¡¡The ultimate purpose of elementary particle theory is to find the so¡¾called "theory of everything". The superstring theory is considered to be the most promising candidate for this status, and we are now in a position to be able to understand non¡¾perturbative aspects of quantum gravity. In the field of experimental physics, high¡¾precision experiments at LEP on the Z boson and the discovery of the "top quark" at Tevatron have established the standard model as a highly reliable t heory of nature. Efforts are also made to go beyond the standard model; the solar neutrino experiment at KAMIOKANDE and the LHC project are some examples of the movement in this direction.

¡¡We are working on such front¡¾line problems in the theory of the fundamental constituents of matter and their interaction. Current interests among faculty members include:

1. Superstring theories: dualities, D¡¾branes, constructive definition, and string field theories.
2. Quantum gravity: origin of gravity, topological gravity matrix models, and renormalization group approach.
3. Gauge theories and their applications: nonperturbative analysis of supersymmetric Yang¡¾Mills theories and transport phenomena.
4. Phenomenological study: supersymmetric extension of standard model, physics of high energy collision, and hadronic weak interactions.
5. Exactly solvable models: completely solvable quantum field theories and related mathematical problems.

¡¡The study of nuclear structure and nuclear interactions constitutes one of the traditional research areas of the Institute since the inception of the former RIFP. Yukawa's meson theory played a historical role in research programs on nuclear forces and nuclear many¡¾body problems undertaken at the Institute. The Institute has supported many research programs on developing various nuclear models and concepts appropriate to many different facets of complex nuclear phenomena, such as collective nuclear motions, the cluster structures of light nuclei, nuclear fission, heavy¡¾ion collisions, and hyper nuclei. With its interdisciplinary environment, the Institute also has played a special role in promoting new research areas at the interface of nuclear, astro¡¾ and particle physics, fields such as theory of high density nuclear matter, and manifestation of underlying subnuclear degrees of freedom in extreme physical conditions.

¡¡Current research topics undertaken by the regular staff of the Institute include :

stochastic models for low energy heavy¡¾ion collisions and dissipative

nuclear fusion/fission processes;

theory for synthesis of the superheavy elements;

and chiral symmetry aspects hadron and nuclear physics based on QCD, chiral transition which nuclear (hadronic) matter may undergo at high density and/or temperature to be realized in the intermediate stage of ultra-relativistic heavy ion collisions, in the early universe and possibly in heavy nuclei.

¡¡Since the unification of the former RITP, which had for many years played an essential role in Japanese research activities of astrophysics and gravitation, with the former RIFP, which had made an important contribution to big bang cosmology and general relativity, this section has been acting as one of the national centers in the field, hosting a number of workshops as well as visitors annually.

¡¡Current research activities are divided into three representative fields. The first one is cosmology. One of the major subjects in this field is the study of the very early universe making use of the high energy theories. The construction of a new framework for a fully quantum treatment of spacetime evolution, and investigations of the evolution of the early universe in the framework of unified theories are two examples of research activities in this branch. Another important subject is the research in observational cosmology brought about by various new techniques and equipments such as the Cosmic Background Explorer and the Hubble Space Telescope. In this promising field much effort has been made to constrain the values of cosmological parameters including the density parameter, the Hubble constant, and the cosmological constant, combining various data from different means of observations. Theoretical studies to support their determination are also under way, such as studies in the statistics of gravitational lensing. Further, the Sloan Digital Sky Survey, to be completed in the beginning of the next century, will certainly provide information which will assist in the determination of a correct model of the formation of large¡¾scale structures.

¡¡The second major field is mathematical general relativity. Researches in this field cover investigations of fundamental problems in general relativity or other gravity theories such as spacetime singularities and global structures of spacetimes, and those of cross-disciplinary problems such as gauge theories in curved spacetimes. In particular, the structures of spacetime singularities and their physical effects are becoming major subjects in this field in connection with recent developments in the gravitational wave astronomy.

¡¡The third one is the relativistic astrophysics, which is also a central subject of research in this Institute. One very successful direction in the study of this subject is numerical or computer¡¾aided relativity in 3+1 dimensional spacetime. The fully general¡¾relativistic calculations of gravitational radiation from coalescing binary neutron stars that are being investigated here will serve as a theoretical template to guide experimental projects seeking to detect gravitational waves with laser interferometers, an entirely new channel of astronomical observation. Another important direction in this field is the investigation of new exciting objects called gamma ray bursters, which seems to be extremely high¡¾energy objects distributed at cosmological distances according to recent observational and theoretical studies. The clarification of their origin is expected to give us a new insight to the relativistic dynamics of compact stellar objects.

¡¡Since its foundation, the former RIFP, and now YITP, has been a center of theoretical physics in Japan. Subjects or fields of research carried out in the Institute have varied from time to time, covering a wide range, from mathematical approaches to biophysics.

¡¡The Non¡¾Equilibrium Physics Section has been oriented toward fundamental research, whose subjects are reflected in the section's titles: The Section of 'Statistical Physics' was established in 1980, and it was renewed as `'Non¡¾Linear Physics' Section in 1987, then recently in 1997, it has been replaced by the present Section of `Non¡¾Equilibrium Physics.'

¡¡The subjects which have been pursued concern establishing bridges among different areas, for example,

(i) quantum mechanics and classical dynamics including chaos,
(ii) local dynamical couplings and global organization of structures, or
(iii) mechanical or stochastic descriptions and equilibrium and non¡¾equilibrium thermodynamic descriptions.

The research in Condensed Matter Physics covers various aspects of the physics of electrons in solids. A large variety of complex phenomena appear in new materials such as cuprates and ruthenates due to strong correlation of electrons, and in nanoscale devices due to mesoscopic interference effects. Subjects studied in the current research group include spontaneous symmetry breaking phenomena in various electronic degrees of freedom (in particular, unconventional superconductivity) and the quantum phase transitions between ordered and disordered phases. Another set of subjects are transport and magnetic properties of low-dimensional systems with disorder and related issues in Quantum Hall systems.

¡¡The studies in both Sections are greatly encouraged by the rapid development of recent nano¡¾technologies including molecular biology and information science, as well as solid state and optical devices.