287 research outputs found
Quantum Rings and Recursion Relations in 2D Quantum Gravity
I study tachyon condensate perturbations to the action of the two dimensional
string theory corresponding to the c=1 matrix model. These are shown to deform
the action of the ground ring on the tachyon modules, confirming a conjecture
of Witten. The ground ring structure is used to derive recursion relations
which relate (N+1) and N tachyon bulk scattering amplitudes. These recursion
relations allow one to compute all bulk amplitudes.Comment: 11 page
On Vanishing Two Loop Cosmological Constants in Nonsupersymmetric Strings
It has recently been suggested that in certain special nonsupersymmetric type
II string compactifications, at least the first two perturbative contributions
to the cosmological constant vanish. Support for perturbative
vanishing beyond 1-loop (as well as evidence for the absence of some
nonperturbative contributions) has come from duality arguments. There was also
a direct 2-loop computation which was incomplete; in this note we explain the
deficiency of the previous 2-loop calculation and discuss the complete 2-loop
computation in two different models. The corrected analysis yields a vanishing
2-loop contribution to in these models.Comment: 16 pages, harvmac bi
M-theory on Manifolds of G_2 Holonomy and Type IIA Orientifolds
We demonstrate that M-theory compactifications on 7-manifolds of G_2
holonomy, which yield 4d N=1 supersymmetric systems, often admit at special
loci in their moduli space a description as type IIA orientifolds. In this way,
we are able to find new dualities of special IIA orientifolds, including
dualities which relate orientifolds of IIA strings on manifolds of different
topology with different numbers of wrapped D-branes. We also discuss models
which incorporate, in a natural way, compact embeddings of gauge theory/gravity
dualities similar to those studied in the recent work of Atiyah, Maldacena and
Vafa.Comment: 14 pages, minor correction and references adde
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