Shinichiro Akiyama, University of Tsukuba
Tensor renormalization group approach to (1+1)-dimensional Hubbard model
Online (Zoom), indico page, slides (kek.jp only)
Tensor renormalization group (TRG) approach is a variant of the real-space renormalization group to evaluate the path integral in the thermodynamic limit, without resorting to any probabilistic interpretation for the given Boltzmann weight. Moreover, since the TRG can directly deal with the Grassmann variables, this approach can be formulated in the same manner for the systems with bosons, fermions, or both of them. These advantages of the TRG approach have been confirmed by the earlier studies of various lattice theories, which suggest that the TRG potentially enables us to investigate the parameter regimes where it is difficult to access with the standard stochastic numerical methods, such as the Monte Carlo simulation. In this talk, we explain recent our numerical study of the (1+1)-dimensional Hubbard model with the TRG approach. Our results of the critical chemical potential and the critical exponent ν are consistent with the exact solutions obtained by the Bethe Ansatz. This talk is based on arXiv:2105.00372.
Hajime Otsuka, KEK
理論センタープロジェクト「弦からヒッグズ／フレーバー」セミナー Sharpening the Boundaries Between Flux Landscape and Swampland by Tadpole Charge
Online (Zoom) We investigate the vacuum structure of four-dimensional effective theory arising from Type IIB flux compactifications on a mirror of the rigid Calabi-Yau threefold, corresponding to a T-dual of the DeWolfe-Giryavets-Kachru-Taylor model in Type IIA flux compactifications. By analyzing the vacuum structure of this interesting corner of string landscape, it turns out that there exist perturbatively unstable de Sitter (dS) vacua in addition to supersymmetric and non-supersymmetric anti-de Sitter vacua. On the other hand, the stable dS vacua appearing in the low-energy effective action violate the tadpole cancellation condition, indicating a strong correlation between the existence of dS vacua and the flux-induced D3-brane charge (tadpole charge). We also find analytically that the tadpole charge constrained by the tadpole cancellation condition emerges in the scalar potential in a nontrivial way. Thus, the tadpole charge would restrict the existence of stable dS vacua, and this fact underlies the statement of the dS conjecture. Furthermore, our analytical and numerical results exhibit that distributions of O(1) parameters in expressions of several swampland conjectures peak at specific values.
We investigate the vacuum structure of four-dimensional effective theory arising from Type IIB flux compactifications on a mirror of the rigid Calabi-Yau threefold, corresponding to a T-dual of the DeWolfe-Giryavets-Kachru-Taylor model in Type IIA flux compactifications. By analyzing the vacuum structure of this interesting corner of string landscape, it turns out that there exist perturbatively unstable de Sitter (dS) vacua in addition to supersymmetric and non-supersymmetric anti-de Sitter vacua. On the other hand, the stable dS vacua appearing in the low-energy effective action violate the tadpole cancellation condition, indicating a strong correlation between the existence of dS vacua and the flux-induced D3-brane charge (tadpole charge). We also find analytically that the tadpole charge constrained by the tadpole cancellation condition emerges in the scalar potential in a nontrivial way. Thus, the tadpole charge would restrict the existence of stable dS vacua, and this fact underlies the statement of the dS conjecture. Furthermore, our analytical and numerical results exhibit that distributions of O(1) parameters in expressions of several swampland conjectures peak at specific values.
Reference: arXiv:2104.15030v1 [hep-th]
Yang Bai, University of Wisconsin-Madison
Magnetic Black Holes with Electroweak-Symmetric Coronas
Online (Zoom) https://kds.kek.jp/event/38766/
Magnetically charged black holes are interesting solutions of the Standard Model and general relativity. They may possess a “hairy” electroweak-symmetric corona outside the event horizon, which speeds up their Hawking radiation and leads them to become nearly extremal on short timescales. In this talk, I will discuss their properties and various approaches to search for them in our current universe.
Ulf Danielsson, Uppsala University
Better than nothing - a higher dimensional view on quantum cosmology
Online (Zoom), indico page, slides (kek.jp only)
Recent developments in string theory indicates a fundamental problem in constructing de Sitter space and dark energy. I will review a new way to obtain de Sitter space compatible with string theory, where our universe is riding an expanding bubble of true vacuum in AdS5. I will also demonstrate how the model solves important problems in quantum cosmology.
Yuji Hirono, APCTP
[QCD theory Seminar] Counting Nambu-Goldstone modes of higher-form global symmetries
Online (Zoom) When continuous symmetries are spontaneously broken, there appear gapless modes called Nambu-Goldstone (NG) modes. Due to their gapless nature, they are important degrees of freedom at low energies. Recently, a generalized kind of symmetries, called higher-form symmetries, have been discussed, whose charged objects are extended. The analogue of the NG theorem exists, and photons can be regarded as NG modes for a spontaneously broken higher-form symmetry. In this talk, I will discuss how to count the number of NG modes associated with spontaneously broken symmetries that can include higher-form ones [1]. I will give a formula for the number of NG modes, which is also applicable for systems without Lorentz invariance.
When continuous symmetries are spontaneously broken, there appear gapless modes called Nambu-Goldstone (NG) modes. Due to their gapless nature, they are important degrees of freedom at low energies. Recently, a generalized kind of symmetries, called higher-form symmetries, have been discussed, whose charged objects are extended. The analogue of the NG theorem exists, and photons can be regarded as NG modes for a spontaneously broken higher-form symmetry. In this talk, I will discuss how to count the number of NG modes associated with spontaneously broken symmetries that can include higher-form ones [1]. I will give a formula for the number of NG modes, which is also applicable for systems without Lorentz invariance.
Reference:
[1] Y. Hidaka, Y. Hirono, R. Yokokura, Phys. Rev. Lett. 126, 071601(2021).
[arXiv:2007.15901]
Yuta Hamada, Harvard University
Probe branes and the Swampland
Online (Zoom), indico page, slides (kek.jp only)
Probe branes are useful to obtain constraints on the low energy effective field theory coupled to the gravity. I will talk about the new swampland constraints based on the consistency condition of the 3-brane probe in 8d supergravity with 16 supercharges.
Akira Ohnishi, YITP Kyoto University
[EX] (Part II) Femtoscopic approach to hadron-hadron interactions
Online (Zoom), indico page, slides (kek.jp only)
Hadron-hadron interactions are the basic inputs to discuss hadronic molecules and hadronic nuclei. Flavored hadron interactions, however, are generally difficult to access in standard scattering experiments. Recent research activities on hadron-hadron correlation functions open the ways to systematically access flavored hadron interactions such as Ω, Ξ, − and even (¯. Since the correlation function is given as the average of the wave function squared with the normalized source function weight (Koonin-Pratt formula), it contains the information of the hadron-hadron interaction. Thus, provided that the source function is known, one can examine the hadron-hadron interaction. In this seminar, after a short introduction, I first explain how we can calculate the correlation function in simple two cases; (1) quantum statistics operates but there is no pairwise interaction (Hanbury-Brown–Twiss effects), and (2) non-identical particle pairs with a short-range interaction in an analytic model (Lednicky-Lyuboshits model). Next I explain some other effects such as the Coulomb potential and coupled-channel effects. In the third part, I show some of the recent correlation function data reported by the RHIC-STAR and LHC-ALICE collaborations. These data give constraints on the low-energy scattering parameters, and seem to suggest the existence of bound states in some of the hadron-hadron pairs. In the last part, I will give an outlook.
Takumi Doi, RIKEN
[EX] (Part I) Hadron-hadron interactions from Lattice QCD
Online (Zoom), indico page, slides (kek.jp only)
In this talk, I review the first-principles calculations of hadron-hadron interactions from lattice QCD. I introduce a theoretical framework, HAL QCD method, where it is shown that the notion of potential can be rigorously introduced/calculated as a representation of the S-matrix of QCD. Recent numerical results are presented, in particular, for hyperon forces obtained near the physical point. The physical implications for exotic dibaryons, hyper-nuclei, equation of state of high dense matter and the structure of neutron stars are also discussed and future prospects will be given.
Milad Delfan Azari, Waseda University
Physics of fast collective neutrino oscillations in core-collapse supernovae
Online (Zoom), indico page, slides (kek.jp only)
Neutrinos are highly populated inside the core of massive stars. They play an important role in the explosion mechanism of core-collapse supernovae. It is known that, almost all of the energy in the gravitational collapse is emitted in the form of neutrinos. They may change their identity through so-called fast flavor conversion induced by mutual forward scatterings. If this fast flavor conversion happens, it may have an impact on the dynamics of supernova explosions, since it may occur near the neutrino sphere. In this presentation, the latest results of our understanding of the neutrino fast flavor conversions in core-collapse supernovae will be reported.
Graham White, Kavli IPMU
Learning about cosmology using astrometry
Online (Zoom), indico page, slides (kek.jp only)
