Study Explores Inflationary Interpretation of European Pulsar Timing Array Gravitational-Wave Signal
Researchers have analyzed whether the gravitational-wave background signal detected in the European Pulsar Timing Array's second data release (EPTA DR2) could be explained by primordial inflation, deriving tight constraints on key cosmological parameters. Incorporating data from the CMB, Big Bang Nucleosynthesis, and LIGO-Virgo-KAGRA, they narrowed the viable parameter space to specific ranges for the tensor-to-scalar ratio, spectral index, reheating temperature, and cut-off frequency. The findings suggest a viable but theoretically challenging inflationary interpretation, particularly because the required reheating temperatures are unusually low.
A new preprint submitted to arXiv investigates whether the gravitational-wave (GW) background evidenced in the European Pulsar Timing Array's second data release (EPTA DR2) can be attributed to primordial inflationary tensor modes. The authors parametrize the tensor power spectrum using four quantities — the tensor-to-scalar ratio r, the tensor spectral index n_t, the reheating temperature T_rh, and a cut-off frequency f_end — and apply a comprehensive set of observational constraints from the Cosmic Microwave Background, Big Bang Nucleosynthesis, and the LIGO-Virgo-KAGRA gravitational-wave detector network. After imposing all constraints simultaneously, the viable parameter space at 95% confidence is substantially reduced: log₁₀r between roughly −11.66 and −1.45, n_t between 1.32 and 2.47, T_rh between 1.78 MeV and 28.2 GeV, and f_end between 75.86 nHz and 14.45 Hz. The preferred scenario is one in which the GW spectrum observed by EPTA arises from tensor modes that re-entered the Hubble radius during the radiation-dominated era, which permits a higher tensor-to-scalar ratio and a relatively flat spectrum. However, the analysis highlights a significant theoretical tension: the reheating temperatures required are very low, making them difficult to accommodate within standard inflationary model-building. The work underscores both the promise and the challenges of interpreting nanohertz GW signals as relics of cosmic inflation.
What's missing
The paper is a preprint and has not yet undergone peer review, so its conclusions should be treated as preliminary.
What different sources said
- arXiv astro-phCenter
Irreducible Gravitational Wave Background as a Particle Detector
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