12,162 research outputs found
Two-loop scalar diagrams from string theory
We show how to obtain correctly normalized expressions for the Feynman
diagrams of theory with an internal symmetry group, starting
from tachyon amplitudes of the open bosonic string, and suitably performing the
zero--slope limit by giving an arbitrary mass to the tachyon. In particular
we present explicit results for the two--loop amplitudes of theory, in
preparation for the more interesting case of the multiloop amplitudes of
non--abelian gauge theories.Comment: 15 pages, plain Latex, 5 figures include
A unique theory of all forces
In discussing the construction of a consistent theory of quantum gravity
unified with the gauge interactions we are naturally led to a string theory. We
review its properties and the five consistent supersymmetric string theories in
ten dimensions. We finally discuss the evidence that these theories are
actually special limits of a unique 11-dimensional theory, called M-theory, and
a recent conjecture for its explicit formulation as a supersymmetric Matrix
theory.Comment: 11 pages, Latex. Talk given at the Conference `Beyond the standard
model', V, Balholm, Norway, May 199
Non conformal gauge theories from D branes
We use fractional and wrapped branes to describe perturbative and
nonperturbative properties of the gauge theories living on their worldvolume.
(Talk given at the 35th International Symposium Ahrenshoop on the Theory of
Elementary Particles, Wernsdorf, August 26-30, 2002.)Comment: 7 pages, Late
The Gauge/Gravity Correspondence for Non-Supersymmetric Theories
We review the string construction of the ``orientifold field theories'' and
we show that for these theories the gauge/gravity correspondence is only valid
for a large number of colours.Comment: 7 pages, Latex, Talk given at 37. International Symposium Ahrenshoop,
Berlin, August 2004. Added references and acknowledgements; corrected typo
String techniques for the calculation of renormalization constants in field theory
We describe a set of methods to calculate gauge theory renormalization
constants from string theory, all based on a consistent prescription to
continue off shell open bosonic string amplitudes. We prove the consistency of
our prescription by explicitly evaluating the renormalizations of the two,
three and four-gluon amplitudes, and showing that they obey the appropriate
Ward identities. The field theory limit thus performed corresponds to the
background field method in Feynman gauge. We identify precisely the regions in
string moduli space that correspond to different classes of Feynman diagrams,
and in particular we show how to isolate contributions to the effective action.
Ultraviolet divergent terms are then encoded in a single string integral over
the modular parameter . Finally, we derive a multiloop expression for the
effective action by computing the partition function of an open bosonic string
interacting with an external non-abelian background gauge field.Comment: 54 pages, Latex, uses FEYNMAN.te
String-derived renormalization of Yang-Mills theory
We review the application of bosonic string techniques to the calculation of
renormalization constants and effective actions in Yang-Mills theory. We
display the multiloop string formulas needed to compute Yang-Mills amplitudes,
and we discuss how the renormalizations of proper vertices can be extracted in
the field theory limit. We show how string techniques lead to the background
field method in field theory, and indicate how the gauge invariance of the
multiloop effective action can be inferred form the string formalism.
(Proceedings of the 29th International Symposium on the Theory of Elementary
Particles, Buckow (Germany), Aug.-Sept. 1995. Preprint DFTT 04/96)Comment: 11 pages. Latex, uses espcrc2.sty. Proceedings Buckow '9
Visualization of topological objects in the deconfinement phase of pure QCD
In the last years it turned out that instantons and monopoles have a certain
local correlation in four-dimensional QCD. It was demonstrated by several
groups independently and by different methods that at the locations of
instantons also monopoles in the maximal abelian projection can be found with
enhanced probability. Further we observed such nontrivial correlation functions
in the deconfinement phase. We continue our visualization project to analyze
several specific gauge-field configurations.Comment: 3 pages, 2 EPS figures, Poster presented at "Lattice'97", to appear
in Nucl. Phys. B (Proc. Suppl.
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