2020 Fiscal Year Annual Research Report
Probing Modified Gravity and Non-Abelian Gauge Fields by Gravitational Waves
| Project/Area Number |
19F19313
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| Research Institution | Kyoto University |
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Principal Investigator |
向山 信治 京都大学, 基礎物理学研究所, 教授 (40396809)
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| Co-Investigator(Kenkyū-buntansha) |
GORJI MOHAMMAD ALI 京都大学, 基礎物理学研究所, 外国人特別研究員
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| Project Period (FY) |
2019-11-08 – 2022-03-31
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| Keywords | gravitation / cosmology / gravitatioal waves |
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| Outline of Annual Research Achievements |
Probing dark sector via GWs: We obtained an analytical expression for the stochastic gravitational wave (GW) spectrum which encodes effects of axions and dark photons. In a multiple vector field inflation, we obtained the spectra of primordial GWs. [Papers: 1 in JHEP and 1 in JCAP]
Dark photon dark matter: We have shown that dark photons can be produced during inflation and play the role of dark matter. [Papers: 1 in PRD and 1 in JHEP (under consideration)]
Probing modified gravity: We investigated a four-dimensional Einstein-Gauss-Bonnet gravity and we studied its cosmological consequences. In another scenario, we investigated a new dark energy model. We found large-scale observables such as effective gravitational coupling and slip parameter for this model.
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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
Currently, we are working on three different projects:
(i) Scordatura inflation: In our previous work, we have found a viable dark energy model based on a stealth de Sitter solution. In a work in continuation, we are constructing an inflationary model in this context. We expect to find some observational signature for this model.
(ii) Petrov classification in modified theories of gravity: We are studying null geodesic congruences in the context of higher derivative scalar-tensor and vector-tensor theories. In order to do this, we have implemented the so-called Newman-Penrose tetrad formalism.
(iii) Dark photon dark matter: In a continuation of our previous works, we are constructing a model of dark matter based on the dark photons which are excited during the inflation.
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| Strategy for Future Research Activity |
(i) Gravitational memory effect: One of the interesting features of GWs is the so-called gravitational memory effect. This effect can be studied for different theories by looking at the corresponding GW spectrum. We have in mind to study these effects in the context of modified gravity models.
(ii) Probing dark sector: Detection of GWs made it possible to study dark sector of our Universe otherwise impossible to be probed. We are interested in the idea of exploring particles with different spins, like axions and dark photons in the dark sector with GWs. As the observation of GWs will be more accurate in future through the data coming from the detectors like LISA and KAGRA, the theoretical development in this direction seems to us interesting.
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