Has NANOGrav Found First Evidence for Cosmic Strings?

Area of Science:

• Cosmology and Astrophysics
• Gravitational Wave Astronomy
• Theoretical Physics

Background:

• The North American Nanohertz Observatory for Gravitational Waves (NANOGrav) analyzed 12.5 years of pulsar timing data.
• A stochastic common-spectrum process was detected in pulsar timing residuals, indicating a potential background signal.

Purpose of the Study:

• To interpret the observed stochastic process as a gravitational wave background.
• To investigate the potential source of this background as a cosmic-string network from the early Universe.
• To analyze the parameter space of cosmic strings, including tension (Gμ) and loop size (α).

Main Methods:

• Analysis of pulsar timing residuals from the NANOGrav 12.5-year data set.
• Modeling of a stochastic gravitational-wave background produced by cosmic strings.
• Theoretical study of stable Nambu-Goto strings and their observational implications.

Main Results:

• Strong evidence for a stochastic common-spectrum process in NANOGrav data.
• Demonstration that this process is consistent with a cosmic-string gravitational wave background.
• Identification of cosmic string tension and loop size as key parameters.

Conclusions:

• The observed signal provides compelling evidence for a cosmic-string network in the early Universe.
• Future experiments will be capable of probing the entire viable parameter space of cosmic strings.
• This research links pulsar timing arrays to fundamental physics of the early Universe.