41,024 research outputs found
The low energy expansion of the one-loop type II superstring amplitude
The one-loop four-graviton amplitude in either of the type II superstring
theories is expanded in powers of the external momenta up to and including
terms of order s^4 log s R^4, where R^4 denotes a specific contraction of four
linearized Weyl tensors and s is a Mandelstam invariant. Terms in this series
are obtained by integrating powers of the two-dimensional scalar field theory
propagator over the toroidal world-sheet as well as the moduli of the torus.
The values of these coefficients match expectations based on duality relations
between string theory and eleven-dimensional supergravity.Comment: harvmac (b), 25 pages, 3 eps figures. v2: Factors of 2 corrected.
Conclusion unchange
Non-renormalisation Conditions in Type II String Theory and Maximal Supergravity
This paper considers general features of the derivative expansion of Feynman
diagram contributions to the four-graviton scattering amplitude in
eleven-dimensional supergravity compactified on a two-torus. These are
translated into statements about interactions of the form D^2k R^4 in type II
superstring theories, assuming the standard M-theory/string theory duality
relationships, which provide powerful constraints on the effective
interactions. In the ten-dimensional IIA limit we find that there can be no
perturbative contributions beyond k string loops (for k>0). Furthermore, the
genus h=k contributions are determined exactly by the one-loop
eleven-dimensional supergravity amplitude for all values of k. A plausible
interpretation of these observations is that the sum of h-loop Feynman diagrams
of maximally extended supergravity is less divergent than might be expected and
could be ultraviolet finite in dimensions d < 4 + 6/h -- the same bound as for
N=4 Yang--Mills.Comment: 30 pages, 4 figures. v3 Some rewording, typos corrected and some
references added. v4: Abstract rephrased. More typos corrected. Version to be
publishe
Covariant Matrix Model of Superparticle in the Pure Spinor Formalism
On the basis of the Berkovits pure spinor formalism of covariant quantization
of supermembrane, we attempt to construct a M(atrix) theory which is covariant
under Lorentz group. We first construct a bosonic M(atrix) theory by
starting with the first-order formalism of bosonic membrane, which precisely
gives us a bosonic sector of M(atrix) theory by BFSS. Next we generalize this
method to the construction of M(atrix) theory of supermembranes. However, it
seems to be difficult to obtain a covariant and supersymmetric M(atrix) theory
from the Berkovits pure spinor formalism of supermembrane because of the matrix
character of the BRST symmetry. Instead, in this paper, we construct a
supersymmetric and covariant matrix model of 11D superparticle, which
corresponds to a particle limit of covariant M(atrix) theory. By an explicit
calculation, we show that the one-loop effective potential is trivial, thereby
implying that this matrix model is a free theory at least at the one-loop
level.Comment: 13 pages, no figures, two references adde
Supersymmetry Constraints on Type IIB Supergravity
Supersymmetry is used to derive conditions on higher derivative terms in the
effective action of type IIB supergravity. Using these conditions, we are able
to prove earlier conjectures that certain modular invariant interactions of
order alpha' **3 relative to the Einstein-Hilbert term are proportional to
eigenfunctions of the Laplace operator on the fundamental domain of SL(2,Z). We
also discuss how these arguments generalize to terms of higher order in alpha',
as well as to compactifications of supergravity.Comment: 31 pages, harvmac (b); minor correction
Anisotropic higher derivative gravity and inflationary universe
Stability analysis of the Kantowski-Sachs type universe in pure higher
derivative gravity theory is studied in details. The non-redundant generalized
Friedmann equation of the system is derived by introducing a reduced one
dimensional generalized KS type action. This method greatly reduces the labor
in deriving field equations of any complicate models. Existence and stability
of inflationary solution in the presence of higher derivative terms are also
studied in details. Implications to the choice of physical theories are
discussed in details in this paper.Comment: 9 page
Simulation of the Aerodynamic Interaction between Rotor and Ground Obstacle Using Vortex Method
The mutual aerodynamic interaction between rotor wake and surrounding obstacles is complex, and generates high compensatory workload for pilots, degradation of the handling qualities, and performance, and unsteady force on the structure of the obstacles. The interaction also affects the minimum distance between rotorcrafts and obstacles to operate safely. A vortex-based approach is then employed to investigate the complex aerodynamic interaction between rotors and ground obstacle, and identify the distance where the interaction ends, and this is also the objective of the GARTEUR AG22 working group activities. In this approach, the aerodynamic loads of the rotor blades are described through a panel method, and the unsteady behaviour of the rotor wake is modelled using a vortex particle method. The effects of the ground plane and obstacle are accounted for via a viscous boundary model. The method is then applied to a “Large” and a “Wee” rotor near the ground and obstacle, and compared with the earlier experiments carried out at the University of Glasgow. The results show that predicted rotor induced inflow and flow field compare reasonably well with the experiments. Furthermore, at certain conditions, the tip vortices are pushed up and re-injected into the rotor wake due to the effect of the obstacle resulting in a recirculation. Moreover, contrary to without the obstacle case, peak and thickness of the radial outwash near the obstacle are smaller due to the barrier effect of the obstacle, and an upwash is observed. In addition, as the rotor closes to the obstacle, the rotor slipstreams impinge directly on the obstacle, and the upwash near the obstacle is faster, indicating a stronger interaction between the rotor wake and the obstacle. In addition, contrary to the case without the obstacle, the fluctuations of the rotor thrust, and rolling and pitching moments are obviously strengthened. When the distance between the rotor and the obstacle is larger than 3R, the effect of the obstacle is small
Maximum temperature for an Ideal Gas of Kac-Moody Fermions
A lagrangian for gauge fields coupled to fermions with the Kac-Moody group as
its gauge group yields, for the pure fermions sector, an ideal gas of Kac-Moody
fermions. The canonical partition function for the case is shown to
have a maximum temperature , where is the
coupling of the super charge operator to the fermions. This result is
similar to the case of strings but unlike strings the result is obtained from a
well-defined lagrangian.Comment: Needs subeqnarray.sty; To be published in Phys. Rev. D, Dec 15, 1995.
Some typographical errors have been corrected in the revised versio
D-instanton partition functions
Duality arguments are used to determine D-instanton contributions to certain
effective interaction terms of type II supergravity theories in various
dimensions. This leads to exact expressions for the partition functions of the
finite N D-instanton matrix model in d=4 and 6 dimensions that generalize our
previous expression for the case d=10. These results are consistent with the
fact that the Witten index of the T-dual D-particle process should only be
non-vanishing for d=10.Comment: 20 pages, harvmac, typos corrected, reference adde
The Standard Model on a D-brane
We present a consistent string theory model which reproduces the Standard
Model, consisting of a D3-brane at a simple orbifold singularity. We study some
simple features of the phenomenology of the model. We find that the scale of
stringy physics must be in the multi-TeV range. There are natural hierarchies
in the fermion spectrum and there are several possible experimental signatures
of the model.Comment: 8 pages Latex, 1 fig. v2: discussion improved, added new reference
- …