Akira Sakai

My major research field is mathematical physics (probability and statistical mechanics). The topics I have been most fascinated with are phase transitions and critical phenomena, as well as associated scaling limits. For example, the Ising model, a statistical-mechanical model of ferromagnetism, is known to take on positive spontaneous magnetization as soon as the temperature of the system is turned down below the critical point. Various other observables also exhibit singular behavior around the critical point, due to cooperation of infinitely many interacting variables. To fully understand such phenomena, it would require development of a theory beyond the standard probability theory. This is a challenging and intriguing problem, towards which I would love to make even a tiny contribution.

The mathematical models I have been studying are

· the Ising model (for magnets),

· the φ⁴ model (in lattice scalar-field theory),

· self-avoiding walk (for linear polymers),

· lattice trees (for branched polymers),

· percolation (for random media),

· the contact process (for the spread of an infectious disease),

· random walk with reinforcement.

II. Research papers

1. S. Handa, K. Kamakura, Y. Kamijima and A. Sakai. Finding optimal solutions by stochastic cellular automata. Submitted. arXiv:1906.06645.

2. Akira Sakai. Crossover phenomena in the critical behavior for long-range models with power-law couplings. To appear in RIMS Kokyuroku Bessatsu. arXiv:1812.10275.

3. S. Handa, Y. Kamijima and A. Sakai. A survey on the lace expansion for the nearest-neighbor models on the BCC lattice. To appear in Taiwanese Journal of Mathematics. arXiv:1712.05573.

4. L.-C. Chen and A. Sakai. Critical two-point function for long-range models with power-law couplings: The marginal case for d ³ d_c. Commun. Math. Phys. 372 (2019): 543–572 (the full-text view-only version). arXiv:1808.06789.

5. S. Handa, M. Heydenreich and A. Sakai. Mean-field bound on the 1-arm exponent for Ising ferromagnets in high dimensions. A chapter in Sojourns in Probability and Statistical Physics - I (V. Sidoravicius ed., Springer, 2019). arXiv:1612.08809.

6. A. Sakai and G. Slade. Spatial moments for high-dimensional critical contact process, oriented percolation and lattice trees. Electron. J. Probab. 24 (2019): no. 65, 1–18. arXiv:1810.04011.

7. Akira Sakai. Hyperscaling for oriented percolation in 1+1 space-time dimensions. J. Stat. Phys. 171 (2018): 462–469 (the full-text view-only version). arXiv:1709.08291.

8. T. Arae, S. Isai, A. Sakai, K. Mineta, M. Yokota-Hirai, Y. Suzuki, S. Kanaya, J. Yamaguchi, S. Naito and Y. Chiba. Coordinated regulations of mRNA synthesis and decay during cold acclimation in arabidopsis cells. Plant Cell Physiol. 58 (2017): 1090–1102.

9. Y. Chino and A. Sakai. The quenched critical point for self-avoiding walk on random conductors. J. Stat. Phys. 163 (2016): 754–764. arXiv:1508.01262.

10. Akira Sakai. Application of the lace expansion to the φ⁴ model. Commun. Math. Phys. 336 (2015): 619–648. arXiv:1403.5714.

11. L.-C. Chen and A. Sakai. Critical two-point functions for long-range statistical-mechanical models in high dimensions. Ann. Probab. 43 (2015): 639–681. arXiv:1204.1180.

12. L.-C. Chen and A. Sakai. Asymptotic behavior of the gyration radius for long-range self-avoiding walk and long-range oriented percolation. Ann. Probab. 39 (2011): 507–548. arXiv:1002.0875.

13. Akira Sakai. Large-time asymptotics of the gyration radius for long-range statistical-mechanical models. RIMS Kokyuroku Bessatsu B21 (2011): 53–62. arXiv:0912.5117.

14. R. van der Hofstad and A. Sakai. Convergence of the critical finite-range contact process to super-Brownian motion above the upper critical dimension: The higher-point functions. Electron. J. Probab. 15 (2010): no. 27, 801–894. arXiv:0809.1712.

15. L.-C. Chen and A. Sakai. Critical behavior and the limit distribution for long-range oriented percolation. II: Spatial correlation. Probab. Theory Relat. Fields 145 (2009): 435–458. arXiv:0804.2039.

16. Akira Sakai. Applications of the lace expansion to statistical-mechanical models. A chapter in Analysis and Stochastics of Growth Processes and Interface Models (P. Mörters et al. eds., Oxford University Press, 2008).

17. M. Heydenreich, R. van der Hofstad and A. Sakai. Mean-field behavior for long- and finite range Ising model, percolation and self-avoiding walk. J. Stat. Phys. 132 (2008): 1001–1049. arXiv:0712.0312.

18. L.-C. Chen and A. Sakai. Critical behavior and the limit distribution for long-range oriented percolation. I. Probab. Theory Relat. Fields 142 (2008): 151–188. arXiv:0703455.

19. Akira Sakai. Diagrammatic bounds on the lace-expansion coefficients for oriented percolation. arXiv:0708.2897.

20. M. Holmes and A. Sakai. Senile reinforced random walks. Stoch. Proc. Appl. 117 (2007): 1519–1539.

21. Akira Sakai. Lace expansion for the Ising model. Commun. Math. Phys. 272 (2007): 283–344. arXiv:math-ph/0510093.

22. R. van der Hofstad and A. Sakai. Critical points for spread-out self-avoiding walk, percolation and the contact process above the upper critical dimensions. Probab. Theory Relat. Fields 132 (2005): 438–470. arXiv:math/0402050.

23. Akira Sakai. Mean-field behavior for the survival probability and the percolation point-to-surface connectivity. J. Stat. Phys. 117 (2004): 111–130.

24. R. van der Hofstad and A. Sakai. Gaussian scaling for the critical spread-out contact process above the upper critical dimension. Electron. J. Probab. 9 (2004): no. 24, 710–769. arXiv:math/0402049.

25. M. Holmes, A.A. Járai, A. Sakai and G. Slade. High-dimensional graphical networks of self-avoiding walks. Canad. J. Math. 56 (2004): 77–114.

26. Akira Sakai. Hyperscaling inequalities for the contact process and oriented percolation. J. Stat. Phys. 106 (2002): 201–211.

27. Akira Sakai. Mean-field critical behavior for the contact process. J. Stat. Phys. 104 (2001): 111–143.

III. Scientific talks

Year 2019

1. Finding optimal solutions by stochastic cellular automata.

· 7^th Wellington Workshop in Probability and Mathematical Statistics (December 5–7). Wellington, New Zealand.

· Workshop on Probabilistic Methods in Statistical Mechanics of Random Media and Random Fields (May 27–31). Universiteit Leiden, the Netherlands.

· AIMaP 1-day Workshop (March 26). RIES, Hokkaido University, Japan.

2. Critical two-point function for long-range models with power-law couplings: The marginal case for d ³ d_c.

· The 12^th MSJ-SI “Stochastic Analysis, Random Fields and Integrable Probability” (July 31–August 9). Kyushu University, Japan.

· Seminar in Statistics (January 16). The University of Auckland, New Zealand.

Year 2018

1. Critical two-point function for long-range models with power-law couplings: The marginal case for d ³ d_c.

· 17^th International Symposium “Stochastic Analysis on Large-scale Interacting Systems” (November 5–8). RIMS, Kyoto University, Japan.

· High-dimensional Critical Phenomena in Random Environments (September 24–26). The University of Bristol, UK.

· 2018 Spring Probability Workshop (June 4–8). Academia Sinica, Taiwan.

2. Hyperscaling for oriented percolation in 1+1 space-time dimensions.

· Rikkyo Math Phys Seminar (May 23). Rikkyo University, Japan

· NUS Probability Seminar (February 12). National University of Singapore, Singapore.

Year 2017

1. Hyperscaling for oriented percolation in 1+1 space-time dimensions.

· NTU Math Colloquium (November 27). National Taiwan University, Taiwan.

2. Recent progress in researches on phase transitions and critical behavior for Ising ferromagnets（強磁性イジング模型の相転移・臨界現象に関する研究の最近の動向).

· MSJ Fall Meeting (September 11–14). Yamagata University, Japan.

3. Critical behavior for oriented percolation: From a mathematically rigorous standpoint.

· Summer School in Mathematical Physics (August 25–27). The University of Tokyo, Japan.

4. The lace expansion for self-avoiding walk and percolation on the BCC lattice.

· Seminar on Probability (July 18). Osaka University, Japan.

5. Mean-field bound on the 1-arm exponent for high-dimensional Ising ferromagnets.

· Physical and Mathematical Approaches to Interacting Particle Systems – In Honer of 70^th Birthday of Herbert Spohn (January 11–12). Tokyo Institute of Technology, Japan.

Previous years

IV. Organizing scientific meetings

1. The 10^th World Congress in Probability and Statistics (August 17–21, 2020). Seoul National University, South Korea.

2. The 3^rd workshop on Universality and Scaling Limits in Probability and Statistical Mechanics (July 13–17, 2020). Hokkaido University, Japan.

3. The RIMS Workshop “Rigorous Statistical Mechanics and Related Topics” (November 18–21, 2019). RIMS, Kyoto University, Japan.

4. The 1-day workshop “Recent Progress in Probability Theory and Its Applications” (July 28, 2017). Hokkaido University, Japan.

5. 2017 Spring Probability Workshop (March 6–8, 2017). Academia Sinica, Taiwan.

6. The 2^nd workshop on Universality and Scaling Limits in Probability and Statistical Mechanics (August 5–9, 2013). Hokkaido University, Japan.

7. International Workshop on Potential Theory (February 4, 2013). Hokkaido University, Japan.

8. The RIMS workshop “Applications of Renormalization Group Methods in Mathematical Sciences” (September 12–14, 2011). Kyoto University, Japan.

9. The SPA Satellite workshop “Universality and Scaling Limits in Probability and Statistical Mechanics” (August 30–September 3, 2010). Hokkaido University, Japan.

V. Teaching (April 2019 – February 2020)

2^nd semester	Monday	Tuesday	Wednesday	Thursday	Friday
8:45 – 10:15	N.A.	Calculus I(L)	N.A.	N.A.	Analysis F(L)
10:30 – 12:00	N.A.	Calculus I(P)	N.A.	N.A.	Analysis F(P)
12:00 – 13:00	Lunch	Lunch	Lunch	Lunch	Lunch
13:00 – 14:30	CREST(Stability)	N.A.	Kamakura	Nishimura	Moriya
14:45 – 16:15	CREST(SCA)	Kawamoto	Tanaka	Mizushiri	Matsunuma
16:30 – 18:00	N.A.	Kamijima	Noda	N.A.	N.A.
18:00 – 20:00	HITACHI	Liang & O.H.	N.A.	N.A.	N.A.

(Lectures-Preparation; Office Hour; Seminars; Not Available )

1. Seminar on Mathematics (2^nd semester @ Science Bldg 4-506).

· B3 Seminar (Noda, Liang) on Introduction to Stochastic Processes.

· B3 Seminar (Matsunuma) on Random Walks and Electric Networks.

· B4 Seminar (Moriya) on Percolation.

· B4 Seminar (Tanaka) on Introduction to Probability Theory.

· M1 Seminar (Kamakura) on Markov Chains and Mixing Times.

· M1 Seminar (Kawamoto) on Lecture Notes on Particle Systems and Percolation.

· M2 Seminar (Mizushiri) on Random Graphs and Complex Networks.

· M2 Seminar (Nishimura) on Introduction to Stochastic Integration.

· D3 Seminar (Kamijima) on Quantum effect on the divergence around the critical temperature of the Ising susceptibility.

· CREST Seminar (Kimura, Ueda, Toyokawa) on Stability of energy landscape.

· CREST Seminar (Kimura, Kamijima, Kamakura) on Stochastic cellular automata (SCA).

· HITACHI Seminar (Kimura, Aoki, Kamijima, Ueda, Toyokawa, Ishibashi, Kamakura) @ Creative Research Institution SOUSEI.

2. Calculus I (2^nd semester, Tuesdays 8:45–10:15 @ Multimedia Education Bldg E-319); WeBWorK for self-studies (need ELMS ID & Password).

3. Analysis F (2^nd semester, Fridays 8:45–10:15 @ Science Bldg 3-309).

4. Power-up Seminar, FB (September 10–13, 2019, @ National Taisetsu Youth Friendship Center).

5. Seminar on Mathematics (1^st semester @ Science Bldg 4-506).

· B4 Seminar (Moriya) on Percolation.

· B4 Seminar (Naruoka) on Essence of Probability Models.

· B4 Seminar (Tanaka) on Introduction to Probability Theory.

· M1 Seminar (Kamakura) on Markov Chains and Mixing Times.

· M1 Seminar (Kawamoto) on Lecture Notes on Particle Systems and Percolation.

· M2 Seminar (Mizushiri) on Random Graphs and Complex Networks.

· M2 Seminar (Nishimura) on Introduction to Stochastic Integration.

· D3 Seminar (Kamijima) on Quantum effect on the divergence around the critical temperature of the Ising susceptibility.

· PD Seminar (Chino) on Critical properties for 1+1 dimensional oriented percolation in a random environment.

· CREST Seminar (Ueda, Toyokawa) on Stability of energy landscape.

· CREST Seminar (Kamijima, Kamakura) on Finding optimal solutions by stochastic cellular automata (SCA).

· HITACHI Seminar (Aoki, Kamijima, Ueda, Toyokawa, Ishibashi, Kamakura) @ FMI.

6. Calculus I (1^st semester, Mondays 10:30–12:00 @ Multimedia Education Bldg E301; Fridays 14:45–16:15 @ Multimedia Education Bldg E311); WeBWorK for self-studies (need ELMS ID & Password).

Past academic years (since 2019)

VI. Curriculum vitae

· September 2015 – August 2019

Councilor of the Bernoulli Society.

· Excellent Teachers 2018, 2015, 2012, 2011

The Hokkaido University President’s Award for Teaching Excellence in 2013 and in 2012.

· April 2011 – present

Associate professor of the Department of Mathematics, Hokkaido University, Japan.

· March 2008 – March 2011

Tenure-track assistant professor of Creative Research Institution SOUSEI, Hokkaido University, Japan.

· April 2006 – February 2008

Lecturer in Probability of the Department of Mathematical Sciences, the University of Bath, UK.

· April 2004 – March 2006

Postdoctoral researcher of Wiskunde en Informatica, Technische Universiteit Eindhoven (TU/e), the Netherlands.

· January 2003 – March 2004

Postdoctoral researcher of the Interacting-Stochastic-Systems (ISS) group, EURANDOM, the Netherlands.

· January 2001 – December 2002

Postdoctoral researcher of the Department of Mathematics, the University of British Columbia, Canada.

· April 1996 – December 2000

Ph.D. study in Applied Physics, Tokyo Institute of Technology, Japan.

Awarded Ph.D. for the thesis “Analyses of the Critical Behavior for the Contact Process based on a Percolation Structure” supervised by Professor Takashi Hara.

· April 1994 – March 1996

Master study in Applied Physics, Tokyo Institute of Technology, Japan.

Awarded M.Sc. for the thesis “Approach to Fractal Growth Phenomena” supervised by Professor Takashi Hara.

· April 1990 – March 1994

Undergraduate study in Applied Physics, Tokyo Institute of Technology, Japan.

Awarded B.Sc. for the thesis “Recurrent in the Plane, Transient in Space” supervised by Professor Kohei Uchiyama.