42 research outputs found
The Operator Spectrum of the Six-dimensional (1,0) Theory
We study the large N operator spectrum of the (1,0) superconformal chiral
six-dimensional theory with E_8 global symmetry. This spectrum is dual to the
Kaluza-Klein spectrum of supergravity on AdS_7 X S^4/Z_2 with a ten-dimensional
E_8 theory at its singular locus. We identify those operators in short
multiplets of OSp(6,2|2), whose dimensions are exact for any N. We also discuss
more general issues concerning AdS/CFT duality on orbifold supergravity
backgrounds.Comment: 16pp, Late
The AdS/CFT correspondence and Spectrum Generating Algebras
We list the spectrum generating algebras for string theory and M-theory
compactified on various backgrounds of the form . We
identify the representations of these algebras which make up the classical
supergravity spectra and argue for the presence of these spectrum generating
algebras in the classical string/M-theory. We also discuss the role of the
spectrum generating algebras on the conformal field theory side.Comment: 17 pages, 4 Tables, harvma
Brane Transfer Operations and T-Duality of Non-BPS States
Using the relation between D-brane charges and K-theory, we study non-BPS
D-branes and their behavior under T-duality. We point out that in general
compactifications, D-brane charges are classified by relative K-theory groups.
T-duality is found to act as a symmetry between the relative K-theory groups in
Type II and Type I/IA theories. We also study Type \tilde\IA theory (which
contains an O8^- plane and an O8^+ plane), using K-theory and T-duality to
identify its stable D-branes. Comparison with string theory constructions
reveals two interesting effects. One of them involves the transfer of branes
between O-planes, while in the other, a D-brane charge which seems conserved
near one O-plane in fact decays due to the presence of another type of O-plane.Comment: 28 pages harvmac, 4 figures; Expanded argument for relative K-theory
in subsection 2.2, and added explicit K-theory groups of a point in eq.(A.3)
of the appendi
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Black ring deconstruction
We present a sample microstate for a black ring in four and five dimensional language. The microstate consists of a black string microstate with an additional D6-brane. We show that with an appropriate choice of parameters the piece involving the black string microstate falls down a long AdS throat, whose M-theory lift is AdS_3 x S2. We wrap a spinning dipole M2-brane on the S2 in the probe approximation. In IIA, this corresponds to a dielectric D2-brane carrying only D0-charge. We conjecture this is the firstapproximation to a cloud of D0-branes blowing up due to their non-abelian degrees of freedom and the Myers effect
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Black holes in supergravity: the non-BPS branch
We construct extremal, spherically symmetric black hole solutions to 4D supergravity with charge assignments that preclude BPS-saturation. In particular, we determine the ground state energy as a function of charges and moduli. We find that the mass of the non-BPS black hole remains that of a marginal bound state of four basic constituents throughout the entire moduli space and that there is always a non-zero gap above the BPS bound
Astrophysical Violations of the Kerr Bound as a Possible Signature of String Theory
In 4D general relativity, the angular momentum of a black hole is limited by
the Kerr bound. We suggest that in string theory, this bound can be breached
and compact black-hole-like objects can spin faster. Near such "superspinars,"
the efficiency of energy transfer from the accreting matter to radiation can
reach 100%, compared to the maximum efficiency of 42% of the extremal Kerr (or
6% of the Schwarzschild) black hole. Finding such superspinning objects as
active galactic nuclei, GBHCs, or sources of gamma ray bursts, could be viewed
as experimental support for string theory.Comment: 4 page
Magic Supergravities, N= 8 and Black Hole Composites
We present explicit U-duality invariants for the R, C, Q, O$ (real, complex,
quaternionic and octonionic) magic supergravities in four and five dimensions
using complex forms with a reality condition. From these invariants we derive
an explicit entropy function and corresponding stabilization equations which we
use to exhibit stationary multi-center 1/2 BPS solutions of these N=2 d=4
theories, starting with the octonionic one with E_{7(-25)} duality symmetry. We
generalize to stationary 1/8 BPS multicenter solutions of N=8, d=4
supergravity, using the consistent truncation to the quaternionic magic N=2
supergravity. We present a general solution of non-BPS attractor equations of
the STU truncation of magic models. We finish with a discussion of the
BPS-non-BPS relations and attractors in N=2 versus N= 5, 6, 8.Comment: 33 pages, references added plus brief outline at end of introductio
Multiple Realisations of N=1 Vacua in Six Dimensions
A while ago, examples of N=1 vacua in D=6 were constructed as orientifolds of
Type IIB string theory compactified on the K3 surface. Among the interesting
features of those models was the presence of D5-branes behaving like small
instantons, and the appearance of extra tensor multiplets. These are both
non-perturbative phenomena from the point of view of heterotic string theory.
Although the orientifold models are a natural setting in which to study these
non-perturbative Heterotic string phenomena, it is interesting and instructive
to explore how such vacua are realised in Heterotic string theory, M-theory and
F-theory, and consider the relations between them. In particular, we consider
models of M-theory compactified on K3 x S^1/Z_2 with fivebranes present on the
interval. There is a family of such models which yields the same spectra as a
subfamily of the orientifold models. By further compactifying on T^2 to four
dimensions we relate them to Heterotic string spectra. We then use
Heterotic/Type IIA duality to deduce the existence of Calabi-Yau 3-folds which
should yield the original six dimensional orientifold spectra if we use them to
compactify F-theory. Finally, we show in detail how to take a limit of such an
F-theory compactification which returns us to the Type IIB orientifold models.Comment: Uses harvmac.tex and epsf.tex, 22 pages (harvmac `b'), 1 figur