上島芳倫
Random Fields and Processes on Graphs and Fractals 2024年06月 口頭発表(一般) 京都大学数理解析研究所 阿部圭宏;David Croydon;梶野直孝
The lace expansion is one of the powerful tools to investigate critical phenomena. It has succeeded in getting an asymptotic expansion for the critical point for several models, e.g., the self-avoiding walk, ordinary/oriented percolation, the contact process, etc. Our purpose is to obtain such an asymptotic expansion for the quantum Ising model, in which the different type of the phase transition from the classical Ising model is caused by a transverse field, by use of a lace expansion. The lace expansion for the classical Ising model was derived in [Sakai (2007) \textit{Commun. Math. Phys.}], whereas it has not derived for the quantum Ising model yet.
In this talk, I show a new derivation of a lace expansion for the classical Ising model, which is the special case of the quantum Ising model without the transverse field. The Hamiltonian in the quantum Ising model are expressed by operators. Thanks to the Lie-Trotter product formula, it is enough to consider the ($d+1$)-dimensional space-time Ising model, which are not given by operator language, instead of the $d$-dimensional Ising model. So far, we have derived a new type of the lace expansion without the transverse field based on the random current representation [Bj\"{o}rnberg and Grimmett (2009) \textit{J. Stat. Phys.}] [Crawford and Ioffe (2010) \textit{Commun. Math. Phys.}] on the space-time. We also expect that this approach helps us to derive a lace expansion in the case that the transverse field is finite.
This talk is based on joint work with Akira Sakai (Hokkaido University, Japan).