117,739 research outputs found
NEW CLASS OF RESONANCE IN THE E+H+ SCATTERING IN AN EXCIMER LASER FIELD
No full textDIMOU L, Faisal F. NEW CLASS OF RESONANCE IN THE E+H+ SCATTERING IN AN EXCIMER LASER FIELD. PHYSICAL REVIEW LETTERS. 1987;59(8):872-875
LINE NARROWING IN A H ATOM IN INTENSE LASER FIELDS AT SUBTHRESHOLD AND ABOVE-THRESHOLD FREQUENCIES
No full textDIMOU L, Faisal F. LINE NARROWING IN A H ATOM IN INTENSE LASER FIELDS AT SUBTHRESHOLD AND ABOVE-THRESHOLD FREQUENCIES. PHYSICS LETTERS A. 1992;171(3-4):211-214.Line widths due to ionization decay of a H atom in intense laser fields are investigated by solving the (3 + 1)-D Schrodinger equation numerically exactly. Quantitative results for line narrowing both at sub-threshold and above-threshold frequencies are given and a mechanism for the appearance of minima in the line widths is discussed
DECAY OF METASTABLE H-ATOMS IN INTENSE EXCIMER LASERS
No full textDIMOU L, Faisal F. DECAY OF METASTABLE H-ATOMS IN INTENSE EXCIMER LASERS. PHYSICAL REVIEW A. 1992;46(7):4442-4444.Decay widths of metastable hydrogen atoms subjected to the intense field of the currently available KrF* laser (lambda = 248 nm) and ArF* laser (lambda = 193 nm) are calculated by solving the full (3+1)-dimensional Schrodinger equation in the space-translated frame of reference. The critical intensities, above which the suppression of ionization decay sets in, are found to be I(c) congruent to 2.5 x 10(14) and 7 x 10(14) W/cm2 for lambda = 248 and 193 nm, respectively
Flavour predictions in the Standard Model and beyond
No full textThis thesis reports on two projects concerning flavour physics. In the first project it is shown how approximate Minimal Flavour Violation (MFV) can emerge from an SU(5) Supersymmetric Grand Unified Theory (SUSY GUT) supplemented by an S4 x U(1) family symmetry, which provides a good description of all quark and lepton (including neutrino) masses, mixings and CP violation. Assuming a SUSY breaking mechanism which respects the family symmetry, the low energy mass insertion parameters are calculated in full explicit detail in the super-CKM basis, including the effects of canonical normalisation and renormalisation group running. It is found that the very simple family symmetry S4 x U(1) is sufficient to approximately reproduce the effects of low energy MFV where required but there is also a suggestion of testable new physics. Numerical estimates of the low energy mass insertion parameters are presented for well-defined ranges of SUSY parameters and the naive model expectations are compared to the numerical scans and the experimental bounds. The results are then used to estimate the predictions for Electric Dipole Moments (EDMs), Lepton Flavour Violation (LFV), B and K meson mixing as well as rare B decays. The largest observable deviations from MFV come from the LFV process μ → eγ and the EDMs.In the second project, matrix elements of the chromomagnetic operator, often denoted by O8, between B/D-states and light mesons plus an off-shell photon are calculated, by employing the method of light-cone sum rules (LCSR) at leading twist 2. These matrix elements are relevant for flavour changing transition processes, such as B → K*l+l- and they can be seen as the analogues of the well-known penguin form factors T1;2;3 and fT . A large CP-even phase is found, for which a long-distance (LD) interpretation is given. Results are compared to QCD factorisation (QCDF), for which the spectator photon emission is end-point divergent. The analytic structure of the correlation function used in the LCSR method, admits a complex anomalous threshold on the physical sheet, the meaning and handling of which is discussed
Reply to Comment on 'Differential cross sections of low-energy electron-hydrogen scattering in a CO2-laser field'
No full textCionga A, Dimou L, Faisal F. Reply to Comment on 'Differential cross sections of low-energy electron-hydrogen scattering in a CO2-laser field'. JOURNAL OF PHYSICS B-ATOMIC MOLECULAR AND OPTICAL PHYSICS. 1998;31(7):1629-1630.The long-range asymptotic behaviour of the interaction potential is of crucial significance for low-energy laser-assisted electron-atom scattering for emission/absorption of one or more photons, especially for the small scattering angles; this is not satisfied by the ansatz of the comment by Rabadan and co-workers, equation (9)
The Radiative Close Coupling Theory and Its Application to Ionization; Scattering in Intense Laser Fields
No full textDimou L, Faisal F. The Radiative Close Coupling Theory and Its Application to Ionization; Scattering in Intense Laser Fields. LASER PHYSICS. 1993;3(2):440-448.In this paper we describe the recently developed fully nonperturbative radiative close coupling theory of laser-atom interaction and illustrate it in terms of the solution of the (3 + 1)-dimensional Schrodinger problem for strong field ionization of the H-atom and the related problem of stimulated bremsstrahlung processes in intense laser fields. Numerical results are presented for the probability of ionization of the ground state as well as of the metastable excited state for both sub-threshold and above-threshold frequencies over a wide range of intensities (including those of the currently available powerful KrF* and ArF* lasers). Multiphoton stimulated bremsstrahlung cross sections are given for the electron-proton (e(-) + p(+))-scattering system as functions of the incident electron energy. Modification of the Rutherford scattering due to interaction with the laser field is demonstrated. The phenomenon of "capture-escape" Rydberg resonance, which is found numerically, is illustrated for several different laser frequencies and intensities. These resonances are directly relevant for the charge conjugated positron-antiproton (e(+) + p(-))-system in a laser field, and can provide an efficient process of generation of anti-matter by laser induced capture of a positron by an antiproton in high energy parallel-beam experiments in particle accelerators
AB-INITIO RESULTS OF ADIABATIC STABILITY OF THE HYDROGEN-ATOM
No full textDIMOU L, Faisal F. AB-INITIO RESULTS OF ADIABATIC STABILITY OF THE HYDROGEN-ATOM. PHYSICAL REVIEW A. 1994;49(6):4564-4569.The Schrodinger equation of the hydrogen atom in an intense monochromatic radiation field is solved numerically exactly by applying the Floquet close-coupling method. Intensity dependence of the rates of ionization in the region of adiabatic stability is determined. Their dependence on the principal quantum number, on the angular momentum, and on the magnetic quantum number is investigated at lambda = 1064, 620, and 248 nm. The calculated critical parameters show good agreement with the independent calculations of Potvliege and Smith [Phys. Rev. A 48, R46 (1993)]; those for the hydrogenic 5g circular state are consistent with the results of the first observation of stability in the Ne atom by de Boer et al. [Phys. Rev. Lett. 71, 3263 (1993)]. In connection with the ongoing experiments in the H atom, these parameters and the calculated ionization rates in the stability region can provide stringent quantitative tests of the basic Floquet ansatz, which underlies a wide class of ab initio theories of matter-light interaction
Exclusive chromomagnetism in heavy-to-light FCNCs
No full textWe compute matrix elements of the chromomagnetic operator, often denoted by O 8 , between B/D states and light mesons plus an off-shell photon by employing the method of light-cone sum rules at leading twist-2. These matrix elements are relevant for processes such as B?K ? l + l ? and they can be seen as the analogues of the well-known penguin form factors T 1,2,3 and f T . We find a large CP -even phase for which we give a long-distance interpretation. We compare our results to QCD factorization for which the spectator photon emission is end-point divergent. The analytic structure of the correlation function used in our method admits a complex anomalous threshold on the physical sheet. The meaning and handling within the sum rule approach of the anomalous threshold is discussed
NONPERTURBATIVE DYNAMICS OF ATOMS IN STRONG LASER FIELDS - ADIABATIC STABILITY OF HYDROGEN-ATOM
No full textFaisal F, DIMOU L. NONPERTURBATIVE DYNAMICS OF ATOMS IN STRONG LASER FIELDS - ADIABATIC STABILITY OF HYDROGEN-ATOM. In: Acta Physica Polonica A. ACTA PHYSICA POLONICA A. Vol 86. POLISH ACAD SCIENCES INST PHYSICS; 1994: 201-211.Recent investigations of laser-atom interaction at high intensities have led to the discovery of several unexpected phenomena, and their studies have deepened our understanding of non-perturbative dynamics of quantum systems subjected to unusually strong radiation fields. For the analysis and interpretation of these phenomena. We have developed an ab initio non-perturbative method, the Floquet close-coupling method, and applied it to analyse the highly non-perturbative problem of adiabatic stability of hydrogen atom. Ab initio rates of ionization as a function of the laser intensity for the excited circular states as well as related non-circular states are obtained. Our quantitatively accurate results clearly show that the predictions of the previous approximate theories such as the well-known ''high-frequency'' theory are qualitatively similar but differ quantitatively. The analysis of the dependence of adiabatic stability on the principal quantum number, the angular momentum, as well as on the magnetic quantum number for the Rydberg states are complemented by investigations of the behavior of the ground state for frequencies below the ionization threshold. In the latter situation we found the existence of stability windows within which the ionization probability decreases with increasing intensity but outside of which the atom becomes more unstable. It is shown here that the mechanism for the occurrence of stability windows is the self-tuned anti-resonance at specific intensities
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