15 research outputs found
Implementing invariant mass cuts and finite lifetime effects in top-antitop production at threshold
The effects of the finite top quark width in the top pair production cross
section close to the threshold are discussed in this talk. We introduce a
cross section with a cut on the invariant masses of the top and
antitop that can be calculated theoretically with effective field theory (EFT)
methods. The matching procedure to implement the physical phase-space
boundaries in the NRQCD framework (``phase-space matching'') is briefly
outlined.Comment: 4 pages, 4 figures. Talk given at the 14th International QCD
Conference (Montpellier 7-12th July 2008
Structure of the Membrane Anchor of Pestivirus Glycoprotein Erns, a Long Tilted Amphipathic Helix
Erns is an essential virion glycoprotein with RNase activity that suppresses host cellular innate immune responses upon being partially secreted from the infected cells. Its unusual C-terminus plays multiple roles, as the amphiphilic helix acts as a membrane anchor, as a signal peptidase cleavage site, and as a retention/secretion signal. We analyzed the structure and membrane binding properties of this sequence to gain a better understanding of the underlying mechanisms. CD spectroscopy in different setups, as well as Monte Carlo and molecular dynamics simulations confirmed the helical folding and showed that the helix is accommodated in the amphiphilic region of the lipid bilayer with a slight tilt rather than lying parallel to the surface. This model was confirmed by NMR analyses that also identified a central stretch of 15 residues within the helix that is fully shielded from the aqueous layer, which is C-terminally followed by a putative hairpin structure. These findings explain the strong membrane binding of the protein and provide clues to establishing the Erns membrane contact, processing and secretion
O(alpha_s^2) corrections to fermionic Higgs decays in the MSSM
We compute the two-loop corrections of O(alpha_s^2) to the Yukawa couplings
in the framework of the Minimal Supersymmetric Standard Model (MSSM). The
calculation is performed using the effective Lagrangian approach under the
approximation of neglecting the Higgs boson mass with respect to the top quark,
gluino and all squark flavour masses. As an application we derive the
O(alpha_s^2) corrections to the partial decay width of the lightest Higgs boson
to a bottom quark pair. We find that the two-loop corrections are sizable for
large values of tan_beta and low CP-odd Higgs boson mass. With our calculation
of the O(alpha_s^2) corrections the remaining theoretical uncertainties reduce
below a few percent.Comment: 22 pages, 10 figure