Masafumi Fukuma, Kyoto University
Sign problem in Monte Carlo simulations and the tempered Lefschetz thimble method
Seminar room, Kenkyu honkan 3F, slides (kek.jp only)
When numerically estimating observables on a large-scale system with a complex-valued action, one needs an exponentially long computational time for precise estimation. After reviewing various approaches to this “sign problem”, we explain “the tempered Lefschetz thimble method”, which was introduced by MF and N. Umeda in [arXiv:1703.00861]. We argue that this has a potential to be a universal solution to the sign problem, by explicitly showing that this algorithm gives correct estimates for problems that have been difficult by other algorithms.
Matthew Dodelson, IPMU
High energy behavior of Mellin amplitudes
Seminar room, Kenkyu honkan 3F
I will describe recent work with Ooguri, in which we obtained bounds on the Mellin amplitude at high energies. I’ll start with a general overview of Mellin space, and then move on to our derivation of the bounds. The bounds are obtained by demanding that position space correlators don’t have spurious singularities. At the end I might talk about related ongoing work on black holes, if I have time.
Tomomi Sunayama, IPMU
Cosmology with Subaru Prime Focus Spectrograph (PFS)
Meeting room 1, Kenkyu honkan 1F
PFS (Prime Focus Spectrograph), a next generation facility instruments on the Subaru telescope, is a wide-field, massively multiplexed, and optical & near-infrared spectrograph. In the PFS cosmology survey, emission line galaxies (ELGs) in the wide redshift range from z= 0.6to2.4 over 1400 square-degree will be observed. The unique redshift range for the PFS cosmology survey is at z>2. We envision that we will start our survey from 2022, and I will describe strategies to achieve the scientific goals as well as the possible systematic problems for future fiber-fed spectroscopic surveys.
Po-Yen Tseng, Yonsei University
Light gauge boson interpretation for muon g-2 and J-PARC KOTO anomalies
Meeting room 3, Kenkyu honkan 1F
We discuss a list of possible light gauge boson interpretations for the long-standing experimental anomaly in $(g-2)\mu$ and also recent anomalous excess in $KL \rightarrow \pi^0 + \text{(invisible)}$ events at the J-PARC KOTO experiment. We consider two models: i) $L\mu – L\tau$ gauge boson with heavy vector-like quarks and ii) $(L\mu – L\tau) + \epsilon (B3 – L\tau)$ gauge boson in the presence of right-handed neutrinos. When the light gauge boson has mass close to the neutral pion in order to satisfy the Grossman-Nir bound, the models successfully explain the anomalies simultaneously while satisfying all known experimental constraints. We extensively provide the future prospect of suggested models.
Tatsuhiro Misumi, Akita University
Central-branch Wilson fermion, Spin chain and Aoki phase
Meeting room 1, Kenkyu honkan 1F In this talk, we first discuss the central-branch Wilson fermion, which is defined by imposing a specific relation between the mass and the Wilson parameter [1]. This setup gives two massless Dirac fermions in the continuum limit, and it turns out that no fine-tuning of m is required because the extra U(1) symmetry at the central branch prohibits the additive mass renormalization [2,3]. We show that Dirac determinant is positive semi-definite and this formulation is free from the sign problem, so the Monte Carlo simulation of the path integral is possible. By identifying the symmetry at low energy, we find that this lattice model has the mixed ’t Hooft anomaly between the extra U(1) symmetry, lattice translation, and lattice rotation, which means that the trivially gapped phase is forbidden at the central branch [4]. We discuss its relation to the anomaly of half-integer anti-ferromagnetic spin chains, so our lattice gauge theory is suitable for numerical simulation of Haldane conjecture. We also argue that it gives new and strict understanding on parity-broken phase (Aoki phase) of 2d Wilson fermion [4]. Furthermore, we show that our study can be extended to 4d lattice QCD with Wilson fermion, leading to a novel insight into the question which of Aoki-phase or Sharpe-Singleton scenarios is valid.
In this talk, we first discuss the central-branch Wilson fermion, which is defined by imposing a specific relation between the mass and the Wilson parameter [1]. This setup gives two massless Dirac fermions in the continuum limit, and it turns out that no fine-tuning of m is required because the extra U(1) symmetry at the central branch prohibits the additive mass renormalization [2,3]. We show that Dirac determinant is positive semi-definite and this formulation is free from the sign problem, so the Monte Carlo simulation of the path integral is possible. By identifying the symmetry at low energy, we find that this lattice model has the mixed ’t Hooft anomaly between the extra U(1) symmetry, lattice translation, and lattice rotation, which means that the trivially gapped phase is forbidden at the central branch [4]. We discuss its relation to the anomaly of half-integer anti-ferromagnetic spin chains, so our lattice gauge theory is suitable for numerical simulation of Haldane conjecture. We also argue that it gives new and strict understanding on parity-broken phase (Aoki phase) of 2d Wilson fermion [4]. Furthermore, we show that our study can be extended to 4d lattice QCD with Wilson fermion, leading to a novel insight into the question which of Aoki-phase or Sharpe-Singleton scenarios is valid.
[References]
[1] M. Creutz, T. Kimura, T. Misumi, Phys. Rev. D83 (2011) 094506, [arXiv:1101.4239].
[2] T. Kimura, S. Komatsu, T. Misumi, T. Noumi, S. Torii, S. Aoki, JHEP 01 (2012) 048, [arXiv:1111.0402].
[3] T. Misumi, PoS LATTICE2012 (2012) 005, [arXiv:1211.6999].
[4] T. Misumi, Y. Tanizaki, [arXiv:1910:09604].
Sanefumi Moriyama, Osaka City University
ABJM Matrix Model and 2D Toda Lattice Hierarchy
Meeting room 1, Kenkyu honkan 1F
It was known that the worldvolume of multiple M2-branes is described by 3D supersymmetric Chern-Simons theory (known as ABJM theory). After moving to the grand canonical ensemble, it was found in our previous works that the vacuum expectation values of half-BPS Wilson loops in the ABJM theory satisfy Giambelli relations and Jacobi-Trudi relations, which imply integrability directly. To investigate the integrable structure, we further defined two-point functions in ABJM matrix model and identified the structure as 2D Toda lattice hierarchy. In this talk I will give an overview of the recent progress on integrability in the ABJM theory.
Noriyuki Sogabe, Keio U
Triangle anomalies and nonrelativistic Nambu-Goldstone modes of generalized global symmetries
Meeting room 1, Kenkyu honkan 1F In massless QCD coupled to QED in an external magnetic field, a photon with the linear polarization in the direction of the external magnetic field mixes with the charge neutral pion through the triangle anomaly, leading to one gapless mode with the quadratic dispersion relation ω?k^2 and one gapped mode. In this talk, we show that this gapless mode can be interpreted as the so-called type-B Nambu-Goldstone (NG) mode associated with the spontaneous breaking of the generalized global symmetries and that its presence is solely dictated by the anomalous commutator in the symmetry algebra. We also argue a possible realization of such nonrelativistic NG modes in 3-dimensional Dirac semimetals.
In massless QCD coupled to QED in an external magnetic field, a photon with the linear polarization in the direction of the external magnetic field mixes with the charge neutral pion through the triangle anomaly, leading to one gapless mode with the quadratic dispersion relation ω?k^2 and one gapped mode. In this talk, we show that this gapless mode can be interpreted as the so-called type-B Nambu-Goldstone (NG) mode associated with the spontaneous breaking of the generalized global symmetries and that its presence is solely dictated by the anomalous commutator in the symmetry algebra. We also argue a possible realization of such nonrelativistic NG modes in 3-dimensional Dirac semimetals.
Syuhei Iguro, Nagoya University
Testing the 2HDM explanation of the muon g-2 anomaly at the LHC
Meeting room 3, Kenkyu honkan 1F
The discrepancy between the measured value and the Standard Model prediction for the muon anomalous magnetic moment is one of the important issues in the particle physics. In this talk, we consider a two Higgs doublet model (2HDM) where the extra Higgs doublet couples to muon and tau in lepton flavor violating (LFV) way and the one-loop correction involving the scalars largely contributes to the muon anomalous magnetic moment. The couplings should be sizable to explain the discrepancy, so that the extra Higgs bosons would dominantly decay into μτ LFV modes, which makes the model testable at the LHC through multi-lepton signatures even though they are produced via the electroweak interaction. We discuss the current status and the future prospect for the extra Higgs searches at the LHC, and demonstrate the reconstruction of the mass spectrum using the multi-lepton events.
Shintaro Eijima, KEK
Sterile neutrino dark matter and heavy neutral leptons
Meeting room 1, Kenkyu honkan 1F
Sterile neutrino as a possible dark matter candidate is reviewed. I will give an overview of the current status of the research on the dark matter particle, and discuss the motivation and limits obtained through astrophysical observations. Originally the thermal production via mixing was suggested which, however, is ruled out in current constraints. I will introduce different mechanisms to produce the dark matter. In particular a resonant production with lepton asymmetry in thermal plasma and the asymmetry originated by heavy neutral leptons are explained.
Etsuko Itou, Keio University
Two-colour QCD phases and the topology at low temperature and high density
Meeting room 1, Kenkyu honkan 1F
