Naritaka Oshita, RIKEN

Probing gravity with ringing black holes

##### 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

##### 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

##### 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

##### 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

##### 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.

Kazushi Yamashiro, Shizuoka University

Target space entanglement in a matrix model for the bubbling geometry

##### We study the target space entanglement entropy in a complex matrix model that describes the chiral primary sector in N=4super Yang-Mills theory, which is associated with the bubbling AdS geometry. The target space for the matrix model is a two-dimensional plane where the eigenvalues of the complex matrix distribute. The eigenvalues are regarded as the position coordinates of fermions, and the eigenvalue distribution can be viewed as a droplet formed by the fermions, which is identified with one that specifies a boundary condition in the bubbling geometry. We consider states in the matrix model that correspond to AdS5× S5, an AdS giant graviton and a giant graviton in the bubbling geometry. We calculate the target space entanglement entropy of a subregion for each of such states in the matrix model as well as the area of the boundary of the subregion in the bubbling geometry, and find a qualitative agreement between them.

Masaaki Tomii, Univ. of Connecticut

Lattice calculation of $K ¥to ¥pi¥pi$ decay on the lattice with periodic boundary conditions

##### Since RBC/UKQCD’s latest publication of lattice result for direct CP violation and the Delta I = 1/2 rule in $K ¥to ¥pi¥pi$ decay, which was made with G-parity boundary conditions in 2020, we have been revisiting this problem with a different lattice setup with periodic boundary conditions and multiple lattice spacings to see the consistency with our previous result and to improve the precision. While there was an expectation that it could be difficult to extract physical kinematics of K to pipi decay with periodic boundary conditions, we overcome it through the variational method. Also periodic boundary conditions provide a relatively easy way to introduce electromagnetic and isospin breaking corrections, which is desired to be implemented in near future.

In this talk, we show our preliminary result and discuss prospect of high-precision calculation of $K ¥to ¥pi¥pi$ decay with periodic boundary conditions.

Choong Sun Kim, Yonsei University

[EX] Is the sub-eV active neutrino Dirac or Majorana? (New alternative method to 0-nu-beta-beta decay, by using B^0 (or Upsiol(1s)) --> mu+ mu- nu nu-bar)

##### The nature of neutrino, whether it is a Dirac type or Majorana type, may be comprehensively probed using their quantum statistical properties. If neutrino is a Majorana fermion, then by definition it is identical and indistinguishable from the corresponding antineutrino. When a Majorana neutrino and antineutrino are pair produced, the corresponding state has to obey Pauli principle unlike in the Dirac case. We use this property to distinguish between the two cases using the process B^0 → µ− µ+ νµ ¯νµ. We show that the two cases differ dramatically in a special kinematic scenario where, in the rest frame of the parent B meson, the muons fly away back-to-back (i.e. fly with 3-momenta of equal magnitudes but opposite directions), and so do the neutrino and antineutrino.

Kei-ichi Maeda, Waseda University

Relativistic Dynamical System and Gravitational Waves

##### After the discovery of the gravitational waves, gravitational wave physics and astronomy have provided us new information about strong gravitational phenomena and new physics. For example, speed of gravitational waves, equation of state at very high dense region, constraint on gravitational theories, and so on.

In order to observe gravitational waves, we have used the templates of emitted gravitational waves from a binary system. However, we may have more complicated relativistic dynamical system in nature, which may not be integrable. We may expect chaotic behavior in such a system, for which it is very difficult to make appropriate templates.

In this talk, we study chaos in a relativistic dynamical system of compact objects and the gravitational waves emitted from such a system. We then look for some characteristic feature of the gravitational waves, which could be used in gravitational wave observation.

We also discuss about a hierarchical triple system with the Kozai-Lidov mechanism, which shows the oscillation between the eccentricity of inner binary and relative inclination. The evolution curve of the cumulative perihelion shift, which is indirect evidence of gravitational wave emission, will be bended since the gravitational waves are emitted strongly when the eccentricity becomes large. We then show the observability of gravitational waves from such a triple system. We also consider relativistic effects such as Lense-Thirring precession.

Hikaru Kawai, National Taiwan University

Do different observers see different physics?