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Whispers from the dark side: Confronting light new physics with NANOGrav data

by Wolfram Ratzinger, Pedro Schwaller

Submission summary

As Contributors: Pedro Schwaller
Preprint link: scipost_202010_00008v2
Date accepted: 2021-02-17
Date submitted: 2021-01-06 13:40
Submitted by: Schwaller, Pedro
Submitted to: SciPost Physics
Academic field: Physics
  • Gravitation, Cosmology and Astroparticle Physics
  • High-Energy Physics - Phenomenology
Approaches: Theoretical, Phenomenological


The NANOGrav collaboration has recently observed first evidence of a grav- itational wave background (GWB) in pulsar timing data. Here we explore the possibility that this GWB is due to new physics, and show that the signal can be well fit also with peaked spectra like the ones expected from phase transitions (PTs) or from the dynamics of axion like particles (ALPs) in the early universe. We find that a good fit to the data is obtained for a very strong PT at temperatures around 1 MeV to 10 MeV. For the ALP explanation the best fit is obtained for a decay constant of F ≈ 5 × 10^17 GeV and an axion mass of 2 × 10^−13 eV. We also illustrate the ability of PTAs to constrain the parameter space of these models, and obtain limits which are already comparable to other cosmological bounds.

Published as SciPost Phys. 10, 047 (2021)

Reports on this Submission

Anonymous Report 2 on 2021-2-12 Invited Report

  • Cite as: Anonymous, Report on arXiv:scipost_202010_00008v2, delivered 2021-02-11, doi: 10.21468/SciPost.Report.2541


1- Interesting analysis of potential physics implications of new experimental result with two different models
2- Main ideas and results are clearly presented


The model agnostic approach to the phase-transition scenario makes it difficult to access the cosmological viability of these scenarios.


The authors have addressed all the points I had brought up in my first report. I recommend publication of the manuscript.

  • validity: -
  • significance: good
  • originality: high
  • clarity: good
  • formatting: -
  • grammar: -

Anonymous Report 1 on 2021-2-1 Invited Report

  • Cite as: Anonymous, Report on arXiv:scipost_202010_00008v2, delivered 2021-02-01, doi: 10.21468/SciPost.Report.2489


The paper discusses a recent NANOGraph anomaly in terms of several primordial signals. It is clear and well written.


The discussion is partially agnostic when it comes to concrete models which makes some bounds (like BBN) hard to assess.


The authors amended the issues I had with the previous version. I recommend publication.

  • validity: good
  • significance: good
  • originality: good
  • clarity: high
  • formatting: good
  • grammar: good

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