224 research outputs found
Recent Progress in Intersecting D-brane Models
The aim of this article is to review some recent progress in the field of
intersecting D-brane models. This includes the construction of chiral,
semi-realistic flux compactifications, the systematic study of Gepner model
orientifolds, the computation of various terms in the low energy effective
action and the investigation of the statistics of solutions to the tadpole
cancellation conditions.Comment: 13 pages, 1 figure, contribution to the proceedings of the 37.
Symposium Ahrenshoop, 23-27 August 2004, Wernsdorf, Germany, v3: more refs.
adde
Gauge Coupling Unification in F-theory GUT Models
We investigate gauge coupling unification for F-theory respectively Type IIB
orientifold constructions of SU(5) GUT theories with gauge symmetry breaking
via non-trivial hypercharge flux. This flux has the non-trivial effect that it
splits the values of the three MSSM gauge couplings at the string scale, thus
potentially spoiling the celebrated one-loop gauge coupling unification. It is
shown how F-theory can evade this problem in a natural way.Comment: 4 pages, 3 figures, v2: clarifying comments and refs. added, v3:
footnote [24] adde
Discrete Deformations in Type I Vacua
We study supersymmetric orientifolds where the world-sheet parity
transformation is combined with a conjugation of some compact complex
coordinates. We investigate their T-duality relation to standard orientifolds
and discuss the origin of continuous and discrete moduli. In contrast to
standard orientifolds, the antisymmetric tensor describes a continuous
deformation, while the off-diagonal part of the metric is frozen to quantized
values and is responsible for the rank reduction of the gauge group. We also
give a geometrical interpretation of some recently constructed six-dimensional
permutational orientifolds.Comment: 12 pages, TeX, harvmac, 4 figures, eq.(3.15) change
T-duality, Non-geometry and Lie Algebroids in Heterotic Double Field Theory
A number of issues in heterotic double field theory are studied. This
includes the analysis of the T-dual configurations of a flat constant gauge
flux background, which turn out to be non-geometric. Performing a field
redefinition to a non-geometric frame, these T-duals take a very simple form
reminiscent of the constant Q- and R-flux backgrounds. In addition, it is shown
how the analysis of arXiv:1304.2784 generalizes to heterotic generalized
geometry. For every field redefinition specified by an O(D,D+n) transformation,
the structure of the resulting supergravity action is governed by the
differential geometry of a corresponding Lie algebroid.Comment: 27 pages, 1 figure, v2: refs adde
Nonassociative Gravity in String Theory?
In an on-shell conformal field theory approach, we find indications of a
three-bracket structure for target space coordinates in general closed string
backgrounds. This generalizes the appearance of noncommutative gauge theories
for open strings in two-form backgrounds to a putative
noncommutative/nonassociative gravity theory for closed strings probing curved
backgrounds with non-vanishing three-form flux. Several aspects and
consequences of the three-bracket structure are discussed and a new type of
generalized uncertainty principle is proposed.Comment: v2: references added, discussion in section 5 extended; v3: published
version, minor technical mistake corrected (discussion & conclusions
unchanged
Exactly Solvable Points in the Moduli Space of Heterotic N=2 Strings
We investigate the subset of exactly solvable (0,4) world sheet
supersymmetric string vacua contained in a recent class of Gepner-like (0,2)
superconformal models. The identification of these models with certain points
of enhanced gauge symmetry on K_3 x T_2 can be achieved completely.
Furthermore, we extend the construction of in general (0,2) supersymmetric
exactly solvable models to the case where also a nontrivial part of the vector
bundle is embedded into the hidden E_8 gauge group. For some examples we
explicitly calculate the enhanced gauge symmetries and show that they open up
the way to interesting branches of the N=2 moduli space. For some of these
models candidates of typeII dual descriptions exist.Comment: 13 pages, plain TeX, no postscript figure
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