24 research outputs found
A worldsheet extension of O(d,d;Z)
We study superconformal interfaces between N=(1,1) supersymmetric sigma
models on tori, which preserve a u(1)^{2d} current algebra. Their fusion is
non-singular and, using parallel transport on CFT deformation space, it can be
reduced to fusion of defect lines in a single torus model. We show that the
latter is described by a semi-group extension of O(d,d;Q), and that (on the
level of Ramond charges) fusion of interfaces agrees with composition of
associated geometric integral transformations. This generalizes the well-known
fact that T-duality can be geometrically represented by Fourier-Mukai
transformations. Interestingly, we find that the topological interfaces between
torus models form the same semi-group upon fusion. We argue that this
semi-group of orbifold equivalences can be regarded as the \alpha' deformation
of the continuous O(d,d) symmetry of classical supergravity.Comment: 71 pages, 1 figure, minor additions and correction
Fusion of Critical Defect Lines in the 2D Ising Model
Two defect lines separated by a distance delta look from much larger
distances like a single defect. In the critical theory, when all scales are
large compared to the cutoff scale, this fusion of defect lines is universal.
We calculate the universal fusion rule in the critical 2D Ising model and show
that it is given by the Verlinde algebra of primary fields, combined with group
multiplication in O(1,1)/Z_2. Fusion is in general singular and requires the
subtraction of a divergent Casimir energy.Comment: 17 page
Holographic Duals of D=3 N=4 Superconformal Field Theories
We find the warped AdS_4 x K type-IIB supergravity solutions holographically
dual to a large family of three dimensional \cN=4 superconformal field theories
labeled by a pair (\rho,\hat\rho) of partitions of N. These superconformal
theories arise as renormalization group fixed points of three dimensional
mirror symmetric quiver gauge theories, denoted by T^{\rho}_{\hat \rho}(SU(N))
and T_{\rho}^{\hat \rho}(SU(N)) respectively. We give a supergravity derivation
of the conjectured field theory constraints that must be satisfied in order for
these gauge theories to flow to a non-trivial supersymmetric fixed point in the
infrared. The exotic global symmetries of these superconformal field theories
are precisely realized in our explicit supergravity description.Comment: 33 pages, LaTeX; added a comment mentioning that these solutions have
all moduli fixed; typos corrected; references adde
Infrared behavior of Closed Superstrings in Strong Magnetic and Gravitational Fields
A large class of four-dimensional supersymmetric ground states of closed
superstrings with a non-zero mass gap are constructed. For such ground states
we turn on chromo-magnetic fields as well as curvature. The exact spectrum as
function of the chromo-magnetic fields and curvature is derived. We examine the
behavior of the spectrum, and find that there is a maximal value for the
magnetic field . At this value all states
that couple to the magnetic field become infinitely massive and decouple. We
also find tachyonic instabilities for strong background fields of the order
where is the mass gap of the theory.
Unlike the field theory case, we find that such ground states become stable
again for magnetic fields of the order . The
implications of these results are discussed.Comment: Minor corrections. Version to appear in Nucl. Phys.
Non-perturbative triality in heterotic and type II N=2 strings
The non-perturbative equivalence of four-dimensional N=2 superstrings with
three vector multiplets and four hypermultiplets is analysed. These models are
obtained through freely acting orbifold compactifications from the heterotic,
the symmetric and the asymmetric type II strings. The heterotic scalar
manifolds are (SU(1,1) / U(1))^3 for the S,T,U moduli sitting in the vector
multiplets and SO(4,4)/ (SO(4) X SO(4)) for those in the hypermultiplets. The
type II symmetric duals correspond to a self-mirror Calabi-Yau threefold
compactification with Hodge numbers h(1,1)=h(2,1)=3, while the type II
asymmetric construction corresponds to a spontaneous breaking of the N=(4,4)
supersymmetry to N=(2,0). Both have already been considered in the literature.
The heterotic construction instead is new and we show that there is a
weak/strong coupling S-duality relation between the heterotic and the
asymmetric type IIA ground state with S(Het)=-1/S(As); we also show that there
is a partial restoration of N=8 supersymmetry in the heterotic strong-coupling
regime. We compute the full (non-)perturbative R2 and F2 corrections and
determine the prepotential.Comment: Latex, no figures, 24 page
Dynamical Topology Change in String Theory
Exact string solutions are presented, providing backgrounds where a dynamical
change of topology is occuring. This is induced by the time variation of a
modulus field. Some lessons are drawn concerning the region of validity of
effective theories and how they can be glued together, using stringy
information in the region where the topology changes.Comment: LaTeX file, 17pp., CERN-TH.7219/94, LPTENS-94/11. (Discussions have
been clarified in several places
Infrared Regularization of Superstring Theory and the One-Loop Calculation of Coupling Constants
Infrared regularized versions of 4-D N=1 superstring ground states are
constructed by curving the spacetime. A similar regularization can be performed
in field theory. For the IR regularized string ground states we derive the
exact one-loop effective action for non-zero U(1) or chromo-magnetic fields as
well as gravitational and axionic-dilatonic fields. This effective action is IR
and UV finite. Thus, the one-loop corrections to all couplings (gravitational,
gauge and Yukawas) are unabiguously computed. These corrections are necessary
for quantitative string superunification predictions at low energies. The
one-loop corrections to the couplings are also found to satisfy Infrared Flow
Equations.Comment: Version to appear in Nucl. Phys. B. (several parts have been
expanded, and extra results have been added.
Dynamical Topology Change, Compactification and Waves in String Cosmology
Exact string solutions are presented, where moduli fields are varying with
time. They provide examples where a dynamical change of the topology of space
is occurring. Some other solutions give cosmological examples where some
dimensions are compactified dynamically or simulate pre-big bang type
scenarios. Some lessons are drawn concerning the region of validity of
effective theories and how they can be glued together, using stringy
information in the region where the geometry and topology are not well defined
from the low energy point of view. Other time dependent solutions are presented
where a hierarchy of scales is absent. Such solutions have dynamics which is
qualitatively different and resemble plane gravitational waves. (Talk given at
the Trieste Spring School and Workshop, 1994.)Comment: 29pp. LateX, no figures
One Loop Corrections to Coupling Constants in IR-regulated String Theory
Exact Superstring solutions are constructed moving in 4-D space-time with
positive curvature and non-trivial dilaton and antisymmetric tensor fields. The
full spectrum of string excitations is derived as a function of moduli fields
and the scale which induced by the non-zero background
fields. The spectrum of string excitations has a non-zero mass gap and
in the weak curvature limit ( small) plays the role of a well
defined infrared regulator, consistent with modular invariance, gauge
invariance, supersymmetry and chirality.
The effects of a covariantly constant chomo-magnetic field as well as
additional curvature can be derived exactly up to one string-loop level. Thus,
the one-loop corrections to all couplings (gravitational, gauge and Yukawas)
are unambiguously computed and are finite both in the Ultra-Violet and the
Infra-Red regime. These corrections are necessary for quantitative string
superunification predictions at low energies. Similar calculations are done in
the effective field theory. The one-loop corrections to the couplings are also
found to satisfy Infrared Flow Equations.Comment: Based on a talk given by the first author at the Trieste Spring
Workshop, 1995. Contains some new result