Yoske Sumitomo

Non-supersymmetric infrared perturbations to the warped deformed conifold

Abstract We analyze properties of non-supersymmetric, isometry-preserving perturbations to the infrared region of the warped deformed conifold, i.e. the Klebanov–Strassler solution. We discuss both perturbations that “squash” the geometry, so that the internal space is no longer conformally Calabi–Yau, and perturbations that do not squash the geometry. Among the perturbations that we discuss is the solution that describes the linearized near-tip backreaction of a smeared collection of D 3 ¯ -branes positioned in the deep infrared. Such a configuration is a candidate gravity dual of a non-supersymmetric state in a large-rank cascading gauge theory. Although D 3 ¯ -branes do not directly couple to the 3-form flux, we argue that, due to the presence of the background imaginary self-dual flux, D 3 ¯ -branes in the Klebanov–Strassler geometry necessarily produce singular non-imaginary self-dual flux. Moreover, since conformally Calabi–Yau geometries cannot be supported by non-imaginary self-dual flux, the D 3 ¯ -branes squash the geometry as our explicit solution shows. We also briefly discuss supersymmetry-breaking perturbations at large radii and the effect of the non-supersymmetric perturbations on the gravitino mass.

Janus field theories from multiple M2 branes

Based on the recent proposal of N = 8 superconformal gauge theories of the multiple M2 branes, we derive (2 + 1)-dimensional supersymmetric Janus field theories with a space-time dependent coupling constant. From the original Bagger-Lambert model, we get a supersymmetric field theory with a similar action to the N D2 branes, but the coupling varies with the space-time as a function of the light-cone coordinate, g(t + x). Half of the supersymmetries can be preserved. We further investigate the M2 brane action deformed by mass and Myers-like terms. In this case, the final Yang-Mills action is deformed by mass and Myers terms, and the coupling behaves as exp(μx) where μ is a constant mass parameter. Weak coupling gauge theory is continuously changed to strong coupling in the large x region.

A Global View on The Search for de-Sitter Vacua in (Type IIA) String Theory

A bstractThe search for classically stable Type IIA de Sitter vacua typically starts with an ansatz that gives Anti-de Sitter supersymmetric vacua and then raises the cosmological constant by modifying the compactification. As one raises the cosmological constant, the couplings typically destabilize the classically stable vacuum, so the probability that this approach will lead to a classically stable de Sitter vacuum is Gaussianly suppressed. This suggests that classically stable de Sitter vacua in string theory (at least in the Type IIA region), especially those with relatively high cosmological constants, are very rare. The probability that a typical de Sitter extremum is classically stable (i.e., tachyon-free) is argued to be Gaussianly suppressed as a function of the number of moduli.

Stability constraints on classical de Sitter vacua

We present further no-go theorems for classical de Sitter vacua in Type II string theory, i.e., de Sitter constructions that do not invoke non-perturbative effects or explicit supersymmetry breaking localized sources. By analyzing the stability of the 4D potential arising from compactification on manfiolds with curvature, fluxes, and orientifold planes, we found that additional ingredients, beyond the minimal ones presented so far, are necessary to avoid the presence of unstable modes. We enumerate the minimal setups for (meta)stable de Sitter vacua to arise in this context.

Axions as Quintessence in String Theory

We construct a model of quintessence in string theory based on the idea of axion monodromy as discussed by McAllister, Silverstein and Westphal [L. McAllister, E. Silverstein, and A. Westphal, Phys. Rev. D 82, 046003 (2010)]. In the model, the quintessence field is an axion whose shift symmetry is broken by the presence of 5-branes which are placed in highly warped throats. This gives rise to a potential for the axion field which is slowly varying, even after incorporating the effects of moduli stabilization and supersymmetry breaking. We find that the resulting time dependence in the equation of state of dark energy is potentially detectable, depending on the initial conditions. The model has many very light extra particles which live in the highly warped throats, but these are hard to detect. A signal in the rotation of the CMB polarization can also possibly arise.

Stringy mechanism for a small cosmological constant

Based on the probability distributions of products of random variables, we propose a simple stringy mechanism that prefers the meta-stable vacua with a small cosmological constant. We state some relevant properties of the probability distributions of functions of random variables. We then illustrate the mechanism within the flux compactification models in Type IIB string theory. As a result of the stringy dynamics, we argue that the generic probability distribution for the meta-stable vacua typically peaks with a divergent behavior at the zero value of the cosmological constant. However, its suppression in the single modulus model studied here is modest.

A stringy mechanism for a small cosmological constant — multi-moduli cases

Based on the properties of probability distributions of functions of random variables, we proposed earlier a simple stringy mechanism that prefers the meta-stable vacua with a small cosmological constant ?. As an illustration of this approach, we study in this paper particularly simple but non-trivial models of the K?hler uplift in the large volume flux compactification scenario in Type IIB string theory, where all parameters introduced in the model are treated either as fixed constants motivated by physics, or as random variables with some given uniform probability distributions. We determine the value w0 of the superpotential W0 at the supersymmetric minima, and find that the resulting probability distribution P(w0) peaks at w0 = 0; furthermore, this peaking behavior strengthens as the number of complex structure moduli increases. The resulting probability distribution P(?) for meta-stable vacua also peaks as ? ? 0, for both positive and negative ?. This peaking/divergent behavior of P(?) strengthens as the number of moduli increases. In some scenarios for ? > 0, the likely value of ? decreases exponentially as the number of moduli increases. The light cosmological moduli issue accompanying a very small ? is also mentioned.

Preference for a Vanishingly Small Cosmological Constant in Supersymmetric Vacua in a Type IIB String Theory Model

Abstract We study the probability distribution P ( Λ ) of the cosmological constant Λ in a specific set of KKLT type models of supersymmetric IIB vacua. We show that, as we sweep through the quantized flux values in this flux compactification, P ( Λ ) behaves divergent at Λ = 0 − and the median magnitude of Λ drops exponentially as the number of complex structure moduli h 2 , 1 increases. Also, owing to the hierarchical and approximate no-scale structure, the probability of having a positive Hessian (mass-squared matrix) approaches unity as h 2 , 1 increases.

De Sitter vacua from a D-term generated racetrack uplift

A bstractWe propose an uplift mechanism using a structure of multi-Kähler moduli dependence in the F-term potential of type IIB string theory compactifications. This mechanism requires a D-term condition that fixes one modulus to be proportional to another modulus, resulting in a trivial D-term potential. De Sitter minima are realized along with an enhancement of the volume in the Large Volume Scenario and no additional suppression of the uplift term such as warping is required. We further show the possibility to realize the uplift mechanism in the presence of more Kähler moduli such that we expect the uplift mechanism to work in many other compactifications.

Statistical Distribution of the Vacuum Energy Density in Racetrack Kahler Uplift Models in String Theory

A bstractWe study a racetrack model in the presence of the leading α′-correction in flux compactification in Type IIB string theory, for the purpose of getting conceivable de-Sitter vacua in the large compactified volume approximation. Unlike the Kähler Uplift model studied previously, the α′-correction is more controllable for the meta-stable de-Sitter vacua in the racetrack case since the constraint on the compactified volume size is very much relaxed. We find that the vacuum energy density Λ for de-Sitter vacua approaches zero exponentially as the volume grows. We also analyze properties of the probability distribution of Λ in this class of models. As in other cases studied earlier, the probability distribution again peaks sharply at Λ = 0. We also study the Racetrack Kähler Uplift model in the Swiss-Cheese type model.