A bosonic string is a relativistic one-dimensional object whose embedding coordinates are bosonic fields on a two-dimensional worldsheet. Its classical motion can be described by the Nambu–Goto action, proportional to the worldsheet area, or by the equivalent Polyakov action with an auxiliary worldsheet metric.
An open string has endpoints; a closed string forms a loop and has independent left- and right-moving oscillations. Quantization produces a tower of particle states. In the ordinary flat critical bosonic string theory, anomaly cancellation selects 26 spacetime dimensions, and the closed-string spectrum includes a massless graviton. The tachyonic ground state indicates instability of the chosen vacuum.[ref]
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