Paper Recovers String Theory Amplitudes From Four Assumptions Using Bootstrapping

A paper by Clifford Cheung and colleagues was accepted to Physical Review Letters after the researchers used a strategy known as bootstrapping to show that string theory stands alone among possible theories of everything. Given just four basic assumptions, the only scattering amplitudes that emerge are the Veneziano amplitude and the Virasoro-Shapiro amplitude, which are precisely those predicted by string theory.

Clifford Cheung, a theoretical physicist at Caltech, and his collaborators focused on scattering amplitudes, mathematical expressions that determine the probability that two particles will interact in a particular way.

Without assumptions, a vast range of such amplitudes are possible. By imposing four conditions, the team bootstrapped its way to the specific amplitudes demanded by string theory without starting from the premise that subatomic particles are made of vibrating strings of energy.

The four assumptions were unitarity, Lorentz invariance, physics is well-behaved at extremely high energies, and minimal zeroes.

Unitarity comes from quantum mechanics and means that the probabilities of all possible options must add up to 100 percent. Lorentz invariance is a principle of Einstein’s special theory of relativity. The high-energy assumption addresses a realm where general relativity stops working.

The minimal zeroes assumption selects the simplest possible version of the scattering amplitude. Based on those constraints the researchers landed on the Veneziano amplitude and the Virasoro-Shapiro amplitude.

The result suggests that, given tenets of quantum mechanics and special relativity among other theoretical ideas, string theory follows uniquely. ” Usually physicists write down a beautiful theory based on a deep idea and then calculate something measurable.