Probing Form Factors in Top Quark Pair Production at e−e+e^-e^+ Colliders

We describe how to probe new physics through large CP violation effects and non--standard Z-t-t couplings via the scattering process e^-e^+ -> t tbar. [Talk presented at the Workshop on Physics and Experiments with Linear $e^+e^-$ Colliders, Waikoloa, Hawaii, 26-30 April 1993.]Comment: 4 pages, TeXsis, MSUTH 93/0

Electron tomography of late stages of FcRn-mediated antibody transcytosis in neonatal rat small intestine

The neonatal Fc receptor (FcRn) transports maternal immunoglobulin (IgG) across epithelia to confer passive immunity to mammalian young. In newborn rodents, FcRn transcytoses IgG from ingested milk across the intestinal epithelium for release into the bloodstream. We used electron tomography to examine FcRn transport of Nanogold-labeled Fc (Au-Fc) in neonatal rat jejunum, focusing on later aspects of transport by chasing Au-Fc before fixation. We observed pools of Au-Fc in dilated regions of the lateral intercellular space (LIS), likely representing exit sites where Au-Fc accumulates en route to the blood. Before weaning, the jejunum functions primarily in IgG transport and exhibits unusual properties: clathrin-rich regions near/at the basolateral LIS and multivesicular bodies (MVBs) expressing early endosomal markers. To address whether these features are related to IgG transport, we examined LIS and endocytic/transcytotic structures from neonatal and weaned animals. Weaned samples showed less LIS-associated clathrin. MVBs labeled with late endosomal/lysosomal markers were smaller than their neonatal counterparts but contained 10 times more internal compartments. These results are consistent with hypotheses that clathrin-rich basolateral regions in neonatal jejunum are involved in IgG exocytosis and that MVBs function in IgG transport while FcRn is expressed but switch to degradative functions after weaning, when the jejunum does not express FcRn or transport IgG

Low mass lepton pair production in hadron collisions

The hadroproduction of lepton pairs with mass $Q$ and transverse momentum $Q_T$ can be described in perturbative QCD by the same partonic subprocesses as prompt photon production. We demonstrate that, like prompt photon production, lepton pair production is dominated by quark-gluon scattering in the region $Q_T>Q/2$. This leads to sensitivity to the gluon density in kinematical regimes that are accessible both at collider and fixed target experiments while eliminating the theoretical and experimental uncertainties present in prompt photon production.Comment: Talk given by M. Klasen at the International Conference on the Structure and Interactions of the Photon, PHOTON 99, Freiburg i. Brsg., Germany, May 23-27, 1999. To be published in the proceedings. 6 pages, 6 postscript figure

Multiscale imaging of HIV-1 transmission in humanized mice

HIV transmission within lymphoid tissues remains incompletely characterized at the level of individual cells and virions. Here we visually describe our approach to understanding HIV-1 dissemination at different levels of volume and resolution within lymphoid tissues from HIV-1-infected humanized mice. We combined tissue clearing techniques, immunostaining, and light sheet fluorescence microscopy to visualize large-volumes of intact tissue with single-cell resolution from HIV-1-infected humanized mice. In parallel, we imaged adjacent regions of tissue using electron microscopy and electron tomography to gain 3D ultrastructural information about the same tissue samples. This approach can provide spatial information about the density and distribution of target cells, HIV-1-infected cells, and individual budding and free-virions within lymphoid tissues. Multiscale imaging of HIV-1 infected tissues from humanized mice can provide insight into the biological mechanisms of HIV-1 transmission through the correlation of global pathology with structural details and these methods are directly translatable to other animal models and human clinical samples

Production of Two Photons and a Jet Through Gluon Fusion

We have computed the cross-section and distributions for the production of two photons and a jet via the process $g g \to \gamma\gamma g$. In the Standard Model, this process occurs at the one-loop level through pentagon and box diagrams. We show that at the LHC this is a significant mechanism for the production of the two photons and a jet. This process is also an important background to the Higgs boson production, when the Higgs boson decays into two photons. We also explorethis process at the Tevatron