Person:
Fernández Pérez, Luis Antonio

First Name

Luis Antonio

Last Name

Fernández Pérez

URI

https://hdl.handle.net/20.500.14352/75087

Affiliation

Universidad Complutense de Madrid

Faculty / Institute

Ciencias Físicas

Department

Física Teórica

Area

Física Teórica

Identifiers

Full item page

Search Results

Now showing 1 - 10 of 22

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.
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.
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.
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, Antonio
We 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.
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.
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.
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.
Spin-glass dynamics in the presence of a magnetic field: exploration of microscopic properties
(Journal of statistical mechanics: theory and experiment, 2021) Paga, I.; Zhai, Q.; Baity-Jesi, M.; Calore, E.; Cruz, A.; Fernández Pérez, Luis Antonio; Gil-Narvión, J. M.; González-Adalid Pemartín, Isidoro; Gordillo Guerrero, A.; Iñiguez, D.; Maiorano, A.; Marinari, E.; Martín Mayor, Víctor; Moreno Gordo, J.; Muñoz Sudupe, Antonio; Navarro, D.; Orbach, R. L.; Parisi, G.; Perez-Gaviro, S.; Ricci-Tersenghi, F.; Ruiz-Lorenzo, J. J.; Schifano, S. F.; Schlagel, D. L.; Seoane Bartolomé, Beatriz; Tarancón, A.; Tripiccione, R.; Yllanes, D.
The synergy between experiment, theory, and simulations enables a microscopic analysis of spin-glass dynamics in a magnetic field in the vicinity of and below the spin-glass transition temperature T-g. The spin-glass correlation length, xi(t, t(w); T), is analysed both in experiments and in simulations in terms of the waiting time t(w) after the spin glass has been cooled down to a stabilised measuring temperature T < T-g and of the time t after the magnetic field is changed. This correlation length is extracted experimentally for a CuMn 6 at. % single crystal, as well as for simulations on the Janus II special-purpose supercomputer, the latter with time and length scales comparable to experiment. The non-linear magnetic susceptibility is reported from experiment and simulations, using xi(t, t(w); T) as the scaling variable. Previous experiments are reanalysed, and disagreements about the nature of the Zeeman energy are resolved. The growth of the spin-glass magnetisation in zero-field magnetisation experiments, M-ZFC(t, t(w); T), is measured from simulations, verifying the scaling relationships in the dynamical or non-equilibrium regime. Our preliminary search for the de Almeida-Thouless line in D = 3 is discussed.
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.
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.