The ℓ2\ell^2-homology of even Coxeter groups

Given a Coxeter system (W,S), there is an associated CW-complex, Sigma, on which W acts properly and cocompactly. We prove that when the nerve L of (W,S) is a flag triangulation of the 3-sphere, then the reduced $\ell^2$-homology of Sigma vanishes in all but the middle dimension.Comment: 15 pages, 1 figur

Measurement of gauge boson couplings and W spin density matrix

During the LEP2 period the e+e- collider increased its center of mass energy from 161 GeV to 209 GeV and a total integrated luminosity of approximately 700 pb-1 was recorded per experiment. Pairs of W bosons are produced and allow the study of gauge boson couplings involving W, Z and photon. The coupling of the W boson to the neutral gauge bosons have been measured and are in agreement with the Standard Model prediction. Limits are set on CP-violating couplings by a Spin Density Matrix analysis of the W decay products. No evidence has been found for couplings of three neutral gauge bosons. Limits are derived on couplings of four gauge bosons.Comment: 8 pages, 6 figure

Complete N=4 Structure of Low-Energy Effective Action in N=4 Super Yang-Mills Theories

Using the ${\cal N}=2$ superfield approach, we construct full ${\cal N}=4$ supersymmetric low-energy effective actions for ${\cal N}=4$ SYM models, with both ${\cal N}=2$ gauge superfield strengths and hypermultiplet superfields included. The basic idea is to complete the known non-holomorphic effective potentials which depend only on ${\cal N}=2$ superfield strengths $W$ and ${\bar W}$ to the full on-shell ${\cal N}=4$ invariants by adding the appropriate superfield hypermultiplet terms. We prove that the effective potentials of the form ${ln} W {ln} \bar W$ can be ${\cal N} = 4$ completed in this way and present the precise structure of the corresponding completions. However, the effective potentials of the non-logarithmic form suggested in hep-th/9811017 and hep-th/9909020 do not admit the ${\cal N}=4$ completion. Therefore, such potentials cannot come out as (perturbative or non-perturbative) quantum corrections in ${\cal N}=4$ SYM models.Comment: 14 pages, Latex, no figures, slight corrections, refs adde

Diboson production at LHC with warped extra dimensions

From the warped extra-dimensional model interpretation of the two forward-backward asymmetries observed on heavy quarks at LEP1, AFBb, and at Tevatron, AFBt, one predicts that LHC could observe, with the luminosity collected in 2011-2012, significant excesses in the diboson production for large invariant masses of the Z+W system, mZW, and, the W+W system, mWW.Comment: 15 pages, 8 figure

Local calibrations for minimizers of the Mumford-Shah functional with rectilinear discontinuity sets

Using a calibration method, we prove that, if $w$ is a function which satisfies all Euler conditions for the Mumford-Shah functional on a two-dimensional open set $\Omega$, and the discontinuity set of $w$ is a segment connecting two boundary points, then for every point $(x_0, y_0)$ of $\Omega$ there exists a neighbourhood $U$ of $(x_0, y_0)$ such that $w$ is a minimizer of the Mumford-Shah functional on $U$ with respect to its own boundary values on $\partial U$.Comment: 22 pages, 4 figure