Local and Global Casimir Energies: Divergences, Renormalization, and the Coupling to Gravity

From the beginning of the subject, calculations of quantum vacuum energies or Casimir energies have been plagued with two types of divergences: The total energy, which may be thought of as some sort of regularization of the zero-point energy, $\sum\frac12\hbar\omega$, seems manifestly divergent. And local energy densities, obtained from the vacuum expectation value of the energy-momentum tensor, $\langle T_{00}\rangle$, typically diverge near boundaries. The energy of interaction between distinct rigid bodies of whatever type is finite, corresponding to observable forces and torques between the bodies, which can be unambiguously calculated. The self-energy of a body is less well-defined, and suffers divergences which may or may not be removable. Some examples where a unique total self-stress may be evaluated include the perfectly conducting spherical shell first considered by Boyer, a perfectly conducting cylindrical shell, and dilute dielectric balls and cylinders. In these cases the finite part is unique, yet there are divergent contributions which may be subsumed in some sort of renormalization of physical parameters. The divergences that occur in the local energy-momentum tensor near surfaces are distinct from the divergences in the total energy, which are often associated with energy located exactly on the surfaces. However, the local energy-momentum tensor couples to gravity, so what is the significance of infinite quantities here? For the classic situation of parallel plates there are indications that the divergences in the local energy density are consistent with divergences in Einstein's equations; correspondingly, it has been shown that divergences in the total Casimir energy serve to precisely renormalize the masses of the plates, in accordance with the equivalence principle.Comment: 53 pages, 1 figure, invited review paper to Lecture Notes in Physics volume in Casimir physics edited by Diego Dalvit, Peter Milonni, David Roberts, and Felipe da Ros

Produção de resíduos vegetais em áreas de cerrados do Brasil

Litter production was measured in Brazilian Cerrado and Cerradão during three successive years. The average yearly production of total litter is 7,800 kg/ha-1 and 2,100 kg/ha-1 in Cerradão and Cerrado, respectively. The leaf-litter (including grasses) represents 76.7% of the total litter in Cerradão and 84% in Cerrado. The rates of litter decomposition determined by direct litter-bag technique are very slow on surface in both ecosystems. The litters from Cerrado and Cerradão have almost the same nutrient storage ability. Samples of litter composed of the parts of predominant plants contain 0.82%-0.85% of N, 0.06% P, 0.16% K, 0.32%-0,34% Ca and 0.12%-0.14%Mg.Foram efetuadas avaliações de produção de resíduos vegetais de Cerrado e Cerradão, durante três anos consecutivos. A produção média anual de resíduos vegetais foi de 7.800 e 2.100 kg/ha no Cerradão e Cerrado, respectivamente. As folhas senescentes (incluindo gramíneas) representam 76,7% da produção total de resíduos de biomassa no Cerradão, e 84% no Cerrado. A taxa de decomposição deste material foi determinada diretamente em sacos de tela de nylon, sendo considerada muito baixa em ambos os ecosistemas. Os resíduos vegetais coletados no Cerrado e no Cerradão apresentaram semelhante composições de nutrientes: 0,82-0.85% de N; 0,06% de P; 0,16% de K; 0,32%-0,34% de Ca e 0,12-0,14% de Mg

Electromagnetic Casimir densities for a wedge with a coaxial cylindrical shell

Vacuum expectation values of the field square and the energy-momentum tensor for the electromagnetic field are investigated for the geometry of a wedge with a coaxal cylindrical boundary. All boundaries are assumed to be perfectly conducting and both regions inside and outside the shell are considered. By using the generalized Abel-Plana formula, the vacuum expectation values are presented in the form of the sum of two terms. The first one corresponds to the geometry of the wedge without the cylindrical shell and the second term is induced by the presence of the shell. The vacuum energy density induced by the shell is negative for the interior region and is positive for the exterior region. The asymptotic behavior of the vacuum expectation values are investigated in various limiting cases. It is shown that the vacuum forces acting on the wedge sides due to the presence of the cylindrical boundary are always attractive.Comment: 21 pages, 7 figure

The Sudbury Neutrino Observatory

The Sudbury Neutrino Observatory is a second generation water Cherenkov detector designed to determine whether the currently observed solar neutrino deficit is a result of neutrino oscillations. The detector is unique in its use of D2O as a detection medium, permitting it to make a solar model-independent test of the neutrino oscillation hypothesis by comparison of the charged- and neutral-current interaction rates. In this paper the physical properties, construction, and preliminary operation of the Sudbury Neutrino Observatory are described. Data and predicted operating parameters are provided whenever possible.Comment: 58 pages, 12 figures, submitted to Nucl. Inst. Meth. Uses elsart and epsf style files. For additional information about SNO see http://www.sno.phy.queensu.ca . This version has some new reference