3,181 research outputs found
First results from simulations of supersymmetric lattices
We conduct the first numerical simulations of lattice theories with exact
supersymmetry arising from the orbifold constructions of
\cite{Cohen:2003xe,Cohen:2003qw,Kaplan:2005ta}. We consider the \cQ=4 theory
in dimensions and the \cQ=16 theory in dimensions. We show
that the U(N) theories do not possess vacua which are stable
non-perturbatively, but that this problem can be circumvented after truncation
to SU(N). We measure the distribution of scalar field eigenvalues, the spectrum
of the fermion operator and the phase of the Pfaffian arising after integration
over the fermions. We monitor supersymmetry breaking effects by measuring a
simple Ward identity. Our results indicate that simulations of
super Yang-Mills may be achievable in the near future.Comment: 25 pages, 14 figures, 9 tables. 3 references adde
Exact Ward-Takahashi identity for the lattice N=1 Wess-Zumino model
The lattice Wess-Zumino model written in terms of the Ginsparg-Wilson
relation is invariant under a generalized supersymmetry transformation which is
determined by an iterative procedure in the coupling constant. By studying the
associated Ward-Takahashi identity up to order we show that this lattice
supersymmetry automatically leads to restoration of continuum supersymmetry
without fine tuning. In particular, the scalar and fermion renormalization wave
functions coincide.Comment: 6 pages, 5 figures, Talk given at QG05, Cala Gonone, Sardinia, Italy.
12-16 September 200
Learning In the Visual Arts and the Worldviews of Young Children
This paper reports a research study into the effects of rich,sustained visual arts instruction on 103inner city 9-year-olds in two major US cities. We use the lenses of social learning theory, theories of motivation and self-efficacy, and recentresearch on artistic thinking to investigate the programs' effects on children's self-beliefs and creative thinking. The study enlisted a pre -- post measure,treatment-comparison group design along with structured observations of participant andcomparison group classrooms. The arts students made significant comparative gains on a selfefficacy scale and on an 'originality' subscale of a standard creativity test. These effects are attributed to children's engagement in art and to the social organization of instruction includingreinforcing peer and student -- adult relationships. Relationships between self-efficacy beliefs andtendencies to think originally are explored
A geometrical approach to N=2 super Yang-Mills theory on the two dimensional lattice
We propose a discretization of two dimensional Euclidean Yang-Mills theories
with N=2 supersymmetry which preserves exactly both gauge invariance and an
element of supersymmetry. The approach starts from the twisted form of the
continuum super Yang Mills action which we show may be written in terms of two
real Kahler-Dirac fields whose components transform into each other under the
twisted supersymmetry. Once the theory is written in this geometrical language
it is straightforward to discretize by mapping the component tensor fields to
appropriate geometrical structures in the lattice and by replacing the
continuum exterior derivative and its adjoint by appropriate lattice covariant
difference operators. The lattice action is local and possesses a unique vacuum
state while the use of Kahler-Dirac fermions ensures the model does not exhibit
spectrum doubling.Comment: Minor typos fixed. Version to be published in JHE
Deconstruction and other approaches to supersymmetric lattice field theories
This report contains both a review of recent approaches to supersymmetric
lattice field theories and some new results on the deconstruction approach. The
essential reason for the complex phase problem of the fermion determinant is
shown to be derivative interactions that are not present in the continuum.
These irrelevant operators violate the self-conjugacy of the fermion action
that is present in the continuum. It is explained why this complex phase
problem does not disappear in the continuum limit. The fermion determinant
suppression of various branches of the classical moduli space is explored, and
found to be supportive of previous claims regarding the continuum limit.Comment: 70 page
Towards lattice simulation of the gauge theory duals to black holes and hot strings
A generalization of the AdS/CFT conjecture postulates a duality between IIA
string theory and 16 supercharge Yang-Mills quantum mechanics in the large N 't
Hooft limit. At low temperatures string theory describes black holes, whose
thermodynamics may hence be studied using the dual quantum mechanics. This
quantum mechanics is strongly coupled which motivates the use of lattice
techniques. We argue that, contrary to expectation, the theory when discretized
naively will nevertheless recover continuum supersymmetry as the lattice
spacing is sent to zero. We test these ideas by studying the 4 supercharge
version of this Yang-Mills quantum mechanics in the 't Hooft limit. We use both
a naive lattice action and a manifestly supersymmetric action. Using Monte
Carlo methods we simulate the Euclidean theories, and study the lattice
continuum limit, for both thermal and non-thermal periodic boundary conditions,
confirming continuum supersymmetry is recovered for the naive action when
appropriate. We obtain results for the thermal system with N up to 12. These
favor the existence of a single deconfined phase for all non-zero temperatures.
These results are an encouraging indication that the 16 supercharge theory is
within reach using similar methods and resources.Comment: 49 pages, 14 figure
Random manifolds and quantum gravity
The non-perturbative, lattice field theory approach towards the quantization
of Euclidean gravity is reviewed. Included is a tentative summary of the most
significant results and a presentation of the current state of art.Comment: invited plenary talk at LATTICE '99 (Pisa), latex 5p
Various Super Yang-Mills Theories with Exact Supersymmetry on the Lattice
We continue to construct lattice super Yang-Mills theories along the line
discussed in the previous papers \cite{sugino, sugino2}. In our construction of
theories in four dimensions, the problem of degenerate vacua
seen in \cite{sugino} is resolved by extending some fields and soaking up
would-be zero-modes in the continuum limit, while in the weak coupling
expansion some surplus modes appear both in bosonic and fermionic sectors
reflecting the exact supersymmetry. A slight modification to the models is made
such that all the surplus modes are eliminated in two- and three-dimensional
models obtained by dimensional reduction thereof. models in
three dimensions need fine-tuning of three and one parameters respectively to
obtain the desired continuum theories, while two-dimensional models with do not require any fine-tuning.Comment: 28 pages, no figure, LaTeX, JHEP style; (v2) published version to
JHEP; (v3) argument on the vacuum degeneracy revised, 34 page
Shape transformations of a model of self-avoiding triangulated surfaces of sphere topology
We study a surface model with a self-avoiding (SA) interaction using the
canonical Monte Carlo simulation technique on fixed-connectivity (FC)
triangulated lattices of sphere topology. The model is defined by an area
energy, a deficit angle energy, and the SA potential. A pressure term is also
included in the Hamiltonian. The volume enclosed by the surface is well defined
because of the self-avoidance. We focus on whether or not the interaction
influences the phase structure of the FC model under two different conditions
of pressure ; zero and small negative. The results are compared
with the previous results of the self-intersecting model, which has a rich
variety of phases; the smooth spherical phase, the tubular phase, the linear
phase, and the collapsed phase. We find that the influence of the SA
interaction on the multitude of phases is almost negligible except for the
evidence that no crumpled surface appears under {\it \Delta} p\=\0 at least
even in the limit of zero bending rigidity \alpha\to \0. The Hausdorff
dimension is obtained in the limit of \alpha\to \0 and compared with previous
results of SA models, which are different from the one in this paper.Comment: 9 figure
Matrix formulation of superspace on 1D lattice with two supercharges
Following the approach developed by some of the authors in recent papers and
using a matrix representation for the superfields, we formulate an exact
supersymmetric theory with two supercharges on a one dimensional lattice. In
the superfield formalism supersymmetry transformations are uniquely defined and
do not suffer of the ambiguities recently pointed out by some authors. The
action can be written in a unique way and it is invariant under all
supercharges. A modified Leibniz rule applies when supercharges act on a
superfield product and the corresponding Ward identities take a modified form
but hold exactly at least at the tree level, while their validity in presence
of radiative corrections is still an open problem and is not considered here.Comment: 25 page
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