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[Paper Review] First-order Phase Transition interpretation of PTA signal produces solar-mass Black Holes

Yann Gouttenoire|arXiv (Cornell University)|Jul 9, 2023
Pulsars and Gravitational Waves ResearchPhysics and Astronomy139 references9 citations
TL;DR

The paper performs a Bayesian analysis of NG15 and IPTA2 PTA data, showing the stochastic GW background can be attributed to a strong first-order phase transition in the early universe, with implications for primordial black holes in the solar-mass range and multi-messenger detectability.

ABSTRACT

We perform a Bayesian analysis of NANOGrav 15yr and IPTA DR2 pulsar timing residuals and show that the recently detected stochastic gravitational-wave background (SGWB) is compatible with a SGWB produced by bubble dynamics during a cosmological first-order phase transition. The timing data suggests that the phase transition would occur around QCD confinement temperature and would have a slow rate of completion. This scenario can naturally lead to the abundant production of primordial black holes (PBHs) with solar masses. These PBHs can potentially be detected by current and advanced gravitational wave detectors LIGO-Virgo-Kagra, Einstein Telescope, Cosmic Explorer, by astrometry with GAIA and by 21-cm survey.

Motivation & Objective

  • Motivate exploring non-astrophysical origins for the PTA SGWB beyond SMBH binaries.
  • Test whether a strong first-order phase transition (1stOPT) can fit NG15 and IPTA2 PTA residuals.
  • Incorporate PBH production and BBN constraints as priors in the 1stOPT Bayesian analysis.
  • Quantify how well the 1stOPT scenario competes with SMBH binaries using Bayesian model comparison.
  • Forecast observational consequences for PBHs and future GW/astronomy probes.

Proposed method

  • Model the SGWB from a strongly supercooled 1stOPT using the bulk flow GW spectrum (Eq. 6) with alpha>>1.
  • Perform Bayesian inference on NG15 and IPTA2 timing residuals using enterprise/enterprise_extensions and PTMCMC/PTArcade.
  • Incorporate BBN bounds and PBH overproduction priors as constraints on 1stOPT parameters (T_reh, beta/H, alpha).
  • Compare models (1stOPT alone, SMBH binaries, or both) via Bayes factors (BF) following product-space sampling.
  • Explore both detection analyses and exclusion (lower-bound) analyses for the completion rate beta/H.
Figure 1: The violin diagrams depict the posterior probability distribution of the SGWB energy density in each frequency bins of NG15 and IPTA2 data sets. We overlay with solid lines the SWGB from 1stOPT, obtained using Eq. ( 6 ), using mean posterior value for the PT parameters. The dotted lines il
Figure 1: The violin diagrams depict the posterior probability distribution of the SGWB energy density in each frequency bins of NG15 and IPTA2 data sets. We overlay with solid lines the SWGB from 1stOPT, obtained using Eq. ( 6 ), using mean posterior value for the PT parameters. The dotted lines il

Experimental results

Research questions

  • RQ1Can a supercooled first-order phase transition explain the PTA SGWB observed by NG15 and IPTA2?
  • RQ2What are the inferred 1stOPT parameters (T_reh, beta/H, alpha) consistent with PTA data under BBN and PBH priors?
  • RQ3Does including PBH overproduction constraints alter the preference between 1stOPT and SMBH binary interpretations?
  • RQ4Are solar-mass PBHs a viable byproduct of the 1stOPT scenario and detectable by other probes (GW detectors, GAIA, 21-cm)?
  • RQ5What are the conservative bounds on the completion rate beta/H if the PTA SGWB is not from a 1stOPT?

Key findings

  • NG15 data favor a GW signal from strong 1stOPT over SMBH binaries with a Bayes factor of 24 (BBN-only prior).
  • Including PBH overproduction prior reduces the Bayes factor for 1stOPT vs SMBH to 15 in NG15, while IPTA2 remains inconclusive.
  • Mean posterior 1stOPT parameters under NG15 (BBN): log10(T_reh) = -0.80^{+0.23}_{-0.23}, beta/H = 9.8^{+4.0}_{-2.5}; with PBH prior: log10(T_reh) = -0.86^{+0.37}_{-0.26}, beta/H = 10.7^{+2.8}_{-3.3}.
  • IPTA2 results (BBN): log10(T_reh) = -1.34^{+0.3}_{-0.3}, beta/H = 13.8^{+6.6}_{-4.2}.
  • The 1stOPT scenario can produce solar-mass PBHs in the NG15 posterior region, offering a multi-messenger window (LIGO-Virgo-Kagra, ET/CE, GAIA lensing, 21-cm heating).
  • Exclusion bounds imply beta/H ≳ 10–20 if the PTA signal is not from a strong 1stOPT, constraining PBH-detectable scenarios within 1 solar mass to 10^3 solar masses.
Figure 2: Left : Colored regions are posterior distributions in term of the reheating temperature $T_{\rm reh}$ and rate of completion $\beta/H$ of a strong 1stOPT ( $\alpha\gg 1$ ). They are obtained after performing a Bayesian analysis of PTA dataset. We overlay the CMB, LIGO/Virgo and microlensin
Figure 2: Left : Colored regions are posterior distributions in term of the reheating temperature $T_{\rm reh}$ and rate of completion $\beta/H$ of a strong 1stOPT ( $\alpha\gg 1$ ). They are obtained after performing a Bayesian analysis of PTA dataset. We overlay the CMB, LIGO/Virgo and microlensin

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This review was created by AI and reviewed by human editors.