Renormalized Polyakov Loops, Matrix Models and the Gross-Witten Point

The values of renormalized Polyakov loops in the three lowest representations of SU(3) were measured numerically on the lattice. We find that in magnitude, condensates respect the large-N property of factorization. In several ways, the deconfining phase transition for N=3 appears to be like that in the N=infinity matrix model of Gross and Witten. Surprisingly, we find that the values of the renormalized triplet loop are described by an SU(3) matrix model, with an effective action dominated by the triplet loop. Future numerical simulations with a larger number of colors should be able to show whether or not the deconfining phase transition is close to the Gross-Witten point.Comment: 9 pages, 3 figures, Combined contribution to proceedings of Strong and Electroweak Matter 2004 (SEWM 2004), Helsinki, Finland, 16-19 June 200

Coherent Topological Charge Structure in CPN−1CP^{N-1} Models and QCD

In an effort to clarify the significance of the recent observation of long-range topological charge coherence in QCD gauge configurations, we study the local topological charge distributions in two-dimensional $CP^{N-1}$ sigma models, using the overlap Dirac operator to construct the lattice topological charge. We find long-range sign coherence of topological charge along extended one-dimensional structures in two-dimensional spacetime. We discuss the connection between the long range topological structure found in $CP^{N-1}$ and the observed sign coherence along three-dimensional sheets in four-dimensional QCD gauge configurations. In both cases, coherent regions of topological charge form along membrane-like surfaces of codimension one. We show that the Monte Carlo results, for both two-dimensional and four-dimensional gauge theory, support a view of topological charge fluctuations suggested by Luscher and Witten. In this framework, the observed membranes are associated with boundaries between ``k-vacua,'' characterized by an effective local value of $\theta$ which jumps by $\pm 2\pi$ across the boundary.Comment: 26 page

Influence of the U(1)_A Anomaly on the QCD Phase Transition

The SU(3)_{r} \times SU(3)_{\ell} linear sigma model is used to study the chiral symmetry restoring phase transition of QCD at nonzero temperature. The line of second order phase transitions separating the first order and smooth crossover regions is located in the plane of the strange and nonstrange quark masses. It is found that if the U(1)_{A} symmetry is explicitly broken by the U(1)_{A} anomaly then there is a smooth crossover to the chirally symmetric phase for physical values of the quark masses. If the U(1)_{A} anomaly is absent, then there is a phase transition provided that the \sigma meson mass is at least 600 MeV. In both cases, the region of first order phase transitions in the quark mass plane is enlarged as the mass of the \sigma meson is increased.Comment: 5 pages, 3 figures, Revtex, discussion extended and references added. To appear in PR

Deconfinement in Matrix Models about the Gross--Witten Point

We study the deconfining phase transition in SU(N) gauge theories at nonzero temperature using a matrix model of Polyakov loops. The most general effective action, including all terms up to two spatial derivatives, is presented. At large N, the action is dominated by the loop potential: following Aharony et al., we show how the Gross--Witten model represents an ultra-critical point in this potential. Although masses vanish at the Gross--Witten point, the transition is of first order, as the fundamental loop jumps only halfway to its perturbative value. Comparing numerical analysis of the N=3 matrix model to lattice simulations, for three colors the deconfining transition appears to be near the Gross--Witten point. To see if this persists for N >= 4, we suggest measuring within a window ~1/N^2 of the transition temperature.Comment: 22 pages, 7 figures; revtex4. A new Fig. 2 illustrates a strongly first order transition away from the GW point; discussion added to clarify relation to hep-th/0310285. Conclusions include a discussion of recent lattice data for N>3, hep-lat/0411039 and hep-lat/050200

The Abelianization of QCD Plasma Instabilities

QCD plasma instabilities appear to play an important role in the equilibration of quark-gluon plasmas in heavy-ion collisions in the theoretical limit of weak coupling (i.e. asymptotically high energy). It is important to understand what non-linear physics eventually stops the exponential growth of unstable modes. It is already known that the initial growth of plasma instabilities in QCD closely parallels that in QED. However, once the unstable modes of the gauge-fields grow large enough for non-Abelian interactions between them to become important, one might guess that the dynamics of QCD plasma instabilities and QED plasma instabilities become very different. In this paper, we give suggestive arguments that non-Abelian self-interactions between the unstable modes are ineffective at stopping instability growth, and that the growing non-Abelian gauge fields become approximately Abelian after a certain stage in their growth. This in turn suggests that understanding the development of QCD plasma instabilities in the non-linear regime may have close parallels to similar processes in traditional plasma physics. We conjecture that the physics of collisionless plasma instabilities in SU(2) and SU(3) gauge theory becomes equivalent, respectively, to (i) traditional plasma physics, which is U(1) gauge theory, and (ii) plasma physics of U(1)x U(1) gauge theory.Comment: 36 pages; 15 figures [minor changes made to text, and new figure added, to reflect published version

The O(N) Model at Finite Temperature: Renormalization of the Gap Equations in Hartree and Large-N Approximation

The temperature dependence of the sigma meson and pion masses is studied in the framework of the O(N) model. The Cornwall-Jackiw-Tomboulis formalism is applied to derive gap equations for the masses in the Hartree and large-N approximations. Renormalization of the gap equations is carried out within the cut-off and counter-term renormalization schemes. A consistent renormalization of the gap equations within the cut-off scheme is found to be possible only in the large-N approximation and for a finite value of the cut-off. On the other hand, the counter-term scheme allows for a consistent renormalization of both the large-N and Hartree approximations. In these approximations, the meson masses at a given nonzero temperature depend in general on the choice of the cut-off or renormalization scale. As an application, we also discuss the in-medium on-shell decay widths for sigma mesons and pions at rest.Comment: 21 pages, 6 figures, typos corrected and refs. added, accepted in Journal of Physics

Embryogenic cell suspensions for high-capacity genetic transformation and regeneration of switchgrass (Panicum virgatum L.)

Background Switchgrass (Panicum virgatum L.), a North American prairie grassland species, is a potential lignocellulosic biofuel feedstock owing to its wide adaptability and biomass production. Production and genetic manipulation of switchgrass should be useful to improve its biomass composition and production for bioenergy applications. The goal of this project was to develop a high-throughput stable switchgrass transformation method using Agrobacterium tumefaciens with subsequent plant regeneration. Results Regenerable embryogenic cell suspension cultures were established from friable type II callus-derived inflorescences using two genotypes selected from the synthetic switchgrass variety ‘Performer’ tissue culture lines 32 and 605. The cell suspension cultures were composed of a heterogeneous fine mixture culture of single cells and aggregates. Agrobacterium tumefaciens strain GV3101 was optimum to transfer into cells the pANIC-10A vector with a hygromycin-selectable marker gene and a pporRFP orange fluorescent protein marker gene at an 85% transformation efficiency. Liquid cultures gave rise to embryogenic callus and then shoots, of which up to 94% formed roots. The resulting transgenic plants were phenotypically indistinguishable from the non-transgenic parent lines. Conclusion The new cell suspension-based protocol enables high-throughput Agrobacterium-mediated transformation and regeneration of switchgrass in which plants are recovered within 6–7 months from culture establishment