Perturbative Gauge Theory and Closed String Tachyons

We find an interesting connection between perturbative large N gauge theory and closed superstrings. The gauge theory in question is found on N D3-branes placed at the tip of the cone R^6/Gamma. In our previous work we showed that, when the orbifold group Gamma breaks all supersymmetry, then typically the gauge theory is not conformal because of double-trace couplings whose one-loop beta functions do not possess real zeros. In this paper we observe a precise correspondence between the instabilities caused by the flow of these double-trace couplings and the presence of tachyons in the twisted sectors of type IIB theory on orbifolds R^{3,1}x R^6/Gamma. For each twisted sectors that does not contain tachyons, we show that the corresponding double-trace coupling flows to a fixed point and does not cause an instability. However, whenever a twisted sector is tachyonic, we find that the corresponding one-loop beta function does not have a real zero, hence an instability is likely to exist in the gauge theory. We demonstrate explicitly the one-to-one correspondence between the regions of stability/instability in the space of charges under Gamma that arise in the perturbative gauge theory and in the free string theory. Possible implications of this remarkably simple gauge/string correspondence are discussed.Comment: 25 pages, Latex; V2: Clarifications and references adde

Toda systems in closed string tachyon condensation

We consider $tt^*$ equations appearing in the study of localized tachyon condensations. They are described by various Toda system when we consider the condensation by the lowest tachyon corresponding to the monomial $xy$. The tachyon potential is calculated as a solution to these equations. The Toda system appearing in the deformation of \C^2/\Z_n by $xy$ is identical to that of $D_n$ singularity deformed by $x$. For \C^3/\Z_n with $xyz$ deformation, we find only generic non-simple form, similar to the case appearing in \C/\Z_5\to \C/\Z_3 and we discuss the difficulties in these cases.Comment: 20 pages, no figur

Designer requirements for visual capability loss simulator tools: Differences between design disciplines

There is a low uptake of inclusive design tools in industry, partly due to a poor fit between design tools and the thought and work processes of designers. Simulating visual capability losses is a technique with great potential in helping designers improve inclusivity and accessibility. However, we need to understand the needs of designers from different disciplines to improve the fit of these tools and their uptake in industry. This study aims to determine designers’ needs for vision loss simulators, and how this varies between disciplines. Interviews were carried out with 15 designers from five disciplines. The results suggest that one tool is not suitable for all. The graphic and web designers interviewed required a tool to aid communication with clients, hoever, the industrial and engineering designers required two tools, depending on the stage of the design process. To increase their uptake, simulator tools should be used in education.We would like to thank the EPSRC for funding this work, and Wolfson College Cambridge for their support.This is the author accepted manuscript. The final version is available from Springer via http://dx.doi.org/10.1007/978-3-319-07437-5_

Ricci-flat deformation of orbifolds and localized tachyonic modes

We study Ricci-flat deformations of orbifolds in type II theory. We obtain a simple formula for mass corrections to the twisted modes due to the deformations, and apply it to originally tachyonic and massless states in several examples. In the case of supersymmetric orbifolds, we find that tachyonic states appear when the deformation breaks all the supersymmetries. We also study nonsupersymmetric orbifolds C^2/Z_{2N(2N+1)}, which is T-dual to N type 0 NS5-branes. For N>=2, we compute mass corrections for states, which have string scale tachyonic masses. We find that the corrected masses coincide to ones obtained by solving the wave equation for the tachyon field in the smeared type 0 NS5-brane background geometry. For N=1, we show that the unstable mode representing the bubble creation is the unique tachyonic mode.Comment: 20 pages, minor collection

Closed string tachyons, flips and conifolds

Following the analysis of tachyons and orbifold flips described in hep-th/0412337, we study nonsupersymmetric analogs of the supersymmetric conifold singularity and show using their toric geometry description that they are nonsupersymmetric orbifolds of the latter. Using linear sigma models, we see that these are unstable to localized closed string tachyon condensation and exhibit flip transitions between their two small resolutions (involving 2-cycles), in the process mediating mild dynamical topology change. Our analysis shows that the structure of these nonsupersymmetric conifolds as quotients of the supersymmetric conifold obstructs the 3-cycle deformation of such singularities, suggesting that these nonsupersymmetric conifolds decay by evolving towards their stable small resolutions.Comment: Latex, 22 pgs, 2 figs. v4: matches JHEP version, 29 pgs, 3 figures, more elaborate Introduction, various clarifications adde

Residues and World-Sheet Instantons

We reconsider the question of which Calabi-Yau compactifications of the heterotic string are stable under world-sheet instanton corrections to the effective space-time superpotential. For instance, compactifications described by (0,2) linear sigma models are believed to be stable, suggesting a remarkable cancellation among the instanton effects in these theories. Here, we show that this cancellation follows directly from a residue theorem, whose proof relies only upon the right-moving world-sheet supersymmetries and suitable compactness properties of the (0,2) linear sigma model. Our residue theorem also extends to a new class of "half-linear" sigma models. Using these half-linear models, we show that heterotic compactifications on the quintic hypersurface in CP^4 for which the gauge bundle pulls back from a bundle on CP^4 are stable. Finally, we apply similar ideas to compute the superpotential contributions from families of membrane instantons in M-theory compactifications on manifolds of G_2 holonomy.Comment: 47 page

C^2/Z_n Fractional branes and Monodromy

We construct geometric representatives for the C^2/Z_n fractional branes in terms of branes wrapping certain exceptional cycles of the resolution. In the process we use large radius and conifold-type monodromies, and also check some of the orbifold quantum symmetries. We find the explicit Seiberg-duality which connects our fractional branes to the ones given by the McKay correspondence. We also comment on the Harvey-Moore BPS algebras.Comment: 34 pages, v1 identical to v2, v3: typos fixed, discussion of Harvey-Moore BPS algebras update

Brane Inflation, Solitons and Cosmological Solutions: I

In this paper we study various cosmological solutions for a D3/D7 system directly from M-theory with fluxes and M2-branes. In M-theory, these solutions exist only if we incorporate higher derivative corrections from the curvatures as well as G-fluxes. We take these corrections into account and study a number of toy cosmologies, including one with a novel background for the D3/D7 system whose supergravity solution can be completely determined. This new background preserves all the good properties of the original model and opens up avenues to investigate cosmological effects from wrapped branes and brane-antibrane annihilation, to name a few. We also discuss in some detail semilocal defects with higher global symmetries, for example exceptional ones, that could occur in a slightly different regime of our D3/D7 model. We show that the D3/D7 system does have the required ingredients to realise these configurations as non-topological solitons of the theory. These constructions also allow us to give a physical meaning to the existence of certain underlying homogeneous quaternionic Kahler manifolds.Comment: Harvmac, 115 pages, 9 .eps figures; v2: typos corrected, references added and the last section expanded; v3: Few minor typos corrected and references added. Final version to appear in JHE

Topological String Amplitudes, Complete Intersection Calabi-Yau Spaces and Threshold Corrections

We present the most complete list of mirror pairs of Calabi-Yau complete intersections in toric ambient varieties and develop the methods to solve the topological string and to calculate higher genus amplitudes on these compact Calabi-Yau spaces. These symplectic invariants are used to remove redundancies in examples. The construction of the B-model propagators leads to compatibility conditions, which constrain multi-parameter mirror maps. For K3 fibered Calabi-Yau spaces without reducible fibers we find closed formulas for all genus contributions in the fiber direction from the geometry of the fibration. If the heterotic dual to this geometry is known, the higher genus invariants can be identified with the degeneracies of BPS states contributing to gravitational threshold corrections and all genus checks on string duality in the perturbative regime are accomplished. We find, however, that the BPS degeneracies do not uniquely fix the non-perturbative completion of the heterotic string. For these geometries we can write the topological partition function in terms of the Donaldson-Thomas invariants and we perform a non-trivial check of S-duality in topological strings. We further investigate transitions via collapsing D5 del Pezzo surfaces and the occurrence of free Z2 quotients that lead to a new class of heterotic duals.Comment: 117 pages, 1 Postscript figur

AdS Branes Corresponding to Superconformal Defects

We investigate an AdS_4 x L_2 D5-brane in AdS_5 x X_5 space-time, in the context of AdS/dCFT correspondence. Here, X_5 is a Sasaki-Einstein manifold and L_2 is a submanifold of X_5. This brane has the same supersymmetry as the 3-dimensional N=1 superconformal symmetry if L_2 is a special Legendrian submanifold in X_5. In this case, this brane is supposed to correspond to a superconformal wall defect in 4-dimensional N=4 super Yang-Mills theory. We construct these new string backgrounds and show they have the correct supersymmetry, also in the case with non-trivial gauge flux on L_2. The simplest new example is AdS_4 x T^2 brane in AdS_5 x S^5. We construct the brane solution expressing the RG flow between two different defects. We also perform similar analysis for an AdS_3 x L_3 M5-brane in AdS_4 x X_7, for a weak G_2 manifold X_7 and its submanifold L_3. This system has the same supersymmetry as 2-dimensional N=(1,0) global superconformal symmetry, if L_3 is an associative submanifold.Comment: 22 pages, LaTeX, 3 figures. v2: typos corrected, references added. v3: typos correcte