9 research outputs found
Tensors from K3 Orientifolds
Recently Gimon and Johnson (hep-th/9604129) and Dabholkar and Park
(hep-th/9604178) have constructed Type I theories on K3 orbifolds. The spectra
differ from that of Type I on a smooth K3, having extra tensors. We show that
the orbifold theories cannot be blown up to smooth K3's, but rather
orbifold singularities always remain. Douglas's recent proposal to use D-branes
as probes is useful in understanding the geometry. The singularities are
of a new type, with a different orientifold projection from those previously
considered. We also find a new world-sheet consistency condition that must be
satisfied by orientifold models.Comment: References added. 16 pages, LaTe
Consistency Conditions for Orientifolds and D-Manifolds
We study superstrings with orientifold projections and with generalized open
string boundary conditions (D-branes). We find two types of consistency
condition, one related to the algebra of Chan-Paton factors and the other to
cancellation of divergences. One consequence is that the Dirichlet 5-branes of
the Type I theory carry a symplectic gauge group, as required by string
duality. As another application we study the Type I theory on a
orbifold, finding a family of consistent theories with various unitary and
symplectic subgroups of . We argue that the orbifold
with spin connection embedded in gauge connection corresponds to an interacting
conformal field theory in the Type I theory.Comment: Reference added. 27 pages LaTeX, 2 epsf figures. To appear in
Phys.Rev.D (15Jly96
Bubbling Orientifolds
We investigate a class of 1/2-BPS bubbling geometries associated to
orientifolds of type IIB string theory and thereby to excited states of the
SO(N)/Sp(N) N=4 supersymmetric Yang-Mills theory. The geometries are in
correspondence with free fermions moving in a harmonic oscillator potential on
the half-line. Branes wrapped on torsion cycles of these geometries are
identified in the fermi fluid description. Besides being of intrinsic interest,
these solutions may also occur as local geometries in flux compactifications
where orientifold planes are present to ensure global charge cancellation. We
comment on the extension of this procedure to M-theory orientifolds.Comment: 25 pages, 11 figures. v2: few references adde
Supersymmetric Pair Correlation Function of Wilson Loops
We give a path integral derivation of the annulus diagram in a supersymmetric
theory of open and closed strings with Dbranes. We compute the pair correlation
function of Wilson loops in the generic weakly coupled supersymmetric flat
spacetime background with Dbranes. We obtain a -u^4/r^9 potential between heavy
nonrelativistic sources in a supersymmetric gauge theory at short distances.Comment: 18 pages, Revte
Instability of hyper-compact Kerr-like objects
Viable alternatives to astrophysical black holes include hyper-compact
objects without horizon, such as gravastars, boson stars, wormholes and
superspinars. The authors have recently shown that typical rapidly-spinning
gravastars and boson stars develop a strong instability. That analysis is
extended in this paper to a wide class of horizonless objects with approximate
Kerr-like geometry. A detailed investigation of wormholes and superspinars is
presented, using plausible models and mirror boundary conditions at the
surface. Like gravastars and boson stars, these objects are unstable with very
short instability timescales. This result strengthens previous conclusions that
observed hyper-compact astrophysical objects with large rotation are likely to
be black holes.Comment: 15 pages, 3 figures. To be published in CQ
The quantum structure of black holes
We give an elementary review of black holes in string theory. We discuss
black hole entropy from string microstates and Hawking radiation from these
states. We then review the structure of 2-charge microstates, and explore how
`fractionation' can lead to quantum effects over macroscopic length scales of
order the horizon radius.Comment: Review article, 58 pages, 2 figures; references added, note about
topics covere
A deformation of AdS_5 x S^5
We analyse a one parameter family of supersymmetric solutions of type IIB
supergravity that includes AdS_5 x S^5. For small values of the parameter the
solutions are causally well-behaved, but beyond a critical value closed
timelike curves (CTC's) appear. The solutions are holographically dual to N=4
supersymmetric Yang-Mills theory on a non-conformally flat background with
non-vanishing R-currents. We compute the holographic energy-momentum tensor for
the spacetime and show that it remains finite even when the CTC's appear. The
solutions, as well as the uplift of some recently discovered AdS_5 black hole
solutions, are shown to preserve precisely two supersymmetries.Comment: 16 pages, v2: typos corrected and references adde
D = 4 chiral string compactifications from intersecting branes
Intersecting Dp -branes often give rise to chiral fermions living on their intersections. We study the construction of four-dimensional chiralgauge theories by considering configurations of type II D(3+n) -branes wrapped on nontrivial n -cycles on T 2n Ă(R 2(3ân) /Z N ), for n=1,â2,â3. The gauge theories on the four noncompact dimensions of the brane world-volume are generically chiral and nonsupersymmetric. We analyze consistency conditions (RR tadpole cancellation) for these models, and their relation to four-dimensional anomaly cancellation. Cancellation of U(1) gauge anomalies involves a GreenâSchwarz mechanism mediated by RR partners of untwisted and/or twisted moduli. This class of models is of potential phenomenological interest, and we construct explicit examples of SU(3)ĂSU(2)ĂU(1) three-generation models. The models are nonsupersymmetric, but the string scale may be lowered close to the weak scale so that the standard hierarchy problem is avoided. We also comment on the presence of scalar tachyons and possible ways to avoid the associated instabilities. We discuss the existence of (meta)stable configurations of D-branes on 3-cycles in (T 2 ) 3 , free of tachyons for certain ranges of the six-torus moduli