Electron-positron pair production by linearly polarized photon in the nuclear field

Process of lepton pair production by polarized photon on nuclei can be used to measure the degree of linear polarization of high energy photon. The differential cross section and the analyzing power are calculated with taking into account higher powers of expansion on $Z\alpha$. Pure Coulomb and screened potential are considered.Comment: 12 page

Geometrical Approach to the Gauge Field Mass Problem. Possible Reasons for which the Higgs Bosons Are Not Observable

In the Kaluza - Klein approach the (4+d)-dimensional Einstein--Hilbert gravity action is considered. The extra d-dimensional manifold V_d is a Riemann space with the d-parametric group of isometry $G_d$ which acts on V_d by the left shifts and with arbitrary nondegenerated left-invariant metric g_{ab}. The gauge fields A_{\mu} are introduced as the affine connection coefficients of the fibre bundle with V_d being the fibre. The effective Lagrangian as invariant integral over extra-dimensional manifold of the curvative scalar of mentioned structure is obtained. It is shown that such effective Lagrangian contains beside the square of gauge field strength tensor also quadratic form of A_{\mu} and all other fields have only pure gauge degrees of freedom when g_{ab}. satisfy some conditions. This conditions may be regarded as generalization of the General Relativity Principle to the extra dimensions. The eigenvalues of the quadratic form of A_{\mu} are calculated for the case of gauge group SO(3). It is shown that they are not equal to zero in the case when g_{ab} is not proportional to the unit matrix.Comment: LaTeX2e file, espcrc2.sty, 7 pages. Based on the talk given at the D. V. Volkov Memorial Conference "Supersymmetry and Quantum Field Theory"(25-29 July, 2000, Kharkov, Ukraine). To be published in Nuclear Physics B Conference Supplement