Research topics of current interest


1. Invisible axions: After the introduction of the invisible axion, currently works on the axion and dark energy. A recent review is published in Reviews of Modern Physics 82, 557-601 (2010).
2. WIMP cold dark matter (CDM): Currently, the hottest topic in cosmology is to identify what is the CDM. Axion is one candidate and the lightest supersymmetric particle(LSP) is another. In view of the recent sattelite search of anti-matter in the universe, the LSP possibility has attracted a great deal of attention. I look for a possible explanation of the anomalies observed in the sattelite experiments. In particular, the minimal extension of the MSSM with just one chiral field N has been studied, Phys. Rev. D79, 063529 (2009) and Phys. Rev. D80, 075012 (2009).
3. Laboratory for Axion Search Experiments (LASE): Indend to establish a laboratory for solar and cosmic axions.
4. The problem: The symmetry principle is invoked to resolve the term in H1H2 [Phys. Lett. 138, 150 (1984)]
5. Standard model from superstring: The gauge coupling unification is possible in string models if the gauge group arises from the level 1 sector. In this case, the complexity of GUT symmetry breaking and the proton stability can be avoided. The first model realizing the doublet-triplet splitting is given in [Phys. Lett. B191, 282 (1987)], but the sin2w problem is not resolved here. In 2006, Z_12 orbifold models have been searched to find the best superstring models: Nucl. Phys. B770, 47 (2007).
6. Particle cosmology and eWIMP: Application of particle physics in cosmology, e.g. in obtaining the upper bound on the reheating temperature after inflation [Phys. Lett. B145, 181(1984)], saxion cosmology [Phys. Rev. Lett 67,3465(1991)], axino-gravitino cosmology [Phys. Rev. Lett. 72, 1956 (1994)], and axino as CDM [Phys. Rev. Lett. 82, 4180 (1999)].
7. Standard model: Neutral currents and other novel effects within the standard model, reviewed in Reviews of Modern Physics 53, 211 (1981).
8. R-parity: Origin of R-parity has been studied in the superstring framework.
9. The problem of vacuum energy: Constructing a theory with vanishing cosmological constant is the final goal. But at the moment we try to explain the tiny nonvanishing vacuum energy given by Type 1a supernova observation (1998). The WMAP data confirmed this (2004). The cosmological constant problem is one of the most promising research topics since there seems to be a solution in the near future. One self-tuning solution has been obtained [Phys. Rev. Lett. 86, 4223 (2002); JHEP 0301, 042 (2003)]. (Dec., 2004)
10. The Randall-Sundrum model: The compactification with a non-factorizable geometry may solve the gauge hierarchy problem. I am interested in this type of compactification, the Gauss-Bonnet term modification [Nucl. Phys. B582, 296 (2000)] , and related cosmological problems. (April, 2002)