Browsing by Author "Delfino, Gesualdo"

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    The composite operator T-Tbar in sinh-Gordon and a series of massive minimal models
    (2006-04-12T11:33:52Z) Delfino, Gesualdo; Niccoli, Giuliano; Physics; Elementary Particle Theory
    The composite operator T\bar{T}, obtained from the components of the energy-momentum tensor, enjoys a quite general characterization in two-dimensional quantum field theory also away from criticality. We use the form factor bootstrap supplemented by asymptotic conditions to determine its matrix elements in the sinh-Gordon model. The results extend to the breather sector of the sine-Gordon model and to the minimal models M_{2/(2N+3)} perturbed by the operator phi_{1,3}.
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    Decay of particles above threshold in Ising field theory with magnetic field
    (2005) Delfino, Gesualdo; Grinza, Paolo; Mussardo, Giuseppe; Mathematics; Mathematical Physics
    The two-dimensional scaling Ising model in a magnetic field at critical temperature is integrable and possesses eight stable particles Ai (i = 1, . . . , 8) with different masses. The heaviest five lie above threshold and owe their stability to integrability. We use form factor perturbation theory to compute the decay widths of the first two particles above threshold when integrability is broken by a small deviation from the critical temperature. The lifetime ratio t4/t5 is found to be 0.233; the particle A5 decays at 47% in the channel A1A1 and for the remaining fraction in the channel A1A2. The increase of the lifetime with the mass, a feature which can be expected in two dimensions from phase space considerations, is in this model further enhanced by the dynamics.
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    Form factors of descendant operators in the massive Lee-Yang model
    (2005) Delfino, Gesualdo; Niccoli, Giuliano; Mathematics; Mathematical Physics
    The form factors of the descendant operators in the massive Lee-Yang model are determined up to level 7. This is first done by exploiting the conserved quantities of the integrable theory to generate the solutions for the descendants starting from the lowest non-trivial solutions in each operator family. We then show that the operator space generated in this way, which is isomorphic to the conformal one, coincides, level by level, with that implied by the S-matrix through the form factor bootstrap. The solutions we determine satisfy asymptotic conditions carrying the information about the level that we conjecture to hold for all the operators of the model.
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    Particle decay in Ising field theory with magnetic field
    (2007-05-15T12:24:26Z) Delfino, Gesualdo; Physics; Elementary Particle Theory
    The scaling limit of the two-dimensional Ising model in the plane of temperature and magnetic field defines a field theory which provides the simplest illustration of non-trivial phenomena such as spontaneous symmetry breaking and confinement. Here we discuss how Ising field theory also gives the simplest model for particle decay. The decay widths computed in this theory provide the obvious test ground for the numerical methods designed to study unstable particles in quantum field theories discretized on a lattice.
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    Potts correlators and the static three-quark potential
    (2005) Caselle, Michele; Delfino, Gesualdo; Grinza, Paolo; Jahn, O.; Magnoli, Nicodemo; Mathematics; Mathematical Physics
    We discuss the two- and three-point correlators in the two-dimensional three-state Potts model in the high-temperature phase of the model. By using the form factor approach and perturbed conformal field theory methods we are able to describe both the large distance and the short distance behaviours of the correlators. We compare our predictions with a set of high precision Monte-Carlo simulations (performed on the triangular lattice realization of the model) finding a complete agreement in both regimes. In particular we use the two-point correlators to fix the various non-universal constants involved in the comparison (whose determination is one of the results of our analysis) and then use these constants to compare numerical results and theoretical predictions for the three-point correlator with no free parameter. Our results can be used to shed some light on the behaviour of the three-quark correlator in the confining phase of the (2+1)-dimensional SU(3) lattice gauge theory which is related by dimensional reduction to the three-spin correlator in the high-temperature phase of the three-state Potts model. The picture which emerges is that of a smooth crossover between a \Delta type law at short distances and a Y type law at large distances.