1,278 research outputs found
Non-geometric orbifolds and wrapping rules
We show that the number of half-supersymmetric p-branes in the Type II
theories compactified on orbifolds is determined by the wrapping rules recently
introduced, provided that one accounts correctly for both geometric and
non-geometric T-dual configurations. Starting from the Type II theories
compactified on K3, we analyze their toroidal dimensional reductions, showing
how the resulting half-supersymmetric p-branes satisfy the wrapping rules only
by taking into account all the possible higher-dimensional origins. We then
consider Type II theories compactified on the orbifold T^6/(Z_2 \times Z_2 ),
whose massless four-dimensional theory is an N=2 supergravity. Again, the
wrapping rules are obeyed only if one includes the complete orbit of the
T-duality group, namely either Type IIA or Type IIB theories compactified on
either the geometric or the non-geometric T-dual orbifold. Finally, we comment
on the interpretation of our results in the framework of the duality between
the Heterotic string compactified on K3 \times T^2 and the Type II string
compactified on a Calabi-Yau threefold.Comment: 26 pages, 8 table
The Universality of M-branes
We review the evidence for the various dualities amongst the five D=10
superstring theories and for the existence of M-theory using the associated
effective supergravity theories. We also summarise the combinatorial technics
developed for constructing BPS solutions in D=11 supergravity theory and
conjecture that all the BPS solutions of D<11 supergravity theories can be
derived from the BPS solutions of D=11 supergravity that preserve 1/2 the
supersymmetry. To demonstrate this, we derive the dyonic p-brane solutions from
eleven dimensions.Comment: Many changes have been made in the text and some references have been
added. 8 pages, Latex, Talk at the Imperial College Workshop 5-10 Jul
Towards a classification of branes in theories with eight supercharges
We provide a classification of half-supersymmetric branes in quarter-maximal
supergravity theories with scalars parametrising coset manifolds. Guided by the
results previously obtained for the half-maximal theories, we are able to show
that half-supersymmetric branes correspond to the real longest weights of the
representations of the brane charges, where the reality properties of the
weights are determined from the Tits-Satake diagrams associated to the global
symmetry groups. We show that the resulting brane structure is universal for
all theories that can be uplifted to six dimensions. We also show that when
viewing these theories as low-energy theories for the suitably compactified
heterotic string, the classification we obtain is in perfect agreement with the
wrapping rules derived in previous works for the same theory compactified on
tori. Finally, we relate the branes to the R-symmetry representations of the
central charges and we show that in general the degeneracies of the BPS
conditions are twice those of the half-maximal theories and four times those of
the maximal ones.Comment: 47 pages, 8 figure
Swampland Bounds on the Abelian Gauge Sector
We derive bounds on the number of abelian gauge group factors in
six-dimensional gravitational theories with minimal supersymmetry and in their
F-theoretic realisations. These bounds follow by requiring consistency of
certain BPS strings in the spectrum of the theory, as recently proposed in the
literature. Under certain assumptions this approach constrains the number of
abelian gauge group factors in six-dimensional supergravity theories with at
least one tensor multiplet to be (or in absence of
charged matter). For any geometric F-theory realisation with at least one
tensor multiplet we establish the bound by demanding unitarity of a
heterotic solitonic string which exists even in absence of a perturbative
heterotic dual. This result extends to four-dimensional F-theory vacua on any
blowup of a rational fibration. Our findings lead to universal bounds on the
rank of the Mordell-Weil group of elliptically fibered Calabi-Yau threefolds.Comment: 10 pages, 2-column forma
Spacetime Instanton Corrections in 4D String Vacua - The Seesaw Mechanism for D-Brane Models
We systematically investigate instanton corrections from wrapped Euclidean
D-branes to the matter field superpotential of various classes of N=1
supersymmetric D-brane models in four dimensions. Both gauge invariance and the
counting of fermionic zero modes provide strong constraints on the allowed
non-perturbative superpotential couplings. We outline how the complete
instanton computation boils down to the computation of open string disc
diagrams for boundary changing operators multiplied by a one-loop vacuum
diagram. For concreteness we focus on E2-instanton effects in Type IIA vacua
with intersecting D6-branes, however the same structure emerges for Type IIB
and heterotic vacua. The instantons wrapping rigid cycles can potentially
destabilise the vacuum or generate perturbatively absent matter couplings such
as proton decay operators, mu-parameter or right-handed neutrino Majorana mass
terms. The latter allow the realization of the seesaw mechanism for MSSM-like
intersecting D-brane models.Comment: 40 pages, 3 tables, 7 figures; v2: typos corrected, references added;
v3: minor sign adjustments, some comments added; v4: published versio
Supersymmetric dyonic black holes of IIA string on Six Torus
A class of four-dimensional static supersymmetric black hole solutions of
effective supergravity Lagrangian of IIA superstring compactified on is
constructed by explicitly solving Killing spinor equations (KSEs). These
solutions are dyonic black holes parametrized by four charges, with dilaton and
diagonal internal metric components as the only non-zero scalar fields, and
preserve of supersymmetry. The KSEs with only
Neveu-Schwarz-Neveu-Schwarz charges relate spinors with opposite chirality from
ten-dimensional view point, and have identical structures with KSEs of
toroidally compactified heterotic string. We also find a solution with four
Ramond-Ramond charges which is U-dual to the solution with four
Neveu-Schwarz-Neveu-Schwarz charges, and corresponds to the intersecting
D-brane configuration with two 2-branes and two 4-branes. A configuration with
both Neveu-Schwarz-Neveu-Schwarz charges and Ramond-Ramond charges is also
found. We show that the configurations T-dual to the above solutions are also
solutions of the KSEs. The patterns of supersymmetry breaking are studied in
detail.Comment: LaTeX with RevTeX, 41 page
Lectures on Superstring and M Theory Dualities
These lectures begin by reviewing the evidence for S duality of the
toroidally compactified heterotic string in 4d that was obtained in the period
1992--94. Next they review recently discovered dualities that relate all five
of the 10d superstring theories and a quantum extension of 11d supergravity
called M theory. The study of p-branes of various dimensions (some of which are
D-branes) plays a central role. The final sections survey supersymmetric string
vacua in 6d and some of the dual constructions by which they can be obtained.
Special emphasis is given to a class of N=1 models that exhibit
``heterotic-heterotic duality.''Comment: 67 pages, latex, 1 figure; Lectures given at the ICTP Spring School
(March 1996) and the TASI Summer School (June 1996), TASI9
Open string instantons and superpotentials
We study the F-terms in N=1 supersymmetric, d=4 gauge theories arising from
D(p+3)-branes wrapping supersymmetric p-cycles in a Calabi-Yau threefold. If p
is even the spectrum and superpotential for a single brane are determined by
purely classical () considerations. If p=3,
superpotentials for massless modes are forbidden to all orders in
and may only be generated by open string instantons. For this
latter case we find that such instanton effects are generically present. Mirror
symmetry relates even and odd p and thus perturbative and nonperturbative
superpotentials; we provide a preliminary discussion of a class of examples of
such mirror pairs.Comment: 22 pages, harvmac big; v2, corrected some typo
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