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Koji Hashimoto | Osaka univ. | Japan

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Visiting Nagoya university.

Last Tuesday, I have visited Nagoya university, to give a talk at GCOE colloquium. The talk was on cosmic superstrings, which I have been working on for more than 5 years. I hope I could deliver my feeling that in fact this fascinating possibility to find superstrings in the sky. The break-through work by Copeland, Myers and Polchinski revived the possibility from the 1985 Witten’s work — It would be wondeful if one can see the macroscopic gigantic superstring/D-brane in the sky! I am rather involved with purely theoretical aspects of this problem, the reconnection of colliding strings. The reconnection probability of the cosmic strings, whatever the identity of them is, is in fact relevant for any observation of them. Interestingly, this physics is related to tachyon condensation in Sen’s conjecture on D-brane annihilation.  Field theory strings appear not only in cosmology but also in condensed matter theory and even in low energy QCD and high density QCD : and they are all realized in a certain limit by a low energy limit of D-brane configurations, that is intriguing.

I wanted to ask a question to a collegue there, how GUTs and cosmic strings are seriously unified. In fact, there is an interesting paper which states that, under some assumptions, viable SUSY GUTs should support existence of cosmic strings. I liked to know how viable the assupmtions are. At the dinner after the talk, I could enjoy an opinion by the person who works on GUTs, and I am very satisfied. Well, long time ago, monopoles are one of the serious identifier of GUTs, and nowadays, after we have seen WMAP data coninciding with inflationary scenario of the universe,  I think we can say that cosmic strings are at the same stage, or rather to say, we need to add cosmic strings as serious ones for GUT study. I really hope that some gravitational wave bursts may be observed in the near future.

This morning, in a train to commute to my office, I found a tiny but new idea on my project. It was really a happy moment. I was about to miss my station to get off. Sometimes it is good to be confined in a crowded train, since you cannot read any paper, you cannot calculate on papers, you cannot do any other things, than just thinking. Every day I commute to my office by train for about one hour, and I feel that it is good for my physics. This morning was evidence for the statement —  or maybe just a justification for my statement which was made not to face my reality to spend two hours in trains everyday….

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