Isolated lepton events at HERA: SUSY R-parity violation?

Events with an isolated high p_T lepton, a hadron jet and missing energy as observed in the H1 experiment at HERA, are potentially associated with R-parity violation in supersymmetric theories. However, stringent kinematic constraints must be fulfilled if the production of supersymmetric particles in R-parity violating scenarios were the correct path for explaining these puzzling events. A reference point ℝ/   is specified for which these constraints are illustrated and implications of the supersymmetric interpretation for new classes of multi-lepton events are indicated.     

Perquinolines A–C: Unprecedented Bacterial Tetrahydroisoquinolines Involving an Intriguing Biosynthesis

Metabolic profiling of Streptomyces sp. IB2014/016‐6 led to the identification of three new tetrahydroisoquinoline natural products, perquinolines A–C ( 1 – 3 ). Labelled precursor feeding studies and the cloning of the pqr biosynthetic gene cluster revealed that 1 – 3 are assembled by the action of several unusual enzymes. The biosynthesis starts with the condensation of succinyl‐CoA and l ‐phenylalanine catalyzed by the amino‐7‐oxononanoate synthase‐like enzyme PqrA, representing rare chemistry in natural product assembly. The second condensation and cyclization events are conducted by PqrG, an enzyme resembling an acyl‐CoA ligase. Last, ATP‐grasp RimK‐type ligase PqrI completes the biosynthesis by transferring a γ‐aminobutyric acid or β‐alanine moiety. The discovered pathway represents a new route for assembling the tetrahydroisoquinoline cores of natural products.     

On the Sign of Solutions of Systems of Ordinary Differential Equations

We show that Theorems 1 and 3 in A. G. Gritsai's paper Monotonicity properties of solutions of systems of nonlinear differential equations published in the collection of works Approximate and Qualitative Methods in the Theory of Differential and Functional Differential-Equations (Institute of Mathematics, Ukrainian Academy of Sciences, Kiev, 1979) are not true in the formulation presented.     

CP-Nonconservation and electric dipole moment of fermions in the nonsymmetric Kaluza-Klein theory

A generalization of minimal coupling is proposed and the usual Dirac equation is generalized within the nonsymmetric Kaluza-Klein theory and the nonsymmetric Jordan-Thiry theory. The dipole electric moment of fermions of order 10^–31 cm is obtained.     

Analytical and numerical treatment of the Mott-Hubbard insulator in infinite dimensions

We calculate the density of states in the half-filled Hubbard model on a Bethe lattice with infinite connectivity. Based on our analytical results to second order in t/U, we propose a new Fixed-Energy Exact Diagonalization scheme for the numerical study of the Dynamical Mean-Field Theory. Corroborated by results from the Random Dispersion Approximation, we find that the gap opens at . Moreover, the density of states near the gap increases algebraically as a function of frequency with an exponent in the insulating phase. We critically examine other analytical and numerical approaches and specify their merits and limitations when applied to the Mott-Hubbard insulator.Received: 14 July 2003, Published online: 2 October 2003PACS: 71.10.Fd Lattice fermion models (Hubbard model, etc.) - 71.27.+a Strongly correlated electron systems; heavy fermions - 71.30.+h Metal-insulator transitions and other electronic transitions