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/
Studying the thermodynamic aspect of a black hole, including its apparent contradiction with the principles of quantum mechanics, has been driving our understanding of spacetime and gravity at the fundamental level. While we have found that the principles of quantum mechanics prevail in the end, paradoxes still remain; the latest form of these is the difficulty of reconciling unitary evolution of a black hole with the existence of its interior, often called the firewall paradox. I will discuss how this conundrum can be solved by carefully analyzing the degrees of freedom associated with the black hole, which I refer to as hard modes, soft modes, and far modes (early radiation). The resulting picture reveals an intriguing relation between the chaotic behavior of the UV dynamics near the horizon and the IR aspect of emergent spacetime inside the horizon. It also elucidates what the semiclassical description of spacetime and gravity really is. This talk is based on the work presented in arXiv:1810.09453, 1908.05728, and 1911.13120.
Shi Chen, University of Tokyo
[QCD theory seminar] Deconfinement and CP-breaking at θ=π in a softly-broken N=1 SYM
Online (Zoom)
At θ=π in pure Yang-Mills theories, the CP-symmetry is spontaneously broken in the confined phase, justified by an ‘t Hooft anomaly between center symmetry and CP-symmetry. In this talk, we want to see when the deconfinement phase transition occurs, whether CP-symmetry is restored at the same time. We deform the pure Yang-Mills theory to a softly-broken N=1 Super Yang-Mills theory (SYM). In this softly-broken SYM, both deconfinement and CP-restoration can occur in the weakly-coupled region where reliable evaluations can be made. We will show that for gauge groups other than SU(2), these two transitions occur synchronously. For SU(2), the CP-restoration occurs strictly later than the deconfinement, and a CP-breaking deconfined phase appears between the two transitions.
Yoshihisa Kitazawa, KEK
Why now? A History of Dark Energy (in Japanese)
Online (Zoom) https://kds.kek.jp/indico/event/35122/ We investigate the reheating process by the gluon pair productions through QCD trace anomaly. Energy densities of inflaton efficiently transferred into thermal radiation. We identify the conformal zero mode as inflaton The potential energy of inflaton is dark energy.
We investigate the reheating process by the gluon pair productions through QCD trace anomaly. Energy densities of inflaton efficiently transferred into thermal radiation. We identify the conformal zero mode as inflaton The potential energy of inflaton is dark energy.
We argue dark energy decays rapidly by gluon pair emission during reheating and even after the big bang. The reheating temperature is determined by the decay width ¥sqrt{M_p ¥Gamma} as 10^6 GeV. As the Universe cools below the hadronic scale, dark energy density is almost frozen. The energy density of dark energy still decreases by emitting two photons through QED trace anomaly. We can estimate the magnitude of dark energy from the QED decay width ¥sqrt{M_p ¥Delta} ¥sim eV. We have come a long way to give the upper bound on the present magnitude of dark energy as (10^{-2.5} eV)^4.
Kazushi Yamashiro, Shizuoka University
Information geometry encoded in bulk geometry (in Japanese)
Online (Zoom), indico page, slides (kek.jp only)
We study how information geometry is described by bulk geometry in the gauge/gravity correspondence. We consider a quantum information metric that measures the distance between the ground states of a CFT and a theory obtained by perturbing the CFT. We find a universal formula that represents the quantum information metric in terms of back reaction to the AdS bulk geometry. This talk is based on arXiv:2002.11365.
Tomohiro Fujita, ICRR
Hunting axion-like dark matter and dark energy
Online (Zoom) ALP (axion like particle) is one of the best candidates for dark matter.
ALP (axion like particle) is one of the best candidates for dark matter.
ALP dark matter oscillates around its small mass potential, and may be coupled to photons.
The axion-photon coupling causes the rotation of the linear polarization plane of a traveling photon, and several techniques exploiting this “axion-birefringence” have been developed to search for ALP dark matter.
Moreover, in a smaller mass region, ALP can play a role of dark energy (i.e. quintessence). CMB observation is sensitive to ALP dark energy coupled to photons which causes the isotropic conversion of E-mode polarization into B-mode, known as “cosmic birefringence”.
In this talk, I introduce the new techniques to search for ALP dark matter and discuss the sensitivity of the upcoming CMB experiment to ALP dark energy.
Naoki Yamamoto, Keio University
Magnetic monopoles and fermion number violation in chiral matter
Online (Zoom), indico page, slides (kek.jp only) In this talk, we show that the presence of a magnetic monopole in position space gives rise to a violation of the fermion number conservation in chiral matter. Using the chiral kinetic theory, we derive a model-independent expression of such a violation in nonequilibrium many-body systems of chiral fermions. In local thermal equilibrium at finite temperature and chemical potential, this violation is proportional to the chemical potential with a topologically quantized coefficient.
