2019 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
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| Research Institution | The University of Tokyo |
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Principal Investigator |
HE MINXI 東京大学, 理学系研究科, 特別研究員(DC1)
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| Project Period (FY) |
2019-04-25 – 2022-03-31
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| Keywords | Reheating / Inflation |
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| Outline of Annual Research Achievements |
Reheating is essential for an inflationary model to connect with the successful hot Big Bang cosmology, through which high-energy particles are produced and thermalized in the ``empty" space resulting from the exponential expansion. Careful analysis on reheating process is needed to determine the relation between the pivot scale of curvature perturbation and the duration of inflation so as to contrast the prediction of inflation with observation. Since the prediction of inflation in the mixed Higgs-R^2 model (MHRM) is favored by experiment (M. He et al 2018), it is of significance to go further to study its reheating process in depth. While the research on the first stage of preheating in MHRM (M. He et al 2019) showed that the violent preheating mechanism in the single-field Higgs inflation becomes insufficient to complete preheating, one possibility was pointed out (F. Bezrukov et al 2019) that the preheating can be completed right after the first stage by tachyonic instability that leads to exponential production of the Higgs particles and longitudinal modes of gauge bosons. However, it is important to clarify whether this instability is strong and robust compared with other mechanisms like parametric resonance in our original plan. So we are using both analytical and precise numerical methods complementarily to find out the conditions and likelihood for the tachyonic preheating to happen. Due to the complexity of the system, it costs greater effort and time to analyze the tachyonic preheating in MHRM. We are now finishing the paper to report our results.
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| Current Status of Research Progress |
Current Status of Research Progress
2: Research has progressed on the whole more than it was originally planned.
Reason
We are now about to finish writing the paper to report our study on tachyonic preheating in the mixed Higgs-R^2 model. It has cost longer time than we expected due to the complication of tachyonic preheating mechanism, the high-precision and heavy numerical calculation, and nearly chaotic behavior of the inflaton in this model.
The tachyonic instability was not written in the original plan because it is, in the usual case, very unlikely to happen since it needs severe fine-tuning of model parameters and initial conditions. But since it was reported by another research group (F. Bezrukov et al 2019) that it is still possible to happen after our first preheating paper (M. He et al 2019), it is important to clarify the details of this situation so that our subsequent study written in the original plan can be carried out smoothly. The reason is that if the tachyonic instability is unlikely to happen or it is not efficient, it is necessary to consider other mechanisms, for example the parametric resonance written in our original proposal, as an alternative or subsequent evolution to reheat the universe. Therefore, the current study on tachyonic preheating should be regarded as a complementary and supporting research of the original plan.
Besides, I am studying primordial black holes (PBHs) in collaboration with Professor Teruaki Suyama in Tokyo Institute of Technology, which is related to the second-year plan in the proposal.
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| Strategy for Future Research Activity |
After finishing the study about tachyonic preheating, I would continue to study the preheating process in the mixed Higgs-R^2 model (MHRM) with other preheating mechanisms. Especially, parametric resonance can occur in a wide range of models with inflaton oscillation after the end of inflation. Since both my current collaborator Professor Alexei A. Starobinsky and former collaborator Professor Robert Brandenberger are pioneers to study such mechanisms, it is a precious opportunity to work with them on this topic. On the other hand, I would further study primordial black holes (PBHs), which would allow me to explore a much broader field, including the possibility to generate PBHs in MHRM and induced gravitational waves as a consequence of large curvature perturbations which are responsible for the formation of PBHs.
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