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Disk amplitudes of tachyons in two-dimensional open string theories (two-dimensional quantum gravity coupled to $c \leq 1$ conformal field theories) are obtained using the continuum Liouville field approach. The structure of momentum…
We extend an earlier proposal for a gauge invariant description of off-shell open strings (at tree level), using loop variables, to off-shell closed strings (at tree level). The basic idea is to describe the closed string amplitudes as a…
In the context of the bosonic closed string theory, by using the operatorial formalism, we give a simple expression of the off-shell amplitude with an arbitrary number of external massless states inserted on the Klein bottle.
We derive an explicit formula for the evaluation of the classical closed string action for any off-shell string field, and for the calculation of arbitrary off-shell amplitudes. The formulae require a parametrization, in terms of some…
Recent advances in non-critical string theory allow a unique continuation of critical Polyakov string amplitudes to off-shell momenta, while preserving conformal invariance. These continuations possess unusual, apparently stringy,…
Computing the renormalized masses and S-matrix elements in string theory, involving states whose masses are not protected from quantum corrections, requires defining off-shell amplitude with certain factorization properties. While in the…
Using recent advances in the understanding of non-critical strings, we construct a unique, conformally invariant continuation to off-shell momenta of Polyakov amplitudes in critical string theory. Three-point amplitudes are explicitly…
We give a construction of off-shell tree bosonic string amplitudes, based on the operatorial formalism of the $N$-string Vertex, with three external massless states both for open and closed strings by requiring their being projective…
We give a simple prescription for computing, in the framework of the bosonic string theory, off-shell one-loop amplitudes with any number of external massless particles, both for the open and for the closed string. We discuss their…
We give, in the framework of the bosonic string theory, simple prescriptions for computing, at tree and one-loop levels, off-shell string amplitudes for open and closed string massless states. In particular we obtain a tree amplitude for…
The two-point string amplitude at tree level in flat spacetime reproduces the expected expression for free particles. This has been proven by Erbin, Maldacena and Skliros in [JHEP 07 (2019) 139] by two methods. Here, we provide an…
We compute directly in covariant formalism various four point massive scalar amplitudes in bosonic string with scalars up to level 11. The most ``difficult'' amplitude we consider is four identical scalars at level 4, i.e. the first non…
Recent advances in non-critical string theory allow a unique continuation, preserving conformal invariance, of critical Polyakov string amplitudes to off-shell momenta. These continuations possess unusual, apparently stringy,…
We compute off-shell three- and four-tachyon amplitudes at tree level by using a prescription based on the requirement of projective invariance. In particular we show that the off-shell four-tachyon amplitude can be put in the same form as…
In two recent papers, a new method was developed for calculating ten-dimensional superstring amplitudes with an arbitrary number of loops and external massless particles, and for expressing them in manifestly Lorentz-invariant form. By…
A new term in the p-adic world-sheet action is proposed, which couples a constant B-field to the boundary of the world-sheet at disk level. The induced deformation of tachyon scattering amplitudes by star-products is derived. This is in…
Scattering amplitudes in quantum field theory are independent of the field parameterization, which has a natural geometric interpretation as a form of `coordinate invariance.' Amplitudes can be expressed in terms of Riemannian curvature…
In the cubic string field theory, using the gauge invariant operators corresponding to the on-shell closed string vertex operators, we have explicitly evaluated the decay amplitudes of two open string tachyons or gauge fields to one closed…
We study on-shell scattering amplitudes for continuous-spin particles (CSPs). Poincar\'e invariance, little-group $ISO(2)$ covariance, analyticity, and on-shell factorisation (unitarity) impose stringent conditions on these amplitudes. We…
So far we have considered that a two-point string amplitude vanishes due to the infinite volume of residual gauge symmetry. However recently Erbin-Maldacena-Skliros have suggested that the two-point amplitude can have non-zero value,…