Charge asymmetry is studied theoretically for multiphoton ionization (nγ e ± , e e ± ) of a hydrogen atom from its metastable (2S) state using coplanar geometry. The external laser field is chosen to be single-mode, spatially homogeneous, linearly polarized with laser intensity that is quite high by laboratory standards. The continuum states of the impinging electron (e) or positron (e + ) are represented by plane wave Volkov states, while the wavefunctions for the ejected electron and the scattered electron/positron are chosen to be of Coulomb-Volkov type. The dressed wavefunction for the metastable (2S) hydrogen is constructed in the framework of degenerate perturbation theory. Charge asymmetry is noted in the triple differential cross sections (TDCS) of the two projectiles both in the field-free (FF) and laser-assisted situations. The positron binary peak intensity is much higher than that of the electron, while the reverse is true for the recoil peak. As for the laser modifications, the single-photon TDCS exhibits a distinct four lobed structure in contrast to the FF (two lobed) and is highly suppressed w.r.t. the latter, while the multiphoton TDCS usually tends to approach the FF (with some exceptions), obeying the famous Kroll-Watson (KW) sum rule for both projectiles. For e + impact, the electron capture to the continuum (ECC) effect is also studied (for the symmetric geometry), where enhancement is noted in both the single and multiphoton ECC peaks thereby deviating from the KW sum rules.

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Three dimensional (3D) wave group dynamics of ion acoustic wave is studied in electron–positron–ion (EPI) plasmas incorporating the effects of an external uniform magnetic field through the Laedke–Spatschek equation. In the presence of self-interaction (self-focusing effect), the wave group dynamics is shown to be governed by a (3 + 1) nonlinear Schrödinger equation. The derived nonlinear equations are solved analytically and the solutions predict a wide class of nonlinear structures in EPI plasma in the presence of magnetic field. The boundaries of stable and unstable solutions are also specified in parametric space. The results are expected to provide deeper insights into the ionic processes occurring in both astrophysical and laboratory plasmas.

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