1,729 research outputs found
BPS States, String Duality, and Nodal Curves on K3
We describe the counting of BPS states of Type II strings on K3 by relating
the supersymmetric cycles of genus to the number of rational curves with
double points on K3. The generating function for the number of such curves
is the left-moving partition function of the bosonic string.Comment: 12 pages, harvma
D-Branes and Topological Field Theories
In the presence of a D-brane a string theory develops a new subsector. We
show that for curved D-branes the corresponding sector is a (partially twisted)
topological field theory. We use this result to compute the degeneracy of
2-branes wrapped around cycles as well as 3-branes wrapped around CY
threefold vanishing 3-cycles. In both cases we find the degeneracy is in accord
with expectation. The counting of BPS states of a gas of 0-branes in the
presence of a 4-brane in is considered and it is noted that the effective
0-brane charge is shifted by 1, due to a quantum correction. This is in accord
with string duality and the fact that left-moving ground state energy of
heterotic string starts at . We also show that all the three different
topological twistings of four dimensional Yang-Mills theory do arise from
curved three-branes embedded in different spaces (Calabi-Yau manifolds and
manifolds with exceptional holonomy groups).Comment: 22 page
D-Brane Boundary State Dynamics
We construct the open string boundary states corresponding to various
time-dependent deformations of the D-brane and explore several ways in which
they may be used to study stringy soliton collective coordinate quantum
dynamics. Among other things, we find that D-strings have exact moduli
corresponding to arbitrary chiral excitations of the basic soliton. These are
presumably the duals of the BPS-saturated excitations of the fundamental Type
IIB string. These first steps in a systematic study of the dynamics and
interactions of Dirichlet-brane solitons give further evidence of the
consistency of Polchinski's new approach to string soliton physics.Comment: 14 pages, harvmac; reference added, end of section 3 modifie
Classical and quantum aspects of 4 dimensional black holes
In this talk I address some aspects in the recent developments for N=2 black
holes in 4 dimensions. I restrict myself on axion-free solutions that can
classically be related to intersections of isotropic - or -branes. After
reviewing of some classical properties I include corrections coming from a
general cubic prepotential. On the heterotic side these are quantum corrections
for these black hole solutions. Finally, I discuss a microscopic interpretation
of the entropy for the extremal as well as near-extremal black hole.Comment: 12 pages, 7 figure, LaTeX, small correction
D-Branes and Bundles on Elliptic Fibrations
We study the D-brane spectrum on a two-parameter Calabi-Yau model. The
analysis is based on different tools in distinct regions of the moduli space:
wrapped brane configurations on elliptic fibrations near the large radius
limit, and SCFT boundary states at the Gepner point. We develop an explicit
correspondence between these two classes of objects, suggesting that boundary
states are natural quantum generalizations of bundles. We also find interesting
D-brane dynamics in deep stringy regimes. The most striking example is,
perhaps, that nonsupersymmetric D6-D0 and D4-D2 large radius configurations
become stable BPS states at the Gepner point.Comment: 22 page
Four Dimensional String/String/String Triality
In six spacetime dimensions, the heterotic string is dual to a Type
string. On further toroidal compactification to four spacetime dimensions, the
heterotic string acquires an SL(2,\BbbZ)_S strong/weak coupling duality and
an SL(2,\BbbZ)_T \times SL(2,\BbbZ)_U target space duality acting on the
dilaton/axion, complex Kahler form and the complex structure fields
respectively. Strong/weak duality in interchanges the roles of and
in yielding a Type string with fields . This suggests
the existence of a third string (whose six-dimensional interpretation is more
obscure) that interchanges the roles of and . It corresponds in fact to
a Type string with fields leading to a four-dimensional
string/string/string triality. Since SL(2,\BbbZ)_S is perturbative for the
Type string, this triality implies -duality for the heterotic
string and thus fills a gap left by duality. For all three strings the
total symmetry is SL(2,\BbbZ)_S \times O(6,22;\BbbZ)_{TU}. The
O(6,22;\BbbZ) is {\it perturbative} for the heterotic string but contains the
conjectured {\it non-perturbative} SL(2,\BbbZ)_X, where is the complex
scalar of the Type string. Thus four-dimensional triality also
provides a (post-compactification) justification for this conjecture. We
interpret the Bogomol'nyi spectrum from all three points of view. In
particular we generalize the Sen-Schwarz formula for short multiplets to
include intermediate multiplets also and discuss the corresponding black hole
spectrum both for the theory and for a truncated ---- symmetric
theory. Just as the first two strings are described by the
four-dimensional {\it elementary} and {\it dual solitonic} solutions, so theComment: 36 pages, Latex, 2 figures, some references changed, minor changes in
formulas and tables; to appear in Nucl. Phys.
Open P-Branes
It is shown that many of the -branes of type II string theory and
supergravity can have boundaries on other -branes. The rules for when this
can and cannot occur are derived from charge conservation. For example it is
found that membranes in supergravity and IIA string theory can have
boundaries on fivebranes. The boundary dynamics are governed by the self-dual
string. A collection of parallel fivebranes contains \half N(N-1)
self-dual strings which become tensionless as the fivebranes approach one
another.Comment: harvmac, 8 page
Nonperturbative Effects in Noncritical Strings with Soliton Backgrounds
We explicitly construct soliton operators in (or ) string theory,
and show that the Schwinger-Dyson equations allow solutions with these solitons
as backgrounds. The dominant contributions from 1-soliton background are
explicitly evaluated in the weak coupling limit, and shown to agree with the
nonperturbative analysis of string equations. We suggest that fermions should
be treated as fundamental dynamical variables since both macroscopic loops and
solitons are constructed in their bilinear forms.Comment: 15 pages + 1 eps figure, LaTeX, Minor Change
D-brane Analyses for BPS Mass Spectra and U-duality
We give a confirmation of U-duality of type II superstring by discussing mass
spectrum of the BPS states. We first evaluate the mass spectrum of BPS solitons
with one kind of R-R charges. Our analysis is based on the 1-loop effective
action of D-brane, which is known as ``Dirac-Born-Infeld (DBI) action'', and
the fact that BPS states correspond to the SUSY cycles with minimal volumes. We
show the mass formula derived in this manner is completely fitted with that
given by U-duality. We further discuss the cases of BPS solitons possessing
several kinds of R-R charges. These are cases of ``intersecting D-branes'',
which cannot be described by simple DBI actions. We claim that, in these cases,
higher loop corrections should be incorporated as binding energies between the
branes. It is remarkable that the summation of the contributions from all loops
reproduces the correct mass formula predicted by U-duality.Comment: 44 pages, Latex, 9 figures (eps. files), Analyses based on M-theory
are added. final version to appear in Nucl. Phys.
Superstring Dualities
This talk is divided into two parts. The first part reviews some of the
duality relationships between superstring theories. These relationships are
interpreted as providing evidence for the existence of a unique underlying
fundamental theory. The second part describes my recent work on the SL(2,Z)
duality group of the type IIB superstring theory in ten dimensions and its
interpretation in terms of a possible theory of supermembranes in eleven
dimensions.Comment: 14 pages; latex; an error has been correcte
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