A Study Of The Characteristic Of Primordial Gravitational Wave In Bounce Cosmological Model By Phenomenological String Theory

With the fast development of the astronomical observation,the accumulation of the observational data and the research of the theory,the new era of precision cosmology has come for human beings.It is an attractive topic that we could analyze and validate the very early universe with the detection and the accurate measurements of the primordial gravitational wave in the near future.At present,the model that have been widely accepted to describe the universe is the standard cosmological model,i.e.the slow-roll inflation model.The slow-roll inflation model is very successful,but there are two problems in this model: “initial singularity problem” and “fine tuning problem”.Furthermore the primordial gravitational wave predicted in the slow-roll inflation model have not been detected as expected,which increases the urgency to study a new alternative model.There are a variety of cosmological models,one of which is very competitive – the bounce cosmological model by phenomenological string theory.Not only is there no “initial singularity problem” and “fine tuning problem” in this model,but as with the slow-roll inflation model,the stable and scale invariant power spectrum of primordial perturbation produced in this model corresponds to the observation of the CMB's anisotropy.So the study of the primordial gravitational wave of this model is significant and meaningful in physics.In this paper,we get the magnitude of the primordial gravitational wave predicted in this bounce cosmological model by solving the primordial gravitational wave equation of this model.By the detailed calculation,we get the tensor to scalar ratio and the Hubble parameter of the very early universe so that the string's energy scale in this model can be constrained by the constraint of the tensor to scalar ratio with observation.And we find that the amplitude of the primordial gravitational wave is larger in smaller scale in this bounce cosmological model,which can provide the theoretical foundation to distinguish between the slow-roll inflation cosmological model and the bounce cosmological model.