Stefano Sciuto - Academia.edu (original) (raw)

Papers by Stefano Sciuto

The Birth of String Theory

Geometrical and Algebraic Aspects of Nonlinear Field Theory, 1989

Nuclear Physics B, 1976

The string model with a U(1) colour symmetry is analyzed in detail. It is shown that the critical... more The string model with a U(1) colour symmetry is analyzed in detail. It is shown that the critical dimension of this model is D = 2. There are no tachyons in the U(1) string. Moreover the massless ground state is the only physical particle of the spectrum. All other states are decoupled because of the gauge conditions. The n-point amplitudes of the U(1) string are derived and shown to be equivalent to the tree diagrams of a conventional nonpolynomial field theory in two dimensions, namely the non-linear o model where the pion particle is identified with the massless ground state of the string with an isotopic Chan-Paton symmetry. 77 * Notice that the local generators of the internal symmetry 5rn~" are actually three, because from (2.6) we have eijhk Thnk = 2 ~. * X stands for a Lorentz vector field X~ in a D-dimensional space-time and a Lorentz index/a has been omitted. When X appears in a biUnear from, summation over this index is understood. This convention is used for all the superfields throughout the paper. ** That something is wrong in (3.9) can be inferred by looking at the boundary conditions of the fields that would follow by varying the action (3.9); one would get the trivial result ~ 1-= ~2 = 0. * Here and in the following of this section the upper (lower) sign will refer to the Neveu-Schwarz (Ramond) model.

We consider toroidal compactifications of bosonic string theory with particular regard to the pha... more We consider toroidal compactifications of bosonic string theory with particular regard to the phases (cocycles) necessary for a consistent definition of the vertex operators, the boundary states and the T-duality rules. We use these ingredients to compute the planar multi-loop partition function describing the interaction among magnetized or intersecting D-branes, also in presence of open string moduli. It turns out that unitarity in the open string channel crucially depends on the presence of the cocycles. We then focus on the 2-loop case and study the degeneration limit where this partition function is directly related to the tree-level 3-point correlators between twist fields. These correlators represent the main ingredient in the computation of Yukawa couplings and other terms in the effective action for D-brane phenomenological models. By factorizing the 2-loop partition function we are able to compute the 3-point couplings for abelian twist fields on generic non-factorized tori, thus generalizing previous expressions valid for the 2-torus.

Journal of High Energy Physics, 2018

We present an approach to the parametrization of (super) Schottky space obtained by sewing togeth... more We present an approach to the parametrization of (super) Schottky space obtained by sewing together three-punctured discs with strips. Different cubic ribbon graphs classify distinct sets of pinching parameters; we show how they are mapped onto each other. The parametrization is particularly well-suited to describing the region within (super) moduli space where open bosonic or Neveu-Schwarz string propagators become very long and thin, which dominates the IR behaviour of string theories. We show how worldsheet objects such as the Green's function converge to graph theoretic objects such as the Symanzik polynomials in the α → 0 limit, allowing us to see how string theory reproduces the sum over Feynman graphs. The (super) string measure takes on a simple and elegant form when expressed in terms of these parameters.

Lettere Al Nuovo Cimento Series 2, 1971

Il Nuovo Cimento A Series 11, 1974

Il Nuovo Cimento A, 1971

ABSTRACT

Nuclear Physics B, 1987

We construct in a very simple way a three-reggeon vertex that includes also the contribution of t... more We construct in a very simple way a three-reggeon vertex that includes also the contribution of the ghost coordinates, both for the bosonic and fermionic string. We show its connection with the vertex operators that are usually used to construct dual amplitudes and with the light-cone three-string vertex. Finally, we prove its invariance under BRST transformations.

Physics Letters B, 2017

A parametrization of (super) moduli space near the corners corresponding to bosonic or Neveu-Schw... more A parametrization of (super) moduli space near the corners corresponding to bosonic or Neveu-Schwarz open string degenerations is introduced for worldsheets of arbitrary topology. With this parametrization, Feynman graph polynomials arise as the α → 0 limit of objects on moduli space. Furthermore, the integration measures of string theory take on a very simple and elegant form.

Nuovo Cimento Della Societa Italiana Di Fisica A-nuclei Particles and Fields, 1981

$Research paper thumbnail of Free field representation for SU(2).hat.$_{k}$ WZNW models on Riemann surfaces$

Lecture Notes in Physics

ABSTRACT A geometrical treatment of supersymmetric -models on ordinary and graded manifolds is gi... more ABSTRACT A geometrical treatment of supersymmetric -models on ordinary and graded manifolds is given: It is shown that the SuSy -models on graded manifolds can be reduced to give generalizations of the SuSy sine-Gordon equation, endowed with an associate linear set. In particular the SuSy generalization of the Complex sine-Gordon model is briefly discussed.

Il Nuovo Cimento A, 1985

Summary The Migdal-Kadanoff recursion relations are applied to the most general plaquette action... more Summary The Migdal-Kadanoff recursion relations are applied to the most general plaquette action. The stable action, determined by a weak-coupling expansion, lies between the Manton and the heat kernel ones, in agreement with previous numerical investigations. Moreover, it is shown that certain contributions to the renormalization of the coupling constant exactly coincide with the perturbative ones; this happens for those terms of pure group-theoretical origin, which are the same in the perturbative expansions of the 4D gauge theory and of the corresponding 2D chiral model.

Nuclear Physics B, 1989

Starting from the N-point vertex on the sphere and using the sewing procedure we construct the N-... more Starting from the N-point vertex on the sphere and using the sewing procedure we construct the N-point g-loop vertex for a free bosonic theory, with vacuum charge Q. We then show that, when this vertex is saturated with N highest weight states, it gives their correlation function on an arbitrary Ricmann surface of genus g. We also extend our formalism to the case of a free scalar field compactified on a circle, which is related to the Coulomb gas description of minimal models. * This is strictly speaking correct only if i1, m ~ 0 (see eq. (C.3)). A truc representation is built by means of canonical forms in appendix B (see eq. (B.5)). * With the restriction that their isometric circles are all exterior to one another (see ref. [49] and our following discussion).

This talk is based on work made with L. Magnea and R. Russo. We give an explicit expression of th... more This talk is based on work made with L. Magnea and R. Russo. We give an explicit expression of the multiloop partition function of open bosonic string theory in the presence of a constant gauge field strength. The Schottky parametrization allows to perform the field theory limit, which at two-loop level reproduces the Euler-Heisenberg effective action for adjoint scalars minimally coupled to the background gauge field.