Yuma Furuta
Current Position：Assistant professor
Institutional Affiliation：Kyushu University
Email: furuta.yuma@phys.kyushu-u.ac.jp
Webpage: https://sites.google.com/view/y-furuta/en
Host Scholar: Assis.Prof. Chang-Tse Hsieh
Hosting Department/Institution: Department of Physics, National Taiwan University
Biography:
I am Yuma Furuta, a postdoc and assistant professor at Kyushu University. My research interest is mainly conformal field theory, from the point of view of mathematical physics. Recently I have been interested in the perspective from the condensed-matter field, so I would like to discuss with you all!
Lecture [1]:
Date ＆ Time: Wednesday, 21 October 2026, 10:30 AM
Venue: R618, Department of Physics, NTU
Title: complex conformal manifolds, and conformal interfaces
Abstract: Complex conformal field theories (CFTs) have recently emerged as essential frameworks for understanding non-Hermitian criticality, weakly first-order phase transitions, and walking renormalization group flows, while their general structures remain largely unknown. In this work, we propose a systematic construction of complex CFTs by analytically continuing exactly marginal couplings into the complex plane. This procedure applies uniformly to bulk, boundary, and defect deformations, preserving conformal symmetry while generically complexifying operator spectra and other universal data.
Using the compact free boson as a solvable laboratory, we uncover the global structure of the complexified Gaussian conformal manifold. More generally, we demonstrate that genuinely complex rational CFTs do not exist: rational points remain confined to the real regime, providing a sharp distinction between real and complex theories.
In the defect case, we investigate the one-parameter family of conformal defects in the Ising CFT and derive exact expressions for the defect spectrum, energy transmission coefficient, and effective central charge from analytic continuation. The theoretical predictions are precisely verified in non-Hermitian critical Ising and free fermion chains using bulk-defect correlators, entanglement entropy, and complex energy transport, providing concrete evidence for the complex defect conformal manifold. This is based on arXiv:2606.30720.
Lecture [2]:
Date ＆ Time: Friday, 13 November 2026, 2:30 PM
Venue: R815, Department of Physics, NTU
Title: Conformal interfaces and transmission coefficient
Abstract: Interfaces in conformal field theory (CFT) appear in many contexts and sometimes play a crucial role in characterizing the theory. For example, topological interfaces have long been studied (such as the name of Verlinde lines) and there exist well-developed methods to extract the information they encode. By contrast, conformal interfaces that are not necessarily topological but conformal, such as RG interfaces, are more complicated and typically much harder to analyze.
In this work, we propose a universal method to compute the transmission coefficient associated with a conformal interface between two CFTs that is assumed to be conformal. The key idea is to make use of a spin-2 non-local operator, a “phantom current,” which emerges when folding two theories; under a certain assumption, this allows us to compute the transmission coefficient. In this talk, I will explain this method in detail and discuss its consistency with previously known examples. This talk is based on arXiv:2511.00356.