21 research outputs found

### 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 $CP^{N-1}$ 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 â€˜Performerâ€™ 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 6â€“7 months from culture establishment