https://doi.org/10.1140/epjc/s10052-025-13998-1
Regular Article - Theoretical Physics
Constraining string cosmology with the gravitational-wave background using the NANOGrav 15-year data set
1
Department of Physics, Key Laboratory of Low Dimensional Quantum Structures and Quantum Control of Ministry of Education, Synergetic Innovation Center for Quantum Effects and Applications, Hunan Normal University, 410081, Changsha, Hunan, China
2
Institute of Interdisciplinary Studies, Hunan Normal University, 410081, Changsha, Hunan, China
3
College of Mathematics and Physics, Hunan University of Arts and Science, 415000, Changde, China
4
Faculty of Arts and Sciences, Beijing Normal University, 519087, Zhuhai, China
a
youwuphy@gmail.com
b
liulang@bnu.edu.cn
Received:
26
December
2024
Accepted:
21
February
2025
Published online:
21
March
2025
Multiple pulsar timing array (PTA) collaborations, including the European PTA in partnership with the Indian PTA, the North American Nanohertz Observatory for Gravitational Waves (NANOGrav), the Parkes PTA, and the Chinese PTA have recently reported strong evidence for a signal at nanohertz, potentially the first detection of the stochastic gravitational-wave background (SGWB). We investigate whether the NANOGrav signal is consistent with the SGWB predicted by string cosmology models. By performing Bayesian parameter estimation on the NANOGrav 15-year data set, we constrain the key parameters of a string cosmology model: the frequency 
and the fractional energy density 
of gravitational waves at the end of the dilaton-driven stage, and the Hubble parameter 
at the end of the string phase. Our analysis yields constraints of 
and 
, consistent with theoretical predictions from string cosmology. However, the current NANOGrav data is not sensitive to the parameter. We also compare the string cosmology model to a simple power-law model using Bayesian model selection, finding a Bayes factor of 2.2 in favor of the string cosmology model. Future pulsar timing array observations with improved sensitivity and extended frequency coverage will enable tighter constraints on string cosmology parameters.
© The Author(s) 2025
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Funded by SCOAP3.
