1,037 research outputs found
Low-temperature magnetic circular dichroism studies of native laccase: spectroscopic evidence for exogenous ligand bridging at a trinuclear copper active site.
Top quark associated production of topcolor pions at hadron colliders
We investigate the associated production of a neutral physical pion with top
quarks in the context of topcolor assisted technicolor. We find that single-top
associated production does not yield viable rates at either the Tevatron or
LHC. tt-associated production at the Tevatron is suppressed relative to
Standard Model ttH, but at the LHC is strongly enhanced and would allow for
easy observation of the main decay channels to bottom quarks, and possible
observation of the decay to gluons.Comment: 13 pages, 4 figures, submitted to PR
Alterations in gene expression in T1α null lung: a model of deficient alveolar sac development
BACKGROUND: Development of lung alveolar sacs of normal structure and size at late gestation is necessary for the gas exchange process that sustains respiration at birth. Mice lacking the lung differentiation gene T1α [T1α(-/-)] fail to form expanded alveolar sacs, resulting in respiratory failure at birth. Since little is known about the molecular pathways driving alveolar sacculation, we used expression microarrays to identify genes altered in the abnormal lungs and, by inference, may play roles in normal lung morphogenesis. RESULTS: Altered expression of genes related to cell-cell interaction, such as ephrinA3, are observed in T1α(-/-) at E18.5. At term, FosB, Egr1, MPK-1 and Nur77, which can function as negative regulators of the cell-cycle, are down-regulated. This is consistent with the hyperproliferation of peripheral lung cells in term T1α (-/-) lungs reported earlier. Biochemical assays show that neither PCNA nor p21 are altered at E18.5. At term in contrast, PCNA is increased, and p21 is decreased. CONCLUSION: This global analysis has identified a number of candidate genes that are significantly altered in lungs in which sacculation is abnormal. Many genes identified were not previously associated with lung development and may participate in formation of alveolar sacs prenatally
Formation of microtubule-based traps controls the sorting and concentration of vesicles to restricted sites of regenerating neurons after axotomy
Transformation of a transected axonal tip into a growth cone (GC) is a critical step in the cascade leading to neuronal regeneration. Critical to the regrowth is the supply and concentration of vesicles at restricted sites along the cut axon. The mechanisms underlying these processes are largely unknown. Using online confocal imaging of transected, cultured Aplysia californica neurons, we report that axotomy leads to reorientation of the microtubule (MT) polarities and formation of two distinct MT-based vesicle traps at the cut axonal end. Approximately 100 ÎĽm proximal to the cut end, a selective trap for anterogradely transported vesicles is formed, which is the plus end trap. Distally, a minus end trap is formed that exclusively captures retrogradely transported vesicles. The concentration of anterogradely transported vesicles in the former trap optimizes the formation of a GC after axotomy
Neutral Higgs-Boson Pair Production at Hadron Colliders: QCD Corrections
Neutral Higgs-boson pair production provides the possibility of studying the
trilinear Higgs couplings at future high-energy colliders. We present the QCD
corrections to the gluon-initiated processes in the limit of a heavy top quark
in the loops and the Drell-Yan-like pair production of scalar and pseudoscalar
Higgs particles. The pp cross sections are discussed for LHC energies within
the Standard Model and its minimal supersymmetric extension. The QCD
corrections are large, enhancing the total cross sections significantly.Comment: 26 pages, latex, 9 ps figure
MSSM Higgs Boson Production via Gluon Fusion: The Large Gluino Mass Limit
Scalar MSSM Higgs boson production via gluon fusion gg -> h,H is mediated by
heavy quark and squark loops. The higher order QCD corrections to these
processes turn out to be large. The full supersymmetric QCD corrections have
been calculated recently. In the limit of large SUSY masses a conceptual
problem appears, i.e. the proper treatment of the large gluino mass limit. In
this work we will describe the consistent decoupling of heavy gluino effects
and derive the effective Lagrangian for decoupled gluinos.Comment: 11 pages, 3 figures, latex, references added, slight rewording,
version accepted by JHE
Scalar Particle Contribution to Higgs Production via Gluon Fusion at NLO
We consider the gluon fusion production cross section of a scalar Higgs boson
in models where fermion and scalar massive colored particles are present. We
report analytic expressions for the matrix elements of , , and processes completing the calculation of the NLO QCD
corrections in these extended scenarios. The formulas are written in a complete
general case, allowing a flexible use for different theoretical models.
Applications of our results to two different models are presented: i) a model
in which the SM Higgs sector is augmented by a weak doublet scalar in the
adjoint representation. ii) The MSSM, in the limit of neglecting the
gluino contribution to the cross section.Comment: 20 pages, 5 figures. Minor changes. Refs. adde
Standard Model Higgs-Boson Branching Ratios with Uncertainties
We present an update of the branching ratios for Higgs-boson decays in the
Standard Model. We list results for all relevant branching ratios together with
corresponding uncertainties resulting from input parameters and missing
higher-order corrections. As sources of parametric uncertainties we include the
masses of the charm, bottom, and top quarks as well as the QCD coupling
constant. We compare our results with other predictions in the literature.Comment: 32 pages, 4 figures, contribution to LHC Higgs Cross Section Working
Group https://twiki.cern.ch/twiki/bin/view/LHCPhysics/CrossSections,
theoretical uncertainties for H->\mu\mu{} added, version to appear in
European Physical Journal
Rompimiento de la Simetria Electrodebil y la Fisica del Higgs: Conceptos Basicos
Presentamos una introduccion a los conceptos basicos del rompimiento de la
simetria electrodebil y la fisica del Higgs dentro del Modelo Estandar y sus
extensiones supersimetricas. Se presenta tambien una breve perspectiva general
de mecanismos alternativos del rompimiento de la simetria. Ademas de las bases
teoricas, se discute el estado actual de la fisica experimental del Higgs y sus
implicaciones para futuros experimentos en el LHC y en colisionadores lineales
e+e-.Comment: Spanish text, including full English translation. Published in the
Proceedings of the XI Mexican School on Particles and Fields, Xalapa,
Veracruz, Mexic
W^+- H^-+ Associated Production at the Large Hadron Collider
We study the production of a charged Higgs boson in association with a W
boson at the CERN Large Hadron Collider in the context of the minimal
supersymmetric extension of the standard model. This production mechanism is
particularly promising if the charged Higgs boson is too heavy to be generated
by top-quark decay. We compare the contributions due to b b-bar annihilation at
the tree level and gg fusion, which proceeds at one loop. Apart from the total
cross section, we also consider distributions in transverse momentum and
rapidity. We also assess the viability of W^+- H^-+ associated production at
the Fermilab Tevatron after the installation of the Main Injector and the
Recycler.Comment: 16 pages (Latex), 8 figures (Postscript
- …