Gravitational waves

Gravitational Waves (GWs) are ripples of spacetime predicted by Einstein's general theory of relativity. GWs could be produced whenever there is a violent displacement of matter or energy in space. For example, binary black holes could produce GWs as they merge; such signals were detected by the LIGO collaboration in 2015. The earth also produces GWs as it rotates around the Sun, but because it is in the stable orbit and because of the small masses of the system, the GWs produced is extremely small.

When there is a superposition of multiple GWs from many different sources, we may observe a stochastic GWs background that could be characterized by its energy density and peak frequency. A GWs background in the nHz frequency regime has been detected by the NANOGrav collaboration in 2023. This GWs background could have been produced due to the mergers of supermassive black holes, but the final-parsec problem and the mismatch between the predicted and observed spectra raised questions about this scenario.

Many new physics phenomena, such as enhancement of primordial curvature power spectrum at small scale or a strong first-order phase transition, could have produced a GWs background in the high-frequency regime. Future experiments such as LISA, BBO, or ET will be able to probe GWs in the mHz-kHz frequency regime that could give us many compelling answers.

I'm  interested in exploring new physics phenomena of cosmological origins that could produce a GWs background.

• Ngo Phuc Duc Loc, "Gravitational waves from burdened primordial black holes dark matter", Phys. Rev. D 111, 023509 (2025)