Generation of surface polaritons in dielectric cylindrical waveguides

We investigate the radiation of surface polaritons by a charged particle rotating around a dielectric waveguide. The general case is considered when the waveguide is immersed in a homogeneous medium. For the evaluation of the corresponding electromagnetic fields the electromagnetic Green tensor is used. A formula is derived for the spectral distribution of the radiation intensity for surface-type modes. It is shown that the corresponding waves are radiated on the eigenmodes of the dielectric cylinde

Fermionic condensate and the mean energy-momentum tensor in the Fulling-Rindler vacuum

We investigate the properties of the fermionic Fulling-Rindler vacuum for a massive Dirac field in a general number of spatial dimensions. As important local characteristics, the fermionic condensate and the expectation value of the energy-momentum tensor are evaluated. The renormalization is reduced to the subtraction of the corresponding expectation values for the Minkowski vacuum. It is shown that the fermion condensate vanishes for a massless field and is negative for nonzero mass. Unlike the case of scalar fields, the fermionic vacuum stresses are isotropic for general case of massive fields. The energy density and the pressures are negative. For a massless field the corresponding spectral distributions exhibit thermal properties with the standard Unruh temperature. However, the density-of-states factor is not Planckian for general number of spatial dimensions. Another interesting feature is that the thermal distribution is of the Bose-Einstein type in even number of spatial dimensions. This feature has been observed previously in the response of a particle detector uniformly accelerating through the Minkowski vacuum. In an even number of space dimensions the fermion condensate and the mean energy-momentum tensor coincide for the fields realizing two inequivalent irreducible representations of the Clifford algebra. In the massless case, we consider also the vacuum energy-momentum tensor for Dirac fields in the conformal vacuum of the Milne universe, in static open universe and in the hyperbolic vacuum of de Sitter spacetime.Comment: 28 pages, 5 figure

Electromagnetic vacuum stresses and energy fluxes induced by a cosmic string in de Sitter spacetime

For the electromagnetic field in (D+1)-dimensional locally de Sitter (dS) spacetime, we analyze the effects of a generalized cosmic string type defect on the vacuum expectation value of the energy-momentum tensor. For the Bunch-Davies vacuum state, the topological contributions are explicitly extracted in both the diagonal and off-diagonal components. The latter describes the presence of radially directed energy flux in the vacuum state. It vanishes for $D=3$ because of the conformal invariance of the electromagnetic field and is directed towards the cosmic string for $D\geq 4$ . The topological contributions in the vacuum stresses are anisotropic and, unlike to the geometry of a cosmic string in the Minkowski spacetime, for $D>3$ the stresses along the directions parallel to the string core differ from the energy density. Depending on the planar angle deficit and the distance from the cosmic string, the corresponding expectation values can be either positive or negative. Near the cosmic string the effect of the gravitational field on the diagonal components of the topological part is weak. The spacetime curvature essentially modifies the behavior of the topological terms at proper distances from the cosmic string larger than the dS curvature radius. In that region, the topological contributions in the diagonal components of the energy-momentum tensor decay in inverse proportion to the fourth power of the proper distance and the energy flux density behaves as inverse-fifth power for all values of the spatial dimension $D$. The exception is the energy density in the special case $D=4$.Comment: 23 pages, 4 figures, Discussion adde

Cosmological evolution with negative energy densities

For general number of spatial dimensions we investigate the cosmological dynamics driven by a cosmological constant and by a source with barotropic equation of state. It is assumed that for both those sources the energy density can be either positive or negative. Exact solutions of the cosmological equations are provided for flat models. For models with curved space and with zero cosmological constant the general solutions are expressed in terms of the hypergeometric function. The qualitative evolution is described for all values of the equation of state parameter. We specify the values of that parameter and the combinations of the signs for the cosmological constant and matter energy density for which the cosmological dynamics is nonsingular. An example is considered with positive cosmological constant and negative matter energy density induced by the polarization of the hyperbolic vacuum.Comment: 12 pages, 3 figures. Discussion and references added, accepted for publication in Astrophysic

Vacuum currents in partially compactified Rindler spacetime with an application to cylindrical black holes

The vacuum expectation value of the current density for a charged scalar field is investigated in Rindler spacetime with a part of spatial dimensions compactified to a torus. It is assumed that the field is prepared in the Fulling-Rindler vacuum state. For general values of the phases in the periodicity conditions and the lengths of compact dimensions, the expressions are provided for the Hadamard function and vacuum currents. The current density along compact dimensions is a periodic function of the magnetic flux enclosed by those dimensions and vanishes on the Rindler horizon. The obtained results are compared with the corresponding currents in the Minkowski vacuum. The near-horizon and large-distance asymptotics are discussed for the vacuum currents around cylindrical black holes. In the near-horizon approximation the lengths of compact dimensions are determined by the horizon radius. At large distances from the horizon the geometry is approximated by a locally anti-de Sitter spacetime with toroidally compact dimensions and the lengths of compact dimensions are determined by negative cosmological constant.Comment: 16 pages, 2 figures, discussion and references adde