68 research outputs found
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 Ă 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
Orientifolds of type IIA strings on Calabi-Yau manifolds
We identify type IIA orientifolds that are dual to M-theory compactifications
on manifolds with G_2-holonomy. We then discuss the construction of crosscap
states in Gepner models. (Based on a talk presented by S.G. at PASCOS 2003 held
at the Tata Institute of Fundamental Research, Mumbai during Jan. 3-8, 2003.)Comment: 3 pages, RevTeX, PASCOS '03 tal
Massless D-strings and moduli stabilization in type I cosmology
We consider the cosmological evolution induced by the free energy F of a gas
of maximally supersymmetric heterotic strings at finite temperature and weak
coupling in dimension D>=4. We show that F, which plays the role of an
effective potential, has minima associated to enhanced gauge symmetries, where
all internal moduli can be attracted and dynamically stabilized. Using the fact
that the heterotic/type I S-duality remains valid at finite temperature and can
be applied at each instant of a quasi-static evolution, we find in the dual
type I cosmology that all internal NS-NS and RR moduli in the closed string
sector and the Wilson lines in the open string sector can be stabilized. For
the special case of D=6, the internal volume modulus remains a flat direction,
while the dilaton is stabilized. An essential role is played by light D-string
modes wrapping the internal manifold and whose contribution to the free energy
cannot be omitted, even when the type I string is at weak coupling. As a
result, the order of magnitude of the internal radii expectation values on the
type I side is (lambda_I alpha')^{1/2}, where lambda_I is the ten-dimensional
string coupling. The non-perturbative corrections to the type I free energy can
alternatively be described as effects of "thermal E1-instantons", whose
worldsheets wrap the compact Euclidean time cycle.Comment: 39 pages, 1 figur
Cosmological Phases of the String Thermal Effective Potential
In a superstring framework, the free energy density, F, can be determined
unambiguously at the full string level once supersymmetry is spontaneously
broken via geometrical fluxes. We show explicitly that only the moduli
associated to the supersymmetry breaking may give relevant contributions. All
other spectator moduli \mu_I give exponentially suppressed contributions for
relatively small (as compared to the string scale) temperature, T, and
supersymmetry breaking scale, M. More concisely, for \mu_I > T and M, F takes
the form
F(T,M; \mu_I)=F(T,M)+O[exp(- {\mu_I\over T}), exp(- {\mu_I\over M})]
We study the cosmological regime where T and M are below the Hagedorn
temperature scale T_H. In this regime, F remains finite for any values of the
spectator moduli \mu_I. We investigate extensively the case of one spectator
modulus \mu_d corresponding to R_d, the radius-modulus field of an internal
compactified dimension. We show that its thermal effective potential admits
five phases, each of which can be described by a distinct but different
effective field theory. For late cosmological times, the Universe is attracted
to a "Radiation-like evolution" with M(t) ~ T(t)~ 1/a(t)~ t^{-2/d}. The
spectator modulus \mu(t) is stabilized either to the stringy enhanced symmetry
point where R_d=1, or fixed at an arbitrary constant \mu_0>T,M. For arbitrary
boundary conditions at some initial time, t_E, \mu(t) may pass through more
than one effective field theory phase before its final attraction.Comment: 60 pages, 1 figur
Non-perturbative orientifold transitions at the conifold
After orientifold projection, the conifold singularity in hypermultiplet
moduli space of Calabi-Yau compactifications cannot be avoided by geometric
deformations. We study the non-perturbative fate of this singularity in a local
model involving O6-planes and D6-branes wrapping the deformed conifold in Type
IIA string theory. We classify possible A-type orientifolds of the deformed
conifold and find that they cannot all be continued to the small resolution.
When passing through the singularity on the deformed side, the O-plane charge
generally jumps by the class of the vanishing cycle. To decide which classical
configurations are dynamically connected, we construct the quantum moduli space
by lifting the orientifold to M-theory as well as by looking at the
superpotential. We find a rich pattern of smooth and phase transitions
depending on the total sixbrane charge. Non-BPS states from branes wrapped on
non-supersymmetric bolts are responsible for a phase transition. We also
clarify the nature of a Z_2 valued D0-brane charge in the 6-brane background.
Along the way, we obtain a new metric of G_2 holonomy corresponding to an
O6-plane on the three sphere of the deformed conifold.Comment: 76 pages, references adde
Polarization and magnetization dynamics of a field-driven multiferroic structure
We consider a multiferroic chain with a linear magnetoelectric coupling
induced by the electrostatic screening at the ferroelectric/ferromagnet
interface. We study theoretically the dynamic ferroelectric and magnetic
response to external magnetic and electric fields by utilizing an approach
based on coupled Landau- Khalatnikov and finite-temperature
Landau-Lifshitz-Gilbert equations. Additionally, we compare with Monte Carlo
calculations. It is demonstrated that for material parameters corresponding to
BaTiO3/Fe the polarization and the magnetization are controllable by external
magnetic and electric fields respectively
Type IIA Orientifold Limit of M-Theory on Compact Joyce 8-Manifold of Spin(7)-Holonomy
We show that M-theory compactified on a compact Joyce 8-manifold of
-holonomy, which yields an effective theory in with = 1
supersymmetry, admits at some special points in it moduli space a description
in terms of type IIA theory on an orientifold of compact Joyce 7-manifold of
-holonomy. We find the evidence in favour of this duality by computing the
massless spectra on both M-thory side and type IIA side. For the latter, we
compute the massless spectra by going to the orbifold limit of the Joyce
7-manifold.Comment: 26 pages, 2 eps figures, Latex file, two references and one footnote
added, corrected some typo
Cohomogeneity One Manifolds of Spin(7) and G(2) Holonomy
In this paper, we look for metrics of cohomogeneity one in D=8 and D=7
dimensions with Spin(7) and G_2 holonomy respectively. In D=8, we first
consider the case of principal orbits that are S^7, viewed as an S^3 bundle
over S^4 with triaxial squashing of the S^3 fibres. This gives a more general
system of first-order equations for Spin(7) holonomy than has been solved
previously. Using numerical methods, we establish the existence of new
non-singular asymptotically locally conical (ALC) Spin(7) metrics on line
bundles over \CP^3, with a non-trivial parameter that characterises the
homogeneous squashing of CP^3. We then consider the case where the principal
orbits are the Aloff-Wallach spaces N(k,\ell)=SU(3)/U(1), where the integers k
and \ell characterise the embedding of U(1). We find new ALC and AC metrics of
Spin(7) holonomy, as solutions of the first-order equations that we obtained
previously in hep-th/0102185. These include certain explicit ALC metrics for
all N(k,\ell), and numerical and perturbative results for ALC families with AC
limits. We then study D=7 metrics of holonomy, and find new explicit
examples, which, however, are singular, where the principal orbits are the flag
manifold SU(3)/(U(1)\times U(1)). We also obtain numerical results for new
non-singular metrics with principal orbits that are S^3\times S^3. Additional
topics include a detailed and explicit discussion of the Einstein metrics on
N(k,\ell), and an explicit parameterisation of SU(3).Comment: Latex, 60 pages, references added, formulae corrected and additional
discussion on the asymptotic flow of N(k,l) cases adde
Partial breaking of global D=4 supersymmetry, constrained superfields, and 3-brane actions
We show that the connection between partial breaking of supersymmetry and
nonlinear actions is not accidental and has to do with constraints that lead
directly to nonlinear actions of the Born-Infeld type. We develop a constrained
superfield approach that gives a universal way of deriving and using these
actions. In particular, we find the manifestly supersymmetric form of the
action of the 3-brane in 6-dimensional space in terms of N=1 superfields by
using the tensor multiplet as a tool. We explain the relation between the
Born-Infeld action and the model of partial N=2 supersymmetry breaking by a
dual D-term. We represent the Born-Infeld action in a novel form quadratic in
the gauge field strengths by introducing two auxiliary complex scalar fields;
this makes duality covariance and the connection with the N=1 supersymmetric
extension of the action very transparent. We also suggest a general procedure
for deriving manifestly duality symmetric actions, explaining in a systematic
way relations between previously discussed Lorentz covariant and noncovariant
actions.Comment: 28 pages, harvmac. v4: a mistake in eq.(3.24) (pointed out by S.
Kuzenko) correcte
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