84 research outputs found
D3-branes dynamics and black holes
Using the D3-brane as the fundamental tool, we adress two aspects of D-branes
physics. The first regards the interaction between two electromagnetic dual
D-branes in 10 dimensions. In particular, we give a meaning to {\it both} even
and odd spin structure contributions, the latter being non vanishing for non
zero relative velocity (and encoding the Lorentz-like contribution). The
second aspect regards the D-brane/black holes correspondence. We show how the 4
dimensional configuration corresponding to a {\it single} D3-brane wrapped on
the orbifold T^6/Z_3 represents a regular Reissner-Nordstrom solution of d=4
N=2 supergravityComment: 8 pages, latex, 1 eps figure. Talk presented by M. Bertolini at the
conference "Quantum aspects of gauge theories, supergravity and unification"
in Corfu`; to appear in the proceeding
Stringy instanton corrections to N=2 gauge couplings
We discuss a string model where a conformal four-dimensional N=2 gauge theory
receives corrections to its gauge kinetic functions from "stringy" instantons.
These contributions are explicitly evaluated by exploiting the localization
properties of the integral over the stringy instanton moduli space. The model
we consider corresponds to a setup with D7/D3-branes in type I' theory
compactified on T4/Z2 x T2, and possesses a perturbatively computable heterotic
dual. In the heteoric side the corrections to the quadratic gauge couplings are
provided by a 1-loop threshold computation and, under the duality map, match
precisely the first few stringy instanton effects in the type I' setup. This
agreement represents a very non-trivial test of our approach to the exotic
instanton calculus.Comment: 63 pages, 5 figures. V2: final version with minor corrections
published on JHEP05(2010)10
N=2 Instanton Effective Action in Omega-background and D3/D(-1)-brane System in R-R Background
We study the relation between the ADHM construction of instantons in the
Omega-background and the fractional D3/D(-1)-branes at the orbifold singularity
of C \times C^2/Z_2 in Ramond-Ramond (R-R) 3-form field strength background. We
calculate disk amplitudes of open strings connecting the D3/D(-1)-branes in
certain R-R background to obtain the D(-1)-brane effective action deformed by
the R-R background. We show that the deformed D(-1)-brane effective action
agrees with the instanton effective action in the Omega-background.Comment: 35 pages, no figures, references adde
The exact 8d chiral ring from 4d recursion relations
We consider the local F-theory set-up corresponding to four D7 branes in type
I' theory, in which the exact axio-dilaton background tau(z) is identified with
the low-energy effective coupling of the four-dimensional N=2 super Yang-Mills
theory with gauge group SU(2) and Nf=4 flavours living on a probe D3 brane
placed at position z. Recently, an intriguing relation has been found between
the correlators forming the chiral ring of the eight-dimensional theory on the
D7 branes and the large-z expansion of the tau profile. Here we apply to the
SU(2), Nf=4 theory some recursion techniques that allow to derive the
coefficients of the large-z expansion of tau in terms of modular functions of
the UV coupling. In this way we obtain exact expressions for the elements of
the eight-dimensional chiral ring that resum their instanton expansions,
previously known only up to the first few orders by means of localization
techniques.Comment: 23 pages, Latex2
Surface defects from fractional branes. Part I
We show that the Gukov-Witten monodromy defects of supersymmetric Yang-Mills theory can be realized in perturbative string theory by considering an orbifold background of the Kanno-Tachikawa type and placing stacks of fractional D3-branes whose world-volume partially extends along the orbifold directions. In particular, we show that turning on a constant background value for some scalar fields in the closed string twisted sectors induces a non-trivial profile for the gauge field and one of the complex scalars of the world-volume theory, and that this profile exactly matches the singular behavior that one expects for a Gukov-Witten surface defect in the N = 4 super Yang-Mills theory. To keep the presentation as simple as possible, in this work we restrict our analysis to surface defects corresponding to a ℤ2 orbifold and defer the study of the most general case to a companion paper
Generalized two-dimensional Yang-Mills theory is a matrix string theory
We consider two-dimensional Yang-Mills theories on arbitrary Riemann
surfaces. We introduce a generalized Yang-Mills action, which coincides with
the ordinary one on flat surfaces but differs from it in its coupling to
two-dimensional gravity. The quantization of this theory in the unitary gauge
can be consistently performed taking into account all the topological sectors
arising from the gauge-fixing procedure. The resulting theory is naturally
interpreted as a Matrix String Theory, that is as a theory of covering maps
from a two-dimensional world-sheet to the target Riemann surface.Comment: LaTeX, 10 pages, uses espcrc2.sty. Presented by A. D'adda at the
Third Meeting on Constrained Dynamics and Quantum Gravity, Villasimius
(Sardinia, Italy) September 13-17, 1999; to appear in the proceeding
Modular anomaly equations and S-duality in N=2 conformal SQCD
We use localization techniques to study the non-perturbative properties of an N = 2 superconformal gauge theory with gauge group SU(3) and six fundamental flavours. The instanton corrections to the prepotential, the dual periods and the period matrix are calculated in a locus of special vacua possessing a ℤ 3 symmetry. In a semiclassical expansion, we show that these observables are constrained by S-duality via a modular anomaly equation which takes the form of a recursion relation. The solutions of the recursion relation are quasi-modular functions of Γ 1 (3), which is a subgroup of the S -duality group and is also a congruence subgroup of SL(2 , ℤ )
Non(anti)commutative SYM theory: Renormalization in superspace
We present a systematic investigation of one-loop renormalizability for
nonanticommutative N=1/2, U(N) SYM theory in superspace. We first discuss
classical gauge invariance of the pure gauge theory and show that in
contradistinction to the ordinary anticommutative case, different
representations of supercovariant derivatives and field strengths do not lead
to equivalent descriptions of the theory. Subsequently we develop background
field methods which allow us to compute a manifestly covariant gauge effective
action. One-loop evaluation of divergent contributions reveals that the theory
simply obtained from the ordinary one by trading products for star products is
not renormalizable. In the case of SYM with no matter we present a N=1/2
improved action which we show to be one-loop renormalizable and which is
perfectly compatible with the algebraic structure of the star product. For this
action we compute the beta functions. A brief discussion on the inclusion of
chiral matter is also presented.Comment: Latex file, 59 pages, 10 figures, One reference adde
N=2 Gauge theories on systems of fractional D3/D7 branes
We study a bound state of fractional D3/D7-branes in the ten-dimensional
space R^{1,5}*R^{4}/Z_2 using the boundary state formalism. We construct the
boundary actions for this system and show that higher order terms in the
twisted fields are needed in order to satisfy the zero-force condition. We then
find the classical background associated to the bound state and show that the
gauge theory living on a probe fractional D3-brane correctly reproduces the
perturbative behavior of a four-dimensional N=2 supersymmetric gauge theory
with fundamental matter.Comment: latex, 22 pages. Typos fixed, appendix expanded, some points
clarified and references adde
- …