Nonplanar integrability at two loops

In this article we compute the action of the two loop dilatation operator on restricted Schur polynomials that belong to the su(2) sector, in the displaced corners approximation. In this non-planar large N limit, operators that diagonalize the one loop dilatation operator are not corrected at two loops. The resulting spectrum of anomalous dimensions is related to a set of decoupled harmonic oscillators, indicating integrability in this sector of the theory at two loops. The anomalous dimensions are a non-trivial function of the 't Hooft coupling, with a spectrum that is continuous and starting at zero at large N, but discrete at finite N.Comment: version to appear in JHE

Spin-1 Particles with Light-Front Approach

For the vector sector, i.e, mesons with spin-1, the electromagnetic form factors and anothers observables are calculated with the light-front approach. However, the light-front quantum field theory have some problems, for example, the rotational symmetry breaking. We solve that problem added the zero modes contribuition to the matrix elements of the electromagnetic current, besides the valence contribuition. We found that among the four independent matrix elements of the plus component in the light-front helicity basis only the $0\to 0$ one carries zero mode contributions.Comment: 5 pages. 3 Figures, use latex and EPJ styl

Vacuum Polarization for a Massless Spin-1/2 Field in the Global Monopole Spacetime at Nonzero Temperature

In this paper we present the effects produced by the temperature in the renormalized vacuum expectation value of the zero-zero component of the energy-momentum tensor associated with massless left-handed spinor field in the pointlike global monopole spacetime. In order to develop this calculation we had to obtain the Euclidean thermal Green function in this background. Because the expression obtained for the thermal energy density cannot be expressed in a closed form, its explicit dependence on the temperature is not completely evident. So, in order to obtain concrete information about its thermal behavior, we develop a numerical analysis of our result in the high-temperature limit for specific values of the parameter $\alpha$ which codify the presence of the monopole.Comment: 22 pages, LaTex format, 5 figure

Verification of Magnitude and Phase Responses in Fixed-Point Digital Filters

In the digital signal processing (DSP) area, one of the most important tasks is digital filter design. Currently, this procedure is performed with the aid of computational tools, which generally assume filter coefficients represented with floating-point arithmetic. Nonetheless, during the implementation phase, which is often done in digital signal processors or field programmable gate arrays, the representation of the obtained coefficients can be carried out through integer or fixed-point arithmetic, which often results in unexpected behavior or even unstable filters. The present work addresses this issue and proposes a verification methodology based on the digital-system verifier (DSVerifier), with the goal of checking fixed-point digital filters w.r.t. implementation aspects. In particular, DSVerifier checks whether the number of bits used in coefficient representation will result in a filter with the same features specified during the design phase. Experimental results show that errors regarding frequency response and overflow are likely to be identified with the proposed methodology, which thus improves overall system's reliability

Electrostatic self-force in (2+1)-dimensional cosmological gravity

Point sources in (2+1)-dimensional gravity are conical singularities that modify the global curvature of the space giving rise to self-interaction effects on classical fields. In this work we study the electrostatic self-interaction of a point charge in the presence of point masses in (2+1)-dimensional gravity with a cosmological constant.Comment: 9 pages, Late

Mechanism of hyaluronan degradation by Streptococcus pneumoniae hyaluronate lyase - Structures of complexes with the substrate

Hyaluronate lyase enzymes degrade hyaluronan, the main polysaccharide component of the host connective tissues, predominantly into unsaturated disaccharide units, thereby destroying the normal connective tissue structure and exposing the tissue cells to various endo-and exogenous factors, including bacterial toxins. The crystal structures of Streptococcus pneumoniae hyaluronate lyase with tetra- and hexasaccharide hyaluronan substrates bound in the active site were determined at 1.52- and 2.0-Angstrom resolution, respectively. Hexasaccharide is the longest substrate segment that binds entirely within the active site of these enzymes. The enzyme residues responsible for substrate binding, positioning, catalysis, and product release were thereby identified and their specific roles characterized. The involvement of three residues in catalysis, Asn(349), His(399), and Tyro(408), is confirmed, and the details of proton acceptance and donation within the catalytic machinery are described. The mechanism of processivity of the enzyme is analyzed. The flexibility (allosteric) behavior of the enzyme may be understood in terms of the results of flexibility analysis of this protein, which identified two modes of motion that are also proposed to be involved in the hyaluronan degradation process. The first motion describes an opening and closing of the catalytic cleft located between the alpha- and beta-domains. The second motion demonstrates the mobility of a binding cleft, which may facilitate the binding of the negatively charged hyaluronan to the enzyme

Global monopole, dark matter and scalar tensor theory

In this article, we discuss the space-time of a global monopole field as a candidate for galactic dark matter in the context of scalar tensor theory.Comment: 8 pages, Accepted in Mod. Phys. Lett.

Electromagnetic Structure of the Pion

In this work, we analyze the electromagnetic structure of the pion. We calculate its electromagnetic radius and electromagnetic form factor in low and intermediate momentum range. Such observables are determined by means of a theoretical model that takes into account the constituent quark and antiquark of the pion within the formalism of light-front field theory. In particular, we consider a nonsymmetrical vertex in this model, with which we calculate the electromagnetic form factor of the pion in an optimized way, so that we obtain a value closer to the experimental charge radius of the pion. The theoretical calculations are also compared with the most recent experimental data involving the pion electromagnetic form factor and the results show very good agreement.Comment: Paper with 4 pages, 1 figure, presented in XII HADRON PHYSICS Conference - to appear in AIP Conference Proceeding