ABSTRACT
The idea of strings was first proposed in the 1960s, in order to describe strong nuclear interactions. After it was realised in the 1970s that the massless spectrum of string theory contains a spin-2 particle, it was suggested as a consistent framework which unifies all fundemantal forces of Nature, including gravity. By replacing the notion of a point particle by a string, a consistent quantum theory of gravity emerges which reproduces Einstein’s general theory of relativity and the forces of the SM. String theory is still in progress and there is no complete description of the SM based on it. Although the energy scale of the string theory effects ( ∼ 10 19 $ \sim 10^{19} $ https://s3-euw1-ap-pe-df-pch-content-public-p.s3.eu-west-1.amazonaws.com/9781315367903/c2682a74-a79a-4ae8-b55f-fb03894f6bcd/content/inline-math18_1.tif"/> GeV) is much higher than the current values at the LHC ( ∼ 10 3 $ \sim 10^3 $ https://s3-euw1-ap-pe-df-pch-content-public-p.s3.eu-west-1.amazonaws.com/9781315367903/c2682a74-a79a-4ae8-b55f-fb03894f6bcd/content/inline-math18_2.tif"/> GeV), some predictions of the theory such as large extra dimensions and SUSY are accessible at current energies.
