277 research outputs found
Multi instanton tests of holography
Gauge theories living on stacks of D7-branes are holographically related to
IIB gravitational backgrounds with a varying axion-dilaton field (F-theory).
The axion-dilaton field is generated by D7, O7 and D-instanton sources and can
be written in terms of the chiral correlators of the eight dimensional gauge
theory living on the D7-branes. Using localization techniques, we prove that
the same correlators determine the gauge coupling of the four-dimensional N=2
supersymmetric SU(2) gauge theories living on the elementary D3-brane which
probes the F-theory geometries.Comment: 18 page
Stringy Instantons in SU(N) N=2 Non-Conformal Gauge Theories
In this paper we explicitly obtain the leading corrections to the SU(N) N=2
prepotential due to stringy instantons both in flat space-time and in the
presence of a non-trivial graviphoton background field. We show that the
stringy corrections to the prepotential are expressible in terms of the
elementary symmetric polynomials. For N>2 the theory is not conformal; we
discuss the introduction of an explicit dependence on the string scale \alpha'
in the low-energy effective action through the stringy non-perturbative sector.Comment: 22 pages, 1 figur
Non-perturbative gauge/gravity correspondence in N=2 theories
We derive the exact supergravity profile for the twisted scalar field emitted
by a system of fractional D3 branes at a Z2 orbifold singularity supporting N=2
quiver gauge theories with unitary groups and bifundamental matter. At the
perturbative level this twisted field is "dual" to the gauge coupling but it is
corrected non-perturbatively by an infinite tower of fractional D-instantons.
The explicit microscopic description allows to derive the gravity profile from
disk amplitudes computing the emission rate of the twisted scalar field in
terms of chiral correlators in the dual gauge theory. We compute these quantum
correlators using multi-instanton localization techniques and/or Seiberg-Witten
analysis. Finally, we discuss a non-perturbative relation between the twisted
scalar and the effective coupling of the gauge theory for some simple choices
of the brane set ups.Comment: 42 pages. 3 figures, PDFLaTe
Holographic non-perturbative corrections to gauge couplings
We give a direct microscopic derivation of the F-theory background that
corresponds to four D7 branes of type I' theory by taking into account the
D-instanton contributions to the emission of the axio-dilaton field in the
directions transverse to the D7's. The couplings of the axio-dilaton to the
D-instanton moduli modify its classical source terms which are shown to be
proportional to the elements of the D7 brane chiral ring. Solving the bulk
field equations with the non-perturbatively corrected sources yields the full
F-theory background. This solution represents the gravitational dual of the
four-dimensional theory living on a probe D3 brane of type I', namely of the
N=2, Sp(1) SYM theory with Nf=4. Our results provide an explicit microscopic
derivation of the non-perturbative gravitational dual of this theory. They also
explain the recent observation that the exact coupling for this theory can be
entirely reconstructed from its perturbative part plus the knowledge of the
chiral ring on the D7 branes supporting its flavor degrees of freedom.Comment: Latex, 39 pages, 6 figure
Corrections to Nambu-Goto energy levels from the effective string action
The effective action on long strings, such as confining strings in pure
Yang-Mills theories, is well-approximated by the Nambu-Goto action, but this
action cannot be exact. The leading possible corrections to this action (in a
long string expansion in the static gauge), allowed by Lorentz invariance, were
recently identified, both for closed strings and for open strings. In this
paper we compute explicitly in a Hamiltonian formalism the leading corrections
to the lowest-lying Nambu-Goto energy levels in both cases, and verify that
they are consistent with the previously computed effective string partition
functions. For open strings of length R the leading correction is of order
1/R^4, for excited closed strings of length R in D>3 space-time dimensions it
is of order 1/R^5, while for the ground state of the closed string in any
dimension it is of order 1/R^7. We attempt to match our closed string
corrections to lattice results, but the latter are still mostly outside the
range of convergence of the 1/R expansion that we use.Comment: 18 pages, 1 figure, JHEP format. v2: added remark on 1/R^7
corrections to ground state energ
Instantons in N=2 magnetized D-brane worlds
In a toroidal orbifold of type IIB string theory we study instanton effects
in N=2 super Yang-Mills theories engineered with systems of wrapped magnetized
D9 branes and Euclidean D5 branes. We analyze the various open string sectors
in this brane system and study the 1-loop amplitudes described by annulus
diagrams with mixed boundary conditions, explaining their role in the stringy
instanton calculus. We show in particular that the non-holomorphic terms in
these annulus amplitudes precisely reconstruct the appropriate Kahler metric
factors that are needed to write the instanton correlators in terms of purely
holomorphic variables. We also explicitly derive the correct holomorphic
structure of the instanton induced low energy effective action in the Coulomb
branch.Comment: 40 pages, 5 figures, JHEP class. Some footnotes added and typos
corrected. Version published in JHE
Modular anomaly equation, heat kernel and S-duality in N=2 theories
We investigate epsilon-deformed N=2 superconformal gauge theories in four
dimensions, focusing on the N=2* and Nf=4 SU(2) cases. We show how the modular
anomaly equation obeyed by the deformed prepotential can be efficiently used to
derive its non-perturbative expression starting from the perturbative one. We
also show that the modular anomaly equation implies that S-duality is
implemented by means of an exact Fourier transform even for arbitrary values of
the deformation parameters, and then we argue that it is possible,
perturbatively in the deformation, to choose appropriate variables such that it
reduces to a Legendre transform.Comment: 30 pages, LeTeX2e. V2: references added, appendix B expanded, a few
typos correcte
Non-perturbative effective interactions from fluxes
Motivated by possible implications on the problem of moduli stabilization and
other phenomenological aspects, we study D-brane instanton effects in flux
compactifications. We focus on a local model and compute non-perturbative
interactions generated by gauge and stringy instantons in a N = 1 quiver theory
with gauge group U(N_0) x U(N_1) and matter in the bifundamentals. This model
is engineered with fractional D3-branes at a C^3/(Z_2 x Z_2) singularity, and
its non-perturbative sectors are described by introducing fractional
D-instantons. We find a rich variety of instanton-generated F- and D-term
interactions, ranging from superpotentials and Beasley-Witten like
multi-fermion terms to non-supersymmetric flux-induced instanton interactions.Comment: 37 pages, 7 figures. Final version published on JHEP. Section 4
modified in several points regarding string corrections in absence of fluxes;
in particular, section 4.3 is removed. Some other minor changes and two
references adde
ALE manifolds and Conformal Field Theory
We address the problem of constructing the family of (4,4) theories
associated with the sigma-model on a parametrized family of
Asymptotically Locally Euclidean (ALE) manifolds. We rely on the ADE
classification of these manifolds and on their construction as HyperK\"ahler
quotients, due to Kronheimer.
So doing we are able to define the family of (4,4) theories corresponding to
a family of ALE manifolds as the deformation of a solvable
orbifold conformal field-theory, being a
Kleinian group. We discuss the relation among the algebraic structure
underlying the topological and metric properties of self-dual 4-manifolds and
the algebraic properties of non-rational (4,4)-theories admitting an infinite
spectrum of primary fields. In particular, we identify the Hirzebruch signature
with the dimension of the local polynomial ring {\cal R}=\o {{\bf
C}[x,y,z]}{\partial W} associated with the ADE singularity, with the number of
non-trivial conjugacy classes in the corresponding Kleinian group and with the
number of short representations of the (4,4)-theory minus four.Comment: 48 pages, Latex, SISSA/44/92/EP, IFUM/443/F
Branched Coverings and Interacting Matrix Strings in Two Dimensions
We construct the lattice gauge theory of the group G_N, the semidirect
product of the permutation group S_N with U(1)^N, on an arbitrary Riemann
surface. This theory describes the branched coverings of a two-dimensional
target surface by strings carrying a U(1) gauge field on the world sheet. These
are the non-supersymmetric Matrix Strings that arise in the unitary gauge
quantization of a generalized two-dimensional Yang-Mills theory. By classifying
the irreducible representations of G_N, we give the most general formulation of
the lattice gauge theory of G_N, which includes arbitrary branching points on
the world sheet and describes the splitting and joining of strings.Comment: LaTeX2e, 25 pages, 4 figure
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