 # Superstrings

B. E. Baaquie and Marakani Srikant, Department of Physics, National University of Singapore

A classical string is a one-dimensional extended object existing in four-dimensional space-time. A typical example of a classical string is a piece of thread.

A classical string is specified by the string tension T, and can exist in a space-time of arbitrary dimension. Quantum strings can only exist in certain critical space-time dimensions such as 26 and 10. Quantum bosonic strings can be made supersymmetric yielding the superstring.

## Fundamental Postulate

 All of physical reality is made out of different states of the superstring. Roughly speaking, each vibrational mode of the string can be thought of as a point particle. Hence, one superstring gives rise to infinitely many local fermion and boson fields. All of the observed bosons and fermions can be cosidered as a vibrational mode of the fundamental superstring. It must be noted that the string is both constituent and interaction. Superstrings can be either open or closed.   Quantum strings inherently contain a quantum theory of gravity! For this purpose, the size of the strings must be of Planck length scale.

Consider a particle at the point x0. Conventionally, the properties of the point-particle are then specified by a field A(x0).

However, for a string, we have to determine infinitely many points (along the whole string). This is fundamentally the reason why a single string in effect yields infinitely may point-like particles.

## How long is a superstring? According to the big bang theory, we have the following scenario : Universe starts from a point -> Strings -> Inflation -> Gravity differentiates -> Further differentiation. Since strings occur before any differentiation, they must of Planck scale (10-35m), the distance at which all the forces are equally strong. Note : Distances are inversely related to energy by the uncertainty principle (the smaller the distance, the higher the energy scale).

## String Interaction : Topology vs Geometry

Last updated: 03 March, 2000     