Shi Pi, Kavli IPMU, U. of Tokyo
Some Properties of the Stochastic Induced Gravitational Wave Background
Online (Zoom) https://kds.kek.jp/indico/event/35730/
Our universe is fulfilled by stochastic background of gravitational waves with a large range of frequencies, which may have various astrophysical/cosmological origins in the early universe. As our universe is transparent to gravitational wave, it is a fossil recording the information of its generation and how our universe evolves. In this talk I will briefly review the stochastic background of the gravitational waves from the nonlinear coupling of the scalar and tensor perturbations, as well as their connection to the primordial black holes. I will also talk about the properties of the spectrum shape of such waves: infrared scaling and the peak width.
岡隆史, 東京大学物性研究所/マックスプランク複雑物理学研究所
KEK連携コロキウム「物質科学と高エネルギー物理が拓く非平衡物理のフロンティア」
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Yuji Okawa, The University of Tokyo
Nonperturbative definition of closed string theory via open string field theory
Online (Zoom), indico page, slides (kek.jp only)
In typical examples of the AdS/CFT correspondence, the world-sheet theory with holes in the presence of D-branes is assumed to be equivalent in a low-energy limit to a world-sheet theory without holes for a different background such as $AdS_5 ¥times S^5$. In the case of the bosonic string, we claim under the assumption of this equivalence that open string field theory on $N$ coincident D-branes can be used to provide a nonperturbative definition of closed string theory based on the fact that the $1/N$ expansion of correlation functions of gauge-invariant operators reproduces the world-sheet theory with holes where the moduli space of Riemann surfaces is precisely covered.
Yuji Chinone, RESCEU, U of Tokyo
The results and achievements of the POLARBEAR experiment in the 2010s and its future in the 2020s
Online (Zoom) https://kds.kek.jp/indico/event/35385/
POLARBEAR is a ground-based experiment designed to measure polarization of the Cosmic Microwave Background (CMB) at 150 GHz at an elevation of 5,190m in the Atacama Desert in Chile. Our main science goals are for searching for the B-mode signal created by primordial gravitational waves (PGWs) seen at degree scales, as well as for characterizing the B-mode signal from gravitational lensing with high angular resolution seen at sub-degree scales. POLARBEAR was deployed in 2011 and started science observations in 2012 focusing on small patches of the sky (deep survey). In 2014, we started to observe a large patch of the sky focusing on search for PGWs (wide survey). We have published a series of results from the deep survey, including the first/update measurement of a non-zero B-mode auto-power spectrum at sub-degree scales induced by gravitational lensing, constraint of cosmic birefringence and primordial magnetic fields, and demonstration of delensing. We also have achieved the measurement of cross-correlations of gravitational lensing between our CMB data and optical surveys by the Subaru Hyper Suprime-Cam. With the wide survey, we have reported the measurement of large angular scale B-mode signals induced by the Galactic dust foreground and successfully put an upper limit on PGWs. In this talk, I summarize the science results and achievements of the POLARBEAR experiment. I also show the status of Simons Array, which is an upgraded experiment from POLARBEAR and consists of three new receivers. Finally I describe future CMB projects which Japanese institutes have been contributing to.
Masahiro Isaka, Hosei University
Low-lying level structure of p-sd shell Lambda hypernuclei with antisymmetrized molecular dynamics
Online (Zoom), indico page, slides (kek.jp only)
We focus on low-lying level structure such as ΛΛN spin-spin and spin-orbit splittings in excitation spectra of p-sd shell Lambda hypernuclei. One of the major goals of hypernuclear physics is to understand properties of the baryon-baryon interaction including hyperon(s). Another important issue is to clarify dynamics of baryon many-body systems. In the last decades, by the developments of the experimental studies, the low-lying level structure of light ΛΛ hypernuclei has been revealed precisely. It is expected that crucial information on both properties of ΛΛN interaction and hypernuclear structure from the low-lying level structure. In this study, we use the antisymmetrized molecular dynamics with the ΛΛN G-matrix interaction derived from the baryon-baryon interaction model ESC. It is found that the ground-state spin-parity is systematically reproduced in the p-shell ΛΛ hypernuclei by tuning the ΛΛN spin-spin and spin-orbit interactions so as to reproduce the experimental data of 4ΛΛ4H, 7ΛΛ7Li, and 9ΛΛ9Be. Furthermore, it is found that the energy spacing of the ground-state doublet in 19ΛΛ19F is successfully reproduced using the same ΛΛN interaction. We also focus on the excitation energies and energy shifts of the excited doublets by the addition of a ΛΛ particle. In this talk, we will discuss how the spin-dependent properties of the ΛΛN interactions and structure of the core nuclei affect the low-lying spectra of the ΛΛ hypernucle
Masaki Yamada, Tohoku University
Unified Origin of Axion and Monopole Dark Matter, and Solution to the Domain-wall Problem
Online (Zoom) https://kds.kek.jp/indico/event/35279/
A ‘t Hooft-Polyakov monopole in a dark sector is a viable dark-matter candidate as it is stable due to its topological charge. If the spontaneous symmetry breaking proceeds via the first order phase transition, monopoles can be produced from the collisions of expanding bubbles. In the case with a Coleman-Weinberg potential, a monopole with mass of O(10^{10}) GeV can explain the observed DM density. Interestingly, this is within a viable window for the PQ-symmetry breaking. Motivated by the coincidence of the energy scales, we have pursued a possibility of unifying the PQ symmetry breaking and the production of the monopole DM. Even simple models lead to interesting phenomena in cosmological history, like the Witten effect on the axion in the presence of the monopoles, the Lazarides-Shafi mechanism to avoid the domain wall problem, and the formation of Alice strings. I will explain these effects in a KSVZ-type axion model as well as a DFSZ-type axion model and will show how the cosmological domain wall problem of the axion models is avoided by these effects.
Yasuro Funaki, Kanto Gakuin University
Alpha-particle condensate and cluster evolution in nuclei
Online (Zoom), indico page, slides (kek.jp only)
Nuclear cluster dynamics is reviewed from its historical point of view to a new aspect developed recently. After a great success of the model wave function of alpha-particle condensation is explained, the picture of alpha condensation is extended to a general concept of nonlocalized clustering, which is applicable to promisingly all the cluster structures. The competition between the localized and nonlocalized cluster motions is discussed in terms of the inter-cluster Pauli repulsion and dynamical character contained in a new wave function proposed recently. It is also shown that the path of cluster evolution, which is indicated by the Ikeda diagram, can be described by the evolution of a “container”, which plays a role in trapping the constituent clusters in a flexible way.
Yuko Urakawa, Bielefeld University
Anisotropic separate Universe
Online (Zoom)
The essence of the separate Universe approach, which has been widely used in cosmology, is to rephrase an inhomogeneous Universe with glued numerous homogeneous local patches. We show that the separate Universe approach can be generically used, as long as a theory under consideration is local and preserves the spatial diffeomorphism invariance. Remarkably, the separate Universe approach and subsequently the $¥delta N$ formalism can also apply to a Universe with large scale anisotropic pressure and also to modified theories of gravity, accepting a violation of Lorentz invariance. We also show that the same condition ensures the approximate existence of Weinberg’s adiabatic mode, the constant solution of the curvature perturbation.
Koichi Hattori, YITP, Kyoto
Transport phenomena in magnetic and vortical fields from hydrodynamic frameworks
Online (Zoom), indico page, slides (kek.jp only)
I will discuss recent formulation of the relativistic magnetohydrodynamics on the basis of the magnetic (one-form) symmetry inherent in QED. I will then cover some related topics such as an unstable helical magnetohydrodynamic mode induced by the chiral anomaly and “spin hydrodynamics” in the presence of fluid vorticity.
Yasunori Nomura, BCTP, U. of California, Berkeley
Black Hole Conundrum: Information vs Interior
Online (Zoom) https://kds.kek.jp/indico/event/35124/
