Two-Loop O(αt2){\cal O}(\alpha_t^2) Corrections to the Neutral Higgs Boson Masses in the CP-Violating NMSSM

We present our calculation of the two-loop corrections of ${\cal O}(\alpha_t^2)$ to the neutral Higgs boson masses of the CP-violating Next-to-Minimal Supersymmetric extension of the Standard Model (NMSSM). The calculation is performed in the Feynman diagrammatic approach in the gaugeless limit at vanishing external momentum. We apply a mixed $\overline{\mathrm{DR}}$-on-shell (OS) renormalization scheme for the NMSSM input parameters. Furthermore, we exploit a $\overline{\mathrm{DR}}$ as well as an OS renormalization in the top/stop sector. The corrections are implemented in the Fortran code NMSSMCALC for the calculation of the Higgs spectrum both in the CP-conserving and CP-violating NMSSM. The code also provides the Higgs boson decays including the state-of-the-art higher-order corrections. The corrections computed in this work improve the already available corrections in NMSSMCALC which are the full one-loop corrections without any approximation and the two-loop ${\cal O}(\alpha_t \alpha_s)$ corrections in the gaugeless limit and at vanishing external momentum. Depending on the chosen parameter point, we find that the ${\cal O}(\alpha_t \alpha_s + \alpha_t^2)$ corrections add about 4-7% to the one-loop mass of the SM-like Higgs boson for $\overline{\mathrm{DR}}$ renormalization in the top/stop sector and they reduce the mass by about 6-9% if OS renormalization is applied. For an estimate of the theoretical uncertainty we vary the renormalization scale and change the renormalization scheme and show that care has to be taken in the corresponding interpretation

Experimenting from a distance in case of diffraction and interference

Diffraction and interference are basic phenomena of waves. They are treated in wave optics extensively, because experimental setups are easy to built, diffraction patterns are visible and because of their importance for further subjects at school and university (diffraction of X-rays, cristallography, Fourier-Transformation, . . . ). Unfortunately, in many cases the experiments are demonstration experiments with a few diffracting objects and not enough possibilities for the students to participate. Therefore we developed a very flexible Remotely Controlled Laboratory (RCL) about diffraction and interference—a real experiment, which can be performed over the internet. The user can choose from among 5 different wavelengths, about 150 diffracting objects and 3 different techniques of qualitative and quantitative measurement. In this contribution we describe the experimental setup, give an overview about experimental results and end with the added value of the experiment

Higgs-boson masses and mixing matrices in the NMSSM: analysis of on-shell calculations

We analyze the Higgs-boson masses and mixing matrices in the NMSSM based on an on-shell (OS) renormalization of the gauge-boson and Higgs-boson masses and the parameters of the top/scalar top sector. We compare the implementation of the OS calculations in the codes NMSSMCALC and NMSSM-FeynHiggs up to O(αtαs). We identify the sources of discrepancies at the one- and at the twoloop level. Finally we compare the OS and DR evaluation as implemented in NMSSMCALC. The results are important ingredients for an estimate of the theoretical precision of Higgs-boson mass calculations in the NMSSM

Screened-interaction expansion for the Hubbard model and determination of the quantum Monte Carlo Fermi surface

We develop a systematic self-consistent perturbative expansion for the self energy of Hubbard-like models. The interaction lines in the Feynman diagrams are dynamically screened by the charge fluctuations in the system. Although the formal expansion is exact-assuming that the model under the study is perturbative-only if diagrams to all orders are included, it is shown that for large-on-site-Coulomb-repulsion-U systems weak-coupling expansions to a few orders may already converge. We show that the screened interaction for the large-U system can be vanishingly small at a certain intermediate electron filling; and it is found that our approximation for the imaginary part of the one-particle self energy agrees well with the QMC results in the low energy scales at this particular filling. But, the usefulness of the approximation is hindered by the fact that it has the incorrect filling dependence when the filling deviates from this value. We also calculate the exact QMC Fermi surfaces for the two-dimensional (2-D) Hubbard model for several fillings. Our results near half filling show extreme violation of the concepts of the band theory; in fact, instead of growing, Fermi surface vanishes when doped toward the half-filled Mott-Hubbard insulator. Sufficiently away from half filling, noninteracting-like Fermi surfaces are recovered. These results combined with the Luttinger theorem might show that diagrammatic expansions for the nearly-half-filled Hubbard model are unlikely to be possible; however, the nonperturbative part of the solution seems to be less important as the filling gradually moves away from one half. Results for the 2-D one-band Hubbard model for several hole dopings are presented. Implications of this study for the high-temperature superconductors are also discussed.Comment: 11 pages, 12 eps figures embedded, REVTeX, submitted to Phys. Rev. B; (v2) minor revisions, scheduled for publication on November 1

Temperature dependent band structure of the Kondo insulator

We present a Qantum Monte Carlo (QMC) study of the temperature dependent dynamics of the Kondo insulator. Working at the so-called symmetrical point allows to perform minus-sign free QMC simulations and thus reach temperatures of less than 1% of the conduction electron bandwidth. Study of the temperature dependence of the single particle Green's function and dynamical spin correlation function shows a surprisingly intricate low temperature band structure and gives evidence for two characteristic temperatures, which we identify with the Kondo and coherence temperature, respectively. In particular, the data show a temperature induced metal-insulator transition at the coherence temperature.Comment: RevTex-file, 4 PRB pages with 4 eps figures. Hardcopies of figures (or the entire manuscript) can be obtained by e-mail request to: [email protected]

Kink Structure in the Quasiparticle Band of Doped Hubbard Systems

By making use of the self-consistent projection operator method with high-momentum and high-energy resolutions, we find a kink structure in the quasiparticle excitation spectrum of the two-dimensional Hubbard model in the underdoped regime. The kink is caused by a mixing between the quasiparticle state and excitations with short-range antiferromagnetic order. We suggest that this might be the origin of the strong concentration dependence of the 'kink' found in La_{2-x}Sr_{x}CuO_{4} (x=0.03-0.07).Comment: 3 pages, 4 figures. to be published in J. Phys. Soc. Jpn., Vol. 74, No. 9, September 15, 200

Kondo screening and exhaustion in the periodic Anderson model

We investigate the paramagnetic periodic Anderson model using the dynamical mean-field theory in combination with the modified perturbation theory which interpolates between the weak and strong coupling limits. For the symmetric PAM, the ground state is always a singlet state. However, as function of the hybridization strength, a crossover from collective to local Kondo screening is found. Reducing the number of conduction electrons, the local Kondo singlets remain stable. The unpaired f-electrons dominate the physics of the system. For very low conduction electron densities, a large increase of the effective mass of the quasiparticles is visible, which is interpreted as the approach of the Mott-Hubbard transition.Comment: 10 pages, 8 figures, accepted by Phys. Rev.