Generating enhanced primordial GWs during inflation with intermittent violation of NEC and diminishment of GW propagating speed
Yong Cai (School of Physics and Microelectronics, Zhengzhou University, Zhengzhou, Henan, 450001, China); Yun-Song Piao (School of Physics, University of Chinese Academy of Sciences, Beijing, 100049, China, Institute of Theoretical Physics, Chinese Academy of Sciences, Beijing, 100190, China, School of Fundamental Physics and Mathematical Sciences, Hangzhou Institute for Advanced Study, UCAS, Hangzhou, 310024, China, International Center for Theoretical Physics Asia-Pacific, Hangzhou, Beijing, China)
We investigate both the null energy condition (NEC) violating scenario and the c T -diminishing scenario for generating enhanced power spectrum of primordial gravitational waves (GWs) during inflation, where c T is the propagating speed of primordial GWs. Both of these two scenarios can be realized stably with theories beyond Horndeski, hence can be uniformly implemented within the framework of the effective field theory. We calculate the power spectrum of primordial GWs by assuming that the inflationary Universe undergoes three phases, where the violation of NEC or the diminishment of c T occurs in the intermediate phase. A template of the spectrum is given for the NEC-violating scenario. We also discuss the underlying relation and discrepancy between these two scenarios with a disformal transformation.
