| 研究課題/領域番号 |
18F18315
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| 研究機関 | 京都大学 |
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研究代表者 |
向山 信治 京都大学, 基礎物理学研究所, 教授 (40396809)
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| 研究分担者 |
ZHANG YUN-LONG 京都大学, 基礎物理学研究所, 外国人特別研究員
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| 研究期間 (年度) |
2018-11-09 – 2021-03-31
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| キーワード | gravitation / cosmology / holographic principle / gravitatioal waves |
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| 研究実績の概要 |
Two journal papers have been published under the project 18F18315 in FY2019:
1) In “Emergent Dark Universe and the Swampland Criteria” [Phys.Dark Univ. 26 (2019) 100387], a model of the emergent dark universe was studied. It lives on the time-like hypersurface in the 5D bulk spacetime. The holographic fluid on the cutoff is assumed to play the role of the dark sector, mainly including the dark energy and apparent dark matter. After considering the fitting parameters, an effective potential of the model with a dynamical scalar field is reconstructed. The parameters in the swampland criteria are extracted, and they satisfy the criteria at the present epoch but are in tension with the criteria if the potential is extended to the future direction.
2) In “Hyperbolic field space and swampland conjecture for DBI scalar”[JCAP 1909 (2019) 072], we study a model of two scalar fields with a hyperbolic field space and show that it reduces to a single-field Dirac-Born-Infeld (DBI) model in the limit where the field space becomes infinitely curved. We apply the de Sitter swampland conjecture to the two-field model and take the same limit. It is shown that all quantities appearing in the swampland conjecture remain well defined within the single-field DBI model. Based on a consistency argument, we then speculate that the condition derived in this way can be considered as the de Sitter swampland conjecture for a DBI scalar field by its own. We also propose an extension of the de Sitter swampland conjecture to a more general scalar field with the non-canonical kinetic term.
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| 現在までの達成度 (区分) |
現在までの達成度 (区分)
2: おおむね順調に進展している
理由
In FY2019, three preprint papers have been posted on the arXiv website, which are under the peer review and correspondences on the revisions.
1) In the preprint “Universal Upper Bound on the Inflationary Energy Scale from the Trans-Planckian Censorship Conjecture" by S. Mizuno, S. Mukohyama, S. Pi, and Y. -L. Zhang [arXiv:1910.02979, YITP-19-91], we study the constraint on the inflationary energy scale from the recently proposed Trans-Planckian Censorship Conjecture (TCC). We find a universal upper bound on the inflationary Hubble expansion rate.
2) In the preprint "Notes on the Quantum Corrections of Swampland and Trans-Planckian Censorship Conjecture" by S. Sun and Y.-L. Zhang [arXiv:1912.13509, YITP-19-128], we discuss the swampland and trans-Planckian censorship conjectures (TCC) from the entropy bound with quantum corrections, i.e. quantum version of Bousso's bound and energy conditions. We include the contributions from the entanglement entropy in de Sitter spacetime.
3) In the preprint "Gravitational Waves and Possible Fast Radio Bursts from Axion Clumps" by S. Sun and Y.-L. Zhang [arXiv:2003.10527, YITP-20-28]. We revisit the axion objects such as axion mini-clusters and axion clouds around spinning black holes. In particular, the resonances from the axion with the mass around 10^{－6}eV may explain the observed fast radio bursts (FRBs). Here we argue that similar bursts of high frequency gravitational waves, which we call the fast gravitational wave bursts (FGBs), are generated from axion clumps with the presence of gravitational Chern-Simons (CS) coupling.
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| 今後の研究の推進方策 |
1) One topic is on the cosmological background and perturbations, that focusing on a better connection between cosmological perturbations and the general framework of holographic duality. There are a few models and approaches that have investigated the FRW universe in the paradigms of holographic dualities, such as dS/CFT correspondences, holographic cosmology, and different kinds of dualities in AdS/FRW, AdS/dS, dS/dS, etc, which are still under developing in the community. Here we will focus on a better understanding between the cosmological perturbations and those in the holographic calculations.
2) The other is on the black holes physics and radiation of gravitational waves. The original holographic principle proposed by 't Hooft and Susskind is on the property of quantum gravity that enclosed in a volume of spacetime, which can be encoded on a lower-dimensional boundary region, such as the cosmological horizon, or the black hole horizon. Thus, the old membrane paradigm approach to black hole physics has been playing an important role in the holographic dualities and astrophysical observations. For example, the superradiance of gravitational waves bears similarities with the tidal friction of viscous fluid membranes. Here we will focus on more connections between membrane black hole and gravitational waves, such as investigating the gravitational wave radiation and superradiance from Kerr black hole. The astrophysical process will also be explored. Some suitable approximations from holography are also expected to play important role in the coming studies.
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