The vacuum energy-momentum tensor (EMT) and the vacuum energy corresponding to massive scalar field on ℜ t × [0, l] × ℜ D−2 space-time with boundary condition involving a dimensional parameter (δ) are found. The dependent on the cavity size l Casimir energy E C is a uniquely determinable function of mass m, size l and "skin-depth" δ. This energy includes the "bulk" and the surface (potential energy) contributions. The latter dominates when l ∼ δ. Taking the surface potential energy into account is crucial for the coincidence between the derivative −∂ E C /∂l and the ll-component of the vacuum EMT.Casimir energy E C and the bulk contribution to it are interconnected through Legendre transformation, in which the quantity δ −1 is conjugate to the vacuum surface energy multiplied by δ. The surface singularities of the vacuum EMT do not depend on l and, for even D, δ = 0 or ∞, possess finite interpretation. The corresponding vacuum energy is finite and retains known analytical dependence on the dimension D.

The radiation processes emerging as a result of interaction between spin and orbit degrees of freedom of spinning charge are investigated with the use of the Bargmann–Michel–Telegdi (BMT) model. The spin contribution to the self-energy of the ultrarelativistic particle is imaginary and proportional to invariant constructed from the derivatives of the worldline and from the spin. This invariant determines up to negative numerical factor of the QED spin contribution to the imaginary part of the mass shift (MS). Particular cases of crossed, electric and magnetic external fields are considered in detail. The influence of an ideal boundary upon the self-energy of the particle is analyzed for the crossed field case. In the presence of the "mirror" the imaginary part of the MS gets an addition and the nonzero spin dependent real part appears, both however giving the small corrections to no-boundary MS. An alternative method to obtain the spin magnetic moment correction to the power of synchrotron radiation entails in generalization of the result known for the planar motion. Special attention is given to disagreement between classical and quantum pictures of spin radiation.

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Spin radiative effects in a one-particle sector of QED have a dual nature and can be understood with the Frenkel classical rotating-electron model. In the region of parameters under study ≫ 1 ( = 1 + /m 2 ) and χ ≪ 1 (χ = /m 3 ), the imaginary part of the mass shift and radiation power contain two types of spin contributions. The contributions of the first type are related to the intrinsic magnetic moment of a fermion representing an additional source of electromagnetic radiation. The contributions of the second type have the opposite sign and are caused by a small change in the electron acceleration appearing due to the Frenkel addition to the particle mass. Contributions of the second type dominate, which explains the "wrong" sign of total spin corrections. We show that not only the sign but also the values of coefficients can be explained with specified accuracy using classical electrodynamics if corrections to the mass shift (action) and radiation power are calculated in canonical variables, i.e., for fixed velocity and momentum values, respectively. The results can be treated as a demonstration of the correspondence principle in the field of radiative spin effects, in addition to correspondence between classical and quantum theories at the tree (in the external filed) level. For a e ≡ (g -2)/2 ≲ χ ≪ 1, equations of the Frenkel model lead to generalization of the system of Lorentz-BMT (Bargmann-Michel-Telegdi) equations taking into account the Frenkel addition to mass. Some features of experimental observations of the spin light are discussed.