6,590 research outputs found
Basics of Generalized Unitarity
We review generalized unitarity as a means for obtaining loop amplitudes from
on-shell tree amplitudes. The method is generally applicable to both
supersymmetric and non-supersymmetric amplitudes, including non-planar
contributions. Here we focus mainly on N=4 Yang-Mills theory, in the context of
on-shell superspaces. Given the need for regularization at loop level, we also
review a six-dimensional helicity-based superspace formalism and its
application to dimensional and massive regularizations. An important feature of
the unitarity method is that it offers a means for carrying over any identified
tree-level property of on-shell amplitudes to loop level, though sometimes in a
modified form. We illustrate this with examples of dual conformal symmetry and
a recently discovered duality between color and kinematics.Comment: 37 pages, 10 figures. Invited review for a special issue of Journal
of Physics A devoted to "Scattering Amplitudes in Gauge Theories", R.
Roiban(ed), M. Spradlin(ed), A. Volovich(ed
Regularization for effective field theory with two heavy particles
A regularization for effective field theory with two propagating heavy
particles is constructed. This regularization preserves the low-energy analytic
structure, implements a low-energy power counting for the one-loop diagrams,
and preserves symmetries respected by dimensional regularization.Comment: 12 pages, 4 figures. Some typos have been corrected, a sentence has
been moved, and two formulas have been further simplifie
Divergences in Kaluza-Klein Models and their String Regularization
Effective field theories with (large) extra dimensions are studied within a
physical regularization scheme provided by string theory. Explicit string
calculations then allow us to consistently analyze the ultraviolet sensitivity
of Kaluza--Klein theories in the presence or absence of low energy
supersymmetry.Comment: 50 pages, LaTe
Lattice Regularization of Gauge Theories Without Loss of Chiral Symmetry
A lattice regularization procedure for gauge theories is proposed in which
fermions are given a special treatment such that all chiral flavor symmetries
that are free of Adler-Bell-Jackiw anomalies are kept intact. There is no
doubling of fermionic degrees of freedom. A price paid for this feature is that
the number of fermionic degrees of freedom per unit cell is still infinite,
although finiteness of the complete functional integrals can be proven (details
are outlined in an Appendix). Therefore, although perhaps of limited usefulness
for numerical simulations, our scheme can be applied for studying aspects such
as analytic convergence questions, spontaneous symmetry breakdown and baryon
number violation in non-Abelian gauge theories.Comment: Correction of formula in Appendix, and extra references adde
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