On the Role of Charmed Meson Loops in Charmonium Decays

We investigate the effect of intermediate charmed meson loops on the M1 radiative decays $J/\psi \to \eta_c \gamma$ and $\psi'\rightarrow\eta^{(\prime)}_c\gamma$ as well as the isospin violating hadronic decays $\psi'\rightarrow J/\psi \,\pi^0(\eta)$ using heavy hadron chiral perturbation theory (HH$\chi$PT). The calculations include tree level as well as one loop diagrams and are compared to the latest data from CLEO and BES-III. Our fit constrains the couplings of 1S and 2S charmonium multiplets to charmed mesons, denoted $g_2$ and $g_2^\prime$, respectively. We find that there are two sets of solutions for $g_2$ and $g_2^\prime$. One set, which agrees with previous values of the product $g_2 g_2^\prime$ extracted from analyses that consider only loop contributions to $\psi'\rightarrow J/\psi \,\pi^0(\eta)$, can only fit data on radiative decays with fine-tuned cancellations between tree level diagrams and loops in that process. The other solution for $g_2$ and $g_2^\prime$ leads to couplings that are smaller by a factor of 2.3. In this case tree level and loop contributions are of comparable size and the numerical values of the tree level contributions to radiative decays are consistent with estimates based on the quark model as well as non-relativistic QCD (NRQCD). This result shows that tree level HH$\chi$PT couplings are as important as the one loop graphs with charmed mesons in these charmonium decays. The couplings $g_2$ and $g_2^\prime$ are also important for the calculations of the decays of charmed meson bound states, such as the X(3872), to conventional charmonia.Comment: 16 pages, 3 figures, minor modifications, more references adde

Confinement in QCD

The guiding lines of lattice investigations on colour confinement are reviewed, together with recent results.Comment: 7 pages,3 figures, Plenary talk at PANIC'99,10-16 June 1999,Uppsal

The abelian projection revisited

Abelian projection is reanalysed in the frame of the SU(N) Higgs model. The extension to QCD is discussed. It is shown that dual superconductivity of the vacuum is an intrinsic property independent of the choice of the abelian projection.Comment: 3 pages, 1 figure, Lattice2003(topology

Composite Weak Bosons: a Lattice Analysis

We present a lattice analysis of a confining Yang-Mills theory without Goldstone boson. We have analytically investigated the model by a strong coupling expansion and by an intensive lattice Monte Carlo simulation using standard lattice QCD methods. We show that this theory is an interesting candidate for describing weak bosons as composite particles.Comment: Late

Monopole condensation in the ground state of gauge theories: a disorder parameter

We construct a disorder parameter for dual superconductivity of the ground state of $U(1)$ gauge theory.Comment: 3 pages, contribution to the Lattice '94 conference, shell archive containing uuencoded LATEX file + 2 figure

Chiral Scalar Fields, Custodial Symmetry in Electroweak SU(2)L X U(1) and the Quantization of the Electric Charge

I study the scalar representations of the electroweak group of the Standard Model, which is a subgroup of the chiral group U(N)L x U(N)R with N flavours, for N even, with a special emphasis on their chiral properties and on their behaviour by the discrete symmetries P and CP. They exhaust the $2N^2$ scalar and pseudoscalar degrees of freedom of the chiral group, for which a SU(2)L x U(1) renormalizable, anomaly-free gauge theory naturally springs out. It is shown to have a global diagonal SU(2)V symmetry independently of the value of the hypercharge coupling, which becomes local at the limit when the latter vanishes. When acting in the 4-dimensional space of states spanned by the special representations under scrutiny in this paper, the electric charge is one of the three generators of this ``custodial'' symmetry; that the latter stays an unbroken symmetry is thus correlated with the quantization of the electric charge.Comment: 15 pages Latex. Minor corrections and addenda. Version to be published in Phys. Lett.

Composite Weak Bosons: a Lattice Monte Carlo Analysis

We present a lattice Monte Carlo simulation for the evaluation of the spectrum of a confining Yang-Mills theory without Goldstone boson. We show that this theory is a very good candidate for describing composite weak bosons. In order to perform the spectrum analysis we have used standard lattice QCD Monte Carlo methods. We have also developed an efficient method to evaluate the mass of the pseudoscalar isosinglet which is present in our theory.Comment: Late

G_2 gauge theory at finite temperature

The gauge group being centreless, $G_2$ gauge theory is a good laboratory for studying the role of the centre of the group for colour confinement in Yang-Mills gauge theories. In this paper, we investigate $G_2$ pure gauge theory at finite temperature on the lattice. By studying the finite size scaling of the plaquette, the Polyakov loop and their susceptibilities, we show that a deconfinement phase transition takes place. The analysis of the pseudocritical exponents give strong evidence of the deconfinement transition being first order. Implications of our findings for scenarios of colour confinement are discussed.Comment: 17 pages, 8 figure

The Stefan-Boltzmann law in a small box and the pressure deficit in hot SU(N) lattice gauge theory

The blackbody radiation in a box L^3 with periodic boundary conditions in thermal equilibrium at a temperature T is affected by finite-size effects. These bring about modifications of the thermodynamic functions which can be expressed in a closed form in terms of the dimensionless parameter LT. For instance, when LT~4 - corresponding to the value where the most reliable SU(N) gauge lattice simulations have been performed above the deconfining temperature T_c - the deviation of the free energy density from its thermodynamic limit is about 5%. This may account for almost half of the pressure deficit observed in lattice simulations at T~ 4 T_c.Comment: 9 pages, 2 figures v2:a side remark on the final result and references adde

The problem of the U(1) axial symmetry and the chiral transition in QCD

We discuss the role of the U(1) axial symmetry for the phase structure of QCD at finite temperature. In particular, supported by recent lattice results, we analyse a scenario in which a U(1)-breaking condensate survives across the chiral transition. This scenario can be consistently reproduced using an effective Lagrangian model. The effects of the U(1) chiral condensate on the slope of the topological susceptibility in the full theory with quarks are studied. Further information on the new U(1) chiral order parameter is derived from the study (at zero temperature) of the radiative decays of the light pseudoscalar mesons in two photons.Comment: Talk given at the ``10th High-Energy Physics International Conference in Quantum Chromo-Dynamics'' (QCD 03), Montpellier (France), 2-9 July 2003; 8 pages, LaTeX fil