Why do UV levels vary?

Have you ever suffered the excrutiating pain and discomfort of a severe sunburn followed by the unsightly peeling of the skin? Have you ever wondered why you may receive a sunburn even on a partially cloudy day? There are a number of factors that influence the amount of solar ultraviolet radiation reaching the earth’s surface

Ozone and ultraviolet radiation

Imagine if the earth’s protective atmosphere did not exist and the earth was subjected to the harmful ultraviolet energy from the sun. Life as we know would not exist. Changes in the earth’s layer of atmospheric ozone may be occurring as a result of human activities. This is generating concerns in the community about increases in terrestrial ultraviolet radiation and the associated adverse effects on humans, plants and animals

Glue Ball Masses and the Chameleon Gauge

We introduce a new numerical technique to compute mass spectra, based on difference method and on a new gauge fixing procedure. We show that the method is very effective by test runs on a $SU(2)$ lattice gauge theory.Comment: latex format, 10 pages, 4 figures added in uufiles forma

The Running Coupling from SU(3) Gauge Theory

We present high precision results on the static quark-antiquark-potential on 32^4 and smaller lattices, using the standard Wilson action at BETA = 6.0, 6.2, 6.4, and 6.8 on the Connection Machine CM-2. Within our statistical errors (1%) we did not observe any finite size effects affecting the potential values, on varying the spatial lattice extent from 0.9 fm up to 3.3 fm. We find violations of asymptotic scaling in the bare coupling up to BETA = 6.8. We demonstrate that scaling violations on the string tension can be considerably reduced by introducing effective coupling schemes, which allow for a safer extrapolation of LAMBDA_Lattice to its continuum value. We are also able to see and to quantify the running of the coupling from the interquark force. From this we extract the ratio \sqrt{SIGMA}/LAMBDA_L. Both methods yield consistent values for the LAMBDA-parameter: LAMBDA_MSbar = 0.558(-0.007+0.017)\sqrt{SIGMA} = 246(-3+7) MeV.Comment: (Talk G. Bali at Lattice 92, Amsterdam), 4 Pages, 4 Postscript figures, LaTeX with espcrc2, and epsf style file

String breaking in SU(2) gauge theory with scalar matter fields

We investigate the static potential in the confinement phase of the SU(2) Higgs model on the lattice, where this model is expected to have properties similar to QCD. We observe that Wilson loops are inadequate to determine the potential at large distances, where the formation of two color-neutral mesons is expected. Introducing smeared fields and a suitable matrix correlation function, we are able to overcome this difficulty. We observe string breaking at a distance $r_b \approx 1.8 r_0$, where the length scale $r_0$ has a value $r_0 \approx 0.5 fm$ in QCD. The method presented here may lead the way towards a treatment of string breaking in QCD.Comment: 10 pages, eqs.(7),(9) corrected, small changes in numerics, new figure

Loop Calculus in Statistical Physics and Information Science

Considering a discrete and finite statistical model of a general position we introduce an exact expression for the partition function in terms of a finite series. The leading term in the series is the Bethe-Peierls (Belief Propagation)-BP contribution, the rest are expressed as loop-contributions on the factor graph and calculated directly using the BP solution. The series unveils a small parameter that often makes the BP approximation so successful. Applications of the loop calculus in statistical physics and information science are discussed.Comment: 4 pages, submitted to Phys.Rev.Lett. Changes: More general model, Simpler derivatio

On the screening of the potential between adjoint sources in QCD3QCD_3

We calculate the potential between adjoint sources in $SU(2)$ pure gauge theory in three dimensions. We investigate whether the potential saturates at large separations due to the creation of a pair of gluelumps, colour-singlet states formed when glue binds to an adjoint source.Comment: 3 pages, uuencoded Z-compressed postscript file, contribution to Lattice '9

Breaking of the adjoint string in 2+1 dimensions

The roughly linear rise of the potential found between adjoint sources in SU(N) in lattice simulations is expected to saturate into a state of two `gluelumps' due to gluonic screening. We examine this in SU(2) in 2+1 dimensions. Crossover between string-like and broken states is clearly seen by the mixing-matrix technique, using different operators to probe the two states; the breaking behaviour is rather abrupt. Furthermore, we are able to show that both types of operator have a finite overlap with both states; in the case of the Wilson loops the overlap with the broken string is, as predicted, very small.Comment: LaTeX2e, 20 pages, 15 figures with epsfig; uses amstex, amssymb, a4wide; minor change to presentation (notation for operators) onl