Nature's Laws

Superstring Particle Spectrum

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

Given the almost infinitesimal size of the string, how can we observe its effects? We know that zero mass fields are detectable over infinite distances (for example, we can detect photons from over 16 billion light years away). Hence, the zero mass excitations of the string can be observed at macroscopic scales. In fact, the ranges of the forces in the standard model are explained by the masses of the transmitters. Gravitation and electromagnetism have infinite range while the weak and strong forces have a small range due the large mass of the gluons and the W and Z bosons.

On solving for the particle spectrum of the so called E8xE8 heterotic string we obtain the following

Mass spectrum

The high mass states all decay to the massless states. There are approximately 8,000 massless states for this string and it can accomodate all the known particles.

Due to the enormous tension of the string, the massive states of the string may never be observed since we need ~1019 GeV to produce them. The most we can hope for is 104 GeV in the next decade.

Hence, for practical purposes, all physical reality i.e. matter, interaction and spacetime is the result of the massless excitations of the superstring.

The small masses that observed particles have arise from "soft" long distance effects e.g. screening of the photon in a plasma or a material with a large dielectric constant (such as water). The plasma or material is electrically neutral but screens isolated charges, or effectively reduces the range of the photons. In other words, the photon behaves as if it had a finite mass.

Similarly for the string, the background "plasma-like" vacuum will let the massless excitations have small effective masses similar to the ones observed in our laboratories.



Last updated: 03 March, 2000

NUS Core Curriculum Nature's Laws Physics String Theory