Color Dynamics in External Fields

We investigate the vacuum dynamics of U(1), SU(2), and SU(3) lattice gauge theories in presence of external (chromo)magnetic fields, both in (3+1) and (2+1) dimensions. We find that the critical coupling for the phase transition in compact U(1) gauge theory is independent of the strength of an external magnetic field. On the other hand we find that, both in (3+1) and (2+1) dimensions, the deconfinement temperature for SU(2) and SU(3) gauge systems in a constant abelian chromomagnetic field decreases when the strength of the applied field increases. We conclude that the dependence of the deconfinement temperature on the strength of an external constant chromomagnetic field is a peculiar feature of non abelian gauge theories and could be useful to get insight into color confinement.Comment: 26 pages, 14 figure

Nature and Raman signatures of the Higgs amplitude mode in the coexisting superconducting and charge-density-wave state

We investigate the behavior of the Higgs (amplitude) mode when superconductivity emerges on a preexisting charge-density-wave state. We show that the weak overdamped square-root singularity of the amplitude fluctuations in a standard BCS superconductor is converted in a sharp, undamped power-law divergence in the coexisting state, reminiscent of the Higgs behavior in Lorentz-invariant theories. This effect reflects in a strong superconducting resonance in the Raman spectra, both for an electronic and a phononic mechanism leading to the Raman visibility of the Higgs. In the latter case, our results are relevant to the interpretation of the Raman spectra measured experimentally in NbSe2.Comment: Extended version, accepted for publication in PR

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.Comment: 4 pages, uuencoded compressed (using GNU's gzip) tar file containing 1 LaTeX2e file, 5 encapsulated Postscript figures, and espcrc2.sty. Contribution to Lattice 9

Monopole Condensation in full QCD using the Schroedinger Functional

We use a lattice thermal partition functional to study Abelian monopole condensation in full QCD with $N_f=2$ staggered fermions. We present preliminary results on $16^3\times4$ and $32^3\times4$ lattices.Comment: Lattice2002(topology). 3 pages, 3 figure

Automated preventive maintenance program

Maintenance program which is concise and inexpensive to operate adapts to almost any system that has a FORTRAN compiler. Program operates on a stored data base with an output consisting of scheduling information and various management reports

Non-linear optical effects and third-harmonic generation in superconductors: Cooper-pairs vs Higgs mode contribution

The recent observation of a transmitted Thz pulse oscillating at three times the frequency of the incident light paves the way to a new protocol to access resonant excitations in a superconductor. Here we show that this non-linear optical process is dominated by light-induced excitation of Cooper pairs, in analogy with a standard Raman experiment. The collective amplitude (Higgs) fluctuations of the superconducting order parameter give in general a smaller contribution, unless one designs the experiment by combining properly the light polarization with the lattice symmetry.Comment: Slightly revised introduction, to appear on Phys. Rev. B. as Rapid Communicatio

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 Schr\"odinger 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.Comment: 29 pages, 10 figures, LaTeX2

London Penetration Length and String Tension in SU(2) Lattice Gauge Theory

We study the distribution of the color fields due to a static quark-antiquark pair in SU(2) lattice gauge theory. We find evidence of dual Meissner effect. We put out a simple relation between the penetration length and the string tension.Comment: uuencoded compressed Postscript file (text+figures

Polarization dependence of the third-harmonic generation in multiband superconductors

In a superconductor the third-harmonic generation (THG) of a strong THz pulse is enhanced below Tc by the resonant excitation of lattice-modulated charge fluctuations (LCF), which modulate the response according to the polarization of the field. Here we compute the THG within a multiband model for the prototype NbN superconductor. We show that the non-resonant contribution coming from the instantaneous electronic response and the finite width of the pulse significantly suppress the polarization dependence of the signal, challenging its observation in real systems.Comment: Final version, as publishe

Abelian monopole condensation in lattice gauge theories

We investigate the dynamics of lattice gauge theories in an Abelian monopole background field. By means of the gauge-invariant lattice Schrodinger functional we study the Abelian monopole condensation in U(1) lattice gauge theory at zero temperature and in SU(3) lattice gauge theory at finite temperature.Comment: LATTICE99(Confinement) 3 pages, 3 figure