Gravitational Wave Astronomy: A Revolutionary Window on the Universe
Gravitational wave (GW) astronomy is revolutionizing our understanding of the most cataclysmic events in the universe. The observation of GWs from the mergers of compact object binaries by LIGO and Virgo has already provided unprecedented information on the properties and astrophysical formation channels of neutron stars and stellar-mass black holes, probing general relativity (GR) in the strong-field regime. Anticipated advances with third-generation detectors like the Einstein Telescope and Cosmic Explorer, and space missions like LISA, will extend these observations to lower frequency bands. Concurrently, pulsar timing array experiments have detected evidence of a possible stochastic background of GWs in the nHz frequency band, likely due to mergers of supermassive black holes with masses of billions of solar masses.
TEONGRAV TS has made substantial contributions to various aspects of gravitational astronomy. Recent results include the group's contribution to interpreting data from the European Pulsar Timing Array (EPTA), providing evidence of a stochastic background of GWs at nHz frequencies. More specifically, TEONGRAV TS led the effort to place limits on the presence of possible ultralight scalar/pseudoscalar dark matter particles ('fuzzy' dark matter) in EPTA data. Additionally, TEONGRAV TS leveraged our group's earlier work on semi-analytic models of galaxy formation to show that if the EPTA signal is due to a population of supermassive black hole binaries, the final parsec problem must be efficiently resolved. In a series of papers from 2020 to 2023, our group also studied the generation of GWs in effective field theories (EFT) of dark energy. These theories attempt to classify within a coherent framework the vast array of gravitational theories seeking to reproduce cosmological observables without any actual dark energy/cosmological constant, at the cost of extending GR by introducing an additional scalar graviton. These theories are inherently nonlinear and nonperturbative (and thus challenging to study) and have received much attention because they could provide observational signatures different from the LCDM model in cosmological experiments. While some of these theories are constrained by LIGO/Virgo results on the speed of GW propagation, a broad class of them—including especially theories with self-interactions in derivatives—remains valid under the commonly made assumption that GW generation behaves like GR on local scales. This assumption is based on the (presumed) presence of nonlinear screening mechanisms in these theories, rendering them indistinguishable from GR in quasi-static and spherically symmetric configurations. Our work has shown for the first time that these screening mechanisms are ineffective in masking deviations from GR in non-quasistatic situations. In more detail, we performed the first 3+1 numerical relativity simulations in these theories (for gravitational collapse and neutron star binaries). We discovered that future GW detectors will be able to detect small low-frequency deviations from GR predictions, thus confirming or excluding a modified gravity origin for dark energy.
Structured staff:
- Enrico Barausse (coordinator) (SISSA)
- Mario Spera (SISSA)
- Ugo Niccolò di Carlo (SISSA)
Link to TEONGRAV web site.
