セミナー

Hidenori Fukaya, Osaka University

Curved domain-wall fermion and its anomaly inflow

Online (Zoom)
We consider a fermion system on a square lattice, where a curved domain-wall is assigned to the mass term. In a similar way to the standard flat domain-wall fermion, chiral edge modes appear at the wall. These edge-localized modes feel gravity, through the induced spin connection or metric due to the Einstein’s equivalence principle.
In the cases of circle $S^1$ and sphere $S^2$ domain-walls embedded into higher dimensional square lattices of one dimension higher, we numerically confirm the existence of the edge-localized modes and the effect of gravity encoded in the spectrum. With $U(1)$ link variables, we also find a good consistency to the anomaly inflow described by the Atiyah-Patodi-Singer index theorem in the continuum theory. This talk is based on a work with Shoto Aoki, https://arxiv.org/abs/2203.03782 and some preliminary results.

David J.E. Marsh, King's College London

[JpDe Joint Seminar] Axion Miniclusters: Recent Progress and Open Problems

Online (Zoom)
If the Peccei Quinn symmetry is broken after inflaiton, then axions are produced by the decay of topological defects. This scenario is attractive, since the axion mass is in principle predictable from the relic density, and favours the range ~0.1-10 meV. Miniclusters offer a route to probe this scenario astrophysically. Miniclusters are formed from the overdensities in the axion field left over after the topological defects decay. I will describe recent efforts to understand the mass distribution and density profiles of miniclusters, using theory and simulation. I will also describe efforts to test the minicluster scenario using gravitational microlensing, and radio transients. Open problems surround both scenarios, related to the possible existence and survival fraction of the densest miniclusters.

Miguel Montero, Harvard University

New String Theories from Discrete Theta Angles

Online (Zoom) https://kds.kek.jp/event/44336/
Topological couplings play a prominent role in our understanding of field theories, but their role in string compactifications is much less understood. I explore an example in compactifications of type IIB string theory with sixteen supercharges, showing that they lead to previously unknown components of moduli space in nine, eight, and seven dimensions. I also explain why a similar construction fails to produce a new string theory in ten dimensions. The new components of moduli space thus constructed feature an incomplete lattice of BPS strings, which has implications for a number of Swampland constraints.

Aleksey Cherman, Univ. of Minnesota

[QCD theory Seminar] 1-form symmetry and large N QCD

Online (Zoom)
The most modern way to understand quark confinement involves the notion of `1-form symmetry’. The reason we care about quark confinement is of course because of its implications for real-world QCD, but unfortunately confinement is believed to be only an approximate concept in the real world, so it is not tied to any exact symmetries. However, confinement is supposed to become well-defined in the large N limit of QCD, and so one might expect large N QCD to have a Z_N 1-form symmetry. However, to our surprise, in recent work we found some severe obstructions to the conjecture that large N QCD has a Z_N 1-form symmetry. Our results suggest that a symmetry-based understanding of (approximate) confinement in QCD may require some further generalization of the notion of generalized global symmetries.

Tomohiro Ishizu, Kansai University

[KEK IPNS-IMSS-QUP Joint Colloquium] Empirical approaches to study aesthetic experiences -an introduction to neuroaesthetics-

Online (Zoom)
Art and aesthetic experiences enrich our daily lives. It may appear distant from the empirical sciences at first glance, but it shares similar goals and is closely related to them in that it explores perception and engages with the workings of the mind. Neuroaesthetics is a discipline that studies the relationship between brain function and aesthetic experience (e.g., beauty, ugliness, being moved, sublime) as well as between cognitive processes and artistic activity (e.g. appreciation of artworks, artistic critique, creativity) using empirical methods from cognitive neuroscience. It is an interdisciplinary field that includes researchers from psychology, neuroscience, philosophy, art, art history, to welfare engineering. Following an overview of basic cognitive neuroscience research findings on aesthetic judgements such as beauty and ugliness, I will present research on more complex aesthetic experiences beyond simple beauty, such as sorrow and the sublime. Through these, I hope to explore what beauty means to humanity from a neuroaesthetics point of view.

Naritaka Oshita, RIKEN

Probing gravity with ringing black holes

Hybrid Onsite: Kenkyu Honkan Seminar room, Online: (Zoom) https://kds.kek.jp/event/44132/
A gravitational-wave (GW) signal emitted from a binary black hole merger is an important probe of gravity. The observation of GW ringdown allows us to perform a robust test of gravity as the ringdown waveform is a superposition of quasi-normal (QN) modes of the remnant black hole. It is known that black holes have an infinite number of QN modes. The precise measurement of multiple QN modes puts Einstein’s general relativity to the test. Also, the tentative detection of anomalous signals following the ringdown signal, i.e., GW echoes, has been claimed. The echo is postulated to be the footprint of quantum gravitational effects that can be significant in the vicinity of black hole horizons.I will explain how we can probe classical and quantum gravity with the observation of black hole ringing and will review the open issues and progress in this field.

Xu-Guang Huang, Fudan University

[QCD theory Seminar] QCD phase structure under rotation

Online (Zoom)
Due to the recent experimental breakthrough in heavy ion collisions about the spin polarization measurements, the QCD matter under rotation attracts a lot of attentions. Many novel phenomena are under intensive discussions, like the hyperon spin polarization, vector meson spin alignment, chiral vortical effects, and so on. It would be also interesting to ask what would be the effect of a global rotation on the QCD phase structure. The natural expectation would be that due to the spin polarization by rotation, all the spin-0 condensate, like the chiral condensate, would be unfavored and thus the chiral phase structure may vary under rotation. We will discuss whether this is the case for QCD by either model discussion and by lattice simulation. We will also discuss the confinement-deconfinement transtion under rotation.

Etsuko Itou, RIKEN

Velocity of Sound beyond the High-Density Relativistic Limit from Lattice Simulation of Dense Two-Color QCD

Online (Zoom) https://kds.kek.jp/event/43730/
We obtain the equation of state (EoS) for two-color QCD at low temperature and high density from the lattice Monte Carlo simulation. We find that the velocity of sound exceeds the relativistic limit (c_s^2/c^2=1/3) after BEC-BCS crossover in the superfluid phase. Such an excess of the sound velocity is predicted by several effective theories but is previously unknown from any lattice calculations for QCD-like theories.
This finding might have possible relevance to the EoS of neutron star matter revealed by recent measurements of neutron star masses and radii.
This talk is based on arXiv:2207.01253.

Guang Juan Wang, JAEA

The study of P-wave strange mesons in coupled channel framework

Hybrid On-site: Kenkyu Honkan Seminar room, Online (Zoom) https://kds.kek.jp/event/43887/
In this talk, I will discuss a novel framework to extract resonant states from finite-volume energy levels of lattice QCD and apply it to elucidate structures of the positive parity Ds resonant states nearby the DK and D*K thresholds. In the framework, the Hamiltonian effective field theory is extended by combining it with the quark model. The Hamiltonian contains the bare mesons from the quark model, its coupling with the threshold channels described by quark-pair-creation (QPC) model, and the channel-channel interactions induced by exchanging light mesons. A successful fit of the finite-volume energy levels of lattice QCD with the Hamiltonian model is made. The extracted masses and the predication for an additional state, Ds(2573), are well consistent with experimental measurements. The same framework has also be extended to the P-wave Bs states.

Sung Hak Lim, Rutgers University

Measuring Galactic Dark Matter through Unsupervised Machine Learning

Hybrid On-site: Kenkyu Honkan Seminar room, Online: (Zoom) https://kds.kek.jp/event/43893/
Measuring the density profile of dark matter in the Solar neighborhood has important implications for both dark matter theory and experiment. In this work, we apply autoregressive flows to stars from a realistic simulation of a Milky Way-type galaxy to learn — in an unsupervised way — the stellar phase space density and its derivatives. With these as inputs, and under the assumption of dynamic equilibrium, the gravitational acceleration field and mass density can be calculated directly from the Boltzmann Equation without the need to assume either cylindrical symmetry or specific functional forms for the galaxy’s mass density. We demonstrate our approach can accurately reconstruct the mass density and acceleration profiles of the simulated galaxy, even in the presence of Gaia-like errors in the kinematic measurements.

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