On localized tachyon condensation in and

We study some aspects of localized tachyon condensation on non-supersymmetric orbifolds of the form C²/Z_n and C³/Z_n. We discuss the gauged linear sigma models for these orbifolds. We show how several features of the decay of orbifolds of C³ can be realised in terms of orbifolds of C².     

Correlators of matrix models on homogeneous spaces

We investigate the correlators of TrA_μA_ν in matrix models on homogeneous spaces: S² and S²×S². Their expectation value is a good order parameter to measure the geometry of the space on which non-commutative gauge theory is realized. They also serve as the Wilson lines which carry the minimum momentum. We develop an efficient procedure to calculate them through 1PI diagrams. We determine the large N scaling behavior of the correlators. The order parameter shows that fuzzy S²×S² acquires a 4-dimensional fractal structure in contrast to fuzzy S². We also find that the two point functions exhibit logarithmic scaling violations.     

A study of strange particles produced in neutrino neutral current interactions in the NOMAD experiment

Results of a detailed study of strange particle production in neutrino neutral current interactions are presented using the data from the NOMAD experiment. Integral yields of neutral strange particles (, Λ, ) have been measured. Decays of resonances and heavy hyperons with an identified or Λ in the final state have been analyzed. Clear signals corresponding to and Σ(1385)^± have been observed. First results on the measurements of the Λ polarization in neutral current interactions have been obtained.     

Charmed-meson fragmentation functions with finite-mass corrections

We elaborate the inclusive production of single heavy-flavored hadrons in e⁺e⁻ annihilation at next-to-leading order in the general-mass variable-flavor-number scheme. In this framework, we determine non-perturbative fragmentation functions for D⁰, D⁺, and D^*+ mesons by fitting experimental data from the Belle, CLEO, ALEPH, and OPAL Collaborations, taking dominant electroweak corrections due to photonic initial-state radiation into account. We assess the significance of finite-mass effects through comparisons with a similar analysis in the zero-mass variable-flavor-number scheme. Under Belle and CLEO experimental conditions, charmed-hadron mass effects on the phase space turn out to be appreciable, while charm-quark mass effects on the partonic matrix elements are less important.     

Small x resummation with quarks: Deep-inelastic scattering

We extend our previous results on small-x resummation in the pure Yang–Mills theory to full QCD with n_f quark flavours, with a resummed two-by-two matrix of resummed quark and gluon splitting functions. We also construct the corresponding deep-inelastic coefficient functions, and show how these can be combined with parton densities to give fully resummed deep-inelastic structure functions F₂ and F_L at the next-to-leading logarithmic level. We discuss how this resummation can be performed in different factorization schemes, including the commonly used scheme. We study the importance of the resummation effects by comparison with fixed-order perturbative results, and we discuss the corresponding renormalization and factorization scale variation uncertainties. We find that for x below 10⁻² the resummation effects are comparable in size to the fixed order NNLO corrections, but differ in shape. We finally discuss the phenomenological impact of the small-x resummation, specifically in the extraction of parton distribution from present day experiments and their extrapolation to the kinematics relevant for future colliders such as the LHC.     

Magnetic monopoles in the high temperature phase of Yang–Mills theories

We investigate the properties of thermal Abelian magnetic monopoles in the high temperature phase of Yang–Mills theories, following a recent proposal for their identification on lattice configurations. The study is done for SU(2) pure gauge theory, for temperatures going up to about 10 times the deconfining temperature and using the Maximal Abelian gauge to perform the Abelian projection. We find that the monopole density has a well defined continuum limit. Its temperature dependence disagrees with a free particle gas prediction and is instead well described by a T³/(log(T/Λ)) behaviour in all the explored range, with 2 and Λ100 MeV. Also the study of spatial correlations of thermal monopoles shows the presence of non-trivial interactions among them. Finally, we discuss the gauge dependence of our results, showing that it is significant and that, even within the Maximal Abelian gauge, Gribov copy effects are important.     

The new multiplet, heavy baryon mass predictions, meson–baryon universality and effective supersymmetry in hadron spectrum

The recent measurement by CDF M(Σ_b)−M(Λ_b)=192 MeV is in striking agreement with our theoretical prediction M(Σ_b)−M(Λ_b)=194 MeV. In addition, the measured splitting agrees well with the predicted splitting of 22 MeV. We point out the connection between these predictions and an effective supersymmetry between mesons and baryons related by replacing a light antiquark by a light diquark. We discuss the theoretical framework behind these predictions and use it to provide additional predictions for the masses of spin- and spin- baryons containing heavy quarks, as well as for magnetic moments of Λ_b and Λ_c.     

Enhanced quantum searching via entanglement and partial diffusion

In this paper, we will define a quantum operator that performs the standard inversion about the mean only on a subspace of the system (Partial Diffusion Operator). This operator is used together with entanglement in a quantum search algorithm that runs in for searching an unstructured list of size N with M matches such that 1≤M≤N. We will show that the performance of the algorithm is more reliable than known fixed operators quantum search algorithms especially for multiple matches where we can get a solution after a single iteration with probability over 90% if the number of matches is approximately more than one-third of the search space. We will show that the algorithm will be able to handle the case where the number of matches M is unknown in advance in such that 1≤M≤N.     

Log-periodic behavior of finite size effects in field theories with RG limit cycles

We compute the finite size effects in the ground state energy, equivalently the effective central charge c_eff, based on S-matrix theories recently conjectured to describe a cyclic regime of the Kosterlitz–Thouless renormalization group flows. The effective central charge has periodic properties consistent with renormalization group predictions. Whereas c_eff for the massive case has a singularity in the very deep ultra-violet, we argue that the massless version is non-singular and periodic on all length scales.     

: Hadronic molecules in effective field theory

We consider the implications from the possibility that the recently observed state X(3872) is a meson–antimeson molecule. We write an effective Lagrangian consistent with the heavy-quark and chiral symmetries needed to describe X(3872). We explore the consequences of the assumption that X(3872) is a molecular bound state of D^*0 and mesons for the existence of bound states in the and channels.     

Exact correlated kinetic energy related to the electron density for two-electron model atoms with harmonic confinement

For arbitrary interparticle interaction u(r₁₂), the model two-electron atom in the title is shown to be such that the ground-state electron density ρ(r) is determined uniquely by the correlated kinetic energy density t_R(r) of the relative motion. Explicit results for t_R(r) are presented for the Hookean atom with force constant k=1/4, and also for . Possible relevance of the Hookean atom treatment to the ground state of the helium atom itself is briefly discussed.     

Asymptotic Bethe ansatz from string sigma model on

We derive the asymptotic Bethe ansatz (AFS equations [G. Arutyunov, S. Frolov, M. Staudacher, Bethe ansatz for quantum strings, JHEP 0410 (2004) 016, hep-th/0406256]) for the string on S³×R sector of AdS₅×S⁵ from the integrable nonhomogeneous dynamical spin chain for the string sigma model proposed in [N. Gromov, V. Kazakov, K. Sakai, P. Vieira, Strings as multi-particle states of quantum sigma-models, hep-th/0603043]. It is clear from the derivation that AFS equations can be viewed only as an effective model describing a certain regime of a more fundamental inhomogeneous spin chain.     

Size-dependent linear and non-linear optical response of single carrier two-dimensional quantum dots

We explore the pattern of size dependence of linear and non-linear optical (NLO) responses of one-electron quantum dots in two dimensions with or without anharmonicity in the confinement potential. For some fixed values of transverse magnetic field strength (ω_c) and harmonic confinement potential (ω₀), the influence of the size of the dot on the linear (), the first (β) and the second (γ) NLO responses of the system computed through a finite field linear variational route is analysed. Size-dependent maximization is predicted to be feasible for the quadratic hyperpolarizability.     

Corner bifurcations in non-smoothly forced impact oscillators

We consider an impacting mechanical system in which a particle at position u(t) impacts with a periodically moving obstacle at position z(t), the motion of which is non-smooth. In particular we look at corner events when u impacts with z very close to a point where z loses smoothness. We show that this leads, through a corner bifurcation, to complex dynamics in u which can include periodic orbits of arbitrary period and period-adding cascades. By analysing associated maps close to the corner event, we show that this dynamics can be understood in terms of the iterations of a two-dimensional, piecewise linear, discontinuous map. We also show some links between this analysis and the difficult problem of understanding the motion of three objects which may have simultaneous impacts.     

Materials with a desired refraction coefficient can be made by embedding small particles

A method is proposed to create materials with a desired refraction coefficient, possibly negative one. The method consists of embedding into a given material small particles. Given n₀(x), the refraction coefficient of the original material in a bounded domain , and a desired refraction coefficient n(x), one calculates the number N(x) of small particles, to be embedded in D around a point xD per unit volume of D, in order that the resulting new material has refraction coefficient n(x).     

Dynamic exponents of a probabilistic three-state cellular automaton

In this work, a three-state cellular automaton proposed to describe part of a biological immune system is revisited. We obtain the dynamic critical exponent z of the model by means of a recent technique that mixes different initial conditions. Moreover, by using two distinct approaches, we have also calculated the global persistence exponent θ_g, related to the probability that the order parameter of the model does not change its sign up to time t [P(t)∝t^-θ_g].     

Theoretical analysis of pit formation in GaAs surfaces in picosecond and femtosecond laser ablation regimes

In the present work, the effect of pit formation in laser-ablated GaAs surfaces is analyzed theoretically. The formation of pits has been previously observed during laser ablation experiments in the picosecond (35 ps) and the femtosecond (100 fs) regimes. In the present work, it is shown theoretically that the thermal conductivity of the laser-ablated GaAs surface is changed both in the picosecond and the femtosecond regimes as compared to the unexposed surface. The variation in thermal conductivity of an ablated surface depends upon the fraction of the thermal conductivity of the cracks (), and the fraction of the cross-sectional area of the cracks (γ). In the picosecond regime (35 ps), the thermal conductivity of the ablated GaAs surface decreases (both for single and multiple laser pulses) for all the values of and γ (between 0.1 and 0.9) as compared to the thermal conductivity of a smooth film with no pits. In the femtosecond regime (100 fs), the thermal conductivity of the ablated surface increases or decreases (both for single and multiple laser pulses) depending upon the value of and γ.     

Near tribimaximal neutrino mixing with symmetry

The discrete subgroup Δ(27) of SU(3) has the interesting multiplication rule , which is used to obtain near tribimaximal neutrino mixing. Using present neutrino oscillation data as input, this model predicts that the effective mass m_ee measured in neutrinoless double beta decay will be 0.14 eV.     

Chiral dynamics and antikaon-nuclear quasibound states

Recent developments are summarised concerning low-energy interactions as they relate to the possible existence of antikaon-nuclear quasibound states. An exploratory study of antikaons bound to finite nuclei is performed, with emphasis on the evolution of such states from light to heavy nuclei (A = 16–208). The energy dependent, driving attractive interactions are constructed using the s-wave coupled-channel amplitudes involving the Λ(1405) and resulting from chiral SU(3) dynamics, plus p-wave amplitudes dominated by the Σ(1385). Effects of Pauli and short-range correlations are discussed. The decay width induced by K⁻NN two-body absorption is estimated and found to be substantial. It is concluded that -nuclear quasibound states can possibly exist with binding energies ranging from 60 to 100 MeV, but with short life times corresponding to decay widths of similar magnitudes.     

The finite-size scaling study of the specific heat and the Binder parameter for the six-dimensional Ising model

The six-dimensional Ising model with nearest-neighbor pair interactions is simulated on the Creutz cellular automaton by using the finite-size lattices with the linear dimensions L=4,6,8,10. The temperature variations and the finite-size scaling plots of the specific heat and Binder parameter verify the theoretically predicted expression near the infinite lattice critical temperature. The approximate values for the critical temperature of the infinite lattice T_C=10.838(1), T_C=10.836(20) and T_C=10.835(1) are obtained from the intersection points of specific heat curves, Binder parameter curves and the straight line fit of specific heat maxima, respectively. These results are in agreement with the more precise value of T_C=10.835(5). The value obtained for the critical exponent of the specific heat, i.e., =0.012(2) is also in agreement with =0 predicted by the theory.