arXiv subjects

Pietro Giudice

Publications and source records attributed to Pietro Giudice.

At least 55 records · Page 3Linked to original sources

arXiv2011

Quark number susceptibility at finite density and low temperature

We study the quark number susceptibility in SU(2) lattice gauge theory with two Wilson quark flavours at non-zero chemical potential and low temperature. We present some technical aspects of the issue and numerical results obtained at different lattices and different parameters. We discuss what this observable can teach us about the phase diagram of the model and in particular about the relation between susceptibility and Polyakov loop

hep-lat↗

arXiv2011

Lattice Planar QED in external magnetic field

We investigate planar Quantum ElectroDynamics (QED) with two degenerate staggered fermions in an external magnetic field on the lattice. Our preliminary results indicate that in external magnetic fields there is dynamical generation of mass for two-dimensional massless Dirac fermions in the weak coupling region. We comment on possible implications to the quantum Hall effect in graphene.

hep-lat↗

arXiv2010

Hadronic decay width from finite-volume energy spectrum in lattice QCD

The standard approach to determine the parameters of a resonance is based on the study of the volume dependence of the energy spectrum. In this work we study a non-linear sigma model coupled to a scalar field in which a resonance emerges. Using an analysis method introduced recently, based on the concept of probability distribution, it is possible to determine the mass and the width of the resonance.

hep-lat↗

arXiv2010

Extracting resonance parameters from lattice data

Monte Carlo simulations of the 4d O(4) model in the broken phase are performed to determine the parameters of a resonance. The standard method for extracting them on the lattice is through Lüscher's formula; recently a new method, based on the probability distribution concept, has been proposed. We study the application of these methods and compare them with Monte Carlo data.

hep-lat↗

arXiv2009

The confining string beyond the free-string approximation in the gauge dual of percolation

We simulate five different systems belonging to the universality class of the gauge dual of three-dimensional random percolation to study the underlying effective string theory at finite temperature. All the data for the finite temperature string tension, when expressed by means of adimensional variables, are nicely described by a unique scaling function. We calculate the first few terms of the string tension up to order $T^6$ and compare to different theoretical predictions. We obtain unambiguous evidence that the coefficients of $T^2$ and $T^4$ terms coincide with those of the Nambu-Goto string, as expected, while the $T^6$ term strongly differs and is characteristic of the universality class of this specific gauge theory.

hep-lat↗

arXiv2008

Confining string beyond the free approximation: the case of random percolation

The random percolation model can be viewed as the dual of a well defined confining gauge theory; since this theory, having no Monte Carlo dynamics at all, is simple to simulate, it is possible to study the properties of the flux tube with very high precision; we show it can be described by the effective string picture. Our results are lattice regularisation independent, therefore they are well defined also in the continuum limit, and, for the first time in a gauge theory, it has been possible to determine the next-to-leading quantum corrections throughout the computation of the T^6 coefficient of the Taylor expansion of sigma(T). Furthermore, this coefficient results to be related to the universal ratio T_c/\sqrt{sigma_0}.

hep-lat↗

arXiv2008

The monopole mass in the random percolation gauge theory

We study the behaviour of the monopole at finite temperature in the (2+1)-dimensional lattice gauge theory dual to the percolation model; by exploiting the correspondences to statistical systems, we possess powerful tools to evaluate the monopole mass both above and below the critical temperature with high-precision Monte Carlo simulations.

hep-lat↗

arXiv2008

Non-compact QED3 at finite temperature: the confinement-deconfinement transition

The confinement-deconfinement phase transition is explored by lattice numerical simulations in non-compact (2+1)-dimensional quantum electrodynamics with massive fermions at finite temperature. The existence of two phases, one with and the other without confinement of fractional charges, is related to the realization of the Z symmetry. The order parameter of this transition can be clearly identified. We show that it is possible to detect the critical temperature for a given value of the fermion mass, by exploiting suitable lattice operators as probes of the Z symmetry. Moreover, the large-distance behavior of the correlation of these operators permits to distinguish the phase with Coulomb-confinement from the Debye-screened phase. The resulting scenario is compatible with the existence of a Berezinsky-Kosterlitz-Thouless transition. Some investigations are presented on the possible relation between chiral and deconfinement transitions and on the role of ``monopoles''.

hep-lat↗

arXiv2007

K-string tensions at finite temperature and integrable models

It has recently been pointed out that simple scaling properties of Polyakov correlation functions of gauge systems in the confining phase suggest that the ratios of k-string tensions in the low temperature region is constant up to terms of order T^3. Here we argue that, at least in a three-dimensional Z_4 gauge model, the above ratios are constant in the whole confining phase. This result is obtained by combining numerical experiments with known exact results on the mass spectrum of an integrable two-dimensional spin model describing the infrared behaviour of the gauge system near the deconfining transition.

hep-lat↗

arXiv2007

On the conformal anomaly of k-strings

We discuss the long distance behaviour of the flux tube associated to baryon vertices and argue that, if the gauge system admits stable k-strings, the conformal field theory describing this string in the IR has conformal anomaly c=(d-2)σ_k/σ, where σ_k is the k-string tension and σthat of the fundamental representation. We check this result in a 3D Z_4 gauge model at finite temperature, where a string effect directly related to "c" can be clearly identified.

hep-lat↗

arXiv2007

Universal properties of the confining string in the random percolation model

Random percolation can be fully interpreted as a confining pure gauge theory. With numerical high-precision measurements of Polyakov-Polyakov correlators at finite temperature, we could well observe the presence of shape effects due to rough fluctuations of the confining string, in complete agreement with the universality predictions up to the next-to-leading order.

hep-lat↗

arXiv2007

Two Color Matter in the Quenched Approximation

We study a quenched SU(2) lattice gauge theory in 4d in which the spatial gauge ensemble $\{U_i\}$ is generated from a 3d gauge-Higgs model and the timelike link variables are ``reconstructed'' from the Higgs fields. The resulting ensemble is used to study quenched quark propagation with non-zero chemical potential $μ$. While it proves possible to alter the strength of the inter-quark interaction by changing the parameters of the dimensionally reduced model, there is no evidence for any region of parameter space where quarks exhibit deconfined behaviour or thermodynamic observables scale as if there were a Fermi surface.

hep-lat↗

arXiv2007

Can we study Quark Matter in the Quenched Approximation?

We study a quenched SU(2) lattice gauge theory in which, in an attempt to distinguish between timelike and spacelike gauge fields, the gauge ensemble {U_mu} is generated from a 3 dimensional gauge-Higgs model, the timelike link variables being "reconstructed" from the Higgs fields. The resulting ensemble is used to study quenched quark propagation with non-zero chemical potential mu; in particular, the quark density, chiral and superfluid condensates, meson, baryon and gauge-fixed quark propagators are all studied as functions of mu. While it proves possible to alter the strength of the inter-quark interaction by changing the parameters of the dimensionally reduced model, there is no evidence for any region of parameter space where quarks exhibit deconfined behaviour or thermodynamic observables scale as if there were a Fermi surface.

hep-lat↗

arXiv2007

The conformal anomaly of k-strings

Simple scaling properties of correlation functions of a confining gauge theory in d-dimensions lead to the conclusion that k-string dynamics is described, in the infrared limit, by a two-dimensional conformal field theory with conformal anomaly c=(d-2)T_k/T_1, where T_k is the k-string tension. This result applies to any gauge theory with stable k-strings. We check it in a 3D Z_4 gauge model at finite temperature, where a string effect directly related to c can be clearly identified.

hep-th↗

arXiv2006

Quantum broadening of k-strings in gauge theories

We study the thickness of the confining flux tube generated by a pair of sources in higher representations of the gauge group. Using a simple geometric picture we argue that the area of the cross-section of the flux tube, as measured by a Wilson loop probe, grows logarithmically with source separation, as a consequence of the quantum fluctuations of the underlying k-string. The slope of the logarithm turns out to be universal, i.e. it is the same for all the representations and all the gauge theories. We check these predictions in a 3D Z_4 lattice gauge model by comparing the broadening of the 1-string and the 2-string.

hep-th↗

arXiv2006

Broadening of the confining flux tube joining higher-representation sources

In the context of confining gauge theories we study the flux tube generated by a pair of static sources belonging to higher rank representations of the gauge group. Using a simple geometric approach based on minimal surfaces describing the world-sheet of the underlying k-string, we infer logarithmic broadening of the flux tube as a function of source separation. It turns out that the coefficient of the logarithm does not depend on the specific representation of the source nor on its N-ality and is universal. Numerical results on a Z_4 gauge theory in three dimensions with static sources carrying two units of elementary flux compare very favourably with these predictions.

hep-lat↗

arXiv2006

Quantum fluctuations of k-strings: A case study

K strings in Yang-Mills theory can be considered as bound states of k elementary confining strings carrying one unit of colour flux. Current estimates of k-string tension sigma_k are very sensitive to the leading corrections due to quantum fluctuations of the string. In this study we address this problem by comparing Polyakov-Polyakov correlators in the fundamental representation (k=1) with the corresponding ones with k=2 in the confining phase of a Z_4 gauge theory in three dimensions. Highly efficient simulation techniques are available in this case. Although the k=1 Polyakov-Polyakov correlator matches nicely with the expected bosonic string effects up to the Next-to-Leading-Order, the k=2 Polyakov-Polyakov correlators show large deviations. This is an important source of potential systematic errors in the current estimates of sigma_k.

hep-lat↗

arXiv2005

QED_3 on a space-time lattice: a comparison between compact and noncompact formulation

Quantum electrodynamics in a (2+1)-dimensional space-time has been object of studies both as effective theory for the pseudogap phase of high-T_c superconductors and for the theoretical investigation of mechanisms of confinement in presence of matter fields. We discretize the theory using both compact and noncompact formulations, analyze the behavior of the chiral condensate and of the monopole density and compare them. Finally we draw some conclusions about the possible equivalence of the two lattice formulations.

hep-lat↗