2,838 research outputs found
Symmetry Breaking at enhanced Symmetry Points
The influence of world-sheet boundary condensates on the toroidal
compactification of bosonic string theories is considered. At the special
points in the moduli space at which the closed-string theory possesses an
enhanced unbroken symmetry (where is a semi-simple product of
simply laced groups) a scalar boundary condensate parameterizes the coset
. Fluctuations around this background define an open-string
generalization of the corresponding chiral nonlinear sigma model. Tree-level
scattering amplitudes of on-shell massless states (\lq pions') reduce to the
amplitudes of the principal chiral model for the group in the low energy
limit. Furthermore, the condition for the vanishing of the renormalization
group beta function at one loop results in the familiar equation of motion for
that model. The quantum corrections to the open-string theory generate a mixing
of open and closed strings so that the coset-space pions mix with the
closed-string gauge fields, resulting in a Higgs-like breakdown of
the symmetry to the diagonal group. The case of non-oriented strings is
also discussed.Comment: 32 pages, LaTeX, 2 figures in uuencoded fil
Quantum Black Holes
Static solutions of large- quantum dilaton gravity in dimensions are
analyzed and found to exhibit some unusual behavior. As expected from previous
work, infinite-mass solutions are found describing a black hole in equilibrium
with a bath of Hawking radiation. Surprisingly, the finite mass solutions are
found to approach zero coupling both at the horizon and spatial infinity, with
a ``bounce'' off of strong coupling in between. Several new zero mass solutions
-- candidate quantum vacua -- are also described.Comment: 14 pages + 6 figure
CT-duality as a local property of the world-sheet
In the present article, we study the local features of the world-sheet in the
case when probe bosonic string moves in antisymmetric background field. We
generalize the geometry of surfaces embedded in space-time to the case when the
torsion is present. We define the mean extrinsic curvature for spaces with
Minkowski signature and introduce the concept of mean torsion. Its orthogonal
projection defines the dual mean extrinsic curvature. In this language, the
field equation is just the equality of mean extrinsic curvature and extrinsic
mean torsion, which we call CT-duality. To the world-sheet described by this
relation we will refer as CT-dual surface.Comment: Latex, 15 pages, 2 Figure
Loop Variables and Gauge Invariance in (Open) Bosonic String Theory
We give a simplified and more complete description of the loop variable
approach for writing down gauge invariant equations of motion for the fields of
the open string. A simple proof of gauge invariance to all orders is given. In
terms of loop variables, the interacting equations look exactly like the free
equations, but with a loop variable depending on an extra parameter, thus
making it a band of finite width. The arguments for gauge invariance work
exactly as in the free case. We show that these equations are Wilsonian RG
equations with a finite world-sheet cutoff and that in the infrared limit,
equivalence with the Callan-Symanzik -functions should ensure that they
reproduce the on-shell scattering amplitudes in string theory. It is applied to
the tachyon-photon system and the general arguments for gauge invariance can be
easily checked to the order calculated. One can see that when there is a finite
world sheet cutoff in place, even the U(1) invariance of the equations for the
photon, involves massive mode contributions. A field redefinition involving the
tachyon is required to get the gauge transformations of the photon into
standard form.Comment: 20 pages, Late
Information Loss and Anomalous Scattering
The approach of 't Hooft to the puzzles of black hole evaporation can be
applied to a simpler system with analogous features. The system is
dimensional electrodynamics in a linear dilaton background. Analogues of black
holes, Hawking radiation and evaporation exist in this system. In perturbation
theory there appears to be an information paradox but this gets resolved in the
full quantum theory and there exists an exact -matrix, which is fully
unitary and information conserving. 't Hooft's method gives the leading terms
in a systematic approximation to the exact result.Comment: 18 pages, 3 figures (postscript files available soon on request),
(earlier version got corrupted by mail system
Low-Energy Theorems for Gluodynamics at Finite Temperature
We generalize the low-energy theorems of gluodynamics to finite temperature.
Examples of the theorems in the low and high temperature limits are given.Comment: 8 pages latex plus 1 postscript figur
Comments on Three-Branes
The Born--Infeld-like effective world-volume theory of a single 3-brane is
deduced from a manifestly space-time supersymmetric description of the
corresponding -brane.
This is shown to be invariant under transformations that act on the
abelian gauge field as well as the bulk fields. The effective theory of two
nearby parallel three-branes involves massive world-volume supermultiplets
which transform under into the dyonic solitons of four-dimensional
spontaneously broken Yang--Mills theory.Comment: 13 pages, LATEX. Minor typos correcte
The application of low crude protein wheat-soyabean diets to growing and finishing pigs: 2. The effects on nutrient digestibility, nitrogen excretion, faecal volatile fatty acid concentration and ammonia emission from boars
peer-reviewedThis study received financial support from Telltech Ltd. (Wicklow, Ireland) and Enterprise Ireland (Dublin, Ireland).Diets containing 132, 152, 183 and 206 g/kg crude protein (CP) were fed to growing and
finishing boars to evaluate the effect on nutrient digestibility, N balance, faecal volatile
fatty acids (VFA) and ammonia-N (NH3–N) emission. Dietary CP concentration was
adjusted by altering the ratio of wheat:soyabean meal. Lysine, threonine, tryptophan
and total sulphur-containing amino acids were included in all diets at concentrations
equivalent to that in the highest CP diet. All diets were formulated to provide 9.7 MJ/kg
of net energy. Urine and faeces were collected from 16 boars (4 boars per treatment)
housed in metabolism crates. Collections were performed at 72, 80 and 87 kg live weight.
NH3–N emission was measured over 10 days using a laboratory scale procedure.
Reducing the concentration of dietary CP decreased N intake (linear, P < 0.01), the
excretion of urinary N, ammoniacal N and total N (linear, P < 0.001; cubic, P < 0.001)
and the emission of NH3–N (linear, P < 0.001; cubic, P < 0.01). Total N excretion and
NH3–N emission decreased 8.7% and 10.1% per 10 g/kg reduction in dietary CP
concentration between 205.6 and 131.9 g/kg, respectively. There was no interaction
between dietary CP concentration and collection period. N balance differed between the collection periods and less NH3–N was emitted at 87 kg than at 72 kg. Decreasing
dietary CP reduced faecal VFA concentration (linear, P < 0.05) and the molar proportions
of acetic and butyric acids (quadratic, P < 0.01).Enterprise Irelan
Loop Variables with Chan-Paton Factors
The Loop Variable method that has been developed for the U(1) bosonic open
string is generalized to include non-Abelian gauge invariance by incorporating
"Chan-Paton" gauge group indices. The scale transformation symmetry that was responsible for gauge invariance in the U(1) case
continues to be a symmetry. In addition there is a "rotation" symmetry. Both
symmetries crucially involve the massive modes. However it is plausible that
only a linear combination, which is the usual Yang-Mills transformation on
massless fields, has a smooth (world sheet) continuum limit. We also illustrate
how an infinite number of terms in the equation of motion in the cutoff theory
add up to give a term that has a smooth continuum limit, and thus contributes
to the low energy Yang-Mills equation of motion.Comment: One paragraph has been modified and the connection with the
Renormalization Group is explaine
Integrable boundary interaction in 3D target space: the "pillow-brane" model
We propose a model of boundary interaction, with three-dimensional target
space, and the boundary values of the field {\vec X}\in R^3 constrained to lay
on a two-dimensional surface of the "pillow" shape. We argue that the model is
integrable, and suggest that its exact solution is described in terms of
certain linear ordinary differential equation.Comment: 28 pages, 4 figure
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