Instanton Effective Action Research Articles

Localization of effective actions in open superstring field theory

We consider the construction of the algebraic part of D-branes tree-level effective action from Berkovits open superstring field theory. Applying this construction to the quartic potential of massless fields carrying a specific worldsheet charge, we show that the full contribution to the potential localizes at the boundary of moduli space, reducing to elementary two-point functions. As examples of this general mechanism, we show how the Yang-Mills quartic potential and the instanton effective action of a Dp/D(p − 4) system are reproduced.

Renormalization scheme dependence and renormalization group summation

We consider logarithmic contributions to the free energy, instanton effective action, and Laplace sum rules in QCD that are a consequence of radiative corrections. Upon summing these contributions by using the renormalization group, all dependence on the renormalization scale parameter μ cancels. The renormalization scheme dependence in these processes is examined, and a renormalization scheme is found in which the effect of higher-order radiative corrections is absorbed by the behaviour of the running coupling.

Formula omitted] instanton calculus in Ω and R–R backgrounds

We study the instanton calculus for N=4 super Yang–Mills theory in ten-dimensional Ω-background with the R-symmetry Wilson line gauge field. From the ADHM construction of instantons in the background, we obtain the deformed instanton effective action. For a certain case we get the effective action of N=2⁎ theory in the Ω-background. We also study the low-energy effective D(−1)-brane action for the D3/D(−1)-brane system in the R–R 3-form field strength backgrounds and find that the action agrees with the instanton effective action in the Ω-background.

= 2 Instanton Effective action in Ω-background and D3/D(−1)-brane System in R-R background

We study the relation between the ADHM construction of instantons in the Ω-background and the fractional D3/D(−1)-branes at the orbifold singularity of ℂ × ℂ2/ℤ2 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 Ω-background.

$ \mathcal{N} = 2 $ instanton effective action in Ω-background and D3/D(−1)-brane system in R-R background

We study the relation between the ADHM construction of instantons in the Ω-background and the fractional D3/D(−1)-branes at the orbifold singularity of $ \mathbb{C} \times {{{{\mathbb{C}^2}}} \left/ {{{\mathbb{Z}_2}}} \right.} $ 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 Ω-background.

Topological symmetry of deformed instanton effective action

Topological symmetry of deformed instanton effective action

Instanton calculus in deformed 𝒩 = 4 super Yang-Mills theories

We study the instanton effective action of four-dimensional deformed = 4 supersymmetric Yang-Mills theory in the presence of constant, self-dual Ramond-Ramond (R-R) 3-form background in type IIB superstring theory. We compare the instanton effective action with the low-energy effective action on D(-1)-branes in the D3-D(-1) system in the same background. We find that discrepancy appears at the second order of the R-R background, which was also observed in deformed = 2 theory. This discrepancy is resolved if the action of the deformed gauge theory is improved by introducing a term with coordinate-dependent gauge coupling. We obtain the same deformed instanton effective action from super Yang-Mills theory in ten-dimensional Ω-background by dimensional reduction. We also discuss another type of R-R 3-form background which corresponds to massive deformations of the instanton effective action.

Instanton calculus in R-R 3-form background and deformed 𝒩 = 2 super Yang-Mills theory

We study the ADHM construction of instantons in = 2 supersymmetric Yang-Mills theory deformed in constant Ramond-Ramond (R-R) 3-form field strength background in type IIB superstrings. We compare the deformed instanton effective action with the effective action of fractional D3/D(−1) branes at the orbifold singularity of C2/Z2 in the same R-R background. We find discrepancy between them at the second order in deformation parameters, which comes from the coupling of the translational zero modes of the D(−1)-branes to the R-R background. We improve the deformed action by adding a term with space-time dependent gauge coupling. Although the space-time action differs from the action in the Ω-background, both actions lead to the same instanton equations of motion at the lowest order in gauge coupling.

Instantons and matter in Script N = 1/2 supersymmetric gauge theory

We extend the instanton calculus for N=1/2 U(2) supersymmetric gauge theory by including one massless flavor. We write the equations of motion at leading order in the coupling constant and we solve them exactly in the non(anti)commutativity parameter C. The profile of the matter superfield is deformed through linear and quadratic corrections in C. Higher order corrections are absent because of the fermionic nature of the back-reaction. The instanton effective action, in addition to the usual 't Hooft term, includes a contribution of order C^2 and is N=1/2 invariant. We argue that the N=1 result for the gluino condensate is not modified by the presence of the new term in the effective action.

Instanton effective action formalism for 2-point and 4-point functions

We provide an instanton effective action formalism in terms of which one can investigate the nonperturbative generation of 2-point and 4-point functions.