セミナー

Axel Brandenburg, Nordita

[JpDe Joint Seminar] Origins of cosmic magnetism

Online (Zoom)
The magnetic fields of cosmic bodies like the Earth or the Sun have puzzled scientists for well over a hundred years. The basic principle is that of a self-excited dynamo, which is an electric generator where the weak permanent magnets are replaced by electromagnets. But cosmic dynamos are made of plasma with no wires and uniform conductivity, so they are prone to short-circuiting themselves. We now know of a handful of very different examples where a suitable flow geometry can exponentially amplify weak seed fields. Demonstrating this experimentally is still hard, but it did work in a few case. It is much easier on the computer. After explaining some of the examples, I will address the problem of primordial magnetic fields. For a long time, this was thought to be an alternative to galactic dynamos, but now we know that it is very much a research field in its own right. Not much is known with certainty, but there are believed to be lower observational limits on their strength. The field generation would also leave traces in relic gravitational waves, which is a rapidly growing topic that I will address at the end.

Kanji Mori, Fukuoka University

Core-collapse Supernovae as Laboratories for Axion-like Particles

Hybrid Onsite: Kenkyu-Honkan Seminar room, Online: Zoom
Axion-like particles (ALPs) are a class of hypothetical pseudoscalar particles which feebly interact with ordinary matter. The hot plasma in core-collapse supernovae is a possible laboratory to explore physics beyond the standard model including ALPs. Once produced in a supernova, a part of the ALPs can be absorbed by the supernova matter and affect energy transfer. We recently calculated the ALP emission in core-collapse supernovae and the backreaction on supernova dynamics
consistently. It is found that the stalled bounce shock can be revived even in one-dimensional models if the coupling between ALPs and photons is as high as g_{a gamma} ~ 10^{-9} GeV^{-1} and the ALP mass is 40-400 MeV. In addition, we found that the explosion energy of supernovae can be increased by the ALP heating. This implies that ALPs can be a key to reproduce 10^51 erg explosion.

Valerie Domcke, CERN

Searching for high-frequency GWs with axion haloscopes

Hybrid On-site: Seminar room 322, Online (Zoom) https://kds.kek.jp/event/45204/
Gravitational waves (GWs) generate oscillating electromagnetic effects in the vicinity of external electric and magnetic fields. I will discuss this phenomenon with a particular focus on reinterpreting the results of axion haloscopes based on lumped-element detectors, which probe GWs in the 100 kHz–100 MHz range. Measurements from ABRACADABRA and SHAFT already place bounds on GWs, although the present strain sensitivity is weak. However, the sensitivity scaling with the volume of such instruments is significant—faster than for axions—and so rapid progress will be made in the future. I will discuss opportunities at future facilities with a focus on the DMRadio program.

Daiki Suenaga, RIKEN

[QCD theory Seminar] Heavy-quark spin polarization induced by the Kondo effect in a magnetic field

Online (Zoom)
The Kondo effect is one of the most important quantum many-body effects triggered by condensates made of a heavy impurity and a light fermion. Recently, importance of the Kondo effect in dense QCD has been discussed by regarding a heavy (charm or bottom) quark as the impurity in the light-quark medium, which is referred to as the QCD Kondo effect.
Besides, properties of the Kondo effect were found to be described from a field theoretical approach, e.g., the NJL-type model together with the heavy-quark effective theory. In this talk I summarize the recent development of theoretical study of the QCD Kondo effect. Moreover, I explain the latest results of emergence of the heavy-quark spin polarization induced by the effect in a magnetic field, and show its relation to solid-state physics.

Chengpeng Yu, The University of Tokyo

Anomaly Induced Pulsar Kick

Hybrid On-site:Seminar room 322, Online (Zoom)
Pulsars, a special type of neutron star, often move at very high speed ($\sim 450 \mathrm{km/s}$), referred to as the pulsar kick phenomenon. However, why this high speed occurs is unclear. In this study, starting from realistic cooling model and equation of state, we analyzed the scattering between the neutrinos emitted during the cooling stage of a proto-neutron star and the anomalous axial current induced by the chiral separation effect in the star, and calculated the resulting time-dependent pulsar kick velocity.The result is: for isotropic axial current, the velocity is zero; however, with a 10\% anisotropic component of the axial current and the magnetic field strength $4\times 10^{11} \mathrm{T}$, the velocity is $223 \textrm{km/s}$. This value explains the well-known difference between the observed pulsar kick velocity ($\sim 450 \textrm{km/s}$) and the hydrodynamic simulation of supernova explosions ($\sim 200 \textrm{km/s}$). Hence, for the understanding of neutron star evolution during its early age, quantum anomaly is a crucial mechanism.

Samadrita Mukherjee, TIFR

A twisted tale of the transverse-mass tail in the W-boson mass measurement

Hybrid On-site: Seminar room 321, 322. Online:(Zoom) https://kds.kek.jp/event/44979/
The discrepant measurement of the W mass by the CDF collaboration can be made consistent with all other current measurements, by the ATLAS, the LHCb, the D0, the LEP collaborations, and with the electroweak precision fit for $M_W$ in a minimal—albeit naive— an extension of the Standard Model. In our setup, there is only one new operator and a single new (pseudo-)scalar particle which manifests as an unaccounted-for contribution to missing energy. This simple extension is enough to simultaneously explain the different extractions of $M_W$ for a sizeable chunk of the parameter space. We support our analysis by extracting novel bounds on the new physics scenario from W-cross-section measurements and $WW$ cross-section measurements to show that parts of the parameter space are, indeed, still allowed. We also discuss possible ultraviolet completions of the setup. Finally, we present our predictions for $M_W$ that ATLAS and CMS would extract from their 13 TeV data.

[Cosmophysics Seminar] Impact of half-wave plate systematics on the measurement of cosmic birefringence from CMB polarization

Online (Zoom)
Polarization of the cosmic microwave background (CMB) can probe new parity-violating physics such as cosmic birefringence (CB), which requires exquisite control over instrumental systematics. The non-idealities of the half-wave plate (HWP) represent a source of systematics when used as a polarization modulator. We study their impact on the CMB angular power spectra, which is partially degenerate with CB and miscalibration of the polarization angle. We use full-sky beam convolution simulations including HWP to generate mock noiseless time-ordered data, process them through a bin averaging map-maker, and calculate the power spectra including TB and EB correlations. We also derive analytical formulae which accurately model the observed spectra. For our choice of HWP parameters, the HWP-induced angle amounts to a few degrees, which could be misinterpreted as CB. Accurate knowledge of the HWP is required to mitigate this. Our simulation and analytical formulae will be useful for deriving requirements for the accuracy of HWP calibration.

Junsei Tokuda, Ibs

Swampland program from amplitudes: gravitational positivity bounds

Hybrid Onsite: Kenkyu-Honkan Seminar room, Online: Zoom
It is interesting if there exist non-trivial relations between ultraviolet complete quantum gravity and its low energy effective field theories (EFTs). Such relations are so-called swampland conditions. In this talk, we will develop a method to derive swampland conditions by extending so-called S-matrix positivity bounds to gravitational context. In our formulation, several working assumptions on quantum gravity S-matrix such as unitarity and the Reggeization of graviton exchange are imposed. We will then discuss the implications of positivity bounds on gravitational EFTs. First, we will demonstrate that our bounds are indeed satisfied in the Standard Model. Next, we will show that our bounds provide strong constraints on dark photon models which can be tested against on-going future experiments. This implies the possibility of probing quantum gravity from low-energy observables and the phenomenological importance of studying the properties of quantum gravity S-matrix.

Kyohei Mukaida, KEK

[QCD theory Seminar] Chiral asymmetry in the early Universe

Online (Zoom)
Since the SM model is a chiral theory, asymmetries in matter generically result in chiral asymmetries. Nevertheless, the effect of the primordial chiral asymmetry is often neglected in the study of the early Universe because the baryon asymmetry is tiny. In this talk, I will discuss some examples where the chiral asymmetry plays essential roles, in particular in the context of baryogenesis.

小野 寛太, 大阪大学

[KEK連携コロキウム] 量子ビーム計測の自律化

ハイブリッド形式 : オンライン (Zoom) + セミナールーム(研究本館321)
量子ビーム計測は物性物理学から生命科学までの広範な自然科学分野で重要な役割を果たしている。計測やデータ解析を合理的・高精度で行う計測インフォマティクスに関する研究が近年進展しているが、われわれは現状の計測・解析に熟練者の介在が必須であることに着目し、自律的な計測、すなわち人間の介在なく計測から知識を抽出することを目指した研究を行なっている。講演では、合理的な計測実験計画、実験終了の自動判定、計測データの自動解析について紹介する。

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