Domain wall interpretation of the PTA signal confronting black hole overproduction

Gouttenoire, Yann; Vitagliano, Edoardo

doi:10.1103/physrevd.110.l061306

Phys. Rev. D

2024

DOI: 10.1103/physrevd.110.l061306

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Domain wall interpretation of the PTA signal confronting black hole overproduction

Yann Gouttenoire,

Edoardo Vitagliano

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2024

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Cited by 4 publications

References 103 publications

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Induced domain walls of QCD axion, and gravitational waves

Lee,

Murai,

Takahashi

et al. 2024

J. Cosmol. Astropart. Phys.

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We show that heavy axion domain walls induce domain walls of the QCD axion through a mixing between the heavy axion and the QCD axion, even when the pre-inflationary initial condition is assumed for the QCD axion. The induced domain walls arise because the effective θ parameter changes across the heavy axion domain walls, shifting the potential minimum of the QCD axion. When the heavy axion domain walls collapse, the induced QCD axion domain walls collapse as well. This novel mechanism for producing the QCD axions can explain dark matter even with the axion decay constant as small as 𝒪(109) GeV. In particular, this scenario requires domain wall collapse near the QCD crossover, potentially accounting for the stochastic gravitational wave background suggested by recent pulsar timing array observations, including NANOGrav. Using this mechanism, it is also possible to easily create induced domain walls for string axions or axions with a large decay constant, which would otherwise be challenging. We also comment on the implications for cosmic birefringence using induced axion domain walls.

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Induced domain walls of QCD axion, and gravitational waves

Lee,

Murai,

Takahashi

et al. 2024

J. Cosmol. Astropart. Phys.

View full text Add to dashboard Cite

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Constraints on ultra-slow-roll inflation with the NANOGrav 15-Year dataset

Mu,

Liu,

Cheng

et al. 2024

J. Cosmol. Astropart. Phys.

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Ultra-slow-roll (USR) inflation predicts an exponential amplification of scalar perturbations at small scales, which leads to a stochastic gravitational wave background (SGWB) through the coupling of the scalar and tensor modes at the second-order expansion of the Einstein equation. In this work, we search for such a scalar-induced SGWB from the NANOGrav 15-year (NG15) dataset, and find that the SGWB from USR inflation could explain the observed data. The Bayes factors are 54 ± 5 for the USR inflation model alone and 68 ± 6 for the combined USR inflation plus supermassive black hole binaries (SMBHB) models. We place constraints on the amplitude of the scalar power spectrum to P Rp > 10-1.95 at 95% confidence level (C.L.) at the scale of k ∼ 20 pc-1. We find that log10 P Rp degenerates with the peak scale log10 k p. We also obtain the parameter space allowed by the data in the USR inflationary scenario, where the e-folding numbers of the duration of the USR phase has a lower limit ΔN > 2.80 (95% C.L.) when the USR phase ends at N ≈ 20. With astrophysically motivated priors, the NG15 dataset fits both the USR inflation model and SMBHB model equally well.

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Irreducible cosmological backgrounds of a real scalar with a broken symmetry

D’Eramo,

Tesi,

Vaskonen

2024

Phys. Rev. D

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We explore the irreducible cosmological implications of a singlet real scalar field. Our focus is on theories with an approximate and spontaneously broken Z2 symmetry where quasistable domain walls can form at early times. This seemingly simple framework bears a wealth of phenomenological implications that can be tackled by means of different cosmological and astrophysical probes. We elucidate the connection between domain wall dynamics and the production of dark matter and gravitational waves. In particular, we identify three main benchmark scenarios. The gravitational wave signal observed by pulsar timing arrays can be generated by the domain walls if the mass of the singlet is ms∼PeV. For lower masses, but with ms≳10 GeV, scalars produced in the annihilation of the domain walls can be dark matter with a distinctive feature in their power spectrum. Finally, the thermal bath provides an unavoidable source of unstable scalars via the freeze-in mechanism whose subsequent decays can be tested by their imprints on cosmological and terrestrial observables. Published by the American Physical Society 2024

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Domain wall interpretation of the PTA signal confronting black hole overproduction

Cited by 4 publications

References 103 publications

Induced domain walls of QCD axion, and gravitational waves

Induced domain walls of QCD axion, and gravitational waves

Constraints on ultra-slow-roll inflation with the NANOGrav 15-Year dataset

Irreducible cosmological backgrounds of a real scalar with a broken symmetry

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