# New insights into open string theory

Theoretical physicist Lennaert Huiszoon has described a new family of strings in research conducted at the National Institute for Nuclear Physics and High Energy Physics. He investigated so-called open strings which can describe elementary particles with a strong interaction.

With string theory, physicists are trying to construct a unifying theory for gravity and quantum mechanics. The theory describes extremely heavy and very small objects such as the universe shortly after the Big Bang or black holes. According to string theory our universe has ten dimensions: three spatial dimensions, one time dimension and six dimensions which are possibly rolled up into thin cylinders.

One of the problems of string theory is that five different versions of it exist! Four of these are theories with closed strings, which can be visualised with elastic bands that move in space-time. The fifth theory has open strings, which can be visualised with elastic bands cut open. In string theory the physics is limited to the splitting and joining of strings. This is the interaction between elementary particles. The greater the number of branches, the stronger the interaction between the particles. To make the calculations feasible, string theorists only examine weak interactions, in other words strings with few branches.

Since 1994 it has been known that one of the closed string theories with strong interactions is exactly the same as the open string theory with weak interactions. By investigating the open string theory, the strong interaction can be described without endlessly complicated calculations. A lot of research concentrates on linking the various string theories. It is thought that they are all special variations of the same theory.

The research into the open strings particularly concentrates on the spaces in which the edges of the strings (the start and endpoint of the cut open elastic band) can move. Lennaert Huiszoon carried out mathematical research into these edge spaces. The spaces are called D-branes after the mathematician Dirichlet.

The physicist suspects that our universe is a four-dimensional D-brane. To prove this a D-brane must be found which has all the properties of the universe: the relatively flat structure of the four- dimensional space time and all elementary particles, with the correct charge, spin and mass.

The physicist Huiszoon limited himself to strings in simple symmetrical spaces, so called group spaces. In the flat surface a circle is a group space and in three dimensions a sphere is a group space. In higher dimensions these group spaces become more complex. Using a new mathematical method he demonstrated that in these group spaces, the ends of the strings can only move in very specific lines or surfaces. In subsequent research the physicist hopes to find D-branes that can actually describe the universe.

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