594 research outputs found
Looking at the Haldane Conjecture from a Grouptheoretical Point of View
Based on the Lieb-Schultz-Mattis construction we present a five parameter
family of Spin-1 Hamiltonians with degenerate groundstate. Starting from the
critical symmetric Hamiltonian, we look for those perturbations of the
symmetry, which leave the groundstate degenerate. We also discuss the
spin-3/2 -case.Comment: 9 pages RevTex 3.
A Model-independent Description of New Physics effects in e+e- to t tbar
We study the potential of a future collider for the search of
anomalous gamma t t bar and Z t t bar couplings, assuming that CP-invariance
holds. This is done in a model-independent way, considering that all six
possible couplings do appear. Two experimental situations are envisaged, with
and without electron beam polarization. Observability limits in the form of
domains in the 6-dimensional parameter space are established. Illustrations for
specific constrained models are also presented and implications for new physics
searches are discussed.Comment: 26 pages and 5 figures. e-mail: [email protected]
Orbit spaces of free involutions on the product of two projective spaces
Let be a finitistic space having the mod 2 cohomology algebra of the
product of two projective spaces. We study free involutions on and
determine the possible mod 2 cohomology algebra of orbit space of any free
involution, using the Leray spectral sequence associated to the Borel fibration
. We also
give an application of our result to show that if has the mod 2 cohomology
algebra of the product of two real projective spaces (respectively complex
projective spaces), then there does not exist any -equivariant
map from for (respectively ), where
is equipped with the antipodal involution.Comment: 14 pages, to appear in Results in Mathematic
Potts model on recursive lattices: some new exact results
We compute the partition function of the Potts model with arbitrary values of
and temperature on some strip lattices. We consider strips of width
, for three different lattices: square, diced and `shortest-path' (to be
defined in the text). We also get the exact solution for strips of the Kagome
lattice for widths . As further examples we consider two lattices
with different type of regular symmetry: a strip with alternating layers of
width and , and a strip with variable width. Finally we make
some remarks on the Fisher zeros for the Kagome lattice and their large
q-limit.Comment: 17 pages, 19 figures. v2 typos corrected, title changed and
references, acknowledgements and two further original examples added. v3 one
further example added. v4 final versio
Distribution and density of the partition function zeros for the diamond-decorated Ising model
Exact renormalization map of temperature between two successive decorated
lattices is given, and the distribution of the partition function zeros in the
complex temperature plane is obtained for any decoration-level. The rule
governing the variation of the distribution pattern as the decoration-level
changes is given. The densities of the zeros for the first two
decoration-levels are calculated explicitly, and the qualitative features about
the densities of higher decoration-levels are given by conjecture. The Julia
set associated with the renormalization map is contained in the distribution of
the zeros in the limit of infinite decoration level, and the formation of the
Julia set in the course of increasing the decoration-level is given in terms of
the variations of the zero density.Comment: 8 pages,8figure
The transition from the adiabatic to the sudden limit in core level photoemission: A model study of a localized system
We consider core electron photoemission in a localized system, where there is
a charge transfer excitation. The system is modelled by three electron levels,
one core level and two outer levels. The model has a Coulomb interaction
between these levels and the continuum states into which the core electron is
emitted. The model is simple enough to allow an exact numerical solution, and
with a separable potential an analytic solution. We calculate the ratio
r(omega) between the weights of the satellite and the main peak as a function
of the photon energy omega. The transition from the adiabatic to the sudden
limit takes place for quite small photoelectron kinetic energies. For such
small energies, the variation of the dipole matrix element is substantial and
described by the energy scale Ed. Without the coupling to the photoelectron,
the corresponding ratio r0(omega) is determined by Ed and the satellite
excitation energy dE. When the interaction potential with the continuum states
is introduced, a new energy scale Es=1/(2Rs^2) enters, where Rs is a length
scale of the interaction potential. At threshold there is typically a (weak)
constructive interference between intrinsic and extrinsic contributions, and
the ratio r(omega)/r0(omega) is larger than its limiting value for large omega.
The interference becomes small or weakly destructive for photoelectron energies
of the order Es. For larger energies r(omega)/r0(omega) therefore typically has
a weak undershoot. If this undershoot is neglected, r(omega)/r0(omega) reaches
its limiting value on the energy scale Es.Comment: 18 pages, latex2e, 13 eps figure
Effective Field Theories on Non-Commutative Space-Time
We consider Yang-Mills theories formulated on a non-commutative space-time
described by a space-time dependent anti-symmetric field .
Using Seiberg-Witten map techniques we derive the leading order operators for
the effective field theories that take into account the effects of such a
background field. These effective theories are valid for a weakly
non-commutative space-time. It is remarkable to note that already simple models
for can help to loosen the bounds on space-time
non-commutativity coming from low energy physics. Non-commutative geometry
formulated in our framework is a potential candidate for new physics beyond the
standard model.Comment: 22 pages, 1 figur
The anomalous Higgs-top couplings in the MSSM
The anomalous couplings of the top quark and the Higgs boson has been studied
in an effective theory resulting in the framework of the minimal supersymmetric
extension of the standard model (MSSM) when the heavy fields are integrated
out. Constraints on the parameters of the model from the experimental data on
the ratio are derived.Comment: Latex, 26 pages + 13 ps figures, final version in PR
Symmetries and Elasticity of Nematic Gels
A nematic liquid-crystal gel is a macroscopically homogeneous elastic medium
with the rotational symmetry of a nematic liquid crystal. In this paper, we
develop a general approach to the study of these gels that incorporates all
underlying symmetries. After reviewing traditional elasticity and clarifying
the role of broken rotational symmetries in both the reference space of points
in the undistorted medium and the target space into which these points are
mapped, we explore the unusual properties of nematic gels from a number of
perspectives. We show how symmetries of nematic gels formed via spontaneous
symmetry breaking from an isotropic gel enforce soft elastic response
characterized by the vanishing of a shear modulus and the vanishing of stress
up to a critical value of strain along certain directions. We also study the
phase transition from isotropic to nematic gels. In addition to being fully
consistent with approaches to nematic gels based on rubber elasticity, our
description has the important advantages of being independent of a microscopic
model, of emphasizing and clarifying the role of broken symmetries in
determining elastic response, and of permitting easy incorporation of spatial
variations, thermal fluctuations, and gel heterogeneity, thereby allowing a
full statistical-mechanical treatment of these novel materials.Comment: 21 pages, 4 eps figure
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