2,127 research outputs found
Spontaneous Breaking of N=2 Global Supersymmetry
We study spontaneous supersymmetry breaking in N=2 globally supersymmetric
theories describing a system of abelian vector multiplets. We find that the
most general form of the action admits, in addition to the usual
Fayet-Iliopoulos term, a magnetic Fayet-Iliopoulos term for the auxiliary
components of dual vector multiplets. In a generic case, N=2 supersymmetry is
broken down spontaneously to N=1. In some cases however, the scalar potential
can drive the theory towards a N=2 supersymmetric ground state where massless
dyons condense in the vacuum.Comment: 12 pages, LaTe
One-loop Correction and the Dilaton Runaway Problem
We examine the one-loop vacuum structure of an effective theory of gaugino
condensation coupled to the dilaton for string models in which the gauge
coupling constant does not receive string threshold corrections. The new
ingredients in our treatment are that we take into account the one-loop
correction to the dilaton K\"ahler potential and we use a formulation which
includes a chiral field corresponding to the gaugino bilinear. We find
through explicit calculation that supersymmetry in the Yang-Mills sector is
broken by gaugino condensation.
The dilaton and field have masses on the order of the gaugino
condensation scale independently of the dilaton VEV. Although the calculation
performed here is at best a model of the full gaugino condensation dynamics,
the result shows that the one-loop correction to the dilaton K\"ahler potential
as well as the detailed dynamics at the gaugino condensation scale may play an
important role in solving the dilaton runaway problem.Comment: 19 page
Renormalization of Boundary Fermions and World-Volume Potentials on D-branes
We consider a sigma model formulation of open string theory with boundary
fermions carrying Chan-Paton charges at the string ends. This formalism is
particularly suitable for studying world-volume potentials on D-branes. We
perform explicit two-loop sigma model computations of the potential T-dual to
the non-abelian Born-Infeld action. We also discuss the world-volume couplings
of NS fluxes which are responsible for Myers' dielectric effect.Comment: 17 pages, 8 figure
Aspects of Type I - Type II - Heterotic Triality in Four Dimensions
We discuss equivalence between Type I, Type II and Heterotic N=2 superstring theories in four dimensions. We study the effective field theory of Type I models obtained by orientifold reductions of Type IIB compactifications on K_3 \times T~2$. We compute the one-loop prepotential which is determined in this case by the one-loop correction to the Planck mass and can be written as an index associated to the Ramond open string sector. It receives contributions only from N=2 BPS states that originate from D=6 massless string modes. We apply this result to the so-called S-T-U model which admits simultaneous Type II and Heterotic description, and show that all three prepotentials agree in the appropriate limits as expected from the superstring triality conjecture.We discuss the equivalence between type I, type II and heterotic N = 2 superstring theories in four dimensions. We study the effective field theory of type I models obtained by orientifold reductions of type IIB compactifications on K 3 × T 2 . We show that the perturbative prepotential is determined by the one-loop corrections to the Planck mass and is associated to an index. As is the case for threshold corrections to gauge couplings, this renormalization is entirely due to N = 2 BPS states that originate from D = 6 massless string modes. We apply our result to the so-called S - T - U model which admits simultaneous type II and heterotic descriptions, and show that all three prepotentials agree in the appropriate limits as expected from the superstring triality conjecture
Fermion Masses in Superstring Theory
We give a model-independent discussion of fermion masses in four-dimensional
heterotic superstring theories. We discuss the tree level contributions and
quantum corrections, including one-loop threshold effects and masses generated
as a result of non-perturbative supersymmetry breaking. We also point out that
superstring models give rise to a generic -term in the effective low
energy Lagrangian.Comment: 13 pages, latex. Based on talks presented at the Spring Workshop on
String Theory, ICTP, Trieste, 11-22 April 1994, and at the Joint U.S.-Polish
Workshop on Physics from Planck Scale to Electroweak Scale, Warsaw, Poland,
21-24 September 199
Dynamical Supersymmetry Breaking and the Linear Multiplet
We analyze gaugino condensation in the presence of a dilaton and an
antisymmetric tensor field, with couplings reminiscent of string theories. The
degrees of freedom relevant to a supersymmetric description of the effective
theory below the scale of condensation are discussed in this context.Comment: 17 pages, LaTeX, no figures -- 1 reference correcte
Axion Couplings and Effective Cut-Offs in Superstring Compactifications
We use the linear supermultiplet formalism of supergravity to study axion
couplings and chiral anomalies in the context of field-theoretical Lagrangians
describing orbifold compactifications beyond the classical approximation. By
matching amplitudes computed in the effective low energy theory with the
results of string loop calculations we determine the appropriate counterterm in
this effective theory that assures modular invariance to all loop order. We use
supersymmetry consistency constraints to identify the correct ultra-violet
cut-offs for the effective low energy theory. Our results have a simple
interpretation in terms of two-loop unification of gauge coupling constants at
the string scale.Comment: 25 page
Duality in Superstring Compactifications with Magnetic Field Backgrounds
Motivated by the work of Polchinski and Strominger on type IIA theory, where
the effect of non-trivial field strengths for p-form potentials on a Calabi-Yau
space was discussed, we study four-dimensional heterotic string theory in the
presence of magnetic field on a 2-cycle in the internal manifold, for both N=4
and N=2 cases. We show that at special points in the moduli space, certain
perturbative charged states become tachyonic and stabilize the vacuum by
acquiring vacuum expectation values, thereby restoring supersymmetry. We
discuss both the cases where the tachyons appear with a tower of Landau levels,
which become light in the limit of large volume of the 2-cycle, and the case
where such Landau levels are not present. In the latter case it is sufficient
to restrict the analysis to the quartic potential for the tachyon. On the other
hand, in the former case it is necessary to include the Landau levels in the
analysis of the potential; for toroidal and orbifold examples, we give an
explicit CFT description of the new supersymmetric vacuum. The resulting new
vacuum turns out to be in the same class as the original supersymmetric one.
Finally, using duality, we discuss the role of the Landau levels on the type
IIA side.Comment: 26 pages, LaTeX, 1 figure; Nucl. Phys. B version with typos corrected
and references adde
N=2 Type II- Heterotic duality and Higher derivative F-terms
We test the recently conjectured duality between supersymmetric type II
and heterotic string models by analysing a class of higher dimensional
interactions in the respective low-energy Lagrangians. These are -terms of
the form where is the gravitational superfield. On the type II
side these terms are generated at the -loop level and in fact are given by
topological partition functions of the twisted Calabi-Yau sigma model. We show
that on the heterotic side these terms arise at the one-loop level. We study in
detail a rank 3 example and show that the corresponding couplings satisfy
the same holomorphic anomaly equations as in the type II case. Moreover we
study the leading singularities of 's on the heterotic side, near the
enhanced symmetry point and show that they are universal poles of order
with coefficients that are given by the Euler number of the moduli
space of genus- Riemann surfaces. This confirms a recent conjecture that the
physics near conifold singularity is governed by string theory at the
self-dual point.Comment: 33 pages, latex, no figure
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