| 概要 |
In the standard framework of the early universe, quantum states of graviton generated duringinflation become squeezed states. Since such gravitons tend to enhance their observables, it is expected tha...t gravitons may be detectable by observations in the future. However, if they interact with environmental matter fields, such as primordial magnetic fields generated during inflation, the gravitons may lose their quantum coherence. Thus, it is important to investigate whether the primordial magnetic field affects the squeezed state of graviton or not. As a first step for analyzing the decoherence of the gravitons, we assume two models of the magnetic field. One of the models assumes the case of minimal coupling between gravitons and photons (Model-1). In this case, the primordial magnetic field decays with the negative square of the scale factor, ∝ a^−2, during inflation. Through the analysis of this model, it turns out that the gravitons are robust against the decoherence caused by the cosmological magnetic fields. We also find that the conversion rate of gravitons into photons is at a few percent at most. The other model assumes magnetic fields sustained by a gauge kinetic coupling. In this model, the primordial magnetic field decays with the negative power of the scale factor, ∝ a^−1, during inflation. Not only gravitons as excitations of PGWs, but also photons as excitations of electromagnetic fields are highly squeezed in this model. They become entangled with each other through graviton to photon conversion and vice versa. We derive the reduced density matrix for the gravitons and calculate their entanglement entropy. It turns out that the state of the gravitons is not a squeezed state but a mixed state. These results may provide some hints for future observations of primordial gravitational waves and their quantum nature.続きを見る
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Mendeley出力
