[Paper Review] Waveform Modelling for the Laser Interferometer Space Antenna

LISA Consortium Waveform Working Group, Niayesh Afshordi+144 more|INFM-OAR (INFN Catania)|Nov 2, 2023

Pulsars and Gravitational Waves Research1,962 references19 citations

TL;DR

This white paper reviews the current state of waveform models for LISA sources and outlines the major challenges to meet accuracy, efficiency, and interface requirements for future data analysis.

ABSTRACT

LISA, the Laser Interferometer Space Antenna, will usher in a new era in gravitational-wave astronomy. As the first anticipated space-based gravitational-wave detector, it will expand our view to the millihertz gravitational-wave sky, where a spectacular variety of interesting new sources abound: from millions of ultra-compact binaries in our Galaxy, to mergers of massive black holes at cosmological distances; from the beginnings of inspirals that will venture into the ground-based detectors' view to the death spiral of compact objects into massive black holes, and many sources in between. Central to realising LISA's discovery potential are waveform models, the theoretical and phenomenological predictions of the pattern of gravitational waves that these sources emit. This white paper is presented on behalf of the Waveform Working Group for the LISA Consortium. It provides a review of the current state of waveform models for LISA sources, and describes the significant challenges that must yet be overcome.

Motivation & Objective

• Define the scientific and data-analysis driven needs for waveform models in the LISA era.
• Inventory the expected LISA sources and their parameter ranges to guide model requirements.
• Identify accuracy, efficiency, and interface requirements for waveform models in LISA data analysis.
• Summarize current modelling approaches and their domains of validity to inform future development.
• Highlight challenges and roadmap for waveform modelling, including beyond-GR and exotic sources.

Proposed method

• Survey the landscape of LISA sources and their parameter spaces to set modelling targets.
• Review the four principal first-principles approaches (NR, PN/PM, GSF, BH perturbation theory) and their domains of applicability.
• Discuss how effective-one-body and phenomenological models integrate multiple approaches to cover large parameter spaces.
• Outline data-analysis driven requirements for waveform accuracy, efficiency, and data formats.
• Describe acceleration techniques and hardware considerations for rapid waveform generation.
• Address modelling for beyond-GR, beyond-Standard-Model, and cosmic strings sources.

Figure 1: A sketch of the natural domains of applicability of the four main approaches to solving the relativistic two-body problem. The approaches are largely complementary and building waveforms for LISA will require input from all four. The solid lines shown are illustrative of the reach of each

Experimental results

Research questions

• RQ1 What waveform model accuracy and coverage are required for LISA source classes (MBHBs, EMRIs, IMRIs, GBs, SOBHBs, CS, beyond GR) to enable robust detection and parameter estimation?
• RQ2 How can NR, PN/PM, GSF, and BH perturbation theory be combined into global models (e.g., EOB, Phenom) suitable for LISA data analysis?
• RQ3 What data-format and computational efficiency requirements must waveform models meet for practical LISA pipelines?
• RQ4 What challenges arise in modelling beyond-GR and exotic sources for LISA, and what strategies exist to address them?
• RQ5 What acceleration and computational strategies are feasible to enable rapid waveform generation for large-scale LISA studies?

Key findings

• Waveform models for LISA must span a much broader source class and parameter space than ground-based detectors.
• Effective-one-body and phenomenological approaches synthesize information from NR, PN/PM, and GSF to cover large domains.
• Significant challenges remain in achieving required accuracy for diverse sources and in ensuring computational efficiency and interoperability.
• Modelling beyond GR and exotic sources (e.g., cosmic strings) requires dedicated extensions across multiple modelling frameworks.
• Acceleration techniques and hardware considerations are essential to make rapid waveform generation feasible for LISA-scale data analysis.

Figure 2: Region of applicability of different approximation techniques for non-spinning quasi-circular binary BH inspiral. The 1PA region is a prediction derived from fitting NR data to an expansion of the form ( 14 ). The shaded regions indicate ranges within which the cumulative orbital phase-err