16 research outputs found
Anomalous couplings for D-branes and O-planes
We study anomalous Wess-Zumino couplings of D-branes and O-planes in a
general background and derive them from a direct string computation by
factorizing in the RR channel various one-loop amplitudes. In particular, we
find that Op-planes present gravitational anomalous couplings involving the
Hirzebruch polynomial L, similarly to the roof genus A encoding Dp-brane
anomalous couplings. We determine, in each case, the precise dependence of
these couplings on the curvature of the tangent and normal bundles.Comment: 24 pages, LaTex, 5 figure
The generalized chiral Schwinger model on the two-sphere
A family of theories which interpolate between vector and chiral Schwinger
models is studied on the two--sphere . The conflict between the loss of
gauge invariance and global geometrical properties is solved by introducing a
fixed background connection. In this way the generalized Dirac--Weyl operator
can be globally defined on . The generating functional of the Green
functions is obtained by taking carefully into account the contribution of
gauge fields with non--trivial topological charge and of the related
zero--modes of the Dirac determinant. In the decompactification limit, the
Green functions of the flat case are recovered; in particular the fermionic
condensate in the vacuum vanishes, at variance with its behaviour in the vector
Schwinger model.Comment: 39 pages, latex, no figure
Worldvolume and target space anomalies in the D=10 super--fivebrane sigma--model
The fields of the conjectured ``heterotic" super--fivebrane sigma--model in
ten dimensions are made out of a well known gravitational sector, the and
the , and of a still unknown heterotic sector which should be
coupled to the Yang--Mills fields. We compute the one--loop worldvolume
and target space Lorentz--anomalies which arise from the gravitational
sector of the heterotic super--fivebrane sigma--model, using a method which we
developed previously for the Green--Schwarz heterotic superstring. These
anomalies turn out to carry an overall coefficient which is of that
required by the string/fivebrane duality conjecture. As a consequence the
worldvolume anomaly vanishes if the heterotic fields consist of 16 (rather than
32) complex Weyl fermions on the worldvolume. This implies that the
string/fivebrane duality conjecture can not be based on a ``heterotic"
super--fivebrane sigma--model with only fermions in the heterotic sector.
Possible implications of this result are discussed.Comment: 20 pages, Plain TeX, no figure
Quantum gravity corrections to the Schwarzschild mass
Vacuum spherically symmetric Einstein gravity in dimensions can be
cast in a two-dimensional conformal nonlinear sigma model form by first
integrating on the -dimensional (hyper)sphere and then performing a
canonical transformation. The conformal sigma model is described by two fields
which are related to the Arnowitt-Deser-Misner mass and to the radius of the
-dimensional (hyper)sphere, respectively. By quantizing perturbatively
the theory we estimate the quantum corrections to the ADM mass of a black hole.Comment: 18 pages, 8 figures, LaTeX2e, uses epsfig package, accepted for
publication in Phys. Rev.
Born-Infeld-Goldstone superfield actions for gauge-fixed D-5- and D-3-branes in 6d
The supersymmetric Born-Infeld actions describing gauge-fixed D-5- and
D-3-branes in ambient six-dimensional (6d) spacetime are constructed in
superspace. A new 6d action is the (1,0) supersymmetric extension of the 6d
Born-Infeld action. It is related via dimensional reduction to another
remarkable 4d action describing the N=2 supersymmetric extension of the
Born-Infeld-Nambu-Goto action with two real scalars. Both actions are the
Goldstone actions associated with partial (1/2) spontaneous breaking of
extended supersymmetry having 16 supercharges down to 8 supercharges. Both
actions can be put into the `non-linear sigma-model' form by using certain
non-linear superfield constraints. The unbroken supersymmetry is always
linearly realised in our construction.Comment: 39 pages, LaTeX; a few style and sign corrections, a reference adde
Topological Sigma-Models in Four Dimensions and Triholomorphic Maps
It is well-known that topological sigma-models in 2 dimensions constitute a
path-integral approach to the study of holomorphic maps from a Riemann surface
S to an almost complex manifold K, the most interesting case being that where K
is a Kahler manifold. We show that, in the same way, topological sigma-models
in 4 dimensions introduce a path integral approach to the study of
triholomorphic maps q:M-->N from a 4dimensional Riemannian manifold M to an
almost quaternionic manifold N. The most interesting cases are those where M, N
are hyperKahler or quaternionic Kahler. BRST-cohomology translates into
intersection theory in the moduli-space of this new class of instantonic maps,
named by us hyperinstantons. The definition of triholomorphicity that we
propose is expressed by the equation q_*-J_u q_* j_u = 0, u=1,2,3, where {j_u}
is an almost quaternionic structure on M and {J_u} is an almost quaternionic
structure on N. This is a generalization of the Cauchy-Fueter equations. For M,
N hyperKahler, this generalization naturally arises by obtaining the
topological sigma-model as a twisted version of the N=2 globally supersymmetric
sigma-model. We discuss various examples of hyperinstantons, in particular on
the torus and the K3 surface. We also analyse the coupling of the topological
sigma-model to topological gravity. The study ofComment: 43 pages, LaTeX file, SISSA/ISAS 73/93/EP. (reference [32] corrected
Renormalization Group Study of Chern-Simons Field Coupled to Scalar Matter in a Modified BPHZ Subtraction Scheme
We apply a soft version of the BPHZ subtraction scheme to the computation of
two-loop corrections from an Abelian Chern-Simons field coupled to (massive)
scalar matter with a and
self-interactions. The two-loop renormalization group functions are calculated.
We compare our results with those in the literature.Comment: 15 pages, 7 figures, revtex. To appear in Phys. Rev.
Non-equilibrium Condensation Process in a Holographic Superconductor
We study the non-equilibrium condensation process in a holographic
superconductor. When the temperature T is smaller than a critical temperature
T_c, there are two black hole solutions, the Reissner-Nordstrom-AdS black hole
and a black hole with a scalar hair. In the boundary theory, they can be
regarded as the supercooled normal phase and the superconducting phase,
respectively. We consider perturbations on supercooled Reissner-Nordstrom-AdS
black holes and study their non-linear time evolution to know about physical
phenomena associated with rapidly-cooled superconductors. We find that, for
T<T_c, the initial perturbations grow exponentially and, eventually, spacetimes
approach the hairy black holes. We also clarify how the relaxation process from
a far-from-equilibrium state proceeds in the boundary theory by observing the
time dependence of the superconducting order parameter. Finally, we study the
time evolution of event and apparent horizons and discuss their correspondence
with the entropy of the boundary theory. Our result gives a first step toward
the holographic understanding of the non-equilibrium process in
superconductors.Comment: 20 pages, 7 figure
Covariant Anomalies and Functional Determinants
We analize the algebraic structure of consistent and covariant anomalies in
gauge and gravitational theories: using a complex extension of the Lie algebra
it is possible to describe them in a unified way. Then we study their
representations by means of functional determinants, showing how the algebraic
solution determines the relevant operators for the definition of the effective
action. Particular attention is devoted to the Lorentz anomaly: we obtain by
functional methods the covariant anomaly for the spin-current and for the
energy-momentum tensor in presence of a curved background. With regard to the
consistent sector we are able to give a general functional solution only for
: using the characterization derived from the extended algebra, we find a
continuous family of operators whose determinant describes the effective action
of chiral spinors in curved space. We compute this action and we generalize the
result in presence of a gauge connection. Accepted for publication in
Fortschritte der Physik.Comment: 55 page