Comment on "Casimir energies with finite-width mirrors"

We comment on a recent publication [1] by Fosco, Lombardo and Mazzitelli on Casimir energies for material slabs (`finite width mirrors') and report a discrepancy between results obtained there for a single mirror and some previous calculations. We provide a simple consistency check which proves that the method used in [1] is not reliable when applied to approximations of piecewise constant profile of the mirror. We also present an alternative method for calculation of the Casimir energy in such systems based on our recent work. Our results coincide both with perturbation theory and with some older \cite{Bordag'95} and more recent \cite{Vassilevitch'08} calculations, but differ from those of [1].Comment: Published version, 4 page

Finite temperature Casimir effect for graphene

We adopt the Dirac model for quasiparticles in graphene and calculate the finite temperature Casimir interaction between a suspended graphene layer and a parallel conducting surface. We find that at high temperature the Casimir interaction in such system is just one half of that for two ideal conductors separated by the same distance. In this limit single graphene layer behaves exactly as a Drude metal. In particular, the contribution of the TE mode is suppressed, while one of the TM mode saturates the ideal metal value. Behaviour of the Casimir interaction for intermediate temperatures and separations accessible for an experiment is studied in some detail. We also find an interesting interplay between two fundamental constants of graphene physics: the fine structure constant and the Fermi velocity.Comment: 13 pages, 2 figures, to appear in Physical Review

Violent crime as old as the Bible: Boko Haram uses rape as a weapon of war

Days after Nigerian security forces freed 234 women from Boko Haram’s stronghold in Nigeria’s Sambisa forest it was reported that at least 214 (91%) of them were pregnant. The women were among nearly 700 rescued from the Islamic terrorist group in operations and have been taken to safe camps in Borno State where they will be offered medical and pre-natal care and counselling. It is not yet known whether any of the 230 girls kidnapped by Boko Haram from their school in the town of Chibok in April 2014 were among them

Quest for Casimir repulsion between Chern-Simons surfaces

In this paper we critically reconsider the Casimir repulsion between surfaces that carry the Chern-Simons interaction (corresponding to the Hall type conductivity). We present a derivation of the Lifshitz formula valid for arbitrary planar geometries and discuss its properties. This analysis allows us to resolve some contradictions in the previous literature. We compute the Casimir energy for two surfaces that have constant longitudinal and Hall conductivities. The repulsion is possible only if both surfaces have Hall conductivities of the same sign. However, there is a critical value of the longitudinal conductivity above which the repulsion disappears. We also consider a model where both parity odd and parity even terms in the conductivity are produced by the polarization tensor of surface modes. In contrast to the previous publications L. Chen and S.-L. Wan, Phys. Rev. B84, 075149 (2011); B85, 115102 (2012), we include the parity anomaly term. This term ensures that the conductivities vanish for infinitely massive surface modes. We find that at least for a single mode regardless of the sign and value of its mass, there is no Casimir repulsion

Стратегия формирования здорового образа жизни средствами физической культуры и спорта: опыт, перспективы развития Материалы Всероссийской научно-практической конференции.. С. 175-178. Особенности ладонного гребневого счета татар г. Тюмени и г. Ульяновска, не занимающихся спортом: научно-практическая конференция

We study the polarization tensor of a Dirac field in (3 þ 1) dimensions confined to a half-space—a problem motivated by applications to the condensed matter physics, and to topological insulators in particular. Although the Pauli-Villars regularization scheme has a number of advantages, like explicit gauge invariance and decoupling of heavy modes, it is not applicable on manifolds with boundaries. Here, we modify this scheme by giving an axial mass to the regulators and to the physical field. We compute the renormalized polarization tensor in coordinate representation. We discuss then the induced Chern-Simons type action on the boundary and compare it to the effective action of a (2 þ 1)-dimensional Dirac fermion

Bulk contributions to the Casimir interaction of Dirac materials

Exploiting methods of quantum field theory we compute the bulk polarization tensor and bulk dielectric functions for Dirac materials in the presence of a mass gap, chemical potential, and finite temperature. Using these results (and neglecting eventual boundary effects), we study the Casimir interaction of Dirac materials.We describe in detail the characteristic features of the dielectric functions and their influence on the Casimir pressure