47 research outputs found
Intersecting D-Branes on Shift Z2 x Z2 Orientifolds
We investigate Z2 x Z2 orientifolds with group actions involving shifts. A
complete classification of possible geometries is presented where also previous
work by other authors is included in a unified framework from an intersecting
D-brane perspective. In particular, we show that the additional shifts not only
determine the topology of the orbifold but also independently the presence of
orientifold planes. In the second part, we work out in detail a basis of
homological three cycles on shift Z2 x Z2 orientifolds and construct all
possible fractional D-branes including rigid ones. A Pati-Salam type model with
no open-string moduli in the visible sector is presented.Comment: 36 pages, 4 figures, refs. adde
Gauge Threshold Corrections for Local Orientifolds
We study gauge threshold corrections for systems of fractional branes at
local orientifold singularities and compare with the general Kaplunovsky-Louis
expression for locally supersymmetric N=1 gauge theories. We focus on branes at
orientifolds of the C^3/Z_4, C^3/Z_6 and C^3/Z_6' singularities. We provide a
CFT construction of these theories and compute the threshold corrections. Gauge
coupling running undergoes two phases: one phase running from the bulk winding
scale to the string scale, and a second phase running from the string scale to
the infrared. The first phase is associated to the contribution of N=2 sectors
to the IR beta functions and the second phase to the contribution of both N=1
and N=2 sectors. In contrast, naive application of the Kaplunovsky-Louis
formula gives single running from the bulk winding mode scale. The discrepancy
is resolved through 1-loop non-universality of the holomorphic gauge couplings
at the singularity, induced by a 1-loop redefinition of the twisted blow-up
moduli which couple differently to different gauge nodes. We also study the
physics of anomalous and non-anomalous U(1)s and give a CFT description of how
masses for non-anomalous U(1)s depend on the global properties of cycles.Comment: 44 page
Massive Abelian Gauge Symmetries and Fluxes in F-theory
F-theory compactified on a Calabi-Yau fourfold naturally describes
non-Abelian gauge symmetries through the singularity structure of the elliptic
fibration. In contrast Abelian symmetries are more difficult to study because
of their inherently global nature. We argue that in general F-theory
compactifications there are massive Abelian symmetries, such as the uplift of
the Abelian part of the U(N) gauge group on D7-branes, that arise from
non-Kahler resolutions of the dual M-theory setup. The four-dimensional
F-theory vacuum with vanishing expectation values for the gauge fields
corresponds to the Calabi-Yau limit. We propose that fluxes that are turned on
along these U(1)s are uplifted to non-harmonic four-form fluxes. We derive the
effective four-dimensional gauged supergravity resulting from F-theory
compactifications in the presence of the Abelian gauge factors including the
effects of possible fluxes on the gauging, tadpoles and matter spectrum.Comment: 49 page
Holographic flows in non-Abelian T-dual geometries
We use non-Abelian T-duality to construct new N=1 solutions of type IIA supergravity (and their M-theory lifts) that interpolate between AdS_5 geometries. We initiate a study of the holographic interpretation of these backgrounds as RG flows between conformal fixed points. Along the way we give an elegant formulation of non-Abelian T-duality when acting on a wide class of backgrounds, including those corresponding to such flows, in terms of their SU(2) structure