Worldsheet instantons and (0,2) linear models

We study the stability of heterotic compactifications described by (0,2) gauged linear sigma models with respect to worldsheet instanton corrections to the space-time superpotential following the work of Beasley and Witten. We show that generic models elude the vanishing theorem proved there, and may not determine supersymmetric heterotic vacua. We then construct a subclass of linear models for which a vanishing theorem holds, generating an extensive list of consistent heterotic backgrounds.Comment: 21 pages; v2: minor correction

Testing the (0,2) mirror map

We test a proposed mirror map at the level of correlators for linear models describing the (0,2) moduli space of superconformal field theories with a (2,2) locus associated to Calabi-Yau hypersurfaces in toric varieties. We verify in non-trivial examples that the correlators are exchanged by the mirror map and we derive a correspondence between the observables of the A/2- and B/2-twisted theories. We also comment on the global structure of the (0,2) moduli space and present a simple non-renormalization argument for a large class of B/2 model subfamilies.Comment: 32 page

Accidents in (0,2) Landau-Ginzburg theories

We study the role of accidental symmetries in two-dimensional (0,2) superconformal field theories obtained by RG flow from (0,2) Landau-Ginzburg theories. These accidental symmetries are ubiquitous, and, unlike in the case of (2,2) theories, their identification is key to correctly identifying the IR fixed point and its properties. We develop a number of tools that help to identify such accidental symmetries in the context of (0,2) Landau-Ginzburg models and provide a conjecture for a toric structure of the SCFT moduli space in a large class of models. We also give a self-contained discussion of aspects of (0,2) conformal perturbation theory.Comment: 37 pages; expanded conformal perturbation theory discussion in v2; fixed an accident in section 3.5 in v

On the global symmetries of 6D superconformal field theories

We study global symmetry groups of six-dimensional superconformal field theories (SCFTs). In the Coulomb branch we use field theoretical arguments to predict an upper bound for the global symmetry of the SCFT. We then analyze global symmetry groups of F-theory constructions of SCFTs with a one-dimensional Coulomb branch. While in the vast majority of cases, all of the global symmetries allowed by our Coulomb branch analysis can be realized in F-theory, in a handful of cases we find that F-theory models fail to realize the full symmetry of the theory on the Coulomb branch. In one particularly mysterious case, F-theory models realize several distinct maximal subgroups of the predicted group, but not the predicted group itself.Comment: 47 pages; v2: typos corrected, added the case su(6)* to the analysis of section 5 and section 6.1. v3: references added, minor changes, published versio

Direct CP Violation in B->phi K_s and New Physics

In the presence of large New Physics contributions to loop-induced b->s transitions, sizable direct CP violation in B-> phi K decays is expected on general grounds. We compute explicitly CP-violating effects using QCD factorization and find that, even in the restricted case in which New Physics has the same penguin structure as the Standard Model, the rate asymmetry can be of order one. We briefly discuss a more general scenario and comment on the inclusion of power-suppressed corrections to factorization.Comment: 3 page

The Lisbon Strategy for social inclusion and the Common Agricultural Policy (Strategia di Lisbona per l'inclusione sociale e politica agricola comune: un esempio della difficile coerenza tra azioni di policy europee)

This paper represents a first attempt to evaluate the impact of the Common Agricultural Policy (CAP), the most relevant EU policy in financial terms, on social inclusion, one of the most important issues included in the Lisbon Strategy, launched by the EU in 2000. To do so, the paper focuses on how the various CAP measures have affected rural poverty in the EU and tries to identify the elements of congruence and conflict between the CAP and social inclusion goals. Market-oriented actions seem to exacerbate differences between rich and poor farmers, because they tend to favour those areas where agriculture is already more competitive. By contrast, rural development measures may be more helpful, even if they are still not adequately financed and pose some problems in terms of governance. The new 2007-2013 programming cycle brings some positive innovations, but synergies between the CAP and social inclusion could be more fully exploited.rural poverty; social inclusion; Common Agricultural Policy