (SI) WIMP-nucleon cross section as a function of DM mass from direct detection experiments. The region where astrophysical neutrinos will start to be a limiting background is indicated in blue (neutrino fog). Figure from Refs. ParticleDataGroup:2024cfkBaudis:2025yva, updated (PDG2025). Right: DM density profiles of an accretion disc, a WIMP dark matter spike and a gravitational atom, surrounding a $10^5$ solar masses black hole. For details, see Ref. Cole:2022yzw. Here $r$ is the radial distance and $r_s$ is the Schwarzschild radius of the BH. The resulting DM environment-induced dephasing in the gravitational waveform of intermediate- and extreme-mass-ratio inspirals is potentially detectable with future interferometers.
• Figure 3: Left: The QCD phase diagram showing the domains of high density neutron stars and the physics to be explored in forthcoming experiments at GSI/FAIR as well as measurements with high energy heavy-ion collisions at the LHC and RHIC. Figure credit: GSI. Right: Neutron star properties deduced from the NS merger event GW170817. The posterior for the mass $m$ and areal radius $R$ of each binary component that produced the merger, using an EoS-insensitive relations method. The top blue (bottom orange) posterior corresponds to the heavier (lighter) NS and several model curves are shown for comparison. Figure from Ref. LIGOScientific:2018cki.
• Figure 4: Left: Higgs boson couplings to different particles and masses measured at the LHC. The results are expressed in terms of "coupling modifiers" which describe the level of deviation from SM expectations ATLAS:2022vkf. Right: Parameter space of an extended 2-Higgs doublet model leading to a first-order phase transition in the LISA frequency range with a value of $\lambda$ that is larger than the SM value by a factor about two Biekotter:2022kgfLinearColliderVision:2025hlt. Present LHC constraints on $\lambda$ are shown as horizontal lines with results from ATLAS ATLAS:2024ish and CMS CMS:2024awa. Here $h$, $H$ and $A$ are the lightest, most SM-like, and heaviest neutral scalar bosons in the model; $A$ is an extra pseudoscalar boson which is taken to be degenerate with two extra charged Higgs states in the model. The Higgs self-coupling $\lambda$ awaits precision measurement and is important both for vacuum stability and for determining any possible TeV scale SGWB.