The S-matrix is one of the central objects in quantum field theory and has gained renewed interest recently to better understand the possible structures of low-energy effective field theories, strongly-coupled systems, quantum gravity, etc. However, most of the particles have finite decay widths and thus do not appear in asymptotic states. Therefore, the standard S-matrix arguments may not be directly applied to scatterings of such unstable particles and we need to formulate “the S-matrix theory of unstable particles” to properly understand the availability of the S-matrix arguments in realistic systems. In this talk, I will talk about some progress towards this goal. In particular, I will discuss non-perturbative consequences of unitarity in scattering amplitudes of unstable　particles and their analytic properties.

While the phi meson vacuum properties, such as mass and width, are well known, it is not clear how these properties will change once it is put in a dense environment such as nuclear matter. To study how the phi meson behaves at finite density has been the goal of several past and near future experiments at KEK, COSY-ANKE and J-PARC. Recently, ALICE has also obtained novel experimental data constraining the phi-N interaction. In this talk, I will focus on the in-medium properties of the longitudinal and transverse polarization modes of the phi meson, which due to the breaking of Lorentz symmetry in nuclear matter, can be modified differently. I will review theoretical predictions for these modifications and discuss how the different modes could be measured at the future J-PARC E16 and E88 experiments.

Gravitational waves with frequencies below 1 nHz are notoriously difficult to detect and fall below the typical cutoff frequency for conventional pulsar timing analyses. In this talk, I will present a new means of probing this regime through the correlation of secular drifts in pulsar timing parameters. I will show the results of searches for both continuous and stochastic signals in this regime and will discuss what future observations using this methodology may reveal about the signal recently discovered by pulsar timing collaborations at frequencies above a nanohertz.

In heavy flavour physics, the D- and B-meson sectors continue to be promising realms for precision tests of the Standard Model,where evidence of New Physics can be expected. Lattice QCD offers a powerful ab initio framework to reliably calculate the low-energy hadronic amplitudes, which are crucial for the determination of CKM matrix elements, and thus to significantly reduce the uncertainties of the theory inputs to such tests. This talk presents results on the leptonic D-meson decay constants obtained from a large number of (2+1)-flavour ensembles with O(a) improved Wilson quarks by CLS (including two ensembles at the physical point), spanning 6 lattice spacings down to 0.039 fm and lying on 3 trajectories in the quark mass plane. This allows achieving a phenomenologically relevant precision, while demonstrating control over important sources of systematic uncertainties such as discretisation effects and the quark mass dependence. The second part discusses a strategy how to combine interpolations between relativistic and static computations with a step scaling approach, in order to extract heavy-light B-physics observables in the continuum. We report first numerical results for the b-quark mass and leptonic decay constants from a subset of CLS ensembles and outline how this strategy also applies to semi-leptonic form factors.

https://www-conf.kek.jp/kincha/

Recently, the notion of symmetry is generalized so that we can get further information on low-energy dynamics in strongly coupled field theories. This is described in terms of topological operators and also category. It would be crucial that topology of gauge fields is nontrivial in a fully regularized framework; e.g., continuity appears to be lost under lattice regularization. L¥”uscher addressed this issue for $SU(2)$ gauge fields and defined the topological charge on a lattice explicitly. We apply L¥”uscher’s construction to generalized symmetries. We consider lattice $SU(N)$ gauge theories coupled with $¥mathbb{Z}_N$ $ 2$-form gauge fields, and show the fractionality of the topological charge on $SU(N)/¥mathbb{Z}_N$ principal bundle. Also the mixed ‘t Hooft anomaly and higher-group structure are realized. We become interested in monopole physics as a topological phenomenon on the lattice.

Addressing QCD scattering processes theoretically requires a real-time, nonperturbative method. It is well known that the Schwinger model [QED in (1+1) dimensions] shares many common properties with QCD, including confinement, chiral symmetry breaking, and the existence of vacuum fermion condensate. As a step in developing such an approach, we report here on fully quantum simulations, using classical devices, of a massive Schwinger model. We study the chiral condensate and entanglement entropy caused by jet propagation[2301.11991]. We also explore the propagation of vector and axial charge, i.e., CMW, and observe different oscillation frequencies[2305.05685]. The phase structure of the Schwinger model at finite temperature and chemical potential will also be discussed[2305.00996].

A promising strategy for direct detection of sub-MeV dark matter is to look for phonon excitations in crystals. The crystal targets used in such experiments are typically not completely pure, and have impurities or defects. The point defects of our interest include the Frenkel defects, hydrogen and oxygen impurities, and so on. These defects can diffuse and recombine to emit energy in the form of phonons, and can potentially create a background for direct detection experiments. We estimate the defect densities produced through thermal excitations as well as radiogenic nuclear recoils. For various defect configurations, we quantify the diffusion and recombination rates for both thermal and quantum tunneling mechanisms. We find that the thermally generated Frenkel defects are effectively frozen at cryogenic temperatures and cannot diffuse to recombine with each other. The hydrogen impurity is the unique point defect that has non-negligible diffusion rate at cryogenic temperatures, and possibly contributes to the eV-scale events. The radiogenic defects produced on the surface can be annealed effectively at room temperature for typical defect configurations, but defects produced through radiogenic nuclear recoils in a shielded environment at cryogenic temperatures during the run-time of the experiment can recombine to produce eV-scale events. We provide estimates of these background event rates and give some remarks on subtleties we need to take care of in this kind of experimental setups.

Despite its apparent weakness, gravity is a vital force driving particle production in the early Universe. To explore this production process, two different but well-established frameworks are commonly used, which are known as the Boltzmann and Bogoliubov approaches. I will first discuss a crucial aspect of these frameworks—their equivalence in pure gravitational production—to answer the question of whether these approaches yield consistent outcomes. In doing so, we will see the phase space distribution as a key quantity. This distribution will then serve as a useful tool to address yet another important question: Did the Higgs field predominantly exist as condensate or fluctuations in the earliest times? which will be discussed in the second part of the talk.

https://kds.kek.jp/event/46787/