Particle theory

Abstract:

We investigate on the lattice the metastable confined phase above Tc in SU(N) gauge theories, for N=8,10, and 12. In particular we focus on the decrease with the temperature of the mass of the lightest state that couples to Polyakov loops. We find that at T=Tc the corresponding effective string tension σeff(T) is approximately half its value at T=0, and that as we increase T beyond Tc, while remaining in the confined phase, σeff(T) continues to decrease. We extrapolate σeff(T) to even higher temperatures, and interpret the temperature where it vanishes as the Hagedorn temperature TH. For SU(12) we find that TH/Tc=1.116(9), when we use the exponent of the three-dimensional XY model for the extrapolation, which seems to be slightly preferred over a mean-field exponent by our data. © 2006 The American Physical Society.

Abstract:

The AMANDA neutrino detector has been in operation at the South Pole for several years. A number of searches for extraterrestrial sources of high energy neutrinos have been performed. A selection of results is presented in this paper. The much larger IceCube detector will extend the instrumented ice volume to a cubic kilometer and 9 out of 80 planned IceCube strings have been deployed to date. We present the status for both detectors.

Abstract:

We calculate the energy spectrum of closed strings in SU(N) gauge theories with N 2, 3, 4, 6, 8 in 2 + 1 dimensions to a high accuracy. We attempt to control all systematic errors, and this allows us to perform a precise comparison with different theoretical predictions. When we study the dependence of the string mass on its length L we find that the Nambu-Goto prediction is a very good approximation down to relatively short lengths, where the Lüscher term alone is insufficient. We then isolate the corrections to the Lüscher term, and compare them to recent theoretical predictions, which indeed seem to be mildly preferred by the data. When we take these corrections into account and extract string tensions from the string masses, we find that their continuum limit is lower by 2% - 1% from the predictions of Karabli, Kim, and Nair. The discrepancy decreases with N, but when we extrapolate our results to N = ∞ we still find a discrepancy of 0 88% which is a 4.5σ effect.

Abstract:

We find a strong-to-weak coupling cross-over in D 2 + 1 SU(N) lattice gauge theories that appears to become a third-order phase transition at N = ∞, in a similar way to the Gross-Witten transition in the D = 1 + 1 SU(N → ∞) lattice gauge theory. There is, in addition, a peak in the specific heat at approximately the same coupling that increases with N, which is connected to ZN monopoles (instantons), reminiscent of the first order bulk transition that occurs in D = 3 + 1 for N ≥ 5. Our calculations are not precise enough to determine whether this peak is due to a second-order phase transition at N = ∞ or to a third-order phase transition with different critical behaviour to that of the Gross-Witten transition. We investigate whether the trace of the Wilson loop has a non-analyticity in the coupling at some critical area, but find no evidence for this. However we do find that, just as one can prove occurs in D = 1 + 1, the eigenvalue density of a Wilson loop forms a gap at N = ∞ at a critical value of its trace. We show that this gap formation is in fact a corollary of a remarkable similarity between the eigenvalue spectra of Wilson loops in D = 1 + 1 and D = 2+1 (and indeed D = 3 + 1): for the same value of the trace, the eigenvalue spectra are nearly identical. This holds for finite as well as infinite N; irrespective of the Wilson loop size in lattice units; and for Polyakov as well as Wilson loops.