Compact lattice U(1) and Seiberg-Witten duality: a quantitative comparison

It was conjectured some time ago that an effective description of the Coulomb-confinement transition in compact U(1) lattice gauge field theory could be described by scalar QED obtained by soft breaking of the N=2 Seiberg-Witten model down to N=0 in the strong coupling region where monopoles are light. In two previous works this idea was presented at a qualitative level. In this work we analyze in detail the conjecture and obtain encouraging quantitative agreement with the numerical determination of the monopole mass and the dual photon mass in the vicinity of the Coulomb to confining phase transition.Comment: 14 pag, 5 figure

Vector mesons in the Extended Chiral Quark Model

We extend our previous formulation of low-energy QCD in terms of an effective lagrangian containing operators of dimensionality $d\le 6$ constructed with pseudoscalars and quark fields, describing physics below the scale of chiral symmetry breaking. We include in this paper the vector and axial-vector channels. We follow closely the Extended Chiral Quark Model approach and consistently work in the large-$N_c$ and leading log approximation and take into account the constraints from chiral symmetry and chiral symmetry restoration. The optimal fit of all parameters gives further support to a heavy scalar meson with a mass $\sim 1$ GeV and a value of the axial pion-quark coupling constant $g_A \simeq 0.55$ to 0.66, depending on some assumptions concerning the Weinberg sum rules.Comment: 19 pages, Latex, JHEP class, more typos removed, few refs.adde

COMBINING MCRG AND FOURIER ACCELERATED LANGEVIN ALGORITHM

We study the implementation of Monte Carlo renormalization group (MCRG) in momentum space. This technique is most efficient when used in combination with a Fourier accelerated Langevin algorithm. As a benchmark we calculate the critical exponents $\nu$ and $\eta$ in the vicinity of both the gaussian and the Wilson fixed point in $\lambda \phi^4_3$. The results are very competitive with alternative analytical methods and require a moderate computational effort only.Comment: 11 plain tex pages and 1 figure in a compressed fil

Determination of the Crumpling Fractal Dimension Via k-Space MCRG

Motivated by the successful application of MCRG in momentum space to $\lambda \phi^4_3$ we determine the critical exponents at the crumpling transition in fixed triangulated surfaces. The results are still tentative, but suggest that $-1.0\ge \eta \ge -1.3$, pointing at a value for the fractal Hausdorff dimension at the crumpling transistion fixed point somewhere between 3 and 4.Comment: 4 pages of LATEX (uses espcrc2.sty) and 1 uuencoded ps figure. (Contribution to Lattice'95

Spectrum of Relativistic Fermions in a 2d Doped Lattice

Motivated by some previous work on fermions on random lattices and by suggestions that impurities could trigger parity breaking in 2d crystals, we have analyzed the spectrum of the Dirac equation on a two dimensional square lattice where sites have been removed randomly --- a doped lattice. We have found that the system is well described by a sine-Gordon action. The solitons of this model are the lattice fermions, which pick a quartic interaction due to the doping and become Thirring fermions. They also get an effective mass different from the lagrangian mass. The system seems to exhibit spontaneous symmetry breaking, exactly as it happens for a randomly triangulated lattice. The associated ``Goldstone boson" is the sine-Gordon scalar. We argue, however, that the peculiar behaviour of the chiral condensate is due to finite size effects.Comment: 11 page

Spontaneous parity violation in extreme conditions: an effective lagrangian analysis

We investigate how large baryon densities (and possibly high temperatures) may induce spontaneous parity violation in the composite meson sector of vector-like gauge theory (presumably QCD or techni-QCD) . The analysis at intermediate energy scales is done by using an extended $\sigma$-model lagrangian that includes two scalar and two pseudoscalar multiplets and fulfills low-energy constraints for vector-like gauge theories. We elaborate on a novel mechanism of parity breaking based on the interplay between lightest and heavier meson condensates, which therefore cannot be realized in the simplest $\sigma$ model. The results are relevant for an idealized homogeneous and infinite nuclear (quark or techniquark) matter where the influence of density can be examined with the help of a constant chemical potential. The model is able to describe satisfactorily the first-order phase transition to stable nuclear matter, and predicts a second-order phase transition to a state where parity is spontaneously broken. We argue that the parity breaking phenomenon is quite generic when a large enough chemical potential is present. Current quark masses are explicitly taken into account in this work and shown not to change the general conclusions.Comment: 24 pages, substantial revisio

Stringification of Chiral Dynamics: Wess-Zumino interaction

The QCD hadronic string is supplemented with the reparameterization-invariant boundary interaction to background chiral fields associated with pions in a way compatible with the conformal symmetry. It allows the full reconstruction of the P-even part of the Chiral Lagrangian in a good agreement with the phenomenology of P-even meson interactions. The modification of boundary interaction necessary to induce the parity-odd Chiral Dynamics (WZW action) is outlined.Comment: 5 pages, misprints removed, Talks at the 1th Workshop on Hadron Structure and QCD, 18-22.May 2004, St.Petersburg, Russia, at the Bogolubov Conference on Problems of Theoretical and Mathematical Physics, 2-6.September 2004, Dubna, Russia and at the 6th Conference on Quark Confinement and the Hadron Spectrum, 21-25.September 2004, Villasimius, Sardegna, Ital