283 research outputs found
Thermal effects in perturbative noncommutative gauge theories
The thermodynamics of gauge theories on the noncommutative plane is studied
in perturbation theory. For U(1) noncommutative Yang-Mills we compute the first
quantum correction to the ideal gas free energy density and study their
behavior in the low and high temperature regimes. Since the noncommutativity
scale effectively cutoff interactions at large distances, the theory is regular
in the infrared. In the case of U(N) noncommutative Yang-Mills we evaluate the
two-loop free energy density and find that it depends on the noncommutativity
parameter through the contribution of non-planar diagrams.Comment: 15 pages, harvmac. Minor changes with respect to v2. Footnote
expanded, remark added in Section 3, typos corrected and references added.
Final version to be published in JHE
Accumulation of Mutated Maize Zeins in Transgenic Forage Legumes
Accumulation of zeins, the endosperm storage proteins of maize, in a heterologous plant expression system was attempted. Plants of birdsfoot trefoil (Lotus corniculatus) and alfalfa (Medicago sativa) were transformed by Agrobacterium with binary vectors harboring genes that code for γ-zein and β-zein, two proteins rich in sulphur amino acids. Adding the ER retention signal KDEL to the C-terminal domain modified zein polypeptides. Our long-term goal was to improve birdsfoot trefoil and alfalfa forage quality. Significant levels of γ- zein:KDEL and β-zein:KDEL were detected in primary transformants of birdsfoot trefoil. Moreover, alfalfa plants expressing γ-zein:KDEL in the leaves were obtained. γ-zein:KDEL accumulated in spherical or elliptical electron-dense bodies of birdsfoot trefoil leaves. The protein bodies were present in the cytoplasm of either mesophyll cells or epidermis cells
Implementing holographic projections in Ponzano--Regge gravity
We consider the path-sum of Ponzano-Regge with additional boundary
contributions in the context of the holographic principle of Quantum Gravity.
We calculate an holographic projection in which the bulk partition function
goes to a semi-classical limit while the boundary state functional remains
quantum-mechanical. The properties of the resulting boundary theory are
discussed.Comment: 20 pages, late
The boundary field theory induced by the Chern-Simons theory
The Chern-Simons theory defined on a 3-dimensional manifold with boundary is
written as a two-dimensional field theory defined only on the boundary of the
three-manifold. The resulting theory is, essentially, the pullback to the
boundary of a symplectic structure defined on the space of auxiliary fields in
terms of which the connection one-form of the Chern-Simons theory is expressed
when solving the condition of vanishing curvature. The counting of the physical
degrees of freedom living in the boundary associated to the model is performed
using Dirac's canonical analysis for the particular case of the gauge group
SU(2). The result is that the specific model has one physical local degree of
freedom. Moreover, the role of the boundary conditions on the original Chern-
Simons theory is displayed and clarified in an example, which shows how the
gauge content as well as the structure of the constraints of the induced
boundary theory is affected.Comment: 10 page
Asymptotic Flatness, Little String Theory, and Holography
We argue that any non-gravitational holographic dual to asymptotically flat
string theory in -dimensions naturally resides at spacelike infinity. Since
spacelike infinity can be resovled as a -dimensional timelike
hyperboloid (i.e., as a copy of de Sitter space in dimensions), the
dual theory is defined on a Lorentz signature spacetime. Conceptual issues
regarding such a duality are clarified by comparison with linear dilaton
boundary conditions, such as those dual to little string theory. We compute
both time-ordered and Wightman boundary 2-point functions of operators dual to
massive scalar fields in the asymptotically flat bulk.Comment: 27 pages, 2 figures. Explicit discussion added of using the Wightman
function method to calculate time-ordered boundary 2-point functions. The
resulting branch cuts are linked to the bulk spectrum of state
Expected and unexpected behavior of the orientational order and dynamics induced by azobenzene solutes in a nematic
We have explored the changes in the phase stability, orientational order, and dynamics of the nematic 4-cyano-4¢-n-pentylbiphenyl (5CB) doped with either the trans or the cis form of different p-azobenzene derivatives using the ESR spin-probe technique. In particular, we have studied the effects induced by each of the seven nonmesogenic 4-R-phenylazobenzenes (R = H, F, Br, CH3, CF3, On-Bu, Ot-Bu) at 1% and 7% mole fraction on the order parameter and on the shift of the nematic-isotropic transition temperature (TNI), as reported by a nitroxide spin probe, and we have tried to relate them to the solute shape and charge distribution. In all the cases the presence of the azo-derivative causes a depression of TNI, more pronounced for the cis isomers. The dependence of on the reduced temperature T*=T/TNI remains the same as that of pure 5CB in all trans-doped samples at 1% and 7% and decreases only slightly in the cis at 1%. However, we observe different and in some cases large variations (up to 25%) in for the cis at 7%, showing solute effects that go beyond the shift in TNI. Surprisingly enough, even at the highest concentration, the probe dynamics appears to be essentially independent of the nature, the configuration, and the concentration of the different solutes and very similar to that observed in the pure 5CB
On the Anomalies and Schwinger Terms in Noncommutative Gauge Theories
Invariant (nonplanar) anomaly of noncommutative QED is reexamined. It is
found that just as in ordinary gauge theory UV regularization is needed to
discover anomalies, in noncommutative case, in addition, an IR regularization
is also required to exhibit existence of invariant anomaly. Thus resolving the
controversy in the value of invariant anomaly, an expression for the
unintergrated anomaly is found. Schwinger terms of the current algebra of the
theory are derived.Comment: LaTeX, axodraw.sty, 1 figure; v2: Typos corrected, References added,
Version to appear in Int. J. Mod. Phys. A (2006
Classical central extension for asymptotic symmetries at null infinity in three spacetime dimensions
The symmetry algebra of asymptotically flat spacetimes at null infinity in
three dimensions is the semi-direct sum of the infinitesimal diffeomorphisms on
the circle with an abelian ideal of supertranslations. The associated charge
algebra is shown to admit a non trivial classical central extension of Virasoro
type closely related to that of the anti-de Sitter case.Comment: 4 sign mistakes due to a change of conventions are corrected in
section 2, none of the conclusions are affected, takes precedence over
published version, including corrigendu
Closed Strings Tachyons and Non-Commutative Instabilities
We observe a relation between closed strings tachyons and one-loop
instabilities in non-supersymmetric non-commutative gauge theories. In
particular we analyze the spectra of type IIB string theory on C^3/Z_N orbifold
singularities and the non-commutative field theory that lives on D3 branes
located at the singularity. We find a surprising correspondence between the
existence or not of one-loop low-momentum instabilities in the non-commutative
field theory and the existence or not of tachyons in the closed string twisted
sectors. Moreover, the relevant piece of the non-commutative field theory
effective action is suggestive of an exchange of closed string modes. This
suggests that non-commutative field theories retain some information about the
dynamics of the underlying string configuration. Finally, we also comment on a
possible relation between closed string tachyon condensation and field theory
tachyon condensation.Comment: 27 pages, Latex. v2: Comment about anomalies and refs. added. Version
published in JHEP. v3: minor change
Effective Finite Temperature Partition Function for Fields on Non-Commutative Flat Manifolds
The first quantum correction to the finite temperature partition function for
a self-interacting massless scalar field on a dimensional flat manifold
with non-commutative extra dimensions is evaluated by means of dimensional
regularization, suplemented with zeta-function techniques. It is found that the
zeta function associated with the effective one-loop operator may be nonregular
at the origin. The important issue of the determination of the regularized
vacuum energy, namely the first quantum correction to the energy in such case
is discussed.Comment: amslatex, 14 pages, to appear in Phys. Rev.
- …