Particle theory

Abstract:

This document contains notes from the graduate lecture course, "Symmetries in QFT" given by J.F.Wheater at Oxford University in Hilary term. The course gives an informal introduction to QFT.

Abstract:

We make the first calculation of the electroweak couplings of hybrid mesons to conventional mesons appropriate to photoproduction and to the decays of B or D mesons. E1 amplitudes are found to be large and may contribute in charge exchange gammap-->nH(+) allowing production of (among others) the charged 1(-+) exotic hybrid off a(2) exchange. Axial hybrid meson photoproduction is predicted to be large courtesy of pi exchange, and its strange hybrid counterpart is predicted in B-->psiK(H)(1(+)) with branching ratio B approximately 10(-4). Higher multipoles and some implications for hybrid charmonium are briefly discussed.

Abstract:

We show that long-time, long-distance fluctuations of plane-symmetric horizons exhibit universal hydrodynamic behavior. By considering classical fluctuations around black-brane backgrounds, we find both diffusive and shear modes. The diffusion constant and the shear viscosity are given by simple formulas, in terms of metric components. For a given metric, the answers can be interpreted as corresponding kinetic coefficients in the holographically dual theory. For the near-extremal DP, M2 and M5 branes, the computed kinetic coefficients coincide with the results of independent AdS/CFT calculations. In all the examples, the ratio of shear viscosity to entropy density is equal to ℏ/(4πkB, suggesting a special meaning of this value. © SISSA/ISAS 2003.

Abstract:

We compute glueball masses for even spins ranging from 0 to 6, in the D = 2 + 1 SU(2) lattice gauge theory. We do so over a wide range of lattice spacings, and this allows a well-controlled extrapolation to the continuum limit. When the resulting spectrum is presented in the form of a Chew-Frautschi plot we find that we can draw a straight Regge trajectory going through the lightest glueballs of spin 0, 2, 4 and 6. The slope of this trajectory is small and turns out to lie between the predictions of the adjoint-string and flux-tube glueball models. The intercept we find, α0∼-1, is much lower than is needed for this leading trajectory to play a 'Pomeron-like' role of the kind it is often believed to play in D = 3 + 1. We elaborate the Regge theory of high-energy scattering in 2 space dimensions, and we conclude, from the observed low intercept, that high-energy glueball scattering is not dominated by the leading Regge pole exchange, but rather by a more complex singularity structure in the region 0≤Reλ≤1/2 of the complex angular momentum λ plane. We show that these conclusions do not change if we go to larger groups, SU(N>2), and indeed to SU(∞), and we contrast all this with our very preliminary calculations in the D = 3 + 1 SU(3) gauge theory. © 2003 Elsevier B.V. All rights reserved.