Unstable Modes and Confinement in the Lattice Schr\"odinger 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.Comment: 15 pages, LaTeX2e file, 5 figure

No Primordial Magnetic Field from Domain Walls

It is pointed out that, contrary to some claims in the literature, the domain walls cannot be a source of a correlated at large scales primordial magnetic field, even if the fermionic modes bound on the wall had ferromagnetic properties. In a particular model with massive (2+1) dimensional fermions bound to a domain wall, previously claimed to exhibit a ferromagnetic behavior, it is explicitly shown that the fermionic system in fact has properties of a normal diamagnetic with the susceptibility vanishing at high temperature.Comment: 8 pages. Modified discussion of the baryon density on an axion domain wal

Indications on the Higgs boson mass from lattice simulations

The `triviality' of $\Phi^4_4$ has been traditionally interpreted within perturbation theory where the prediction for the Higgs boson mass depends on the magnitude of the ultraviolet cutoff $\Lambda$. This approach crucially assumes that the vacuum field and its quantum fluctuations rescale in the same way. The results of the present lattice simulation, confirming previous numerical indications, show that this assumption is not true. As a consequence, large values of the Higgs mass $m_H$ can coexist with the limit $\Lambda\to \infty$. As an example, by extrapolating to the Standard Model our results obtained in the Ising limit of the one-component theory, one can obtain a value as large as $m_H=760 \pm 21$ GeV, independently of $\Lambda$.Comment: 3 pages, 2 figures, Lattice2003(higgs

Exploring the Dynamics of Three-Dimensional Lattice Gauge Theories by External Fields

We investigate the dynamics of three-dimensional lattice gauge theories by means of an external Abelian magnetic field. For the SU(2) lattice gauge theory we find evidence of the unstable modes.Comment: 3 pages, PostScript. Contribution to the LATTICE 93 Conference (Dallas, U.S.A., September 1993) preprint BARI-TH-162/9

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.Comment: LaTeX, 8 pages, 1 figur

Probing Confinement with Chromomagnetic Fields

Using the lattice Schr\"odinger functional we study vacuum dynamics of SU(3) gauge theory at finite temperature. The vacuum is probed by means of an external constant Abelian chromomagnetic field. We find that by increasing the strength of the applied external field the deconfinement temperature decreases towards zero. This implies that strong enough Abelian chromomagnetic fields destroy confinement of color.Comment: Lattice2002(topology). 3 pages, 3 figure

RXJ1856.5-3754 and RXJ0720.4-3125 are P-Stars

P-stars are a new class of compact stars made of up and down quarks in $\beta$-equilibrium with electrons in a chromomagnetic condensate. P-stars are able to account for compact stars with $R \lesssim 6 Km$, as well as stars comparable to canonical neutron stars. We show that P-stars once formed are absolutely stable, for they cannot decay into neutron or strange stars. We convincingly argue that the nearest isolated compact stars RXJ1856.5-3754 and RXJ0720.4-3125 could be interpreted as P-stars with $M \simeq 0.8 M_{\bigodot}$ and $R \simeq 5 Km$.Comment: 18 pages, 2 figures, revised version, to appear in JCA

The High Temperature Superconductivity in Cuprates

We discuss the high-temperature superconductivity in copper oxide ceramics. We propose an effective Hamiltonian to describe the dynamics of electrons or holes injected into the copper oxide layers. We show that our approach is able to account for both the pseudogap and the superconductivity gap. For the hole-doped cuprates we discuss in details the underdoped, optimal doped, and overdoped regions of the phase diagram. In the underdoped region we determine the doping dependence of the upper critical magnetic field, the vortex region, and the discrete states bounded to the core of isolated vortices. We explain the origin of the Fermi arcs and Fermi pockets. Moreover, we discuss the recently reported peculiar dependence of the specific heat on the applied magnetic field. We determine the critical doping where the pseudogap vanishes. We find that in the overdoped region the superconducting transition is described by the conventional d-wave BCS theory. We discuss the optimal doping region and the crossover between the underdoped region and the overdoped region. We also discuss briefly the electron-doped cuprate superconductors.Comment: 40 pages, 13 figures, revised version accepted for publication in La Rivista del Nuovo Ciment