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V. Azcoiti

Publications and source records attributed to V. Azcoiti.

48 records · Page 3Linked to original sources
arXiv1996

The Continuum Limit of Non Compact QED

Since four-fermion operators in strongly coupled $QED$ are nonperturbatively renormalizable, we analyze here the phase diagram and critical behaviour of the Gauged Nambu-Jona Lasinio model. Our 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 $QED$. The numerical results for noncompact $QED$ strongly suggest non mean field exponents along the critical line.

hep-lat↗
arXiv1995

Chiral condensate, susceptibilities, critical coupling and indices in QED$_4$

We measure chiral susceptibilities in the Coulomb phase of noncompact QED$_4$ in $8^4, 10^4$ and $12^4$ 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.

hep-lat↗
arXiv1995

Critical Behavior of the Schwinger Model with Wilson Fermions

We present a detailed analysis, in the framework of the MFA approach, of the critical behaviour of the lattice Schwinger model with Wilson fermions on lattices up to $24^2$, through the study of the Lee-Yang zeros and the specific heat. We find compelling evidence for a critical line ending at $κ= 0.25$ at large $β$. Finite size scaling analysis on lattices $8^2,12^2,16^2, 20^2$ and $24^2$ indicates a continuous transition. The hyperscaling relation is verified in the explored $β$ region.

hep-lat↗
arXiv1994

Renormalization Group And Scaling Within The Microcanonical Fermionic Average Approach

The MFA approach for simulations with dynamical fermions in lattice gauge theories allows in principle to explore the parameters space of the theory (e.g. the $β, m$ plane for the study of chiral condensate in QED) without the need of computing the fermionic determinant at each point. We exploit this possibility for extracting both the renormalization group trajectories ("constant physics lines") and the scaling function, and we test it in the Schwinger Model. We discuss the applicability of this method to realistic theories.

hep-lat↗
arXiv1994

The Schwinger Model on the lattice in the Microcanonical Fermionic Average approach

The Microcanonical Fermionic Average method has been used so far in the context of lattice models with phase transitions at finite coupling. To test its applicability to Asymptotically Free theories, we have implemented it in QED$_2$, \it i.e.\rm the Schwinger Model. We exploit the possibility, intrinsic to this method, of studying the whole $β, m$ plane at negligible computer cost, to follow constant physics trajectories and measure the $m \to 0$ limit of the chiral condensate. We recover the continuum result within 3 decimal places.

hep-lat↗
arXiv1993

Some Interesting Features of Noncompact QED_3

We study the phase diagram of non compact $QED_3$ using the $MFA$ method and present evidence for a continuous phase transition line at small $N_f$. We also analyze the chiral structure of the vacuum by means of the computation of the probability distribution function of the order parameter in the exact chiral limit.

hep-lat↗
arXiv1993

New Method for Dynamical Fermions and Chiral-Symmetry Breaking

The reasons for the feasibility of the Microcanonical Fermionic Average ($MFA$) approach to lattice gauge theory with dynamical fermions are discussed. We then present a new exact algorithm, which is free from systematic errors and convergent even in the chiral limit.

hep-lat↗
arXiv1992

Large N Lattice QED

We study the $β, N$ critical behaviour of non compact QED with $N$ species of light fermions, using a method we have proposed for unquenched simulations. We find that there exist two phase transition lines: one, second order, and the other, first order, that approaches asymptotically the $β=0$ axis. These two lines have different physical origin, the second one being entirely due to fermions effects. We discuss the effect of the approximation used, in terms of an expansion of the effective action in powers of $N$, and conclude that the general features should not be affected by this approximation.

hep-lat↗
arXiv1992

Phase Structure of Compact $QED_3$ with Massless Fermions

In the framework of (2+1)-dimensional compact lattice QED with light fermions, we investigate the phase diagram in the $(β, N)$ plane. The approximations involved are related to an expansion of the effective fermionic action as a power series of the flavor number $N$. We also develop a new mechanism for understanding the $N-$critical phenomenon in the full theory. Our results for the specific heat indicate that only one phase does exist. We give strong evidences that this qualitative result should not be changed with the inclusion of higher order terms in the $N$ expansion.

hep-lat↗
arXiv1992

A new approach to noncompact lattice qed with light fermions

We discuss detailed simulations of the non compact abelian model coupled to light fermions, using a method previously developed that includes the effects of the fermionic interactions in an effective action. The approximations involved are related to an expansion in the flavour number. We address the problem of the (non) triviality of the theory through a study of the analytical properties of the effective action as a function of the pure gauge energy. New numerical results for the plaquette energy, chiral condensate and a qualitative analysis of the phase diagram are also presented.

hep-lat↗
arXiv1992

Renormalization group and triviality in noncompact lattice QED with light fermions

In the framework of noncompact lattice QED with light fermions, we derive the functional dependence of the average energy per plaquette on the bare parameters using block-spin Renormalization Group arguments and assuming that the renormalized coupling vanishes. Our numerical results for this quantity in $8^4$ and $10^4$ lattices show evidence for triviality in the weak coupling phase and point to a non vanishing value for the renormalized coupling constant in the strong coupling phase.

hep-lat↗