Takafumi Aoki, U. Tokyo
Small Instanton Effects on Composite Axion Mass
Hybrid On-site: Kenkyu Honkan Seminar room 321, 322 Online: Zoom The Peccei–Quinn (PQ) mechanism is a prominent solution to the strong CP problem. However, it faces the axion quality problem: higher-dimensional, Planck-suppressed operators which explicitly break PQ symmetry can reintroduce the effective QCD theta angle. In composite axion models, where strong dynamics at high energies dynamically break PQ symmetry, certain constructions address this quality problem.
The Peccei–Quinn (PQ) mechanism is a prominent solution to the strong CP problem. However, it faces the axion quality problem: higher-dimensional, Planck-suppressed operators which explicitly break PQ symmetry can reintroduce the effective QCD theta angle. In composite axion models, where strong dynamics at high energies dynamically break PQ symmetry, certain constructions address this quality problem.
In some cases, hidden interactions distinct from QCD appear to contribute to the axion mass through instanton effects. I demonstrate that while these small instantons enhance the axion mass in a toy model, they do not contribute to the axion mass in an explicit model which addresses the quality problem. This talk is based on the following work: https://arxiv.org/abs/2404.19342″
Vittorio Larotonda, University of Bologna
A journey through the non-supersymmetric landscape
Hybrid on-site: Kenkyu Honkan Seminar room 321, 322 Online: Zoom
In this talk, I will discuss my research on non supersymmetric theories and anomalies. In particular, I will revisit the chiral spectra on charged 1- and 5-branes in the 10d non supersymmetric sp(16) string theory and verify anomaly cancellation via inflow. Furthermore, I will show compelling evidence that the global structure of the gauge group is Sp(16)/Z2 along with hints of a possible duality to a non-supersymmetric heterotic theory. Secondly, I will discuss the presence of a discrete topological term in heterotic strings and delve into its relation with anomaly inflow cancellation on the worldvolume of the non-supersymmetric NS5-brane. These insights will allow us to assess the consistency of candidate spectra for the six-dimensional theory living on these defects. Finally I will present a recent study of Type II non-supersymmetric toroidal asymmetric orbifolds with a vanishing cosmological constant at one-loop in string perturbation theory. This talk will be based on 2412.17894, 2507.11610 and 2602.07113.
Fumihiro Naokawa, U. Tokyo
Cosmic Birefringence as a probe of Dark Sectors
Hybrid On-site: Kenkyu Honkan Seminar room 321, 322 Online: Zoom
Multiple studies analyzing CMB polarization have recently reported evidence for cosmic birefringence, which refers to a rotation of the polarization plane of photons during their propagation. This signal violates parity symmetry and suggests the presence of extremely light pseudoscalar fields, such as axion-like particles. Such fields are potential candidates for dark matter or dark energy. In this seminar, we discuss the current observational status of cosmic birefringence, its implications for searches of dark sectors, and future prospects.
Toshimi Suda, Research Center for Accelerator and Radioisotope Science (RARiS), Tohoku University
[KEK-JAEA Joint Seminar] Proton Charge Radius
Hybrid On-site: KEK Tokai Bldg1 room 116 Online: Zoom The “Proton Radius Puzzle,” initiated by the 2010 muonic hydrogen measurement, highlighted a significant discrepancy (about 7\sigma) with respect to values derived from electron scattering and ordinary hydrogen spectroscopy. While recent measurements, such as the PRad experiment at JLab and some of updated hydrogen spectroscopies, look to favor a smaller proton charge radius, consistent with the muonic result, inconsistencies with earlier electron scattering data remain unresolved. In addition, discrepancies among recent 1S–3S transition hydrogen spectroscopy resultsn suggest the presence of unquoted systematic uncertainties. Consequently, a precise determination of the proton charge radius is still critical to resolve this long-standing issue.
The “Proton Radius Puzzle,” initiated by the 2010 muonic hydrogen measurement, highlighted a significant discrepancy (about 7\sigma) with respect to values derived from electron scattering and ordinary hydrogen spectroscopy. While recent measurements, such as the PRad experiment at JLab and some of updated hydrogen spectroscopies, look to favor a smaller proton charge radius, consistent with the muonic result, inconsistencies with earlier electron scattering data remain unresolved. In addition, discrepancies among recent 1S–3S transition hydrogen spectroscopy resultsn suggest the presence of unquoted systematic uncertainties. Consequently, a precise determination of the proton charge radius is still critical to resolve this long-standing issue.
In this seminar, I will report on the current status of our ULQ2 (Ultra-Low Q2) project at the Research Center for Accelerator and Radioisotope Science (RARiS; former ELPH), Tohoku University. Utilizing a 60-MeV electron linac, we have measured the elastic electron–proton scattering cross section in the lowest-ever momentum transfer region, Q^2 = 0.0003–0.008 (GeV/c)^2. A key feature of this project is an absolute cross-section measurement relative to the well-known ^{12}C cross section using a CH_2 target, aiming to control systematic uncertainties at the 10^{-3} level. This approach is expected to provide the least model-dependent determination of the proton charge radius from electron scattering.
In addition to the proton measurement, we have also performed elastic electron–deuteron scattering measurement under the same kinematics, providing the world’s lowest-Q^2 data for the deuteron. A puzzle similar to that of the proton has been pointed out, and our measurement enables a determination of the deuteron charge radius. From this e+d data, we are challenging the determination of the neutron charge radius via electron scattering for the first time by exploiting the fourth moments of the deuteron charge distribution.
I will first review the current status of the Proton Radius Puzzle and recent global experimental efforts. I will then present the details of the ULQ2 project, including the challenges for the neutron charge radius.
Chong-Sun Chu, National Tsing Hua University
Quantum black hole from quantum mechanics of space time
Hybrid On-site: Kenkyu Honkan Seminar room 321, 322 Online: Zoom
We review a recent proposal for a quantum black hole as a certain large N matrix quantum mechanics. In this model, black hole horizon in general relativity is replaced by a fuzzy geometry. The model has past a number of tests: i) the macroscopic mass-size-shape-angular momentum relation for Schwarzschild and Kerr black hole is reproduced. ii) Berkenstein-Hawking entropy is reproduced from a microstates counting. iii) The Hawking radiation is described consistently in terms of quantum mechanical tunneling of the fuzzy sphere via the nucleation of a fuzzy monopole on the horizon. Further directions will be discussed.
Keisuke Harigaya, Chicago University
Phase transition during inflation
Hybrid on-site: Kenkyu Honkan Seminar room 321, 322 Online: Zoom
Symmetry plays important roles in particle physics. In the Standard Model and beyond, phase transition associated with symmetry breaking may occur in the early universe. We will discuss an unexplored possibility that phase transition occurs during inflation rather than after inflation. We first argue that phase transition may naturally occur during inflation, triggered by slow-roll dynamics of an inflation field or a spectator field. We then discuss two applications of phase transition during inflation: enhanced axion dark matter production and gravitational-waves with a characteristic spectrum and anisotropy.
Mohammad Aghaie, Osaka U
Axion Dark Matter from Heavy Quarks
Hybrid On-site: Kenkyu Honkan Semiar room321 322 Online: Zoomid
We propose simple scenarios in which the observed dark matter abundance arises from decays and scatterings of heavy quarks through freeze-in production of an axion-like particle with a mass in the 10 keV–1 MeV range. These models can be tested by future X-ray telescopes and, in some cases, will be almost entirely probed by searches for two-body decays (K \to \pi + \text{invisible}) at NA62. As a byproduct, we discuss the cancellation of infrared divergences in flavor-violating scattering processes relevant for thermal axion production and derive the general contribution to the axion–photon coupling from all three light quarks.
Shuhei Minato, U of Tokyo
Impact of Higher-Order Color-Superconducting Gap Corrections on the Dense-Quark-Matter EoS
Hybrid On-site: Kenkyu Honkan Seminar room 321, 322 Online: Zoom
Recent astrophysical observations suggest that, inside neutron stars, the speed of sound and the trace anomaly may not follow a simple extrapolation from normal-phase quark matter. This possible discrepancy has drawn attention because it could provide observational signatures of color superconductivity. On the theory side, QCD becomes weakly coupled at sufficiently high density, so perturbative methods can be applied. Weak-coupling frameworks that include the color-superconducting gap are well established and allow systematic, order-by-order improvements. In this talk, I summarize current observational constraints on the equation of state, compare them with state-of-the-art theoretical predictions, and discuss whether color superconductivity can occur in neutron-star cores.
Sho Araki, Osaka University
The Arf–Brown–Kervaire (ABK) Invariant in Lattice Fermion Systems
Hybrid on-site: Kenkyu Honkan Seminar room 321, 322 Online: Zoom
Topological invariants in fermionic systems provide sharp probes of symmetry and anomaly. In this talk, we study how to formulate such a topological invariant that is valued in Z_8, known as the Arf-Brown-Kervaire (ABK) invariant, for the lattice fermion systems. The ABK invariant is a two-dimensional invariant that is encoded in the complex phase of the Majorana fermion partition function, and it plays a role analogous to topological terms such as the instanton number in 4D Dirac fermion settings. We employ massive Wilson Dirac operators and numerically demonstrate that the ABK invariant emarges on the partition function. To capture the ABK invariant fully, it is essential to consider various types of manifold including non-orientable ones such as the real projective plane and the Klein bottle. In addition, manifolds with boundaries are also important for understanding anomaly and anomaly inflow. We discuss how to realize the geometries of these manifolds on the lattice and verify numerically (and partly analytically) that our formulation reproduces the known values in continuum theory.
Stephen R. Sharpe, University of Washington
Three-particle scattering amplitudes from lattice QCD
Hybrid On-site: Seminar room 321, 322 Online: Zoom
