Effective-Lagrangian approach to gamma gamma --> WW; II: Results and comparison with e+e- --> WW

We present a study of anomalous electroweak gauge-boson couplings which can be measured in e+e- and gamma gamma collisions at a future linear collider like ILC. We consider the gauge-boson sector of a locally SU(2) x U(1) invariant effective Lagrangian with ten dimension-six operators added to the Lagrangian of the Standard Model. These operators induce anomalous three- and four-gauge-boson couplings and an anomalous gamma gamma H coupling. We calculate the reachable sensitivity for the measurement of the anomalous couplings in gamma gamma --> WW. We compare these results with the reachable precision in the reaction e+e- --> WW on the one hand and with the bounds that one can get from high-precision observables in Z decays on the other hand. We show that one needs both the e+e- and the gamma gamma modes at an ILC to constrain the largest possible number of anomalous couplings and that the Giga-Z mode offers the best sensitivity for certain anomalous couplings.Comment: 25 pages, 1 figure, 7 tables, comments, references and a table added; to appear in EPJ

Photovoltaic effect in an electrically tunable van der Waals heterojunction

Semiconductor heterostructures form the cornerstone of many electronic and optoelectronic devices and are traditionally fabricated using epitaxial growth techniques. More recently, heterostructures have also been obtained by vertical stacking of two-dimensional crystals, such as graphene and related two- dimensional materials. These layered designer materials are held together by van der Waals forces and contain atomically sharp interfaces. Here, we report on a type- II van der Waals heterojunction made of molybdenum disulfide and tungsten diselenide monolayers. The junction is electrically tunable and under appropriate gate bias, an atomically thin diode is realized. Upon optical illumination, charge transfer occurs across the planar interface and the device exhibits a photovoltaic effect. Advances in large-scale production of two-dimensional crystals could thus lead to a new photovoltaic solar technology.Comment: 26 pages, 14 figures, Nano Letters 201

Infectivity of Cryptosporidium parvum genotype I in conventionally reared piglets and lambs

Parasites of the genus Cryptosporidium are intracellular parasites that occur throughout the animal kingdom and have been reported in many species of mammals, including human. Most infections in humans are caused by two C. parvum genotypes, genotype I and genotype II; these are the human and the bovine (zoonotic) genotypes, respectively. Successful experimental infection of Cryptosporidium parvum genotype I "human genotype" is described in four conventionally reared piglets and in a lamb. The inoculum was originally obtained from two diarrheic children, and the Cryptosporidium genotypes were determined by PCR and rDNA sequencing. The infective dose was between 106 and 2×106oocysts. No clinical signs were observed in the infected animals, except in a piglet that showed watery diarrhea. The oocyst shedding period in positive animals ranged between 4 and 10 days. Histopathologic examination of the gastrointestinal tract of two positive piglets revealed shortening of the villi and denudation of the villous tips of the jejunum. In one piglet, the colon mucosa revealed numerous Cryptosporidium oocysts. The storage time of the inocula (≤3 weeks in PBS at 4°C) and the age of the animal (newborn) were important for the successful induction of infectio

Electroproduction of nucleon resonances

The unitary isobar model MAID has been extended and used for a partial wave analysis of pion photo- and electroproduction in the resonance region W < 2 GeV. Older data from the world data base and more recent experimental results from Mainz, Bates, Bonn and JLab for Q^2 up to 4.0 (GeV/c)^2 have been analyzed and the Q^2 dependence of the helicity amplitudes have been extracted for a series of four star resonances. We compare single-Q^2 analyses with a superglobal fit in a new parametrization of Maid2003 together with predictions of the hypercentral constituent quark model. As a result we find that the helicity amplitudes and transition form factors of constituent quark models should be compared with the analysis of bare resonances, where the pion cloud contributions have been subtracted.Comment: 6 pages Latex including 5 figures, Invited talk at ICTP 4th International Conference on Perspectives in Hadronic Physics, Trieste, Italy, 12-16 May 200

Anomalous gauge-boson couplings and the Higgs-boson mass

We study anomalous gauge-boson couplings induced by a locally SU(2) x U(1) invariant effective Lagrangian containing ten operators of dimension six built from the boson fields of the Standard Model (SM) before spontaneous symmetry breaking (SSB). After SSB some operators lead to new three- and four-gauge-boson interactions, some contribute to the diagonal and off-diagonal kinetic terms of the gauge bosons and to the mass terms of the W and Z bosons. This requires a renormalisation of the gauge-boson fields, which, in turn, modifies the charged- and neutral-current interactions, although none of the additional operators contain fermion fields. Bounds on the anomalous couplings from electroweak precision measurements at LEP and SLD are correlated with the Higgs-boson mass m_H. Rather moderate values of anomalous couplings allow m_H up to 500 GeV. At a future linear collider the triple-gauge-boson couplings gammaWW and ZWW can be measured in the reaction e+e- --> WW. We compare three approaches to anomalous gauge-boson couplings: the form-factor approach, the addition of anomalous coupling terms to the SM Lagrangian after and, as outlined above, before SSB. The translation of the bounds on the couplings from one approach to another is not straightforward. We show that it can be done for the process e+e- --> WW by defining new effective ZWW couplings.Comment: 50 pages, 4 figures; version to appear in EPJ

Separated cross sections in \pi^0 electroproduction at threshold at Q^2 = 0.05 GeV^2/c^2

The differential cross sections \sigma_0=\sigma_T+\epsilon \sigma_L, \sigma_{LT}, and \sigma_{TT} of \pi^0 electroproduction from the proton were measured from threshold up to an additional center of mass energy of 40 MeV, at a value of the photon four-momentum transfer of Q^2= 0.05 GeV^2/c^2 and a center of mass angle of \theta=90^\circ. By an additional out-of-plane measurement with polarized electrons \sigma_{LT'} was determined. This showed for the first time the cusp effect above the \pi^+ threshold in the imaginary part of the s-wave. The predictions of Heavy Baryon Chiral Perturbation Theory are in disagreement with these data. On the other hand, the data are somewhat better predicted by the MAID phenomenological model and are in good agreement with the dynamical model DMT.Comment: 6 pages, 4 figure

Acylpeptide hydrolase: inhibitors and some active site residues of the human enzyme.

Acylpeptide hydrolase may be involved in N-terminal deacetylation of nascent polypeptide chains and of bioactive peptides. The activity of this enzyme from human erythrocytes is sensitive to anions such as chloride, nitrate, and fluoride. Furthermore, blocked amino acids act as competitive inhibitors of the enzyme. Acetyl leucine chloromethyl ketone has been employed to identify one active site residue as His-707. Diisopropylfluorophosphate has been used to identify a second active site residue as Ser-587. Chemical modification studies with a water-soluble carbodiimide implicate a carboxyl group in catalytic activity. These results and the sequence around these active site residues, especially near Ser-587, suggest that acylpeptide hydrolase contains a catalytic triad. The presence of a cysteine residue in the vicinity of the active site is suggested by the inactivation of the enzyme by sulfhydryl-modifying agents and also by a low amount of modification by the peptide chloromethyl ketone inhibitor. Ebelactone A, an inhibitor of the formyl aminopeptidase, the bacterial counterpart of eukaryotic acylpeptide hydrolase, was found to be an effective inhibitor of this enzyme. These findings suggest that acylpeptidase hydrolase is a member of a family of enzymes with extremely diverse functions