Introduction

The connection between the Dual Resonance Model (DRM) and the relativistic string, a one-dimensional extended system, was observed soon after Veneziano's fundamental paper. Indeed, the presence of an infinite set of harmonic oscillators, with frequencies that were multiples of a fundamental tune, was clearly suggestive of a vibrating string.

Part IV contains the contributions by the authors who proposed the string interpretation, found the action and studied the quantization. In the years 1969 and 1970, Nambu, Nielsen and Susskind, each from his own perspective, suggested independently that a string model was at the basis of the DRM. In 1970, Nambu, and later Goto, wrote the correct relativistic and reparameterization-invariant form of the string Lagrangian. The different perspectives can be summarized as follows.

1. (i) Susskind's starting point was the comparison of DRM scattering amplitudes with those for the relativistic harmonic oscillator. From the existence of many frequencies of oscillation, i.e. harmonics, Susskind had the idea of a ‘rubber band’ or a ‘violin string’.

2. (ii) Nielsen's intuition came from an analogy of dual diagrams with high-order Feynman diagrams, called ‘fishnet diagrams’ in this approximation particles interact approximately with nearest neighbours and effectively form a one-dimensional chain, i.e. a string.

3. […]