Browsing by Author "Mussardo, Giuseppe"

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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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    Mass generation in perturbed massless integrable models
    (2005) Controzzi, Davide; Mussardo, Giuseppe; Mathematics; Mathematical Physics
    We extend form-factor perturbation theory to non-integrable deformations of massless integrable models, in order to address the problem of mass generation in such systems. With respect to the standard renormalisation group analysis this approach is more suitable for studying the particle content of the perturbed theory. Analogously to the massive case, interesting information can be obtained already at first order, such as the identification of the operators which create a mass gap and those which induce the confinement of the massless particles in the perturbed theory.