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A. Di Giacomo

Publications and source records attributed to A. Di Giacomo.

At least 37 records · Page 2Linked to original sources
arXiv2006

Monopole condensation in two-flavour Adjoint QCD

Two distinct phase transitions occur at different temperatures in QCD with adjoint fermions (aQCD): deconfinement and chiral symmetry restoration. In this model, quarks do no explicitely break the center Z(3) symmetry and therefore the Polyakov loop is a good order parameter for the deconfinement transition. We study monopole condensation by inspecting the expectation value of an operator which creates a monopole. Such a quantity is expected to be an order parameter for the deconfinement transition as in the case of fundamental fermions.

hep-lat↗
arXiv2005

Dynamics of quark-gluon plasma from Field correlators

It is argued that strong dynamics in the quark-gluon plasma and bound states of quarks and gluons is mostly due to nonperturbative effects described by field correlators. The emphasis in the paper is made on two explicit calculations of these effects from the first principles: one analytic using gluelump Green's functions and another using independent lattice data on correlators. The resulting hadron spectra are investigated in the range T_c < T < 2T_c. The spectra of charmonia, bottomonia, light s-sbar mesons, glueballs and quark-gluon states calculated numerically are in general agreement with lattice MEM data. The possible role of these bound states in the thermodynamics of quark-gluon plasma is discussed.

hep-ph↗
arXiv2005

Chiral transition and deconfinement in QCD

The study of QCD with two light dynamical fermions is of fundamental importance to understand the mechanism of color confinement. We present results of a numerical investigation on the order of the chiral phase transition with $N_f = 2$ by use of a novel strategy in finite size scaling analysis. We compare the critical behaviour of the specific heat, of the chiral susceptibility and of the equation of state with the possible critical behaviours. A second order transition in the O(4) and O(2) universality classes are excluded by our data and substantial evidence emerges for a first order transition. Like in most of previous works we have used the standard staggered action with $L_t = 4$: possible scaling violations and the need for further studies are discussed.

hep-lat↗
arXiv2005

Order, Disorder and Confinement

Studying the order of the chiral transition for $N_f=2$ is of fundamental importance to understand the mechanism of color confinement. We present results of a numerical investigation on the order of the transition by use of a novel strategy in finite size scaling analysis. The specific heat and a number of susceptibilities are compared with the possible critical behaviours. A second order transition in the O(4) and O(2) universality classes are excluded. Substantial evidence emerges for a first order transition. Results are in agreement with those found by studying the scaling properties of a disorder parameter related to the dual superconductivity mechanism of color confinement.

hep-lat↗
arXiv2005

An upper limit to the electric dipole moment of the neutron from lattice QCD

A linear increase with the volume of the topological susceptibility can signal spontaneous breaking of parity and time inversion, due to a nonzero vacuum expectation value of the topological charge. Such a breaking would produce a nonzero electric dipole moment of the neutron, d_n. An upper limit to d_n is derived from numerical simulations at increasing volumes.

hep-lat↗
arXiv2005

Study of the systematic errors in the calculation of renormalization constants of the topological susceptibility on the lattice

We present a study of the systematic effects in the nonperturbative evaluation of the renormalization constants which appear in the field-theoretical determination of the topological susceptibility in pure Yang-Mills theory. The study is performed by computing the renormalization constants on configurations that have been calibrated by use of the Ginsparg-Wilson formalism and by cooling.

hep-lat↗
arXiv2005

The chiral transition in two-flavor QCD

QCD with N_f=2 is a specially interesting system to investigate the chiral transition. The order of the transition has still not been established. We report the results of an in-depth numerical investigation performed with staggered fermions on lattices with L_t=4 and L_s=12,16,20,24,32 and quark masses am_q ranging from 0.01335 to 0.307036. Using finite-size techniques we compare the scaling behavior of a number of thermodynamical susceptibilities with the expectations of O(4) and O(2) universality classes. Clear disagreement is observed. Indications of a first order transition are found.

hep-lat↗
arXiv2005

Color confinement and dual superconductivity of the vacuum. IV

A scaling analysis is made of the order parameter describing monopole condensation at the deconfining transition of N_f=2 QCD around the chiral point. In accordance with scaling properties of the specific heat, studied in a previous paper, scaling is consistent with a first order transition. The status of dual superconductivity of the vacuum as a mechanism of color confinement is reviewed.

hep-lat↗
arXiv2005

Two flavor QCD and Confinement

We argue that the order of the chiral transition for N_f=2 is a sensitive probe of the QCD vacuum, in particular of the mechanism of color confinement. A strategy is developed to investigate the order of the transition by use of finite size scaling analysis. An in-depth numerical investigation is performed with staggered fermions on lattices with N_t=4 and N_s=12,16,20,24,32 and quark masses am_q ranging from 0.01335 to 0.307036. The specific heat and a number of susceptibilities are measured and compared with the expectations of an O(4) second order and of a first order phase transition. A second order transition in the O(4) and O(2) universality classes are excluded. Substantial evidence emerges for a first order transition. A detailed comparison with previous works is performed.

hep-lat↗
arXiv2005

Analyticity in theta on the lattice and the large volume limit of the topological susceptibility

Non-analyticity of QCD with a θterm at θ=0 may signal a spontaneous breaking of both parity and time reversal invariance. We address this issue by investigating the large volume limit of the topological susceptibility $χ$ in pure SU(3) gauge theory. We obtain an upper bound for the symmetry breaking order parameter and, as a byproduct, the value χ=(173.4(+/- 0.5)(+/- 1.2)(+1.1 / -0.2) MeV)^4 at β=6 (a approx= 0.1 fermi). The errors are the statistical error from our data, the one derived from the value used for Λ_L and an estimate of the systematic error respectively.

hep-lat↗
arXiv2005

String breaking in QCD: dual superconductor vs. stochastic vacuum model

Effects of dispersion of the chromoelectric field of the flux tube on the string-breaking distance are studied. The leading-order correction is shown to slightly diminish the result following from the Schwinger formula. Instead, accounting for corrections of all orders might result, at certain values of the Landau-Ginzburg parameter, in an increase of the string-breaking distance up to one order of magnitude. An alternative formula for this distance is obtained when produced pairs are treated as holes in a confining pellicle, which spans over the contour of an external quark-antiquark pair. Generalizations of the obtained results to the cases of small temperatures, as well as temperatures close to the critical one are also discussed.

hep-th↗
arXiv2004

On the order of the deconfining transition in N_f=2 QCD

A careful study is made on the lattice of the phase diagram of QCD with two staggered flavors, to investigate the order of the chiral transition of N_f=2 QCD. The specific heat and the susceptibility of the chiral condensate are determined for different spatial sizes of the system, and a finite size scaling analysis provides a determination of the (pseudo)critical indices. The result is a strong indication that the chiral transition is first order.

hep-lat↗
arXiv2004

Chiral transition and deconfinement in N_f = 2 QCD

The transition is studied by means of a disorder parameter detecting condensation of magnetic monopoles in the vacuum. The deconfining transition is found to coincide with the chiral transition and the susceptibility ρ, related to the disorder parameter, is consistent with a first order phase transition.

hep-lat↗
arXiv2004

The order of the chiral transition in N_f=2 QCD

A strategy is developed to investigate the order of the transition using finite size scaling and its relation to color confinement. An in-depth numerical investigation has been performed with KS fermions on lattices with N_t=4 and N_s=12,16,20,24,32 and quark masses am_q ranging from 0.01335 to 0.35. The specific heat and a number of susceptibilities have been measured and compared with the expectation of an O(4) second order and a first order phase transition. A second order O(4) is excluded, whilst data are consistent with a first order.

hep-lat↗
arXiv2004

The quark-gluon Mixed Condensate calculated via Field Correlators

The quark-gluon mixed condensate $g<\bar q σ_{μν} F_{μν} q>$ is calculated in the Gaussian approximation of the Field Correlator Method. In the large N_c limit and for zero mass quarks one obtains a simple result, $m^2_0 \equiv \frac{g<\bar q σ_{μν} F_{μν} q>}{<\bar q q>} = \frac{16σ}π$, where $σ$ is the string tension. For a standard value $σ=0.18 GeV^2$ one obtains $m^2_0=1 GeV^2$ in good agreement with the QCD sum rules estimate $m^2_0 = (0.8\pm 0.2) GeV^2$ and the latest lattice result $m^2_0 \cong 1 GeV^2$.

hep-ph↗