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.
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.
These consequences are due to the interplay between the Dirac monopole in position space and the Berry monopole in momentum space.
Ya-Wen Sun, University of Chinese Academy of Sciences
[QCD theory seminar] Topological modes in relativistic hydrodynamics
Online (Zoom)
In this talk I will show that gapless modes in relativistic hydrodynamics could become topologically nontrivial by weakly breaking the conservation of energy momentum tensor in a specific way. These energy momentum non-conservation terms could naturally be produced by an external gravitational field that comes from a coordinate transformation from the flat spacetime. This suggests that topologically trivial modes could become topologically nontrivial by being observed in a special non-inertial reference frame. I will also introduce a possible holographic realization of this system.
Daisuke Yamauchi, Kanagawa U
[Cosmophys seminar] Testing dark energy with cosmological and astrophysical observations
Online (Zoom)
In the era of precision cosmology, one of the biggest challenges of modern cosmology is the elucidation of the origin of the late time acceleration of the Universe. The most straightforward candidate of its origin, often referred to as dark energy, is a cosmological constant, but there are other various candidates that are still worth considering and should be distinguished by future observations. In this talk, I will consider two interesting possibilities as other candidates of dark energy: One is the modification of gravity theory. We construct the general framework of the scalar-tensor theories that has been developed so far and show that the resultant theories generally break the screening mechanism only inside astrophysical bodies, which leads to a novel probe of dark energy. Other is the remnant of quantum tunneling of the Universe. When we consider the open Universe created by bubble nucleation, the residual of the ancestor vacuum, that is the vacuum energy of the supercurvature mode, can be regarded as a possible candidate of dark energy. we discuss the detectability of this new idea by future observations.
Toyokazu Sekiguchi, KEK
[Cosmophys seminar] Early recombination meets closed Universe: more than a solution to the H0 tension
Online (Zoom)
The discrepancy in measurements of H_0 is the most notable anomaly in contemporary cosmology with significance as large as 6σ. Despite many attempts, there is yet no compelling solution to the H_0 tension. In the first part of my talk, I review the H_0 tension. In particular, I will clarify why it is so diffcult to solve the tension. In the latter part, I will present our model, which is based on modified recombination in a closed Universe. Starting from general discussion on necessary conditions that successful modified recombination models should satisfy to fit CMB observations, I will demonstrate time-varying m_e models indeed satisfy those conditions. To fit low-z distance measurements such as baryon acoustic oscillation and type-Ia supernovae, a positive spatial curvature plays an essential role. Compared to the canonical ΛCDM, our model improves the chi-square by more than 23. We also show our model solves the lensing anomaly in Planck data concurrently.
Shota Imaki, University of Tokyo
[QCD theory seminar] Chiral magnetic effect in the hadronic phase
Online (Zoom)
We study the chiral magnetic effect (CME) in the hadronic phase. The CME current involves pseudoscalar mesons to modify its functional form. This conclusion is independent of microscopic details. The strength of the CME current in the hadronic phase would decrease for two flavors.
Yohei Ema, DESY
Higgs inflation, unitarity, and emergence of scalaron
Online (Zoom) https://kds.kek.jp/indico/event/34753/
