Higgs Searches and Prospects from LEP2

The status of the search at LEP2 for the Higgs in the Standard Model (SM) and in the minimal supersymmetric extension of the Standard Model MSSM) is reviewed. A preliminary lower limit of 95.5/c^2 at 95% C.L. on the SM Higgs is obtained after a preliminary analysis of the data collected at sqrt(s)= 189 GeV. For standard choices of MSSM parameter sets, the search for the neutral Higgs bosons h and A leads to preliminary 95% C.L. exclusion lower limits of 83.5GeV/c^2 and 84.5 GeV/c^2, respectively.Comment: 6 page

Orbital ordering, Jahn-Teller distortion, and resonant x-ray scattering in KCuF3

The orbital, lattice, and spin ordering phenomena in KCuF3 are investigated by means of LDA+U calculations, based on ab-initio pseudopotentials.We examine the Cu-3d orbital ordering and the associated Jahn-Teller distortion in several different spin-ordered structures of KCuF3. The ground state is correctly predicted to be an A-type antiferromagnetic structure, and the calculated Jahn-Teller distortion agrees also well with experiment. Concerning the orbital ordering, we find that even for a highly ionic compound such as KCuF3, the orbital-order parameter is significantly reduced with respect to its nominal value due to Cu(3d)--F(2p) hybridization. We also calculate the Cu K-edge resonant x-ray scattering spectra for Bragg reflections associated with orbital order. Consistent with previous studies, we find that the resonant signal is dominated by the structural anisotropy in the distribution of the F neighbors of the resonant Cu atom, and that the Cu-3d orbital ordering has only a minor influence on the spectra. Our LDA+U results, however, also indicate that a change in the magnetic structure has a small influence on the Jahn-Teller distortion, and hence on the resonant spectrum, in the conventional (room-temperature) crystallographic structure of KCuF3. This may indicate that the large change observed experimentally in the resonant signal near the N\'eel temperature is related to a low-temperature structural transformation in KCuF3.Comment: 11 pages, 9 figure

Parton distributions in a constituent quark scenario

A simple picture of the constituent quark as a composite system of point-like partons is used to construct the unpolarized and polarized parton distributions by a convolution between constituent quark momentum distributions and constituent quark structure functions. We achieve good agreement with experiments in the unpolarized, as well as, in the polarized case. When our results are compared with similar calculations using non-composite constituent quarks, the accord with the experiments of the present scheme is impressive. We conclude that DIS data are consistent with a low energy scenario dominated by composite constituents of the nucleon.Comment: 4 pages; latex using espcrc1.sty; 4 postscript figures; Invited talk at the Workshop ``Nucleon '99'', Frascati; Italy 7-9 June 1999. Submitted to Nuc. Phys.

Optimizing spread dynamics on graphs by message passing

Cascade processes are responsible for many important phenomena in natural and social sciences. Simple models of irreversible dynamics on graphs, in which nodes activate depending on the state of their neighbors, have been successfully applied to describe cascades in a large variety of contexts. Over the last decades, many efforts have been devoted to understand the typical behaviour of the cascades arising from initial conditions extracted at random from some given ensemble. However, the problem of optimizing the trajectory of the system, i.e. of identifying appropriate initial conditions to maximize (or minimize) the final number of active nodes, is still considered to be practically intractable, with the only exception of models that satisfy a sort of diminishing returns property called submodularity. Submodular models can be approximately solved by means of greedy strategies, but by definition they lack cooperative characteristics which are fundamental in many real systems. Here we introduce an efficient algorithm based on statistical physics for the optimization of trajectories in cascade processes on graphs. We show that for a wide class of irreversible dynamics, even in the absence of submodularity, the spread optimization problem can be solved efficiently on large networks. Analytic and algorithmic results on random graphs are complemented by the solution of the spread maximization problem on a real-world network (the Epinions consumer reviews network).Comment: Replacement for "The Spread Optimization Problem

GRSV parton densities revisited

An updated next-to-leading order (NLO) QCD analysis of all presently available longitudinally polarized deep-inelastic scattering (DIS) data is presented in the framework of the radiative parton model.Comment: 3 pages, LaTeX, 2 eps figures, uses amssymb, npb (included), and epsfig styles; Contribution to the Proceedings of the 7th International Workshop on `Deep Inelastic Scattering and QCD (DIS99)' [Nucl. Phys. B (Proc. Suppl.)], Zeuthen, Germany, April 199

Discrete Flavor Symmetries and Models of Neutrino Mixing

We review the application of non abelian discrete groups to the theory of neutrino masses and mixing, which is strongly suggested by the agreement of the Tri-Bimaximal mixing pattern with experiment. After summarizing the motivation and the formalism, we discuss specific models, based on A4, S4 and other finite groups, and their phenomenological implications, including lepton flavor violating processes, leptogenesis and the extension to quarks. In alternative to Tri-Bimaximal mixing the application of discrete flavor symmetries to quark-lepton complementarity and Bimaximal Mixing is also considered.Comment: 54 pages, 3 figures, minor changes in the text and references adde

Neutrino Masses and Mixing, Quark-lepton Symmetry and Strong Right-handed Neutrino Hierarchy

Assuming the same form of all mass matrices as motivated by quark-lepton symmetry, we discuss conditions under which bi-large mixing in the lepton sector can be obtained with a minimal amount of fine tuning requirements for possible models. We assume hierarchical mass matrices, dominated by the 3-3 element, with off-diagonal elements much smaller than the larger neighboring diagonal element. Characteristic features of this scenario are strong hierarchy in masses of right-handed neutrinos, and comparable contributions of both lighter right-handed neutrinos to the resulting left-handed neutrino Majorana mass matrix. Due to obvious quark lepton symmetry, this approach can be embedded into grand unified theories. The mass of the lightest neutrino does not depend on details of a model in the leading order. The right-handed neutrino scale can be identified with the GUT scale in which case the mass of the lightest neutrino is given as (m_{top}^2/M_{GUT}) |U_{\tau 1}|^2.Comment: 7 page

Probing the Majorana nature of the neutrino with neutrinoless double beta decay

Neutrinoless double beta decay (NDBD) is the only experiment that could probe the Majorana nature of the neutrino. Here we study the theoretical implications of NDBD for models yielding tri-bimaximal lepton mixing like A4 and S4.Comment: Talk given at TAUP09, July 1-5, 2009 (Roma).The proceeding will be published in Journal of Physics, Conference Series (Editors: E. Coccia, L. Pandola, N. Fornengo, R. Aloisio

Higgs-Flavor Groups, Naturalness, and Dark Matter

In the absence of low-energy supersymmetry, a multiplicity of weak-scale Higgs doublets would require additional fine-tunings unless they formed an irreducible multiplet of a non-abelian symmetry. Remnants of such symmetry typically render some Higgs fields stable, giving several dark matter particles of various masses. The non-abelian symmetry also typically gives simple, testable mass relations.Comment: Some comments added after Eqs. (2) and (12

Large Transverse Momentum Jet Production and DIS Distributions of the Proton

We have calculated the single jet inclusive cross section as measured at Fermilab in next-to-leading order QCD using recent parton distributions of the CTEQ collaboration. We studied the scheme dependence of the jet cross section by employing the \overline{\mbox{MS}} and DIS factorization schemes consistently. For $E_T > 200$ GeV, we find that the cross section in the DIS scheme is larger than in the \overline{\mbox{MS}} scheme yielding a satisfactory description of the CDF data over the whole $E_T$ range in the DIS scheme.Comment: 7 pages, latex, 2 figures include