27,014 research outputs found
Strings and Supersymmetry as Tools for Perturbative QCD
We review techniques simplifying the analytic calculation of one-loop QCD
amplitudes with many external legs, for use in next-to-leading-order
corrections to multi-jet processes. We explain how a supersymmetry-inspired
organization works well in conjunction with other tools, namely the color and
helicity decompositions of amplitudes, and the constraints imposed by
perturbative unitarity and collinear singularities. String theory seems most
useful as a heuristic guide. Using these techniques, the complete set of
one-loop five-parton QCD amplitudes, as well as certain sequences of special
helicity amplitudes with an arbitrary number of external gluons, have been
obtained.Comment: LaTex, 11 pages with 2 encapsulated figures in a uuencoded file.
Presented at SUSY95, Paris, May, 199
Antenna Factorization in Strongly-Ordered Limits
When energies or angles of gluons emitted in a gauge-theory process are small
and strongly ordered, the emission factorizes in a simple way to all orders in
perturbation theory. I show how to unify the various strongly-ordered soft,
mixed soft-collinear, and collinear limits using antenna factorization
amplitudes, which are generalizations of the Catani--Seymour dipole
factorization function.Comment: 21 pages, 8 figures; final Phys Rev version, corrected definition of
multiple-emission recosnstruction functions for strongly-ordered limit, added
appendix with new form of double-emission antenna function valid in
strongly-ordered limi
Classical String in Curved Backgrounds
The Mathisson-Papapetrou method is originally used for derivation of the
particle world line equation from the covariant conservation of its
stress-energy tensor. We generalize this method to extended objects, such as a
string. Without specifying the type of matter the string is made of, we obtain
both the equations of motion and boundary conditions of the string. The world
sheet equations turn out to be more general than the familiar minimal surface
equations. In particular, they depend on the internal structure of the string.
The relevant cases are classified by examining canonical forms of the effective
2-dimensional stress-energy tensor. The case of homogeneously distributed
matter with the tension that equals its mass density is shown to define the
familiar Nambu-Goto dynamics. The other three cases include physically relevant
massive and massless strings, and unphysical tahyonic strings.Comment: 12 pages, REVTeX 4. Added a note and one referenc
Recommended from our members
Liophis ceii
Number of Pages: 2Integrative BiologyGeological Science
Exponentially Small Couplings between Twisted Fields of Orbifold String Theories
We investigate the natural occurence of exponentially small couplings in
effective field theories deduced from higher dimensional models. We calculate
the coupling between twisted fields of the Z_3 Abelian orbifold
compactification of the heterotic string. Due to the propagation of massive
Kaluza-Klein modes between the fixed points of the orbifold, the massless
twisted fields located at these singular points become weakly coupled. The
resulting small couplings have an exponential dependence on the mass of the
intermediate states and the distance between the fixed points.Comment: 21 pages, 4 figure
Recommended from our members
Liophis jaegeri
Number of Pages: 4Integrative BiologyGeological Science
Sharing storage using dirty vectors
Consider a computation F with n inputs (independent variables) and m outputs (dependent variables) and suppose that we wish to evaluate the Jacobian of F. Automatic differentiation commonly performs this evaluation by associating vector storage either with the program variables (in the case of forward-mode automatic differentiation) or with the adjoint variables (in the case of reverse). Each vector component contains a partial derivative with respect to an independent variable, or a partial derivative of a dependent variable, respectively. The vectors may be full vectors, or they may be dynamically managed sparse data structures. In either case, many of these vectors will be scalar multiples of one another. For example, any intermediate variable produced by a unary operation in the forward mode will have a derivative vector that is a multiple of the derivative for the argument. Any computational graph node that is read just once during its lifetime will have an adjoint vector that is a multiple of the adjoint of the node that reads it. It is frequently wasteful to perform component multiplications explicitly. A scalar multiple of another vector can be replaced by a single multiplicative "scale factor" together with a pointer to the other vector. Automated use of this "dirty vector" technique can save considerable memory management overhead and dramatically reduce the number of floating-point operations required. In particular, dirty vectors often allow shared threads of computation to be reverse-accumulated cheaply. The mechanism permits a number of generalizations, some of which give efficient techniques for preaccumulation
The performance of gender with particular reference to the plays of Shakespeare.
An analytical history of the representation of gender on the English stage from Shakespeare to modern times is followed by a detailed examination of the National Theatre of Great Britain's production of `As You Like It' in 1967, the first production of a play by Shakespeare for over three hundred years in which the female parts were played by male actors. Subsequent cross-cast productions of Shakespeare's plays by Glasgow Citizen's Theatre, Prospect theatre Company, Lindsay Kemp, Theatre du Soleil and Goodman Theatre Chicago are discussed and the views of directors and critics of those productions analysed. The thesis then presents the results of a series of workshops with actors into the playing of gender and examines, by means of an experiment employing Gender Schema Theory, how actors construct gender in a production of `Twelfth Night'.
The final part of the thesis describes a controlled experiment into audience perception of gender using a scene from `Hamlet'. Theories are presented about the nature of the performance of gender on stage and
the use of theatrical conventions, the relationship between social conventions and stage conventions, about the way in which an actor builds a character, the influence of biological sex on actors' creativity, and about audience participation
IMPACTS OF INCREASED CLIMATE VARIABILITY ON THE PROFITABILITY OF MIDWEST AGRICULTURE
Approximate profit functions are estimated using time-series, cross-sectional, county level data for 12 midwest states. Measures of climate variability are included in the profit functions. Simulated impacts of climate changes on profits are derived. Results show that inclusion of measures of climate variation are important for measuring the impact of changes in mean temperature and precipitation levels. Failure to account for the impact of differences in variability leads to an overestimate of damages. If global warming increases diurnal variation, such increases would have negative impacts on the profitability of midwest agriculture.climate change, climate variability, Midwest, profit function, Farm Management,
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