Chargino Production and Decay in Photon-Photon-Collisions

We study the production and leptonic decay of charginos in collisions of polarized photon beams including the complete spin correlations. The photons can be generated by Compton backscattering of polarized laser pulses off a polarized electron beam. Since the production process is determined alone by the electromagnetic coupling of the charginos this process allows to study their decay dynamics. The cross section and the forward-backward asymmetry of the decay lepton are very sensitive to the gaugino mass parameter $M_1$ and to the sneutrino mass without any ambiguities.Comment: 9 pages, 6 figures, LaTeX, Talk presented at the International Workshop on High Energy Photon Collider

The GW space-time method for the self-energy of large systems

We present a detailed account of the GW space-time method. The method increases the size of systems whose electronic structure can be studied with a computational implementation of Hedin's GW approximation. At the heart of the method is a representation of the Green function G and the screened Coulomb interaction W in the real-space and imaginary-time domain, which allows a more efficient computation of the self-energy approximation Sigma = iGW. For intermediate steps we freely change between representations in real and reciprocal space on the one hand, and imaginary time and imaginary energy on the other, using fast Fourier transforms. The power of the method is demonstrated using the example of Si with artificially increased unit cell sizes. (C) 1999 Elsevier Science B.V

Probing CP Violation with and without Momentum Reconstruction at the LHC

We study the potential to observe CP-violating effects in SUSY cascade decay chains at the LHC. We consider squark and gluino production followed by subsequent decays into neutralinos with a three-body leptonic decay in the final step. Asymmetries composed by triple products of momenta of the final state particles are sensitive to CP-violating effects. Due to large boosts these asymmetries can be difficult to observe at a hadron collider. We show that using all available kinematic information one can reconstruct the decay chains on an event-by-event basis even in the case of 3-body decays, neutrinos and LSPs in the final state. We also discuss the most important experimental effects like major backgrounds and momentum smearing due to finite detector resolution. We show that with 300 fb$^{-1}$ of collected data, CP violation may be discovered at the LHC for a wide range of the phase of the bino mass parameter $M_1$.Comment: Version accepted for publication in JHEP. Clarifications added on the assumptions used for plots. New references adde

The long-wavelength behaviour of the exchange-correlation kernel in the Kohn-Sham theory of periodic systems

The polarization-dependence of the exchange-correlation (XC) energy functional of periodic insulators within Kohn-Sham (KS) density-functional theory requires a ${\cal O} (1/q^2)$ divergence in the XC kernel for small vectors q. This behaviour, exemplified for a one-dimensional model semiconductor, is also observed when an insulator happens to be described as a KS metal, or vice-versa. Although it can occur in the exchange-only kernel, it is not found in the usual local, semi-local or even non-local approximations to KS theory. We also show that the test-charge and electronic definitions of the macroscopic dielectric constant differ from one another in exact KS theory, but are equivalent in the above-mentioned approximations

CP Phases in Correlated Production and Decay of Neutralinos in the Minimal Supersymmetric Standard Model

We investigate the associated production of neutralinos $e^+e^-\to\tilde{\chi}^0_1\tilde{\chi}^0_2$ accompanied by the neutralino leptonic decay $\tilde{\chi}^0_2\to\tilde{\chi}^0_1 \ell^+\ell^-$, taking into account initial beam polarization and production-decay spin correlations in the minimal supersymmetric standard model with general CP phases but without generational mixing in the slepton sector. The stringent constraints from the electron EDM on the CP phases are also included in the discussion. Initial beam polarizations lead to three CP--even distributions and one CP--odd distribution, which can be studied independently of the details of the neutralino decays. We find that the production cross section and the branching fractions of the leptonic neutralino decays are very sensitive to the CP phases. In addition, the production--decay spin correlations lead to several CP--even observables such as lepton invariant mass distribution, and lepton angular distribution, and one interesting T--odd (CP--odd) triple product of the initial electron momentum and two final lepton momenta, the size of which might be large enough to be measured at the high--luminosity future electron--positron collider or can play a complementary role in constraining the CP phases with the EDM constraints.Comment: Revtex, 37 pages, 12 eps figure

Decays of the MSSM Higgs Bosons with Explicit CP Violation

We study Higgs boson decays in the minimal supersymmetric standard model where the tree-level CP invariance of the Higgs potential is explicitly broken by loop effects of soft CP-violating Yukawa interactions related to scalar quarks of the third generation. The scalar-pseudoscalar mixing among two neutral CP-even Higgs bosons and one CP-odd Higgs boson due to explicit CP violation modifies their tree-level couplings to fermions, to the W^\pm and Z bosons and to Higgs bosons themselves significantly. We analyze the phenomenological impact of explicit CP violation on the branching ratios of the neutral Higgs boson decays in detail and discuss how to directly confirm the existence of explicit CP violation through \tau^+ \tau^- and t \bar{t} spin correlations in the decays of the neutral Higgs bosons into a tau-lepton pair and a top-quark pair.Comment: 28 pages, 10 figures, some references added and correcte