Null energy condition violation during inflation and pulsar timing array observations
Gen Ye (School of Physics and Microelectronics, Zhengzhou University, Zhengzhou, Henan, 450001, China, Institute Lorentz, Leiden University, Leiden, 2300 RA, The Netherlands); Mian Zhu (Faculty of Physics, Astronomy and Applied Computer Science, Jagiellonian University, Krakow, 30-348, Poland); Yong Cai (School of Physics and Microelectronics, Zhengzhou University, Zhengzhou, Henan, 450001, China)
Recently, evidence of stochastic gravitational wave background (SGWB) signals observed by pulsar timing array (PTA) collaborations, has prompted investigations into their origins. We explore the compatibility of a proposed inflationary scenario, incorporating an intermediate null energy condition (NEC)-violating phase, with the PTA observations. The NEC violation potentially amplifies the primordial tensor power spectrum, offering a promising explanation for PTA observations. Numerical analyses, primarily focused on NANOGrav’s 15-year results, reveal the model’s compatibility with PTA data. Notably, the model predicts a nearly scale-invariant GW spectrum in the mHz frequency range, which sets our scenario apart from other interpretations predicting a red primordial GW spectrum on smaller scales.
