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Search for scalar induced gravitational waves in the International Pulsar Timing Array Data Release 2 and NANOgrav 12.5 years datasets
by Virgile Dandoy, Valerie Domcke, Fabrizio Rompineve
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Submission summary
| Authors (as registered SciPost users): | Fabrizio Rompineve |
| Submission information | |
|---|---|
| Preprint Link: | scipost_202302_00045v1 (pdf) |
| Date submitted: | 2023-02-28 14:11 |
| Submitted by: | Rompineve, Fabrizio |
| Submitted to: | SciPost Physics |
| Ontological classification | |
|---|---|
| Academic field: | Physics |
| Specialties: |
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| Approaches: | Theoretical, Computational, Phenomenological |
Abstract
We perform a Bayesian search in the latest Pulsar Timing Array (PTA) datasets for a stochastic gravitational wave (GW) background sourced by curvature perturbations at scales $10^5~\text{Mpc}^{-1}\lesssim k\lesssim 10^8~\text{Mpc}^{-1}$. These re-enter the Hubble horizon at temperatures around and below the QCD crossover phase transition in the early Universe. We include a stochastic background of astrophysical origin in our search and properly account for constraints on the curvature power spectrum from the overproduction of primordial black holes (PBHs). We find that the International PTA Data Release 2 significantly favors the astrophysical model for its reported common-spectrum process, over the curvature-induced background. On the other hand, the two interpretations fit the NANOgrav 12.5 years dataset equally well. We then set new upper limits on the amplitude of the curvature power spectrum at small scales. These are independent from, and competitive with, indirect astrophysical bounds from the abundance of PBH dark matter. Upcoming PTA data releases will provide the strongest probe of the curvature power spectrum around the QCD epoch.
Current status:
Reports on this Submission
Report #1 by Anonymous (Referee 2) on 2023-6-29 (Invited Report)
- Cite as: Anonymous, Report on arXiv:scipost_202302_00045v1, delivered 2023-06-29, doi: 10.21468/SciPost.Report.7417
Strengths
This paper compares three previous papers (Refs. [42,43,44]) that explain the NANOGrav12.5yr data by using the induced gravitational wave (IGW). This is good for communiteis to understand the current status of the data of the NANOGrav12.5yr collaboration.
Weaknesses
I think there is no weak point in this article.
Report
This paper is very valuable in that it carefully compares three previous papers (Refs. [42,43,44]) that explain the NANOGrav12.5yr data by using the induced gravitational wave (IGW).
However, before accepting this paper for publication, I would like to make one comment.
When one obtains a conservative limit on the free parameters in the analysis of a beyond the standard model, such as IGW, due to a large curvature perturbation that creates a Primordial Black Hole, the most conservative bound is the one obtained without considering the contribution of other models, i.e., the Astrophysical signal components from the Supermassive Black Holes mergers. When both are considered, the limit on each model parameter is always stronger than when only one of them is considered. This is at odds with the position of getting a CONSERVATIVE limit. I think that is the reason why the previous three papers did not
consider possible contributions from such unknown astrophysical sources.
Requested changes
None
Author: Fabrizio Rompineve on 2023-07-03 [id 3777]
(in reply to Report 1 on 2023-06-29)
We thank the referee for the useful comment. We have added a clarification in our manuscript, at the end of the third paragraph on p. 10, mentioning the alternative strategy to set upper limits suggested by the referee and motivating our different strategy.
We agree that the weakest upper limits from PTAs on any gravitational wave (GW) signal are obtained by requiring that the latter is not stronger than the currently reported excess, in the absence of any other contribution to the stochastic background. Our different strategy in this paper is motivated by the cosmological and astrophysical constraints on scalar-induced GWs, which very significantly constrain the possibility that scalar-induced GWs can provide a feasible model of the currently reported common process, as shown in our Figs. 3 and 6 and as discussed extensively in Sec. IV of our paper.
Anonymous on 2023-06-28 [id 3772]
This paper is very valuable in that it carefully compares three previous papers (Refs. [42,43,44]) that explain the NANOGrav12.5yr data by using the induced gravitational wave (IGW).
However, before accepting this paper for publication, I would like to make one comment.
When one obtains a conservative limit on the free parameters in the analysis of a beyond the standard model, such as IGW, due to a large curvature perturbation that creates a Primordial Black Hole, the most conservative bound is the one obtained without considering the contribution of other models, i.e., the Astrophysical signal components from the Supermassive Black Holes mergers. When both are considered, the limit on each model parameter is always stronger than when only one of them is considered. This is at odds with the position of getting a CONSERVATIVE limit. I think that is the reason why the previous three papers did not
consider possible contributions from such unknown astrophysical sources.