Black holes, gravitational waves and fundamental physics: a roadmap (1806.05195v4)

Abstract: The grand challenges of contemporary fundamental physics---dark matter, dark energy, vacuum energy, inflation and early universe cosmology, singularities and the hierarchy problem---all involve gravity as a key component. And of all gravitational phenomena, black holes stand out in their elegant simplicity, while harbouring some of the most remarkable predictions of General Relativity: event horizons, singularities and ergoregions. The hitherto invisible landscape of the gravitational Universe is being unveiled before our eyes: the historical direct detection of gravitational waves by the LIGO-Virgo collaboration marks the dawn of a new era of scientific exploration. Gravitational-wave astronomy will allow us to test models of black hole formation, growth and evolution, as well as models of gravitational-wave generation and propagation. It will provide evidence for event horizons and ergoregions, test the theory of General Relativity itself, and may reveal the existence of new fundamental fields. The synthesis of these results has the potential to radically reshape our understanding of the cosmos and of the laws of Nature. The purpose of this work is to present a concise, yet comprehensive overview of the state of the art in the relevant fields of research, summarize important open problems, and lay out a roadmap for future progress.

• The paper outlines a comprehensive roadmap that synthesizes current research on black holes and gravitational waves to advance fundamental physics.
• It emphasizes the need for enhanced numerical simulations and refined waveform models to improve detection and analysis of high-mass and high-spin binary systems.
• It explores extensions beyond General Relativity, including alternative gravity theories, to address unresolved issues such as dark matter interactions and the hierarchy problem.

Overview of "Black holes, gravitational waves and fundamental physics: a roadmap"

The paper "Black holes, gravitational waves, and fundamental physics: a roadmap" presents an in-depth exploration of the scientific and theoretical challenges in the paper of black holes (BHs), gravitational waves (GWs), and their implications for fundamental physics. The objectives are multifaceted: to synthesize current knowledge, highlight unresolved questions, and provide a strategic plan for future research directions in these areas, particularly in the context of the European Action on Black holes, Gravitational waves and Fundamental Physics (GWverse).

Black Holes and Gravitational Waves in General Relativity

The onset of GW astronomy, heralded by the direct detection of GWs by LIGO and Virgo collaborations, has expanded our understanding of cosmic phenomena. GWs offer a window into the dynamics of compact objects like black holes and neutron stars, allowing tests of General Relativity (GR) beyond the weak-field, low-velocity regime. The paper explores the theoretical modeling of these systems, necessitating sophisticated toolkits like Perturbation Methods, Post-Newtonian (PN) approximations, Numerical Relativity (NR), and Effective-One-Body (EOB) frameworks to achieve high-fidelity waveforms for data analysis.

Challenges in Numerical Simulation and Waveform Modeling

Given the complex nature of two-body problems in GR, particularly the coalescence events involving massive BHs, precise numerical simulations are imperative. The paper underscores the necessity for enhanced numerical techniques to tackle high mass-ratio binaries and spin configurations near extremality, which remain computationally intensive. Current waveform models stand robust, yet their accuracy must scale with sensitivities of future detectors, such as the Einstein Telescope and LISA, to ensure the extraction and interpretation of weak signals buried in noisy data. Presently, systematic errors in waveform generation pose limits on parameter estimation, motivating continued advancements in simulation and phenomenological modeling.

Beyond General Relativity: Exploring Fundamental Physics

The anticipation of new physics through GW observation is predicated on theories extending GR, such as scalar-tensor theories, metric-affine gravity, and massive gravity models. These could address phenomena GR cannot, including the hierarchy problem and dark matter interactions. However, alternative theories must be rigorously tested for viability and uniqueness to ensure physical predictions align with cosmic observations. The paper discusses implications for black holes that deviate from Kerr solutions — "hairy" black holes featuring scalar fields, which could manifest through GW signals differing from GR predictions.

Future Directions and Implications

The roadmap presents an ambitious itinerary for researchers: build comprehensive models incorporating higher-order corrections and eccentricity in binary systems, and pursue multi-messenger astronomy to correlate GW data with electromagnetic phenomena. Experimentally, enhanced precision in gravitational wave interferometry is crucial, alongside analytical strides in mapping the parameter space of compact-object mergers.

Concluding Remarks

This roadmap articulates a trajectory for gravitational physics research intertwining theoretical, observational, and numerical endeavors. Understanding black holes, a keystone of GR, through the GW lens, emboldens both theoretical predictions and fundamental physics, bridging the quantum-gravity frontier. The paper serves as a clarion call for interdisciplinary collaboration, tasked with the translation of GWs into fundamental insights about our universe. As the paper of gravitational phenomena progresses, this document remains a pivotal guidepost for navigating one of physics' ultimate frontiers.