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Paolo Cea

Publications and source records attributed to Paolo Cea.

87 records · Page 5Linked to original sources
arXiv1999

Probing the non-perturbative dynamics of SU(2) vacuum

The vacuum dynamics of SU(2) lattice gauge theory is studied by means of a gauge-invariant effective action defined using the lattice Schrödinger functional. Numerical simulations are performed both at zero and finite temperature. The vacuum is probed using an external constant Abelian chromomagnetic field. The results suggest that at zero temperature the external field is screened in the continuum limit. On the other hand at finite temperature it seems that confinement is restored by increasing the strength of the applied field.

hep-lat↗
arXiv1998

Dynamical Generation of the Primordial Magnetic Field by Ferromagnetic Domain Walls

The spontaneous generation of uniform magnetic condensate in $QED_3$ gives rise to ferromagnetic domain walls at the electroweak phase transition. These ferromagnetic domain walls are caracterized by vanishing effective surface energy density avoiding, thus, the domain wall problem. Moreover we find that the domain walls generate a magnetic field $B \simeq 10^{24} Gauss$ at the electroweak scale which account for the seed field in the so called dynamo mechanism for the cosmological primordial magnetic field. We find that the annihilation processes of walls with size $R \simeq 10^5 Km$ could release an energy of order $10^{52} erg$ indicating the invisible ferromagnetic walls as possible compact sources of Gamma Ray Bursts.

hep-th↗
arXiv1998

SU(2) vacuum dynamics in applied external magnetic field

The vacuum dynamics of SU(2) lattice gauge theory is studied by means of a gauge-invariant effective action, both at zero and finite temperature. Working with lattices up to 32^4 we check the scaling of the energy density with the magnetic length. We find that the screening at zero temperature of the applied external magnetic field weakens by increasing the temperature.

hep-lat↗
arXiv1998

Spontaneous Generation of Magnetic Field in Three Dimensional QED at Finite Temperature

We investigate the effects of thermal fluctuations on the spontaneous magnetic condensate in three dimensional QED coupled with P-odd Dirac fermions. Our results show that the phenomenon of the spontaneous generation of the constant background magnetic field survives to the thermal corrections even at infinite temperature. We also study the thermal corrections to the fermionic condensate in presence of the magnetic field.

hep-th↗
arXiv1996

Unstable Modes and Confinement in the Lattice Schrödinger Functional Approach

We analyze the problem of the Nielsen-Olesen unstable modes in the SU(2) lattice gauge theory by means of a recently introduced gauge-invariant effective action. We perform numerical simulations in the case of a constant Abelian chromomagnetic field. We find that for lattice sizes above a certain critical length the density of effective action shows a behaviour compatible with the presence of the unstable modes. We put out a possible relation between the dynamics of the unstable modes and the confinement.

hep-lat↗
arXiv1996

Perturbation Theory with a Variational Basis: the Generalized Gaussian Effective Potential

The perturbation theory with a variational basis is constructed and analyzed.The generalized Gaussian effective potential is introduced and evaluated up to the second order for selfinteracting scalar fields in one and two spatial dimensions. The problem of the renormalization of the mass is discussed in details. Thermal corrections are incorporated. The comparison between the finite temperature generalized Gaussian effective potential and the finite temperature effective potential is critically analyzed. The phenomenon of the restoration at high temperature of the symmetry broken at zero temperature is discussed.

hep-th↗
arXiv1996

Exploring the Unstable Modes Dynamics by the Lattice Schrodinger Functional

We analyze the problem of the Nielsen-Olesen unstable modes in the $SU(2)$ lattice gauge theory by means of a recently introduced gauge-invariant effective action. We perform numerical simulations in the case of a constant Abelian chromomagnetic field. We find that for lattice sizes above a certain critical length the density of effective action shows a behaviour compatible with the presence of the unstable modes.

hep-lat↗
arXiv1996

Finite Size Analysis of the U(1) Background Field Effective Action

We apply the finite size scaling analysis to the derivative of the density of the effective action for the lattice U(1) pure gauge theory in an external constant magnetic field. We found the presence of a continuous phase transition. Moreover, our extimate of of the critical parameters gives values consistent with those extracted from the analysis of the specific heat.

hep-lat↗
arXiv1996

Lattice Background Effective Action: a Proposal

We propose a method based on the Schrödinger functional for computing on the lattice the gauge invariant effective action for external background fields. We check this method by studying the U(1) lattice gauge theory in presence of a constant magnetic background field.

hep-lat↗
arXiv1996

Vacuum Stability for Dirac Fermions in Three Dimensions

I investigate three dimensional abelian and non-abelian gauge theories interacting with Dirac fermions. Using a variational method I evaluate the vacuum energy density in the one-loop approximation. It turns out that the states with a constant magnetic condensate lie below the perturbative ground state only in the case of three dimensional quantum electrodynamics with massive fermions.

hep-th↗
arXiv1995

Generalized Gaussian Effective Potential: Second Order Thermal Corrections

We discuss the finite temperature generalized Gaussian effective potential. We put out a very simple relation between the thermal corrections to the generalizedGaussian effective potential and those of the effective potential. We evaluate explicitly the second order thermal corrections in the case of the selfinteracting scalar field in one spatial dimension.

hep-ph↗
arXiv1995

The SU(2) Confining Vacuum as a Dual Superconductor

We investigate the dual superconductivity hypothesis in pure SU(2) lattice gauge theory. We find evidence of the dual Meissner effect both in the maximally Abelian gauge and without gauge fixing. We also obtain a rather good extimation of the string tension using the value of the London penetration length.

hep-lat↗
arXiv1995

Dual superconductivity in the SU(2) pure gauge vacuum: a lattice study

We investigate the dual superconductivity hypothesis in pure SU(2) lattice gauge theory. We focus on the dual Meissner effect by analyzing the distribution of the color fields due to a static quark-antiquark pair. We find evidence of the dual Meissner effect both in the maximally Abelian gauge and without gauge fixing. We measure the London penetration length. Our results suggest that the London penetration length is a physical gauge-invariant quantity. We put out a simple relation between the penetration length and the square root of the string tension. We find that our extimation is quite close to the extrapolated continuum limit available in the literature. A remarkable consequence of our study is that an effective Abelian theory can account for the long range properties of the SU(2) confining vacuum.

hep-lat↗
arXiv1995

Generalized Gaussian Effective Potential: Thermal Corrections

We evaluate the thermal corrections to the generalized Gaussian effective potential. We carry out the calculations of the lowest order corrections in the case of self-interacting scalar fields in one and two spatial dimensions, and study the restoration of the symmetry at high temperatures.

hep-ph↗