Molecular hydrogen is classified into ortho (total nuclear spin I=1, rotational quantum number J=odd) and para (I=0, J=even) nuclear-spin modifications. Whereas ortho–para conversion is a key technology for hydrogen storage in a liquid form, relative abundance of the ortho and para hydrogen in astronomical circumstances has been reported to show a value out of equilibrium with the environment temperature in recent years. Physisorption and ortho–para conversion on the surfaces of interstellar media are expected to provide deeper understanding of astronomical phenomena. Although interconversion between these modifications is forbidden in isolated states, it is significantly promoted by inhomogeneous magnetic fields such as those present on the surfaces of magnetic materials. Since the theoretical research by Wigner in 1933, nuclear-spin conversion has been considered not to occur on diamagnetic solid substances. Here we review recent progresses of experimental and theoretical studies of ortho–para conversion on well-defined surfaces, which have revealed unexpected conversion on diamagnetic surfaces.

The superfluid ³He is a condensate of spin-triplet p-wave Cooper pairs, with broken rotational symmetries in orbital and spin spaces as well as gauge symmetry. This multiple symmetry breaking gives rise to many unusual properties in the superfluid ³He. One of the superfluid phases called ³He-A breaks time-reversal symmetry. Although the time-reversal symmetry breaking (TRSB) is the most fundamental property, there has been no direct demonstration of TRSB so far. In this article, we demonstrate TRSB by discovering the intrinsic Magnus force experienced by an electron bubble moving in ³He-A. The intrinsic Magnus force allows for first direct detection of orientation of the angular momentum of Cooper pairs or chirality, which paves the way towards detailed investigations of unusual topological defects formed in the system with broken multiple symmetries.

General Relativity simplifies dramatically in the infinite limit of the spacetime dimension, D. This is because gravitational fields by a black hole are confined in very near region of the black hole horizon at the large D limit. The scales of this confinement are 1/D times smaller than the black hole horizon radius. Then the gravitational fields by a black hole can be integrated out in the Einstein equations by using 1/D expansion, and, as a result, the effective theory of the black hole emerges at the large D limit. This effective theory describes instabilities of various back holes and their non-linear time evolutions in a simple form.

We have developed a new ion-trap apparatus combined with a Stark-velocity filter in order to measure reaction-rate constants between cold trapped ions and slow polar molecules under ultra-high vacuum conditions. The reaction-rate constant of CH₃CN+N₂H⁺→CH₃CNH⁺+N₂ was measured at translational temperatures lower than 10 K. The measured reaction-rate constant is consistent with the capture rates by the classical model and the formula derived by trajectory simulations. The present experimental technique will explore the quantum effects in cold ion-polar molecule reactions which are important problems from a fundamental view point, and also contribute to astrochemistry by the systematic measurement.