Spontaneous CPT Violation in Confined QED

Symmetry breaking induced by untwisted fermions in QED in a nonsimply connected spacetime with topology $S^{1}\times R^{3}$ is investigated. It is found that the discrete CPT symmetry of the theory is spontaneously broken by the appearance of a constant vacuum expectation value of the electromagnetic potential along the direction of space periodicity. The constant potential is shown to be gauge nonequivalent to zero in the nonsimply connected spacetime under consideration. Due to the symmetry breaking, one of the electromagnetic modes of propagation is massive with a mass that depends on the inverse of the compactification length. As a result, the system exhibits a sort of topological directional superconductivity.Comment: 6 pages, revte

Structure and electronic properties of molybdenum monoatomic wires encapsulated in carbon nanotubes

Monoatomic chains of molybdenum encapsulated in single walled carbon nanotubes of different chiralities are investigated using density functional theory. We determine the optimal size of the carbon nanotube for encapsulating a single atomic wire, as well as the most stable atomic arrangement adopted by the wire. We also study the transport properties in the ballistic regime by computing the transmission coefficients and tracing them back to electronic conduction channels of the wire and the host. We predict that carbon nanotubes of appropriate radii encapsulating a Mo wire have metallic behavior, even if both the nanotube and the wire are insulators. Therefore, encapsulating Mo wires in CNT is a way to create conductive quasi one-dimensional hybrid nanostructures.Comment: 8 pages, 10 figure

Effects of Bose-Einstein Condensation on forces among bodies sitting in a boson heat bath

We explore the consequences of Bose-Einstein condensation on two-scalar-exchange mediated forces among bodies that sit in a boson gas. We find that below the condensation temperature the range of the forces becomes infinite while it is finite at temperatures above condensation.Comment: 10 pages, 2 figure

Paramagnetism in color superconductivity and compact stars

It is quite plausible that color superconductivity occurs in the inner regions of neutron stars. At the same time, it is known that strong magnetic fields exist in the interior of these compact objects. In this paper we discuss some important effects that can occur in the color superconducting core of compact stars due to the presence of the stars' magnetic field. In particular, we consider the modification of the gluon dynamics for a color superconductor with three massless quark flavors in the presence of an external magnetic field. We show that the long-range component of the external magnetic field that penetrates the color-flavor locked phase produces an instability for field values larger than the charged gluons' Meissner mass. As a consequence, the ground state is restructured forming a vortex state characterized by the condensation of charged gluons and the creation of magnetic flux tubes. In the vortex state the magnetic field outside the flux tubes is equal to the applied one, while inside the tubes its strength increases by an amount that depends on the amplitude of the gluon condensate. This paramagnetic behavior of the color superconductor can be relevant for the physics of compact stars.Comment: To appear in J. Phys. A: Math. Theor. 40 (2007) 1 (Corrected references

s-s*-d-wave superconductor on a square lattice and its BCs phase diagram

We study an extended Hubbard model with on-site repulsion and nearest neighbors attraction which tries to mimic some of the experimental features of doped cuprates in the superconducting state. We draw and discuss the phase diagram as a function of the effective interactions among electrons for a wide range of doping concentrations. We locate the region which is relevant for the cuprates setting some constraints on the parameters which may be used in this kind of effective models. We also study the effects of temperature and orthorrombicity on the symmetry and magnitude of the gap function, and map the model onto a simpler linearized hamiltonian, which produces similar phase diagrams.Comment: 4 pages, 3 figures included. Accepted for publication in Phys. Rev.

Long range neutrino forces in the cosmic relic neutrino background

Neutrinos mediate long range forces among macroscopic bodies in vacuum. When the bodies are placed in the neutrino cosmic background, these forces are modified. Indeed, at distances long compared to the scale $T^{-1}$, the relic neutrinos completely screen off the 2-neutrino exchange force, whereas for small distances the interaction remains unaffected.Comment: 8 pages, 2 figure