Stefan Junk

Currently

Since August 2021, I am an Assistant Professor at the Mathematical Science Group of AIMR (Advanced Institute for Materials Research) at Tohoku University, Japan. The main focus of my research is probability theory, specifically its applications to problems from mathematical physics and material science.

Previously

Between November 2019 and June 2021, I was a postdoc hosted by David Croydon and Ryoki Fukushima at RIMS, Kyoto University, and at Tsukuba University. I was supported by the JSPS Postdoctoral Fellowship for Research in Japan (Standard Programm).

I have written my PhD thesis supervised by Nina Gantert at TU Munich.

See here for a short CV.

Research interests

I mainly work on the following topics:
  • The directed polymer model and first/last passage percolation.
  • (Branching) random walks in random environment.
  • Stochastic orders, in particular for the above processes.
  • Oriented percolation.
  • The random conductance model, and the Mott random walk in particular.
More broadly, I'm interested in the following areas:
  • Statistical mechanics.
  • Random matrices and integrable probability.
  • Large deviation theory.
  • Random walks on graphs and their resistance forms.

Papers and preprints

Submitted

  • Extremal regime for one-dimensional Mott variable-range hopping, with David Croydon and Ryoki Fukushima. 2022. (arXiv).
  • Fluctuations of partition functions of directed polymers in weak disorder beyond the L^2-phase. 2022. (arXiv).
  • The central limit theorem for directed polymers in weak disorder, revisited. 2021. (arXiv).

Accepted

  • Anomalous scaling regime for one-dimensional Mott variable-range hopping, with David Croydon and Ryoki Fukushima. 2020. To appear in Annals of Applied Probability (arXiv, short video summary).

Published

  • Number of paths in oriented percolation as zero temperature limit of directed polymer, with Ryoki Fukushima. Probability Theory and Related Fields, 2022. (arXiv, short video summary).
  • New characterization of the weak disorder phase of directed polymers in bounded random environments. Communications in Mathematical Physics, 2022 (Journal, arXiv).
  • On large deviation rate functions for a continuous-time directed polymer in weak disorder, with Ryoki Fukushima. Electronic Communications of Probability, 2021(Journal, arXiv).
  • Comparison of partition functions in a space-time random environment. Journal of Statistical Physics, 2020. (Journal, arXiv).
  • Zero temperature limit for the Brownian directed polymer among Poissonian disasters, with Ryoki Fukushima. Annals of Applied Probability, 2019. (Journal, arXiv)
  • A branching random walk among disasters, with Nina Gantert. Electronic Journal of Probability, 2017. (Journal, arXiv)
  • On the survival probability of a random walk in random environment with killing. ALEA Latin American Journal of Probability and Mathematical Statistics, 2014. (Journal, arXiv)

PhD Thesis

Teaching Experience

I have been TA for various courses as a PhD student in Munich, see here for a list.

Contact