Person: Fernández Pérez, Luis Antonio
Loading...
First Name
Luis Antonio
Last Name
Fernández Pérez
Affiliation
Universidad Complutense de Madrid
Faculty / Institute
Ciencias Físicas
Department
Física Teórica
Area
Física Teórica
Identifiers
19 results
Search Results
Now showing 1 - 10 of 19
Item Antiferromagnetic O(N) models in four dimensions(Physics letters B, 1998) Ballesteros, H. G.; Carmona, J. M.; Fernández Pérez, Luis Antonio; Tarancón, A.We study the antiferromagnetic O(N). N model in the F_(4) lattice. Monte Carlo simulations are applied for investigating the behavior of the transition for N = 2,3. The numerical results show a first order nature but with a large correlation length. The N = ∞ limit is also considered with analytical methods.Item Off-equilibrium fluctuation-dissipation relations in the 3d Ising spin glass in a magnetic field(Physical review B, 2003) Cruz, A.; Fernández Pérez, Luis Antonio; Jiménez, S.; Ruiz Lorenzo, J. J.; Tarancón, A.We study the fluctuation-dissipation relations for a three dimensional Ising spin glass in a magnetic field both in the high temperature phase as well as in the low temperature one. In the region of times simulated we have found that our results support a picture of the low temperature phase with broken replica symmetry, but a droplet behavior cannot be completely excluded.Item Study of the Coulomb-Higgs transition in the abelian Higgs model(Physics letters B, 1998) Cruz, A.; Íñiguez, D.; Fernández Pérez, Luis Antonio; Muñoz Sudupe, Antonio; Tarancón, A.The order of the Coulomb-Higgs transition in the U (1) -Higgs model with unfrozen modulus of the scalar field is studied. Large lattices (up to 24^4 in one case) and high statistics are used. We fix β = 1.15 and explore specially a region of λ-values where metastability is observed. We study the thermodynamical limit of several observables, in particular, the latent heat, the specific heat, the decrement of the free energy between the maxima and the central minimum of the two-peaked histogram, the Binder cumulant and the displacement of the critical coupling with the lattice size. The results point towards a second order transition for λ ≥ 0.005, while for smaller values of λ the strong metastability growing with the lattice size seems to derive from a first order character.Item The Coulomb-Higgs transition of the three-parameter U(1)-Higgs model(Nuclear Physics B-Proceedings Supplements, 1995) Cruz, A.; Íñiguez, D.; Tarancón, A.; Fernández Pérez, Luis Antonio; Muñoz Sudupe, AntonioWe find a first order Coulomb-Higgs phase transition at moderately large values of the coupling λ, and no evidence for a change of order at any finite value of it.Item Phase diagram of d=4 Ising model with two couplings(Physics letters B, 1996) Alonso, J. L.; Carmona, J. M.; Clemente Gallardo, J.; Fernández Pérez, Luis Antonio; Íñiguez, D.; Tarancón, A.; Ullod, C. L.We study the phase diagram of the four dimensional king model with first and second neighbour couplings, especially in the antiferromagnetic region, by using Mean Field and Monte Carlo methods. From the latter, all the transition lines seem to be first order except that between ferromagnetic and disordered phases in a region including the first-neighbour Ising transition point.Item Is the antiferromagnetic RP^(2) model in four dimensions trivial?(Physical review D, 1997) Ballesteros, H. G.; Carmona, J. M.; Fernández Pérez, Luis Antonio; Martín Mayor, Víctor; Muñoz Sudupe, Antonio; Tarancón, A.We study the antiferromagnetic RP^(2) model in four dimensions. We find a second order transition with two order parameters, one ferromagnetic and the other antiferromagnetic. The antiferromagnetic sector has mean- field critical exponents and a renormalized coupling which goes to zero in the continuum limit. The exponents of the ferromagnetic channel are not the mean-field ones, but the difference can be interpreted as logarithmic corrections. We perform a detailed analysis of these corrections and conclude the triviality of the continuum limit of this model.Item A proposal of a Monte Carlo renormalization group transformation(Nuclear Physics B-Proceedings Supplements, 1995) Fernández Pérez, Luis Antonio; Muñoz Sudupe, Antonio; Ruiz Lorenzo, J. J.; Tarancón, A.We propose a family of renormalization group transformations characterized by free parameters that may be tuned in order to reduce the truncation effects. As a check we test them in the three dimensional XY model. The Schwinger-Dyson equations are used to study the renormalization group flow.Item Ion heating in transitions to CERC in the stellarator TJ-II(Nuclear fusion, 2008) Castejón, F.; Fernández Pérez, Luis Antonio; Martín Mayor, Víctor; Tarancón, A.; Velasco, J. L.; CX group, .In TJ-II stellarator plasmas, in the electron cyclotron heating regime, an increase in the ion temperature is observed, synchronized with that of the electron temperature, during the transition to the core electron-root confinement (CERC) regime. This rise in ion temperature should be attributed to the joint action of the electron–ion energy transfer (which changes slightly during the CERC formation) and an enhancement of the ion confinement. This improvement must be related to the increase in the positive electric field in the core region. In this paper, we confirm this hypothesis by estimating the ion collisional transport in TJ-II under the physical conditions established before and after the transition to CERC. We calculate a large number of ion orbits in the guiding-centre approximation considering the collisions with a background plasma composed of electrons and ions. The ion temperature profile and the thermal flux are calculated in a self-consistent way, so that the change in the ion heat transport can be assessed.Item Critical behavior of the three-dimensional Ising spin glass(Physical review B, 2000) Ballesteros, H. G.; Cruz, A.; Fernández Pérez, Luis Antonio; Martín Mayor, Víctor; Pech, J.; Ruiz Lorenzo, J. J.; Tarancón, A.; Téllez, P.; Ullod, C. L.; Ungil, C.We have simulated, using parallel tempering, the three-dimensional Ising spin glass model with binary couplings in a helicoidal geometry. The largest lattice (L520) has been studied using a dedicated computer (the SUE machine). We have obtained, measuring the correlation length in the critical region, strong evidence for a second-order finite-temperature phase transition, ruling out other possible scenarios like a KosterlitzThouless phase transition. Precise values for the ν and ƞ critical exponents are also presented.Item Critical properties of the four-state commutative random permutation glassy Potts model in three and four dimensions(Physical review B, 2008) Fernández Pérez, Luis Antonio; Maiorano, A.; Marinari, E.; Martín Mayor, Víctor; Navarro, D.; Sciretti, D.; Tarancón, A.; Velasco, J. L.We investigate the critical properties of the four-state commutative random permutation glassy Potts model in three and four dimensions by means of Monte Carlo simulations and a finite-size scaling analysis. By using a field programmable gate array, we have been able to thermalize a large number of samples of systems with large volume. This has allowed us to observe a spin-glass ordered phase in d=4 and to study the critical properties of the transition. In d=3, our results are consistent with the presence of a Kosterlitz-Thouless transition, but also with different scenarios: transient effects due to a value of the lower critical dimension slightly below 3 could be very important.