Stefan Junk (シュテファンユンク）

Department of Mathematics, Gakushuin University
Mejiro 1–5–1, Toshima–ku, 171–8588 Tokyo, Japan

sjunk@math.gakushuin.ac.jp
www.stefanjunkprob.de
ORCID: 0000–0002–5151–8008

Researchinterests

Probability Theory, specifically random processes in random media:• The KPZ universality class, in particular the Directed Polymer Model.
• Scaling limits for reversible Markov processes.
• Random networks, in particular their degree correlations.
• Mathematical Physics.

Employment

Gakushuin University
Assistant Professor
Tohoku University
Assistant Professor
Kyoto University and Tsukuba University
JSPS Postdoctoral Fellow.
Hosted by David Croydon and Ryoki Fukushima.

Education

Teaching
experience

September 2023 – present
August 2021 – August 2023
November 2019 – June 2021

TU München.
PhD (Mathematics)
Supervised by Nina Gantert, passed summa cum laude.

2014 – 2019

MSc (Mathematics, TopMath Elite Master Study Program)

2012 – 2014

BSc (Mathematics)

2009 – 2012

Gakushuin University
Exercise classes (undergraduate level, in Japanese)
TU München
Exercise classes (mostly master level)

Funding

JSPS Grant-in-Aid for Early-Career Scientists (3.4m JPY)

2023 – 2026

Grant-in-Aid for JSPS Fellows (1.6m JPY)

2019 – 2021

Reviewactivities

Annales de l’Institut Henri Poincaré, Annals of Probability, Communications inMathematical Physics, Electronic Journal of Probability, Probability Theory andRelated Fields.

Languages

German (native speaker), English (fluent) and Japanese (JLPT level N2).

Publication list
Submitted[1] Stefan Junk and Hubert Lacoin. Strong disorder and very strong disorder are equivalent for directed
polymers, February 2024. arXiv:2402.02562.
[2] Stefan Junk and Hubert Lacoin. The tail distribution function of the partition function for directedpolymer in the weak disorder phase, May 2024. arXiv:2405.04335.
[3] Stefan Junk.
Local limit theorem for directed polymers beyond the L2 -phase, July 2023.
arXiv:2307.05097.
[4] Stefan Junk. Fluctuations of partition functions of directed polymers in weak disorder beyond theL2 -phase, February 2022. arXiv:2202.02907.
Published (peer-reviewed)[5] David A. Croydon, Ryoki Fukushima, and Stefan Junk. Anomalous scaling regime for onedimensional Mott variable-range hopping. Ann. Appl. Probab., 33(5):4044 – 4090, 2023. doi:
10.1214/22-AAP1915.
[6] David A. Croydon, Ryoki Fukushima, and Stefan Junk. Extremal regime for one-dimensional Mottvariable-range hopping. Ann. Henri Lebesgue, 6:1169–1211, 2023. doi:10.5802/ahl.186.
[7] Ryoki Fukushima and Stefan Junk. Moment characterization of the weak disorder phase for directed
polymers in a class of unbounded environments. Electron. Comm. Probab., 28:1 – 9, 2023. doi:
10.1214/23-ECP545.
[8] Stefan Junk. Stability of weak disorder phase for directed polymer with applications to limit theorems. ALEA Lat. Am. J. Probab. Math. Stat., 20:861–883, 2023. doi:10.30757/ALEA.v20-31.
[9] Ryoki Fukushima and Stefan Junk. Number of paths in oriented percolation as zero temperature
limit of directed polymer. Probab. Theory Relat. Fields, 2022. doi:10.1007/s00440-022-01130-3.
[10] Stefan Junk. New characterization of the weak disorder phase of directed polymers in bounded random environments. Comm. Math. Phys., 389(2):1087–1097, 2022. doi:10.1007/s00220-021-04259-9.
[11] Ryoki Fukushima and Stefan Junk. On large deviation rate functions for a continuous-time directed
polymer in weak disorder. Electron. Comm. Probab., 26:1 – 10, 2021. doi:10.1214/21-ECP378.
[12] Stefan Junk. Comparison of partition functions in a space-time random environment. J. Stat. Phys.,
181(1):95–115, 2020. ISSN 0022-4715. doi:10.1007/s10955-020-02566-4.
[13] Ryoki Fukushima and Stefan Junk. Zero temperature limit for the Brownian directed polymer among
Poissonian disasters. Ann. Appl. Probab., 29(6):3821–3860, 2019. doi:10.1214/19-AAP1493.
[14] Nina Gantert and Stefan Junk. A branching random walk among disasters. Electron. J. Probab.,
22:Paper No. 67, 34, 2017. doi:10.1214/17-EJP75.

[15] Stefan Junk. On the survival probability of a random walk in random environment with killing.
ALEA Lat. Am. J. Probab. Math. Stat., 11(1):823–844, 2014. Based on results from the Bachelor
thesis.
Thesis[16] Stefan Junk. Random polymers in disastrous environments. Dissertation, Technische Universität
München, München, 2019. http://mediatum.ub.tum.de/?id=1488489.

Invited Talks (since 2019)
Mar. 2023
Feb. 2023
Jan. 2023
Dec. 2023
Nov. 2023
Oct. 2023
Oct. 2023
Dec. 2022
Aug. 2022

May 2022
Feb. 2022

Feb. 2021
Nov. 2020
Nov. 2020Feb. 2020
Nov. 2019Feb. 2019

Probability Seminar, Singapore.
Strong disorder and very strong disorder are equivalent for directed polymers
Probability Seminar, Hong Kong.
Strong disorder and very strong disorder are equivalent for directed polymers
Probability Seminar Series, Shanghai.
The Directed Polymer Model in Weak Disorder beyond the L2 -Phase
Workshop on random interacting systems, Singapore.
Local limit theorem for directed polymer beyond the L2 -phase
Tokyo Probability Seminar, Tokyo.
Local limit theorem for directed polymer in (almost) the whole weak disorder regime
Stochastic Analysis on Large Scale Interacting Systems, Kyoto.
Local Limit Theorem for Directed Polymers beyond the L2 -phase
Random Operators and Related Topics, Sendai.
Local limit theorem for directed polymer in the delocalized phase
Stochastic Analysis on Large Scale Interacting Systems, Fukuoka.
The directed polymer model in weak disorder beyond the L2 -regime.
Probability and Analysis on Random Structures and Related Topics, Kyoto.
Fluctuations for the partition function of directed polymers beyond the L2 -phase.
Probability Seminar, Münster.
Fluctuations for partition function of directed polymers beyond the L2 -phase.
Probability Seminar, Sendai.
Number of paths in oriented percolation as zero-temperature limit of directed polymer.
Statistics Seminar, Bergen.
Zero-temperature limit for the number of open paths in oriented percolation.
Kansai Probability Seminar, Kyoto.
Anomalous scaling regime for one-dimensional Mott variable-range hopping.
Workshop on Microstructure, Sapporo.
Anomalous scaling regime for one-dimensional Mott variable-range hopping.
KTGU Workshop, Kyoto.
Large deviations for directed polymers in the whole weak disorder phase.
Stochastic Analysis in Large Scale Interacting Systems, Osaka.
Zero-temperature limit for the Brownian polymer among Poissonian disasters.
Probability Seminar, Haifa.
Zero-temperature limit for Brownian directed polymers among Poissonian disasters.