475 research outputs found
Wave Functions and Yukawa Couplings in Local String Compactifications
We consider local models of magnetised D7 branes in IIB string
compactifications, focussing on cases where an explicit metric can be written
for the local 4-cycle. The presence of an explicit metric allows analytic
expressions for the gauge bundle and for the chiral matter wavefunctions
through solving the Dirac and Laplace equations. The triple overlap of the
normalised matter wavefunctions generates the physical Yukawa couplings. Our
main examples are the cases of D7 branes on P1xP1 and P2. We consider both
supersymmetric and non-supersymmetric gauge backgrounds and both Abelian and
non-Abelian gauge bundles. We briefly outline potential phenomenological
applications of our results.Comment: 50 pages, 1 figur
Hidden symmetries of two dimensional string effective action
The ten dimensional heterotic string effective action with graviton, dilaton and antisymmetric tensor fields is dimensionally reduced to two spacetime dimensions. The resulting theory, with some constraints on backgrounds, admits infinite sequence of conserved nonlocal currents. It is shown that generators of the infinitesimal transformations associated with these currents satisfy Kac-Moody algebra
De Sitter String Vacua from Dilaton-dependent Non-perturbative Effects
We consider a novel scenario for modulus stabilisation in IIB string
compactifications in which the Kahler moduli are stabilised by a general set-up
with two kinds of non-perturbative effects: (i) standard Kahler
moduli-dependent non-perturbative effects from gaugino condensation on
D7-branes or E3-instantons wrapping four-cycles in the geometric regime; (ii)
dilaton-dependent non-perturbative effects from gaugino condensation on
space-time filling D3-branes or E(-1)-instantons at singularities. For the
LARGE Volume Scenario (LVS), the new dilaton-dependent non-perturbative effects
provide a positive definite contribution to the scalar potential that can be
arbitrarily tuned from fluxes to give rise to de Sitter vacua. Contrary to anti
D3-branes at warped throats, this term arises from a manifestly supersymmetric
effective action. In this new scenario the "uplifting" term comes from F-terms
of blow-up modes resolving the singularity of the non-perturbative quiver. We
discuss phenomenological and cosmological implications of this mechanism. This
set-up also allows a realisation of the LVS for manifolds with zero or positive
Euler number.Comment: 22 pages + two appendices, typos correcte
A Note on the Magnitude of the Flux Superpotential
The magnitude of the flux superpotential plays a crucial role in
determining the scales of IIB string compactifications after moduli
stabilisation. It has been argued that values of much less than one
are preferred, and even required for physical and consistency reasons. This
note revisits these arguments. We establish that the coupling (g) of heavy
Kaluza-Klein modes to light states scales as (hence is
suppressed by two third powers of the inverse volume of compactification) and
argue that consistency of the superspace derivative expansion requires , where is the auxiliary field of the light
fields and the ultraviolet cutoff. This gives only a mild constraint on the
flux superpotential, (where V is the volume of the
compactification), which can be easily satisfied for order one values of
. This regime is also statistically favoured and makes the
Bousso-Polchinski mechanism for the vacuum energy hierarchically more
efficient.Comment: 14 page
Dualities and Hidden Supersymmetry in String Quantum Cosmology
A supersymmetric approach to string quantum cosmology based on the non-compact, global duality symmetries of the effective action is developed. An N=2 supersymmetric action is derived whose bosonic component is the Neveu-Schwarz/Neveu-Schwarz sector of the --dimensional effective action compactified on a --torus. A representation for the supercharges is found and the form of the zero-and one-fermion quantum states is determined. The purely bosonic component of the wavefunction is unique and manifestly invariant under the symmetry of the action. The formalism applies to a wide class of non-linear sigma-models
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