We present a precise calculation of the Lamb shift (2P 1/2 − 2S 1/2 ) in muonic ions (µ 6 3 Li) 2+ , (µ 7 3 Li) 2+ , (µ 9 4 Be) 3+ , (µ 10 4 Be) 3+ , (µ 10 5 B) 4+ , (µ 11 5 B) 4+ . The contributions of orders α 3 ÷α 6 to the vacuum polarization, nuclear structure and recoil, relativistic effects are taken into account. Our numerical results are consistent with previous calculations and improve them due to account of new corrections. The obtained results can be used for the comparison with future experimental data, and extraction more accurate values of nuclear charge radii.

We calculate cross sections of a pair B c meson production on the basis of twophoton mechanism from electron-positron annihilation. We investigate the production cross sections in nonrelativistic approximation and with the account of relativistic corrections. Relativistic production amplitudes of S-wave pair pseudoscalar, vector and pseudoscalar+vector B c -mesons are constructed on the basis of relativistic quark model. Numerical values of the production cross sections are obtained at different center-of-mass energies. The comparison of one-photon and two-photon annihilation contributions is presented.

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We calculate corrections of orders α4, α5, α6 to the (1S – 2S) fine structure interval in muonic hydrogen (μp), muonic tritium (μt) and muonic helium ion $$((\mu _2^3He) + )$$. They are determined by the effects of vacuum polarization, nuclear structure and recoil and relativistic corrections. The nuclear structure effects are taken into account in terms of the charge radii of the nuclei in one-photon interaction and in terms of electromagnetic form-factors in the case of two-photon interaction. The obtained results for the (1S – 2S) splitting can be used for a comparison with future experimental data.