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)
Gaia is observing the position and path of an enormous number of stars. Future experiments promise to do so for even more stars at high precision. If the light from such a star is traveling to us through a stochastic gravitational wave background, the apparent position of the star will be displaced by an amount essentially independent of the distance but dependent on the strength of the gravitational wave. Correlations in such shifts from many stars can be used to detect or constrain a gravitational wave background. The frequency range probed partially fills the gap between pulsar timing arrays and LISA. We explore the potential cosmological consequences of this by looking at phase transitions, topological defects and pbhs.
Zebin Qiu, University of Tokyo
[QCD theory Seminar] Magnetic effects in dense nuclear matter through Skyrme model
Online (Zoom)
Skyrme model is among the simplest extensions of chiral effective theory including anomaly. We investigate how an external magnetic field deforms the classical Skyrmion soliton structure while maintaining the topological winding. We further identify quantized Skyrmions as neutrons and protons, revealing a mass split between them induced by the magnetic field. More intriguing aspects arise when we annex multiple Skyrmions to form a crystal and realize the ¥pi^0 domain wall as a special class of solution. We establish the thermodynamics and phase diagram of different classes of Skyrme crystals, beneath which is the topological transmutation between ¥pi_3(S^3) and ¥pi_1(S^1).
Kazuya Yonekura, Tohoku University
Atiyah-Patodi-Singer index theorem from axial anomaly
Online (Zoom) https://kds.kek.jp/event/38462/
I will talk about a simple physical derivation of the so-called Atiyah-Patodi-Singer (APS) index theorem. The derivation is just a minor modification of Fujikawa’s argument for the axial U(1) anomaly once we we understand a physical interpretation of the APS boundary condition. It is based on my recent work with Shun K. Kobayashi https://arxiv.org/abs/2103.10654
Juan Carlos Vasquez, University of Massachusetts
Resurgence of the QCD Adler function
Online (Zoom) https://kds.kek.jp/event/38304/
