C. Piedrafita - Academia.edu (original) (raw)

Papers by C. Piedrafita

We simulate the compact U ( 1)-Higgs model in a four-dimensional l ttice. We present a numerical ... more We simulate the compact U ( 1)-Higgs model in a four-dimensional l ttice. We present a numerical study for the behaviour around the region where the transition between the confining and Higgs phases disappears. The transition line is found to be first order and to end in a second-order point. We measure the critical exponents ofthe endpoint obtaining the mean field ones within errors. The study of the critical behaviour of lattice gauge theories in four dimensions is crucial to formulate nonperturbatively the underlying continuum quan-tum field theory. Even if a continuum limit is possi-ble, the question remains whether the obtained the-ory is trivial or not. For the selfcoupled scalar field with a quartic term in the action (the 204 theory) no other critical point in d = 4 has been found than an infrared stable gaus-sian fixed point at the origin 2 = 0, m = 0. This means that the only fixed point with infinite correlation

We analyse the phase diagram of the lattice gauged Nambu-Jona Lasinio model with the help of a me... more We analyse the phase diagram of the lattice gauged Nambu-Jona Lasinio model with the help of a mean field approximation plus numerical simulations. We find a phase transition line in the coupling parameters space separating the chirally broken phase from the symmetric phase, which is in good qualitative agreement with results obtained in the quenched-ladder approximation. The mean field approximation relates the critical exponents along the continuous phase transition line with the mass dependence of the chiral condensate in the Coulomb phase of standard noncompact QED. Our numerical results for noncompact QED strongly suggest non mean field exponents along the critical line. 1 The gauged Nambu-Jona Lasinio (GNJL) model has become increasingly interesting in recent time, one of the reasons for this increasing interest being the possibility to define a strongly coupled QED with non trivial dynamics [1]. In fact if a non gaussian fixed point exists in non compact QED, the naive dimens...

We study numerically the critical properties of the U(1)-Higgs lattice model, with fixed Higgs mo... more We study numerically the critical properties of the U(1)-Higgs lattice model, with fixed Higgs modulus, in the region of small gauge coupling where the Higgs and Confining phases merge. We find evidence of a first order transition line that ends in a second order point. By means of a rotation in parameter space we introduce thermodynamic magnitudes and critical exponents in close resemblance with simple models that show analogous critical behaviour. The measured data allow us to fit the critical exponents finding values in agreement with the mean field prediction. The location of the critical point and the slope of the first order line are accurately given. 2 1

Using very precise measurements of the critical couplings for the chiral transition of non compac... more Using very precise measurements of the critical couplings for the chiral transition of non compact QED4 with up to 8 flavours, we analyse the behaviour of the order parameter at the critical point using the equation of state of a logarithmically improved scalar mean field theory, that of the Nambu-Jona Lasinio theory and a pure power law. The first case is definitively excluded by the numerical data. The stability of the fits for the last two cases, as well as the behaviour with the number of flavours of the exponent of the logarithmic violations to the scaling favour clearly a pure power law scaling with non mean field exponents. 1 Non perturbative renormalizable gauge theories are among the most stimulating and less known subjects in theoretical physics. It is not known if it is possible to construct such a theory in four dimensions and the standard prejudice is that only asymptotically free gauge theories with gaussian fixed points are ”good ” field theories.

We measure chiral susceptibilities in the Coulomb phase of noncompact QED4 in 8 , 10 and 12 latti... more We measure chiral susceptibilities in the Coulomb phase of noncompact QED4 in 8 , 10 and 12 lattices. The MFA approach allows simulations in the chiral limit which are therefore free from arbitrary mass extrapolations. Using the critical couplings extracted from these calculations, we study the critical behaviour of the chiral condensate, which we find in disagreement with the predictions of logarithmically improved scalar Mean Field theory.

Nuclear Physics B - Proceedings Supplements, 1994

Physics Letters B, 1993

We study SU (2) lattice gauge theory in small volumes and with twist m = (1, 1, 1). We investigat... more We study SU (2) lattice gauge theory in small volumes and with twist m = (1, 1, 1). We investigate the presence of the periodic instantons of Q = 1 2 and determine their free energy and their contribution to the splitting of energy flux sectors E(e = (1, 1, 1)) − E(e = (0, 0, 0)).

Physics Letters B, 1996