18,097 research outputs found
Cyclic Universe \`{a} la string theory
We shall present a model of the "cyclic universe" that can be constructed
only by assuming a minimal set of properties of string theory. We clarify our
viewpoint of the cyclic universe and show some attempts to mateliarize the idea
as field theoretical manner.Comment: Proceeding of International Workshop "Frontier of Quantum Physics"
February 17(Thu.)-19(Sat.) 200
MHV, CSW and BCFW: field theory structures in string theory amplitudes
Motivated by recent progress in calculating field theory amplitudes, we study
applications of the basic ideas in these developments to the calculation of
amplitudes in string theory. We consider in particular both non-Abelian and
Abelian open superstring disk amplitudes in a flat space background, focusing
mainly on the four-dimensional case. The basic field theory ideas under
consideration split into three separate categories. In the first, we argue that
the calculation of alpha'-corrections to MHV open string disk amplitudes
reduces to the determination of certain classes of polynomials. This line of
reasoning is then used to determine the alpha'^3-correction to the MHV
amplitude for all multiplicities. A second line of attack concerns the
existence of an analog of CSW rules derived from the Abelian Dirac-Born-Infeld
action in four dimensions. We show explicitly that the CSW-like perturbation
series of this action is surprisingly trivial: only helicity conserving
amplitudes are non-zero. Last but not least, we initiate the study of BCFW
on-shell recursion relations in string theory. These should appear very
naturally as the UV properties of the string theory are excellent. We show that
all open four-point string amplitudes in a flat background at the disk level
obey BCFW recursion relations. Based on the naturalness of the proof and some
explicit results for the five-point gluon amplitude, it is expected that this
pattern persists for all higher point amplitudes and for the closed string.Comment: v3: corrected erroneous statement about Virasoro-Shapiro amplitude
and added referenc
The action of long strings in supersymmetric field theories
Long strings emerge in many Quantum Field Theories, for example as vortices
in Abelian Higgs theories, or flux tubes in Yang-Mills theories. The actions of
such objects can be expanded in the number of derivatives, around a long
straight string solution. This corresponds to the expansion of energy levels in
powers of 1/L, with L the length of the string. Doing so reveals that the first
few terms in the expansions are universal, and only from a certain term do they
become dependent on the originating field theory. Such classifications have
been made before for bosonic strings. In this work we expand upon that and
classify also strings with fermionic degrees of freedom, where the string
breaks D=4 N=1 SUSY completely. An example is the confining string in N=1 SYM
theory. We find a general method for generating supersymmetric action terms
from their bosonic counterparts, as well as new fermionic terms which do not
exist in the non-supersymmetric case. These terms lead to energy corrections at
a lower order in 1/L than in the bosonic case
Infinity in string cosmology: A review through open problems
We review recent developments in the field of string cosmology with
particular emphasis on open problems having to do mainly with geometric
asymptotics and singularities. We discuss outstanding issues in a variety of
currently popular themes, such as tree-level string cosmology asymptotics,
higher-order string correction effects, M-theory cosmology, braneworlds, and
finally ambient cosmology.Comment: 37 pages, to appear in the IJMPD, v2: matches published versio
Cosmologies from higher-order string corrections
We study cosmologies based on low-energy effective string theory with
higher-order string corrections to a tree-level action and with a modulus
scalar field (dilaton or compactification modulus). In the presence of such
corrections it is possible to construct nonsingular cosmological solutions in
the context of Pre-Big-Bang and Ekpyrotic universes. We review the construction
of nonsingular bouncing solutions and resulting density perturbations in
Pre-Big-Bang and Ekpyrotic models. We also discuss the effect of higher-order
string corrections on dark energy universe and show several interesting
possibilities of the avoidance of future singularities.Comment: 15 pages, 2 figures, References are added, plenary talk at Pomeranian
Workshop in Fundamental Cosmology (COSMOFUN 05), Pobierowo, Poland, 1-6
September 200
On the Open-Closed B-Model
We study the coupling of the closed string to the open string in the
topological B-model. These couplings can be viewed as gauge invariant
observables in the open string field theory, or as deformations of the
differential graded algebra describing the OSFT. This is interpreted as an
intertwining map from the closed string sector to the deformation (Hochschild)
complex of the open string algebra. By an explicit calculation we show that
this map induces an isomorphism of Gerstenhaber algebras on the level of
cohomology. Reversely, this can be used to derive the closed string from the
open string. We shortly comment on generalizations to other models, such as the
A-model.Comment: LaTeX, 48 pages. Citation adde
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