Relativistic mask method for electron momentum distributions after ionization of hydrogen-like ions in strong laser fields

Wavefunction-splitting or mask method, widely used in the non-relativistic calculations of the photoelectron angular distributions, is extended to the relativistic domain within the dipole approximation. Since the closed-form expressions for the relativistic Volkov states are not available within the dipole approximation, we build such states numerically solving a single second-order differential equation. We calculate the photoelectron energy spectra and angular distributions for highly charged ions under different ionization regimes with both the direct and the relativistic mask methods. We show that the relativistic mask method works very well and reproduces the electron energy and angular distributions calculated by the direct method in the energy range where both methods can be used. On the other hand, the relativistic mask method can be applied for longer laser pulses and/or higher photoelectron energies where the direct method may have difficulties

Theory of high-order harmonic generation from molecules by intense laser pulses

We show that high-order harmonics generated from molecules by intense laser pulses can be expressed as the product of a returning electron wave packet and the photo-recombination cross section (PRCS) where the electron wave packet can be obtained from simple strong-field approximation (SFA) or from a companion atomic target. Using these wave packets but replacing the PRCS obtained from SFA or from the atomic target by the accurate PRCS from molecules, the resulting HHG spectra are shown to agree well with the benchmark results from direct numerical solution of the time-dependent Schr\"odinger equation, for the case of H$_2^+$ in laser fields. The result illustrates that these powerful theoretical tools can be used for obtaining high-order harmonic spectra from molecules. More importantly, the results imply that the PRCS extracted from laser-induced HHG spectra can be used for time-resolved dynamic chemical imaging of transient molecules with temporal resolutions down to a few femtoseconds.Comment: 10 pages, 5 figure

Gold-plated processes at photon colliders

We review the most important topics and objectives of the physics program of the gamma-gamma, gamma-electron collider (photon collider) option for an e+e- linear collider.Comment: 36 pages, Latex, 11 figures(ps,eps), Talk at Intern. Workshop on High Energy Photon Colliders; June 14-17, 2000, DESY, Hamburg, Germany; to be published in Nucl. Instr. and Methods

Sfermion Pair Production in Polarized and Unpolarized γγ\gamma\gamma Collisions

We calculate total and differential cross sections for the production of sfermion pairs in photon-photon collisions, including contributions from resolved photons and arbitrary photon polarization. Sfermion production in photon collisions depends only on the sfermion mass and charge. It is thus independent of the details of the SUSY breaking mechanism, but highly sensitive to the sfermion charge. We compare the total cross sections for bremsstrahlung, beamstrahlung, and laser backscattering photons to those in $e^+e^-$ annihilation. We find that the total cross section at a polarized photon collider is larger than the $e^+e^-$ annihilation cross section up to the kinematic limit of the photon collider.Comment: 19 pages, Latex, 18 (e)ps-figure

The processes e−e+→γγ,Zγ,ZZe^-e^+\to\gamma\gamma, Z \gamma, ZZ in SM and MSSM

We present the results of a complete analysis of the one loop electroweak corrections to $e^-e^+\to\gamma\gamma, ~Z\gamma, ~ZZ$ in the Standard (SM) and the Minimal Supersymmetric Standard Model (MSSM). A special emphasis is put on the high energy behaviour of the various helicity amplitudes and the way the logarithmic structure is generated. The large magnitude of these effects, which induce striking differences between the SM and MSSM cases at high energies, offers the possibility of making global tests which could check the consistency of these models, and even decide whether any additional new physics is required.Comment: Short version (16 pages and 9 figures) of the paper hep-ph/0207273, to appear in Phy.Rev.D. e-mail: [email protected]

Time evolution of non-Hermitian Hamiltonian systems

We provide time-evolution operators, gauge transformations and a perturbative treatment for non-Hermitian Hamiltonian systems, which are explicitly time-dependent. We determine various new equivalence pairs for Hermitian and non-Hermitian Hamiltonians, which are therefore pseudo-Hermitian and in addition in some cases also invariant under PT-symmetry. In particular, for the harmonic oscillator perturbed by a cubic non-Hermitian term, we evaluate explicitly various transition amplitudes, for the situation when these systems are exposed to a monochromatic linearly polarized electric field.Comment: 25 pages Latex, 1 eps figure, references adde

Backward scattering of low-energy antiprotons by highly charged and neutral uranium: Coulomb glory

Collisions of antiprotons with He-, Ne-, Ni-like, bare, and neutral uranium are studied theoretically for scattering angles close to 180$^{\circ}$ and antiproton energies with the interval 100 eV -- 10 keV. We investigate the Coulomb glory effect which is caused by a screening of the Coulomb potential of the nucleus and results in a prominent maximum of the differential cross section in the backward direction at some energies of the incident particle. We found that for larger numbers of electrons in the ion the effect becomes more pronounced and shifts to higher energies of the antiproton. On the other hand, a maximum of the differential cross section in the backward direction can also be found in the scattering of antiprotons on a bare uranium nucleus. The latter case can be regarded as a manifestation of the screening property of the vacuum-polarization potential in non-relativistic collisions of heavy particles.Comment: 14 pages, 5 figure

Hadronic Cross-sections in two photon Processes at a Future Linear Collider

In this note we address the issue of measurability of the hadronic cross-sections at a future photon collider as well as for the two-photon processes at a future high energy linear $e^+e^-$ collider. We extend, to higher energy, our previous estimates of the accuracy with which the \gamgam\ cross-section needs to be measured, in order to distinguish between different theoretical models of energy dependence of the total cross-sections. We show that the necessary precision to discriminate among these models is indeed possible at future linear colliders in the Photon Collider option. Further we note that even in the $e^+e^-$ option a measurement of the hadron production cross-section via \gamgam processes, with an accuracy necessary to allow discrimination between different theoretical models, should be possible. We also comment briefly on the implications of these predictions for hadronic backgrounds at the future TeV energy $e^+e^-$ collider CLIC.Comment: 20 pages, 5 figures, LaTeX. Added an acknowledgemen

The WW Boson Loop Background to H -> ZZ at Photon-photon Colliders

We have performed a complete one-loop calculation of $\gamma \gamma \rightarrow ZZ$ in the Standard Model, including both gauge bosons and fermions in the loop. We confirm the large irreducible continuum background from the $W$-boson loop found by Jikia. We have included the photon-photon luminosity, and find that the continuum background of transverse $Z$ boson pairs prohibits finding a heavy Higgs with mass \gtap 350 GeV in this decay mode.Comment: 16 pages + 4 PS figures included (uuencoded), MAD/PH/77