Two-dimensional non-commutative Yang-Mills theory: coherent effects in open Wilson line correlators

A perturbative calculation of the correlator of three parallel open Wilson lines is performed for the U(N) theory in two non-commutative space-time dimensions. In the large-N planar limit, the perturbative series is fully resummed and asymptotically leads to an exponential increase of the correlator with the lengths of the lines, in spite of an interference effect between lines with the same orientation. This result generalizes a similar increase occurring in the two-line correlator and is likely to persist when more lines are considered provided they share the same direction.Comment: 22 pages, 1 figure, typeset in JHEP styl

Twisted Sector Yukawa Couplings For The ZM×ZN{\bf Z}_M\times {\bf Z}_N Orbifolds

The moduli dependent Yukawa couplings between twisted sectors of ${\bf Z}_M\times {\bf Z}_N$ Coxeter orbifolds are studied.Comment: 40 pages, SUSX-TH-92/1

თბილისის უნივერსიტეტი N13 (2058)

ივანე ჯავახიშვილის სახელობის თბილისის სახელმწიფო უნივერსიტეტის გაზეთ

Thermal entanglement in the mixed three spin XXZ Heisenberg Model on a triangular cell

We numerically investigate thermal entanglement of the spins (1/2,1) and (1/2,1/2) in the three-mixed (1/2,1,1/2) anisotropic Heisenberg XXZ spin system on a simple triangular cell under an inhomogeneous magnetic field. We show that the external magnetic field induces strong plateau formation in pairwise thermal entanglement for fixed parameters of Hamiltonian in the case of the ferromagnetic and anti-ferromagnetic interactions. We also observe an unexpected critical point at finite temperature in the thermal entanglement of the spins (1/2,1) for antiferromagnetic case while the entanglement of the spins (1/2,1) for ferromagnetic case and the entanglement of the spins (1/2,1/2) for both ferromagnetic and antiferromagnetic cases almost decays exponentially to zero with increasing temperature. The critical point in entanglement of the spins (1/2,1) for antiferromagnetic case may be signature of the quantum phase transition at finite temperature.Comment: 7 pages, 9 figure

A Spitzer IRS Survey of NGC 1333: Insights into disk evolution from a very young cluster

We report on the {\lambda} = 5-36{\mu}m Spitzer Infrared Spectrograph spectra of 79 young stellar objects in the very young nearby cluster NGC 1333. NGC 1333's youth enables the study of early protoplanetary disk properties, such as the degree of settling as well as the formation of gaps and clearings. We construct spectral energy distributions (SEDs) using our IRS data as well as published photometry and classify our sample into SED classes. Using "extinction-free" spectral indices, we determine whether the disk, envelope, or photosphere dominates the spectrum. We analyze the dereddened spectra of objects which show disk dominated emission using spectral indices and properties of silicate features in order to study the vertical and radial structure of protoplanetary disks in NGC 1333. At least nine objects in our sample of NGC 1333 show signs of large (several AU) radial gaps or clearings in their inner disk. Disks with radial gaps in NGC 1333 show more-nearly pristine silicate dust than their radially continuous counterparts. We compare properties of disks in NGC 1333 to those in three other well studied regions, Taurus-Auriga, Ophiuchus and Chamaeleon I, and find no difference in their degree of sedimentation and dust processing.Comment: 67 pages, 20 figures, accepted to The Astrophysical Journal Supplement Serie

Calculating three-loop diagrams in Heavy Quark Effective Theory with integration-by-parts recurrence relations

An algorithm for calculation of three-loop propagator diagrams in HQET, based on integration-by-parts recurrence relations, is constructed and implemented as a REDUCE package Grinder, and in Axiom.Comment: LaTeX2e (JHEP documentclass), 33 pages, 13 eps figures included. The complete paper is also available via the www at http://www-ttp.physik.uni-karlsruhe.de/Preprints/ V2: bug fixes in formulas, improvements of the algorithm, some restructuring. REDUCE package Grinder is available at http://www-ttp.physik.uni-karlsruhe.de/Progdata/ttp00/ttp00-01