Some Studies On Relic Gravitational Waves, High Frequency Gravitational Wave Detectors And Cosmic Dark Energy

This thesis presents my researches, under the guidance of my adviser Profes-sor Yang Zhang, on the relic gravitational waves(RGWs), high-frequency gravita-tional wave (GW) detectors and dark energy models. All of them are very active issues in modern cosmology and GW astronomy. This thesis is divided into six chapters.Chapter 1 is the introduction of the knowledge of cosmology, the mainly research status and the recent progresses of RGWs, high-frequency GW detectors and dark energy, and some work we have done on these subjects. RGWs carry a lot of information about the very early Universe, and is one of the most important methods to recognize the inflation happened in very early Universe. So RGWs is very important for us to study the very early Universe. High-frequency GW detector is a new detecting technique, which mainly make use of the observational effects come from the interaction between electromagnetic waves and GWs. It is very new and a wonderful complement for the usual GW detectors aimed on other frequency bands. Dark energy is a very popular field in cosmology. Many dark energy models have been proposed. Among them, of course, there are some problems that can not be resolved such as the coincidence problem and the fine tuning problem, etc. At the same time, we also introduce some knowledge about Friedmann cosmology.In Chapter 2, we firstly introduce the basics of gravitational wave theory, the sources of gravitational waves and the detection on different frequency bands. Then, we discuss the quantum generation of RGWs, the analytic solutions of RGWs in various phases of the Universe and the properties of the transfer functions of RGWs. Next, we study the influences of the tensorial running spectral index at of inflation on RGWs, and found that the spectrum and the energy power spectrum of RGWs in high-frequency band are very sensitive to different at. A lager at leads to a lager spectrum of RGWs h(v,τ0), and meanwhile make the power spectrumΩg(v) deviate from the "flat" k-independent case more obviously. We make a comparison of the RGWs predicted by theories and the sensitivities of various ongoing and forthcoming laser interferometer GW detectors including LIGO, AdvLIGO, LISA, the cryogenic resonant bar detector EXPLORER and the cavity detector MAGO, and then we analyzed the detecting probabilities. At last, we use the latest results of LIGO S5 to constrain the parametersβand at of RGWs, and then calculate the signal-to-noise for different values ofβand at.Two new kinds of high-frequency GW detectors based on the interaction between electromagnetic waves and GWs are introduced in Chapter 3 and Chapter 4, respectively. In Chapter 3, we mainly introduce a new maser GWs whose response frequency is around GHz. Due to the existence of GWs, perturbed photon fluxes are generated which perpendicular to the propagating direction of the maser, and these perturbed photons can be detected by a microwave receiver. First of all, we give the construction of this kind of GW detector. Then we discuss the detecting method in details, and estimate the sensitivity of this detector. Next, we analyze the detecting probabilities aimed at RGWs. Last, we represent the defect of this detector and propose some improving suggestions. The price for the construction of the maser GW detector is not too high, and its sensitivity is very high, so it is worth to be constructed. In Chapter 4, we introduce the annular waveguide GW detector whose response frequency lie in 100MHz or so. Due to GWs, the polarization vector of the electromagnetic waves transporting in a annular waveguide will rotate with time. The rotating angular is proportional to the amplitude of the incoming GWs. The accumulative rotating angular can be detected by a electromagnetic probe, and then the strength of the GWs can be estimated. Similar to Chapter 3, we also discuss the construction, the detecting method and the sensitivity of this kind of GW detector.In Chapter 5, we first introduce some observational evidences of dark energy and the two problems existed generally in dark energy models:the coincidence problem and the fine tuning problem. Then we introduce the most two popular dark energy model:cosmological constant model and the scalar field model. Next, we represent the work we have done on decaying vacuum model, Yang-Mills field condensate (YMC) model and the effective scalar field model. In decaying vacuum model, the energy density of dark energy is proportional to Hubble parameter H, alleviate the fine tuning problem to some extent. Meanwhile, it can explain the high redshift cosmological age problem easily. We plot the Statefinder diagnostic and Om diagnostic for decaying vacuum model and YMC model. Along with the progress of the observational technique, we can extinguish various dark energy models by Statefinder and Om diagnostics using the observational data. Inspired by YMC model, we construct the Lagrangian density for the effective scalar field model. Different from YMC model, the effective scalar field model is not a vector field model but a scalar field model. By calculation, we find that the effective field model can solve the coincidence problem naturally, but the fine tuning problem still exists. After the analysis of the stability, we found that this model has stable attractor solutions. Moreover, we find that the equation of state w of YMC approaches -1 at the present stage during the evolution. If the coupling with the matter component is included, w can cross over -1 naturally. At last, we make a x2 analysis on the effective scalar field model using the observational data from supernova of type Ia, baryon acoustic oscillation (BAO) and cosmic microwave background radiation (CMB).The summary and future outlook are presented in the last Chapter.