754 research outputs found
Flavour from partially resolved singularities
In this letter we study topological open string field theory on D--branes in
a IIB background given by non compact CY geometries on with a singular point at which an extra fiber sits. We wrap
D5-branes on and effective D3-branes at singular points, which
are actually D5--branes wrapped on a shrinking cycle. We calculate the
holomorphic Chern-Simons partition function for the above models in a deformed
complex structure and find that it reduces to multi--matrix models with
flavour. These are the matrix models whose resolvents have been shown to
satisfy the generalized Konishi anomaly equations with flavour. In the
case, corresponding to a partial resolution of the singularity, the
quantum superpotential in the unitary SYM with one adjoint and
fundamentals is obtained. The case is also studied and shown to give rise
to two--matrix models which for a particular set of couplings can be exactly
solved. We explicitly show how to solve such a class of models by a quantum
equation of motion technique
Fermion Zero Modes in the Presence of Fluxes and a Non-perturbative Superpotential
We study the effect of background fluxes of general Hodge type on the
supersymmetry conditions and on the fermionic zero modes on the world-volume of
a Euclidean M5/D3-brane in M-theory/type IIB string theory.
Using the naive susy variation of the modulino fields to determine the number
of zero modes in the presence of a flux of general Hodge type, an inconsistency
appears. This inconsistency is resolved by a modification of the supersymmetry
variation of the modulinos, which captures the back-reaction of the
non-perturbative effects on the background flux and the geometry.Comment: 21 pages, revised version contains a new appendix on dimensional
reduction of spinors and some changes in the spinor equation
D-terms and D-strings in open string models
We study the Fayet-Iliopoulos (FI) D-terms on D-branes in type II Calabi-Yau
backgrounds. We provide a simple worldsheet proof of the fact that, at tree
level, these terms only couple to scalars in closed string hypermultiplets. At
the one-loop level, the D-terms get corrections only if the gauge group has an
anomalous spectrum, with the anomaly cancelled by a Green-Schwarz mechanism. We
study the local type IIA model of D6-branes at SU(3) angles and show that, as
in field theory, the one-loop correction suffers from a quadratic divergence in
the open string channel. By studying the closed string channel, we show that
this divergence is related to a closed string tadpole, and is cancelled when
the tadpole is cancelled. Next, we study the cosmic strings that arise in the
supersymmetric phases of these systems in light of recent work of Dvali et. al.
In the type IIA intersecting D6-brane examples, we identify the D-term strings
as D4-branes ending on the D6-branes. Finally, we use N=1 dualities to relate
these results to previous work on the FI D-term of heterotic strings.Comment: 29 pages, 5 figures; v2: improved referencin
Heterotic-Type II duality in the hypermultiplet sector
We revisit the duality between heterotic string theory compactified on K3 x
T^2 and type IIA compactified on a Calabi-Yau threefold X in the hypermultiplet
sector. We derive an explicit map between the field variables of the respective
moduli spaces at the level of the classical effective actions. We determine the
parametrization of the K3 moduli space consistent with the Ferrara-Sabharwal
form. From the expression of the holomorphic prepotential we are led to
conjecture that both X and its mirror must be K3 fibrations in order for the
type IIA theory to have an heterotic dual. We then focus on the region of the
moduli space where the metric is expressed in terms of a prepotential on both
sides of the duality. Applying the duality we derive the heterotic
hypermultiplet metric for a gauge bundle which is reduced to 24 point-like
instantons. This result is confirmed by using the duality between the heterotic
theory on T^3 and M-theory on K3. We finally study the hyper-Kaehler metric on
the moduli space of an SU(2) bundle on K3.Comment: 27 pages; references added, typos correcte
Calabi-Yau Duals of Torus Orientifolds
We study a duality that relates the T^6/Z_2 orientifold with N=2 flux to
standard fluxless Calabi-Yau compactifications of type IIA string theory. Using
the duality map, we show that the Calabi-Yau manifolds that arise are abelian
surface (T^4) fibrations over P^1. We compute a variety of properties of these
threefolds, including Hodge numbers, intersection numbers, discrete isometries,
and H_1(X,Z). In addition, we show that S-duality in the orientifold
description becomes T-duality of the abelian surface fibers in the dual
Calabi-Yau description. The analysis is facilitated by the existence of an
explicit Calabi-Yau metric on an open subset of the geometry that becomes an
arbitrarily good approximation to the actual metric (at most points) in the
limit that the fiber is much smaller than the base.Comment: 39 pages; uses harvmac.tex, amssym.tex; v4: minor correction
Weierstrass meets Enriques
We study in detail the degeneration of K3 to T^4/Z_2. We obtain an explicit
embedding of the lattice of collapsed cycles of T^4/Z_2 into the lattice of
integral cycles of K3 in two different ways. Our first method exploits the
duality to the heterotic string on T^3. This allows us to describe the
degeneration in terms of Wilson lines. Our second method is based on the
blow-up of T^4/Z_2. From this blow-up, we directly construct the full lattice
of integral cycles of K3. Finally, we use our results to describe the action of
the Enriques involution on elliptic K3 surfaces, finding that a Weierstrass
model description is consistent with the Enriques involution only in the
F-theory limit.Comment: 35 pages, 9 figure
Quantum geometry with intrinsic local causality
The space of states and operators for a large class of background independent
theories of quantum spacetime dynamics is defined. The SU(2) spin networks of
quantum general relativity are replaced by labelled compact two-dimensional
surfaces. The space of states of the theory is the direct sum of the spaces of
invariant tensors of a quantum group G_q over all compact (finite genus)
oriented 2-surfaces. The dynamics is background independent and locally causal.
The dynamics constructs histories with discrete features of spacetime geometry
such as causal structure and multifingered time. For SU(2) the theory satisfies
the Bekenstein bound and the holographic hypothesis is recast in this
formalism.Comment: Latex 33 pages, 7 Figure, epsfi
Attractor Flows in st^2 Black Holes
Following the same treatment of Bellucci et.al., we obtain the hitherto
unknown general solutions of the radial attractor flow equations for extremal
black holes, both for non-BPS with non-vanishing and vanishing central charge Z
for the so-called st^2 model, the minimal rank-2 N=2 symmetric supergravity in
d=4 space-time dimensions.
We also make useful comparisons with results that already exist in
literature,and introduce the fake supergravity (first-order) formalism to be
used in our analysis. An analysis of the BPS bound all along the non-BPS
attractor flows and of the marginal stability of corresponding D-brane charge
configurations has also been presented.Comment: 59 pages,Latex. arXiv admin note: substantial text overlap with
arXiv:0807.3503 by other author
Axionic D3-D7 Inflation
We study the motion of a D3 brane moving within a Type IIB string vacuum
compactified to 4D on K3 x T_2/Z_2 in the presence of D7 and O7 planes. We work
within the effective 4D supergravity describing how the mobile D3 interacts
with the lightest bulk moduli of the compactification, including the effects of
modulus-stabilizing fluxes. We seek inflationary solutions to the resulting
equations, performing our search numerically in order to avoid resorting to
approximate parameterizations of the low-energy potential. We consider
uplifting from D-terms and from the supersymmetry-breaking effects of anti-D3
branes. We find examples of slow-roll inflation (with anti-brane uplifting)
with the mobile D3 moving along the toroidal directions, falling towards a
D7-O7 stack starting from the antipodal point. The inflaton turns out to be a
linear combination of the brane position and the axionic partner of the K3
volume modulus, and the similarity of the potential along the inflaton
direction with that of racetrack inflation leads to the prediction n_s \le 0.95
for the spectral index. The slow roll is insensitive to most of the features of
the effective superpotential, and requires a one-in-10^4 tuning to ensure that
the torus is close to square in shape. We also consider D-term inflation with
the D3 close to the attractive D7, but find that for a broad (but not
exhaustive) class of parameters the conditions for slow roll tend to
destabilize the bulk moduli. In contrast to the axionic case, the best
inflationary example of this kind requires the delicate adjustment of potential
parameters (much more than the part-per-mille level), and gives inflation only
at an inflection point of the potential (and so suffers from additional
fine-tuning of initial conditions to avoid an overshoot problem).Comment: 29 pages, 5 figure
Quantum Fields in a Big Crunch/Big Bang Spacetime
We consider quantum field theory on a spacetime representing the Big
Crunch/Big Bang transition postulated in the ekpyrotic or cyclic cosmologies.
We show via several independent methods that an essentially unique matching
rule holds connecting the incoming state, in which a single extra dimension
shrinks to zero, to the outgoing state in which it re-expands at the same rate.
For free fields in our construction there is no particle production from the
incoming adiabatic vacuum. When interactions are included the total particle
production for fixed external momentum is finite at tree level. We discuss a
formal correspondence between our construction and quantum field theory on de
Sitter spacetime.Comment: 30 pages, RevTex file, five postscript figure file
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