Cosmological Interpretation for the Stochastic Signal in Pulsar Timing Arrays

Abstract

The pulsar timing array (PTA) collaborations have recently reported compelling evidence for the presence of a stochastic signal consistent with a gravitational-wave background. In this letter, we combine the latest data sets from NANOGrav, PPTA and EPTA collaborations to explore the cosmological interpretations for the detected signal from first-order phase transitions, domain walls and cosmic strings, separately. We find that the first-order phase transitions and cosmic strings can give comparable interpretations compared to supermassive black hole binaries (SMBHBs) characterized by a power-law spectrum, but the domain wall model is strongly disfavored with the Bayes factor compared to the SMBHB model being 0.009. Furthermore, the constraints on the parameter spaces indicate that: 1) a strong phase transition at temperatures below the electroweak scale is favored and the bubble collisions make the dominant contribution to the energy density spectrum; 2) the cosmic string tension is $G\mu \in [1.46,15.3]\times 10^{-12}$ at $90\%$ confidence interval and a small reconnection probability $p<6.68\times 10^{-2}$ is preferred at $95\%$ confidence level, implying that the strings in (super)string theory are strongly favored over the classical field strings.

10 pages, 5 figures, 2 tables; References updated

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• Model-independent reconstruction of the primordial curvature power spectrum from PTA data
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• Exploring the NANOGrav Signal and Planet-mass Primordial Black Holes through Higgs Inflation
• Probing the speed of scalar-induced gravitational waves with pulsar timing arrays
• Search for Non-Tensorial Gravitational-Wave Backgrounds in the NANOGrav 15-Year Data Set
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• Prospects for Taiji to detect a gravitational-wave background from cosmic strings
• Spatial and Spectral Characterization of the Gravitational-wave Background with the PTA Optimal Statistic
• Can we distinguish the adiabatic fluctuations and isocurvature fluctuations with pulsar timing arrays?
• Charting the Nanohertz Gravitational Wave Sky with Pulsar Timing Arrays
• Gravitational Waves from Phase Transitions
• General bubble expansion at strong coupling
• Constraining string cosmology with the gravitational-wave background using the NANOGrav 15-year data set
• Polarization modes of gravitational waves in general Einstein-vector theory
• Detecting a Gravitational-Wave Background from Inflation with Null Energy Condition Violation: Prospects for Taiji
• Interpreting Pulsar Timing Array data of Gravitational Waves with Ekpyrosis-Bouncing Cosmology
• Dark Matter Spike surrounding Supermassive Black Holes Binary and the Nanohertz Stochastic Gravitational Wave Background
• Constraining inflation with nonminimal derivative coupling with the Parkes Pulsar Timing Array third data release
• Gravitational-wave effects in the most general vector-tensor theory
• Connecting Inflation to the NANOGrav 15-year Data Set via Massive Gravity
• Bubbles kick off primordial black holes to form more binaries
• Accurate pulsar timing array residual variances and correlation of the stochastic gravitational wave background
• From oversimplified to overlooked: the case for exploring Rich Dark Sectors
• Spatial Correlation between Pulsars from Interfering Gravitational-Wave Sources in Massive Gravity
• Testing No slip model with pulsar timing arrays: NANOGrav and IPTA