1,596 research outputs found
Fully Off-shell Effective Action and its Supersymmetry in Matrix Theory
As a step toward clarification of the power of supersymmetry (SUSY) in Matrix
theory, a complete calculation, including all the spin effects, is performed of
the effective action of a probe D-particle, moving along an arbitrary
trajectory in interaction with a large number of coincident source D-particles,
at one loop at order 4 in the derivative expansion. Furthermore, exploiting the
SUSY Ward identity developed previously, the quantum-corrected effective
supersymmetry transformation laws are obtained explicitly to the relevant order
and are used to verify the SUSY-invariance of the effective action. Assuming
that the agreement with 11-dimensional supergravity persists, our result can be
regarded as a prediction for supergravity calculation, which, yet unavailable,
is known to be highly non-trivial.Comment: 27 page
Power of Supersymmetry in D-particle Dynamics
A new systematic method is developed to study to what extent the symmetry
requirements alone, above all the invariance under 16 supersymmetries (SUSY),
determine the completely off-shell effective action of a D-particle,
i.e. without imposing any restrictions on its position and spin
. Our method consists of (i) writing down the proper
closure relations for general SUSY transformations (which
necessarily involves itself) together with the invariance condition
(ii) and solving this coupled system of functional
differential equations for and simultaneously,
modulo field redefinitions, in a consistent derivative expansion scheme. Our
analysis is facilitated by a novel classification scheme introduced for the
terms in . At order 2 and 4, although no assumption is made on the
underlying theory, we reproduce the effective action previously obtained at the
tree and the 1-loop level in Matrix theory respectively (modulo two constants),
together with the quantum-corrected SUSY transformations which close properly.
This constitutes a complete unambiguous proof of off-shell non-renormalization
theorems.Comment: 44 pages, v2: typos corrected, published versio
A Theorem on the Power of Supersymmetry in Matrix Theory
For the so-called source-probe configuration in Matrix theory, we prove the
following theorem concerning the power of supersymmetry (SUSY): Let be
a quantum-corrected effective SUSY transformation operator expandable in powers
of the coupling constant as ,
where is of the tree-level form. Then, apart from an overall
constant, the SUSY Ward identity determines the off-shell
effective action uniquely to arbitrary order of perturbation theory,
provided that the symmetry is preserved. Our proof depends only on the
properties of the tree-level SUSY transformation laws and does not require the
detailed knowledge of quantum corrections.Comment: 20 page
Structure in Supersymmetric Yang-Mills Theory
We show that requiring sixteen supersymmetries in quantum mechanical gauge
theory implies the existence of a web of constrained interactions. Contrary to
conventional wisdom, these constraints extend to arbitrary orders in the
momentum expansion.Comment: 22 pages, LaTe
The Dirac field in Taub-NUT background
We investigate the SO(4,1) gauge-invariant theory of the Dirac fermions in
the external field of the Kaluza-Klein monopole, pointing out that the quantum
modes can be recovered from a Klein-Gordon equation analogous to the Schr\"
odinger equation in the Taub-NUT background. Moreover, we show that there is a
large collection of observables that can be directly derived from those of the
scalar theory. These offer many possibilities of choosing complete sets of
commuting operators which determine the quantum modes. In addition there are
some spin- like and Dirac-type operators involving the covariantly constant
Killing-Yano tensors of the hyper-K\" ahler Taub-NUT space. The energy
eigenspinors of the central modes in spherical coordinates are completely
evaluated in explicit, closed form.Comment: 20 pages, latex, no figure
Poincare Polynomials and Level Rank Dualities in the Coset Construction
We review the coset construction of conformal field theories; the emphasis is
on the construction of the Hilbert spaces for these models, especially if fixed
points occur. This is applied to the superconformal cosets constructed by
Kazama and Suzuki. To calculate heterotic string spectra we reformulate the
Gepner con- struction in terms of simple currents and introduce the so-called
extended Poincar\'e polynomial. We finally comment on the various equivalences
arising between models of this class, which can be expressed as level rank
dualities. (Invited talk given at the III. International Conference on
Mathematical Physics, String Theory and Quantum Gravity, Alushta, Ukraine, June
1993. To appear in Theor. Math. Phys.)Comment: 14 pages in LaTeX, HD-THEP-93-4
Generalized symmetries and invariant matter couplings in two-dimensional dilaton gravity
New features of the generalized symmetries of generic two-dimensional dilaton
models of gravity are presented and invariant gravity-matter couplings are
introduced. We show that there is a continuum set of Noether symmetries, which
contains half a de Witt algebra. Two of these symmetries are area-preserving
transformations. We show that gravity-matter couplings which are invariant
under area preserving transformations only contribute to the dynamics of the
dilaton-gravity sector with a reshaping of the dilaton potential. The
interaction with matter by means of invariant metrics is also considered. We
show in a constructive way that there are metrics which are invariant under two
of the symmetries. The most general metrics and minimal couplings that fulfil
this condition are found.Comment: LateX file, no macros, 14pp: minor changes have been made and some
misprints have been correcte
Exact non-factorizable O(alpha_s g^2) two-loop contribution to Z -> b bbar
For Z -> b bbar, we calculate all the two-loop top dependent Feynman graphs,
which have mixed QCD and electroweak contributions that are not factorizable.
For evaluating the graphs, without resorting to a mass expansion, we apply a
two-loop extension of the one-loop Passarino-Veltman reduction. This is an
analytic-numerical method, which first converts all diagrams into a set of ten
standard scalar functions, and then integrates them numerically over the
remaining Feynman parameters, with rapid convergence and high accuracy. We
discuss the treatment of infrared singularities within our methods. We do not
resort to unitarity cuts of two-point functionsfor calculating decay rates;
these are useful only to obtain an inclusive rate. For this reason,
experimental cuts and the experimental infrared energy resolution can be
implemented in our calculation, once the corresponding one-loop gluon
Bremsstrahlung process is added to this calculation
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