106 research outputs found
Consequences of t-channel unitarity for the interaction of real and virtual photons at high energies
We analyze the consequences of t-channel unitarity for photon cross sections
and show what assumptions are necessary to allow for the existence of new
singularities at for the and total
cross sections. For virtual photons, such singularities can in general be
present, but we show that, apart from the perturbative singularity associated
with , no new ingredient is needed to
reproduce the data from LEP and HERA, in the Regge region.Comment: 10 pages, LaTeX2e with kluwer.sty, 7 figures. Talk presented at the
Second International "Cetraro" Workshop & NATO Advanced Research Workshop
"Diffraction 2002", Alushta, Crimea, Ukraine, August 31 - September 6, 200
Yangian symmetry and bound states in AdS/CFT boundary scattering
We consider the problem of boundary scattering for Y=0 maximal giant graviton
branes. We show that the boundary S-matrix for the fundamental excitations has
a Yangian symmetry. We then exploit this symmetry to determine the boundary
S-matrix for two-particle bound states. We verify that this boundary S-matrix
satisfies the boundary Yang-Baxter equations.Comment: 17 page
On the Use of Quantum Algebras in Rotation-Vibration Spectroscopy
A two-parameter deformation of the Lie algebra u is used, in conjunction
with the rotor system and the oscillator system, to generate a model for
rotation-vibration spectroscopy of molecules and nuclei.Comment: 10 pages, Latex File, published in Modern Group Theoretical Methods
in Physics, J. Bertrand et al. (eds.), Kluwer Academic Publishers (1995),
27-3
Noncommutative Symmetries and Gravity
Spacetime geometry is twisted (deformed) into noncommutative spacetime
geometry, where functions and tensors are now star-multiplied. Consistently,
spacetime diffeomorhisms are twisted into noncommutative diffeomorphisms. Their
deformed Lie algebra structure and that of infinitesimal Poincare'
transformations is defined and explicitly constructed.
This allows to construct a noncommutative theory of gravity.Comment: 26 pages. Lectures given at the workshop `Noncommutative Geometry in
Field and String Theories', Corfu Summer Institute on EPP, September 2005,
Corfu, Greece. Version 2: Marie Curie European Reintegration Grant
MERG-CT-2004-006374 acknowledge
Conformal algebra: R-matrix and star-triangle relation
The main purpose of this paper is the construction of the R-operator which
acts in the tensor product of two infinite-dimensional representations of the
conformal algebra and solves Yang-Baxter equation. We build the R-operator as a
product of more elementary operators S_1, S_2 and S_3. Operators S_1 and S_3
are identified with intertwining operators of two irreducible representations
of the conformal algebra and the operator S_2 is obtained from the intertwining
operators S_1 and S_3 by a certain duality transformation. There are
star-triangle relations for the basic building blocks S_1, S_2 and S_3 which
produce all other relations for the general R-operators. In the case of the
conformal algebra of n-dimensional Euclidean space we construct the R-operator
for the scalar (spin part is equal to zero) representations and prove that the
star-triangle relation is a well known star-triangle relation for propagators
of scalar fields. In the special case of the conformal algebra of the
4-dimensional Euclidean space, the R-operator is obtained for more general
class of infinite-dimensional (differential) representations with nontrivial
spin parts. As a result, for the case of the 4-dimensional Euclidean space, we
generalize the scalar star-triangle relation to the most general star-triangle
relation for the propagators of particles with arbitrary spins.Comment: Added references and corrected typo
Relating Gauge Theories via Gauge/Bethe Correspondence
In this note, we use techniques from integrable systems to study relations
between gauge theories. The Gauge/Bethe correspondence, introduced by Nekrasov
and Shatashvili, identifies the supersymmetric ground states of an N=(2,2)
supersymmetric gauge theory in two dimensions with the Bethe states of a
quantum integrable system. We make use of this correspondence to relate three
different quiver gauge theories which correspond to three different
formulations of the Bethe equations of an integrable spin chain called the tJ
model.Comment: 30 pages, published in JHEP. LaTeX problem correcte
Observation of a red-blue detuning asymmetry in matter-wave superradiance
We report the first experimental observations of strong suppression of
matter-wave superradiance using blue-detuned pump light and demonstrate a
pump-laser detuning asymmetry in the collective atomic recoil motion. In
contrast to all previous theoretical frameworks, which predict that the process
should be symmetric with respect to the sign of the pump-laser detuning, we
find that for condensates the symmetry is broken. With high condensate
densities and red-detuned light, the familiar distinctive multi-order,
matter-wave scattering pattern is clearly visible, whereas with blue-detuned
light superradiance is strongly suppressed. In the limit of a dilute atomic
gas, however, symmetry is restored.Comment: Accepted by Phys. Rev. Let
Quantum Sine(h)-Gordon Model and Classical Integrable Equations
We study a family of classical solutions of modified sinh-Gordon equation,
$\partial_z\partial_{{\bar z}} \eta-\re^{2\eta}+p(z)\,p({\bar z})\
\re^{-2\eta}=0p(z)=z^{2\alpha}-s^{2\alpha}Q(\alpha>0)(\alpha<-1)$ models.Comment: 35 pages, 3 figure
Twisted Yangians for symmetric pairs of types B, C, D
We study a class of quantized enveloping algebras, called twisted Yangians, associated with the symmetric pairs of types B, C, D in Cartan's classification. These algebras can be regarded as coideal subalgebras of the extended Yangian for orthogonal or symplectic Lie algebras. They can also be presented as quotients of a reflection algebra by additional symmetry relations. We prove an analogue of the Poincare-Birkoff-Witt Theorem, determine their centres and study also extended reflection algebras
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