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Published on: August 12, 2013
Observable Gravitational Wave Strain at Second Order.
Guillem Domènech1,2, Shi Pi3,4,5, Ao Wang1,3,6
1Leibniz University Hannover, Institute for Theoretical Physics, Appelstraße 2, 30167 Hannover, Germany.
Physical Review Letters
|June 22, 2026
Summary
We define second-order gravitational wave strain using observable electromagnetic signals, resolving gauge ambiguities in cosmological perturbation theory. This clarifies secondary gravitational waves, particularly those from primordial fluctuations.
Area of Science:
- Cosmology
- General Relativity
- Gravitational Wave Physics
Background:
- Defining gravitational wave strain at second order in cosmological perturbation theory lacks rigor.
- Gauge dependence of transverse and traceless fluctuations complicates secondary gravitational waves, especially those from primordial fluctuations.
Purpose of the Study:
- To compute the observable gravitational wave strain at second order.
- To resolve gauge ambiguities in the definition of secondary gravitational waves.
Main Methods:
- Gauge-invariant computation of gravitational wave strain.
- Utilizing geodesic observers emitting and receiving electromagnetic signals.
Main Results:
- The observable gravitational wave strain at second order is computed for the first time.
- The measured strain coincides with transverse-traceless components in the Newton gauge.
Conclusions:
- Gauge ambiguities in secondary gravitational wave definitions are settled.
- Provides a rigorous definition for second-order gravitational wave strain in cosmology.
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