3,828 research outputs found
Moving Five-Branes and Cosmology
We discuss low-energy heterotic M-theory with five-branes in four and five
dimensions and its application to moving brane cosmology.Comment: 6 pages, Latex, based on a talk given at the 1st International
Conference on String Phenomenology, Oxford, 6-11 Jul 200
Brane-World Inflation and the Transition to Standard Cosmology
In the context of a five-dimensional brane-world model motivated from
heterotic M-theory, we develop a framework for potential-driven brane-world
inflation. Specifically this involves a classification of the various
background solutions of (A)dS_5 type, an analysis of five-dimensional slow-roll
conditions and a study of how a transition to the flat vacuum state can be
realized. It is shown that solutions with bulk potential and both bane
potentials positive exist but are always non-separating and have a non-static
orbifold. It turns out that, for this class of backgrounds, a transition to the
flat vacuum state during inflation is effectively prevented by the rapidly
expanding orbifold. We demonstrate that such a transition can be realized for
solutions where one boundary potential is negative. For this case, we present
two concrete inflationary models which exhibit the transition explicitly.Comment: 50 pages, 3 figures, minor typos correcte
Discrete Symmetries of Complete Intersection Calabi-Yau Manifolds
In this paper, we classify non-freely acting discrete symmetries of complete
intersection Calabi- Yau manifolds and their quotients by freely-acting
symmetries. These non-freely acting symmetries can appear as symmetries of
low-energy theories resulting from string compactifications on these Calabi-Yau
manifolds, particularly in the context of the heterotic string. Hence, our
results are relevant for four-dimensional model building with discrete
symmetries and they give an indication which symmetries of this kind can be
expected from string theory. For the 1695 known quotients of complete
intersection manifolds by freely-acting discrete symmetries, non-freely-acting,
generic symmetries arise in 381 cases and are, therefore, a relatively common
feature of these manifolds. We find that 9 different discrete groups appear,
ranging in group order from 2 to 18, and that both regular symmetries and
R-symmetries are possible.Comment: 23 pages; minor changes: updated a reference, removed unclear
sentenc
Decoherence in Pre-Big-Bang Cosmology
We analyze the quantum cosmology of the simplest pre--big--bang model without
dilaton potential. In addition to the minisuperspace variables we include
inhomogeneous dilaton fluctuations and determine their wave function on a
semiclassical background. This wave function is used to calculate the reduced
density matrix and to find criteria for the loss of decoherence. It is shown
that coherence between different backgrounds can always be achieved by a
specific choice of vacua though generically decoherence can be expected. In
particular, we discuss the implications of these results on the ``exit
problem'' of pre--big--bang cosmology.Comment: 15 pages, 2 postscript figures include
Heterotic Anomaly Cancellation in Five Dimensions
We study the constraints on five-dimensional N=1 heterotic M-theory imposed
by a consistent anomaly-free coupling of bulk and boundary theory. This
requires analyzing the cancellation of triangle gauge anomalies on the
four-dimensional orbifold planes due to anomaly inflow from the bulk. We find
that the semi-simple part of the orbifold gauge groups and certain U(1)
symmetries have to be free of quantum anomalies. In addition there can be
several anomalous U(1) symmetries on each orbifold plane whose anomalies are
cancelled by a non-trivial variation of the bulk vector fields. The mixed U(1)
non-abelian anomaly is universal and there is at most one U(1) symmetry with
such an anomaly on each plane. In an alternative approach, we also analyze the
coupling of five-dimensional gauged supergravity to orbifold gauge theories. We
find a somewhat generalized structure of anomaly cancellation in this case
which allows, for example, non-universal mixed U(1) gauge anomalies. Anomaly
cancellation from the perspective of four-dimensional N=1 effective actions
obtained from E_8xE_8 heterotic string- or M-theory by reduction on a
Calabi-Yau three-fold is studied as well. The results are consistent with the
ones found for five-dimensional heterotic M-theory. Finally, we consider some
related issues of phenomenological interest such as model building with
anomalous U(1) symmetries, Fayet-Illiopoulos terms and threshold corrections to
gauge kinetic functions.Comment: 46 pages, Late
Gauge Five Brane Dynamics And Small Instanton Transitions In Heterotic Models
We present the first examples of cosmological solutions to four-dimensional
heterotic models which include an evolving bundle modulus. The particular
bundle modulus we consider corresponds to the width of a gauge five brane. As
such our solutions can be used to describe the evolution in one of these models
after a small instanton transition. We find that certain properties are generic
to these solutions, regardless of initial conditions. This enables us to make
some definite statements about the dynamics subsequent to a small instanton
transition despite the fact that we cannot microscopically describe the process
itself. We also show that an effective description of the small instanton
transition by a continuous matching of fields and their first derivatives is
precluded by the form of the respective low-energy theories before and after
the transition.Comment: 16 pages, 3 figure
An Abundance of Heterotic Vacua
We explicitly construct the largest dataset to date of heterotic vacua
arising from stable vector bundles on Calabi-Yau threefolds. Focusing on
elliptically fibered Calabi-Yau manifolds with spectral cover bundles, we show
that the number of heterotic models with non-zero number of generations is
finite. We classify these models according to the complex base of their
Calabi-Yau threefold and to the unification gauge group that they preserve in
four dimensions. This database of the order of models, which includes
potential Standard Model candidates, is subjected to some preliminary
statistical analyses. The additional constraint that there should be three net
generations of particles gives a dramatic reduction of the number of vacua.Comment: 27 pages, 12 figures, added reference
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