330 research outputs found
Generalized instantons in N = 4 super Yang-Mills theory and spinorial geometry
Using spinorial geometry techniques, we classify the supersymmetric solutions
of euclidean super Yang-Mills theory. These backgrounds represent
generalizations of instantons with nontrivial scalar fields turned on, and
satisfy some constraints that bear a similarity with the Hitchin equations, and
contain the Donaldson equations as a special subcase. It turns out that these
constraints can be obtained by dimensional reduction of the octonionic
instanton equations, and may be rephrased in terms of a selfduality-like
condition for a complex connection. We also show that the supersymmetry
conditions imply the equations of motion only partially.Comment: 29 pages, 3 tables. v2: references added. v3: conclusion extended,
version published in JHE
A note on instanton counting for N=2 gauge theories with classical gauge groups
We study the prepotential of N=2 gauge theories using the instanton counting
techniques introduced by Nekrasov. For the SO theories without matter we find a
closed expression for the full prepotential and its string theory gravitational
corrections. For the more subtle case of Sp theories without matter we discuss
general features and compute the prepotential up to instanton number three. We
also briefly discuss SU theories with matter in the symmetric and antisymmetric
representations. We check all our results against the predictions of the
corresponding Seiberg-Witten geometries.Comment: 24 pages, LaTeX. v2: refs added. v3: typos correcte
Instanton calculus in R-R background and the topological string
We study a system of fractional D3 and D(-1) branes in a Ramond-Ramond closed
string background and show that it describes the gauge instantons of N=2 super
Yang-Mills theory and their interactions with the graviphoton of N=2
supergravity. In particular, we analyze the instanton moduli space using string
theory methods and compute the prepotential of the effective gauge theory
exploiting the localization methods of the instanton calculus showing that this
leads to the same information given by the topological string. We also comment
on the relation between our approach and the so-called Omega-background.Comment: 38 pages, 2 figures, JHEP class (included); final version to be
pubished in JHE
An N=1 duality cascade from a deformation of N=4 SUSY Yang-Mills
We study relevant deformations of an N=1 superconformal theory which is an
exactly marginal deformation of U(N) N=4 SUSY Yang-Mills. The resulting theory
has a classical Higgs branch that is a complex deformation of the orbifold
C^3/Z_n x Z_n that is a non-compact Calabi-Yau space with isolated conifold
singularities. At these singular points in moduli space the theory exhibits a
duality cascade and flows to a confining theory with a mass gap. By exactly
solving the corresponding holomorphic matrix model we compute the exact quantum
superpotential generated at the end of the duality cascade and calculate
precisely how quantum effects deform the classical moduli space by replacing
the conifold singularities with three-cycles of finite size. Locally the
structure is that of the deformed conifold, but the global geometry is
different. This desingularized quantum deformed geometry is the moduli space of
probe D3-branes at the end of a duality cascade realized on the worldvolume of
(fractional) D3-branes placed at the isolated conifold singularities in the
deformation of the orbifold C^3/Z_n x Z_n with discrete torsion.Comment: Uses Latex, JHEP.cls, 43 pages, 3 figure
Instantons on Quivers and Orientifolds
We compute the prepotential for gauge theories descending from
SYM via quiver projections and mass deformations.
This accounts for gauge theories with product gauge groups and bifundamental
matter. The case of massive orientifold gauge theories with gauge group SO/Sp
is also described. In the case with no gravitational corrections the results
are shown to be in agreement with Seiberg-Witten analysis and previous results
in the literature.Comment: 28 pages, revised version, references added, some typos correcte
Multi-Instanton Calculus and Equivariant Cohomology
We present a systematic derivation of multi-instanton amplitudes in terms of
ADHM equivariant cohomology. The results rely on a supersymmetric formulation
of the localization formula for equivariant forms. We examine the cases of N=4
and N=2 gauge theories with adjoint and fundamental matter.Comment: 29 pages, one more reference adde
Effective actions, Wilson lines and the IR/UV mixing in noncommutative supersymmetric gauge theories
We study IR/UV mixing effects in noncommutative supersymmetric Yang-Mills
theories with gauge group U(N) using background field perturbation theory. We
compute three- and four-point functions of background fields, and show that the
IR/UV mixed contributions to these correlators can be reproduced from an
explicitly gauge-invariant effective action, which is expressed in terms of
open Wilson lines.Comment: 23 pages, 8 figures. v2: new section and references added, effective
action expressed only in terms of open Wilson lines operator
Noncommutativity from the string perspective: modification of gravity at a mm without mm sized extra dimensions
We explore how the IR pathologies of noncommutative field theory are resolved
when the theory is realized as open strings in background B-fields:
essentially, since the IR singularities are induced by UV/IR mixing, string
theory brings them under control in much the same way as it does the UV
singularities. We show that at intermediate scales (where the Seiberg-Witten
limit is a good approximation) the theory reproduces the noncommutative field
theory with all the (un)usual features such as UV/IR mixing, but that outside
this regime, in the deep infra-red, the theory flows continuously to the
commutative theory and normal Wilsonian behaviour is restored. The resulting
low energy physics resembles normal commutative physics, but with additional
suppressed Lorentz violating operators. We also show that the phenomenon of
UV/IR mixing occurs for the graviton as well, with the result that, in
configurations where Planck's constant receives a significant one-loop
correction (for example brane-induced gravity), the distance scale below which
gravity becomes non-Newtonian can be much greater than any compact dimensions.Comment: 30 pages. Slight revision: clarified some points and added a
referenc
Solving matrix models using holomorphy
We investigate the relationship between supersymmetric gauge theories with
moduli spaces and matrix models. Particular attention is given to situations
where the moduli space gets quantum corrected. These corrections are controlled
by holomorphy. It is argued that these quantum deformations give rise to
non-trivial relations for generalized resolvents that must hold in the
associated matrix model. These relations allow to solve a sector of the
associated matrix model in a similar way to a one-matrix model, by studying a
curve that encodes the generalized resolvents. At the level of loop equations
for the matrix model, the situations with a moduli space can sometimes be
considered as a degeneration of an infinite set of linear equations, and the
quantum moduli space encodes the consistency conditions for these equations to
have a solution.Comment: 38 pages, JHEP style, 1 figur
The DNA Damage Signal for Mdm2 Regulation, Trp53 Induction, and Sunburn Cell Formation In Vivo Originates from Actively Transcribed Genes
The stratum corneum and DNA repair do not completely protect keratinocytes from ultraviolet B. A third defense prevents cells with DNA photoproducts from becoming precancerous mutant cells: apoptosis of ultraviolet-damaged keratinocytes (âsunburn cellsâ). As signals for ultraviolet-induced apoptosis, some studies implicate DNA photoproducts in actively transcribed genes; other studies implicate non-nuclear signals. We traced and quantitated the in vivo DNA signal through several steps in the apoptosis-signaling pathway in haired mice. Homozygous inactivation of Xpa, Csb, or Xpc nucleotide excision repair genes directed the accumulation of DNA photoproducts to specific genome regions. Repair-defective Xpaâ/â mice were 7â10-fold more sensitive to sunburn cell induction than wild-type mice, indicating that 86â90% of the ultraviolet B signal for keratinocyte apoptosis involved repairable photoproducts in DNA; the remainder involves unrepaired DNA lesions or nongenomic targets. Csbâ/â mice, defective only in excising photoproducts from actively transcribed genes, were as sensitive as Xpaâ/â, indicating that virtually all of the DNA signal originates from photoproducts in active genes. Conversely, Xpcâ/â mice, defective in repairing the untranscribed majority of the genome, were as resistant to apoptosis as wild type. Sunburn cell formation requires the Trp53 tumor suppressor protein; 90â96% of the signal for its induction in vivo involved transcribed genes. Mdm2, which regulates the stability of Trp53 through degradation, was induced in vivo by low ultraviolet B doses but was suppressed at erythemal doses. DNA photoproducts in actively transcribed genes were involved in â 89% of the Mdm2 response
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