Talks

The Berry phase, discovered by M.V. Berry in 1984, has been applied to the construction of various invariants in topological phase of matters. The Berry phase measures the non-triviality of a uniquely gapped system as a family and takes its value in $H^2({parameter space};Z)$.

In recent years, there have been several attempts to generalize it to higher-dimensional many-body lattice systems[1,2,3,4], called the “higher” Berry phase. In the case of spatial dimension d it is believed that the higher Berry phase takes its value in $H^{d+2}({parameter space};Z)$. However, in general dimensions, the definition of the higher Berry phase in lattice systems is not yet known.

In my talk, I’ll explain about the way to extract the higher Berry phase in 1-dimensional systems by using the “higher inner product” of three matrix product states and how to construct the topological invariant which takes its value in $H^3({parameter space};Z)$. This talk is based on [3] and [4].

Refs:
[1] A. Kapustin and L. Spodyneiko Phys. Rev. B 101, 235130
[2] X. Wen, M. Qi, A. Beaudry, J. Moreno, M. J. Pflaum, D. Spiegel, A. Vishwanath and M. Hermele arXiv:2112.07748
[3] S. Ohyama, Y. Terashima and  K. Shiozaki arXiv:2303.04252
[4] S. Ohyama and S. Ryu arXiv:2304.05356  

Zoom link:  https://pitp.zoom.us/j/93720709850?pwd=RTliMDNMRWo2V2k1MnBKUjlRMjBqZz09

Taking string theory off shell requires breaking Weyl invariance on the worldsheet, i.e. the worldsheet theory is now a QFT instead of a CFT. I will explain Tseytlin’s first-quantized approach to taking the worldsheet theory off-shell in a consistent manner, with a particular emphasis on the subtleties involved in calculating the sphere amplitude. This approach allows for the derivation of a classical string action which gives rise to the correct equations of motion and S-matrix, to all orders in perturbation theory. 

I'll also explain the underlying conceptual structure of the Susskind and Uglum black hole entropy argument. There I will show explicitly how the classical (tree-level) effective action and entropy S = A/4G_N may be calculated from the sphere diagrams. 

Time permitting, I will discuss ongoing efforts to derive the Ryu-Takayanagi formula in string theory.

Based on arXiv:2211.08607 and arXiv:2211.16448. 

Zoom link:  https://pitp.zoom.us/j/93668017324?pwd=K2pxZEhjalRTWkVVbVRESCtRVDFmUT09

The mixing angles of the quark sectors are constrained by unitarity in the standard model. However, recent data indicates a about 3 sigma deviation from unitarity in the mixing angle between the 1st and 2nd generation down-type quarks, known as the Cabibbo angle anomaly. The observations include the charged-current weak decays of neutrons, nuclei, kaons, and the hadronic decay of tau leptons. Although the issue appears to lie in the quark sector, modifying the neutrino sector may offer a solution. In this talk, we discuss recent findings that suggest a sterile neutrino of MeV mass mixing with the electron-type neutrino can resolve the Cabibbo angle anomaly. We also examine the current bounds and future prospects of this scenario.

Zoom Link:  https://pitp.zoom.us/j/98083942792?pwd=eHFRUmJUVGNJcVpTSHZXVXFKQm95QT09