2020 Fiscal Year Annual Research Report
観測的に支持されているインフレーションモデルの宇宙論的帰結
| Project/Area Number |
19J21472
|
|---|
| Research Institution | High Energy Accelerator Research Organization |
|---|
Principal Investigator |
HE MINXI 大学共同利用機関法人高エネルギー加速器研究機構, 素粒子原子核研究所, 研究員
|
|---|
| Project Period (FY) |
2019-04-25 – 2022-03-31
|
| Keywords | Preheating / Tachyonic instability / Inflation / Higgs |
|---|
| Outline of Annual Research Achievements |
I studied the preheating process in the mixed Higgs-R^2 model, mainly focusing on the tachyonic instability encountered for some specific choice of model parameters. The mixed Higgs-R^2 model is a combination of the Higgs inflation model and the Starobinsky model, which give observationally favored inflation predictions. On the other hand, it is shown that it can be a promising candidate as the UV extension of the Higgs inflation within the setup of the Standard Model and general relativity. It is well motivated to investigate whether it is possible to realize viable inflation without going beyond the Standard Model. The study of reheating can improve the observational constraint on the parameter space in this model. Tachyonic preheating is absent in either single-field case, but it can be the dominant channel in their combination, which leads to interesting observational consequences. The occurrence of tachyonic preheating is not easy to realized. I found out the condition for the occurrence of tachyonic preheating with locally maximal efficiency. After deriving the expression for the efficiency of tachyonic preheating, I used numerical method to compute the efficiency for all the parameters and to estimate the necessary degree of fine-tuning to complete preheating solely with tachyonic instability. Generally, more fine-tuning is needed for the R^2-like parameters than the Higgs-like.
|
| Current Status of Research Progress |
Current Status of Research Progress
2: Research has progressed on the whole more than it was originally planned.
Reason
I continued to study the reheating process in the mixed Higgs-R^2 model as planned, after my preceding study of the first stage of preheating. Since the first stage of preheating is found to be negligible in terms of particle production to reheat the Universe, subsequent evolution of the system should be investigated in depth. The study of reheating is necessary to improve the observational constraint on the model parameters by contrasting the future experimental data, especially for this likely-to-be realistic model. This studied is going on smoothly as planned. Since the reheating process is highly model-dependent and usually involves non-linear dynamics, the study should combine both analytical derivation and numerical simulation, especially for multi-field models where the classical background evolution is already complicated. Also, due to the pandemic situation, the international communication is slowed down, which makes it more difficult to conduct an international collaboration. But we still made considerable progress in the project, so I think it is progressing as planned.
|
| Strategy for Future Research Activity |
The tachyonic preheating is so powerful that it can complete preheating instantaneously, but necessary degree of fine-tuning is needed. Therefore, one needs to consider the case where there is no fine-tuning, i.e. more common cases. Perturbative reheating is common in almost all inflation models with inflaton oscillation after during reheating. In the Starobinsky model, the perturbative decay of scalaron is relatively slow because it is just gravitational interaction. However, the presence of Higgs should greatly enhance the decay efficiency because it interacts with other Standard Model particles in a much stronger way. I will calculate the perturbative decay rates for the Higgs and the scalaron which are expected to be different from the known single-field cases due to the interaction between them. After that, I plan to use numerical method to take them into account to estimate the reheating temperature and duration when entering the radiation-dominated epoch. To consider the effects of preheating, I also plan to set different initial conditions for the system evolution so that we can see the its dependence on the preheating process.
|
Research Products
(7 results)
