Welcome to Yuya Tanizaki's Homepage

NOTICE: I created the new site (you can jump from here), so I will stop update of this site from Jan. 2017.

Tanizaki, Yuya (谷崎佑弥)

Special Postdoctoral Researcher at
Theory Group, RIKEN BNL Research Center

Bldg. 510A #2-68, Physics Dept., BNL
Pennsylvania St., Upton, NY 11973, US




  • I gave an invited talk on the sign problem and Lefschetz thimbles at Resurgence at Kavli IPMU.
  • I gave a lecture on Lefschetz thimbles at VIII Parma International Schoolof Theoretical Physics.
  • I gave an invited talk on Lefschetz thimble and complex Langevin methods at XQCD 2016.
  • I received Research award (Ph.D.) from the Graduate School of Science, the University of Tokyo.
  • I got Ph.D. from the University of Tokyo at March 24th. My thesis can be checked here.
  • Research Interest

      Nonperturbative Quantum Field Theory

      When I came into the game of theoretical physics, quantum field theory already had a long histroy, and then physicists understood its many features (at least in some limiting cases). If the system is weakly coupled, perturbation theory with the mean-field approximation fairly works well. However, there are still many things to be understood in strongly-coupled QFTs! I'm interested in strongly interacting many-body systems from the viewpoint of quantum field theories.
      In the strongly coupled regime, the perturbation theory breaks down and new computational methods becomes required. Roughly speaking, those methods can be classified into two categories: One is numerical computations of the lattice quantum field theory using Monte Carlo integration. This has been powerful, and succeed to reveal nonperturbative aspects of quantum gauge theories. Another one is called functional methods, which establishes nonperturbative relations between the set of Green functions just by using properties of functional integrals: Schwinger-Dyson equation, 2PI formalism, and functional renormalization group (FRG) are famous strategies belonging to this category.
      These methods are complementary to each other, and thus it is very important to develop and apply these various formalisms to deepen our understandings of strongly interacting systems.

      Path Integral via Lefschetz Thimbles

      Recently, Picard-Lefschetz theory attracts theoretical attention as a new approach to nonperturbative aspects of quantum mechanics. Its usefulness is found through its application to Chern-Simons theory, and it might provide a theoretical foundation of the resurgent trans-series expansion of quantum mechanics.
      This technique rewrites an oscillatory multiple integration as a sum of non-oscillatory integrals in an exact way, and the saddle-point analysis is available in a systematic manner. Therefore, this method is also regarded as a new possible way to solve the sign problem. The origin of the sign problem is appearance of an oscillatory integral in the path-integral expression, because it forbids us from using the importance sampling of the Monte Carlo integration, and it also induces some difficulties in the mean-field approximation.
      I am quite interested in this new technology, and it is indeed found to be useful for some practical applications to physical systems. Although its theoretical foundation is still missing when we would like to apply it to quantum systems in general, we can still be optimistic and should study its various aspects.

      Superfluidity and Superconductivity in Ultracold Atoms and Neutron Stars; BCS-BEC crossover

      Phase structure of Gauge Theories