2019 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 |
In a project and in collaboration with my host and a postdoc from Iran, who visited YITP for January 30, 2020 to February 9, 2020, we looked for astronomical and cosmological observational bounds on the gauge-gravity coupling. In the case of bounds come from the Neutron stars, we found the strongest bound that ever found and we also shaw that the bound is consistent with that is coming from the gravitational waves (GWs) observations. We reported our result very soon on February 27 in [1], which is now accepted in Journal of Cosmology and Astroparticle Physics (JCAP) for publication.
In another project and in collaboration with people from Iran, we found static spherically symmetric solutions in the so-called mimetic gravity scenario. The results are reported in [2] and the paper is under revision in the journal Physical Review D (PRD).
There are two papers both with international collaborators:
[1] Bounds on the Horndeski Gauge-Gravity Coupling, Alireza Allahyari, Mohammad Ali Gorji, Shinji Mukohyama, accepted for publication in JCAP, (reference number: arXiv:2002.11932 [astro-ph.CO], YITP-20-21).
[2] Mohammad Ali Gorji, Alireza Allahyari, Mohsen Khodadi, Hassan Firouzjahi, submitted to PRD, (reference number: arXiv:1912.04636 [gr-qc], YITP-20-20).
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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 the following three projects.
[Weakly Coupled Cosmological Models in scordatura DHOST] Along with the host researcher and another collaborator, I am working on cosmology in Degenerate Higher Order Scalar-Tensor (DHOST) theories with the scordatura mechanism. We will probably be able to write a paper in a couple of months.
[Production of Gravitational Waves via Axions' Resonance] In this project, with my host and in collaboration with two people from Iran, we are proposing a cosmological scenario in which GWs can be produced from the resonance of axions. We are close to the end of this project.
[4D limit of Einstein-Gauss-Bonnet Gravity] According to the Lovelock theorem, in four dimensional spacetime and under reasonable assumptions, Einstein-Hilbert action and cosmological constant are the only possible terms in gravitational action. There is also Gauss-Bonnet term which does not contribute to the equations of motion in four dimension. Very recently, it was shown that there is a nontrivial 4D limit so that Gauss-Bonnet term can contribute to the dynamics. In collaboration with my host and a postdoc in YITP, we formulated the theory in a fully nonlinear way which allows us to understand the origin of subtleties and formulate the model in a consistent way. We will write a paper soon.
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| Strategy for Future Research Activity |
[DHOST Theories] We have found viable weakly coupled stealth de Sitter solution in scordatura DHOST theories. We have two directions in mind to study applications of this solution: i) adding standard matter in cosmology to the solution and construct a viable dark energy model, ii) construct an inflationary scenario based on this solution.
[Mimetic Gauge Field Scenario] With my host, we already constructed a mimetic gauge field scenario. In the cosmological background, the setup provides a dark sector energy density component which scales like spatial curvature. We are interested in the observational consequences of this model to see whether it is able to address/alleviate late time observational tensions.
[Perturbations of Non-Abelian Gauge Fields in spatially curved FLRW spacetime] Recently, some cosmological observations show that spatially curved cosmological background fit the data better than common spatially flat one. On the other hand, the roles of non-Abelian gauge fields is widely studied in cosmology in recent years for spatially flat background. We, therefore, plan to study cosmology of non-Abelian gauge field in spatially curved background. Apart from the recent observational interests, it is also an interesting question from the theoretical point of view.
[Axions in Non-Abelian Gauge Fields] As we mentioned before in this report, we have studied the role of axion's oscillation to indirectly produce GWs through resonance of the dark photons which are coupled to axions. We plan to consider non-Abelian gauge fields instead of Abelian.
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