Form Factors from String Amplitudes

In this Letter, we propose a stringy model for n-point tree-level form factor with the off-shell operator in the scalar and gluon theories from the bosonic string disk amplitude: n open string states and one closed string state scatter on the disk. In the field-theory limit (α^{'}→0), the "stringy form factor" reduces to the form factor, which helps us to investigate the hidden properties of the field-theory form factors, manifest the factorization and soft behaviors, and uncover more nontrivial relations between form factors and scattering amplitudes.