On the Explicit Construction and Statistics of Calabi-Yau Flux Vacua

We explicitly construct and study the statistics of flux vacua for type IIB string theory on an orientifold of the Calabi-Yau hypersurface $P^4_{[1,1,2,2,6]}$, parametrised by two relevant complex structure moduli. We solve for these moduli and the dilaton field in terms of the set of integers defining the 3-form fluxes and examine the distribution of vacua. We compare our numerical results with the predictions of the Ashok-Douglas density $\det (-R - \omega)$, finding good overall agreement in different regions of moduli space. The number of vacua are found to scale with the distance in flux space. Vacua cluster in the region close to the conifold singularity. Large supersymmetry breaking is more generic but supersymmetric and hierarchical supersymmetry breaking vacua can also be obtained. In particular, the small superpotentials and large dilaton VEVs needed to obtain de Sitter space in a controllable approximation are possible but not generic. We argue that in a general flux compactification, the rank of the gauge group coming from D3 branes could be statistically preferred to be very small.Comment: 26 pages, 9 figures; v2: references adde

Does Gender Matter for Political Leadership? The Case of U.S. Mayors

What are the consequences of electing a female leader for policy and political outcomes? We answer this question in the context of U.S. cities, where women’s participation in mayoral elections increased from negligible numbers in 1970 to about one-third of the elections in the 2000’s. We use a novel data set of U.S. mayoral elections from 1950 to 2005, and apply a regression discontinuity design to deal with the endogeneity of female candidacy to city characteristics. In contrast to most research on the influence of female leadership, we find no effect of gender of the mayor on policy outcomes related to the size of local government, the composition of municipal spending and employment, or crime rates. While female mayors do not implement different policies, they do appear to have higher unobserved political skills, as they have a 6-7 percentage point higher incumbent effect than a comparable male. But we find no evidence of political spillovers: exogenously electing a female mayor does not change the long run political success of other female mayoral candidates in the same city or of female candidates in local congressional elections.

Do Political Parties Matter? Evidence from U.S. Cities

We examine whether partisan political differences have important effects on policy outcomes at the local level using a new panel data set of mayoral elections in the United States. Applying a regression discontinuity design to deal with the endogeneity of the mayor's party, we find that party labels do not affect the size of government, the allocation of spending or crime rates, even though there is a large political advantage to incumbency in terms of the probability of winning the next election. The absence of a strong partisan impact on policy in American cities, which is in stark contrast to results at the state and federal levels of government, appears due to certain features of the urban environment associated with Tiebout sorting. In particular, there is a relatively high degree of household homogeneity at the local level that appears to provide the proper incentives for local politicians to be able to credibly commit to moderation and discourages strategic extremism.

Dark Radiation in LARGE Volume Models

We consider reheating driven by volume modulus decays in the LARGE Volume Scenario. Such reheating always generates non-zero dark radiation through the decays to the axion partner, while the only competitive visible sector decays are Higgs pairs via the Giudice-Masiero term. In the framework of sequestered models where the cosmological moduli problem is absent, the simplest model with a shift-symmetric Higgs sector generates 1.56 < N_{eff} - N_{eff,SM} < 1.74. For more general cases, the known experimental bounds on N_{eff} strongly constrain the parameters and matter content of the models.Comment: 6 pages; v2. refs update

Wave Functions and Yukawa Couplings in Local String Compactifications

We consider local models of magnetised D7 branes in IIB string compactifications, focussing on cases where an explicit metric can be written for the local 4-cycle. The presence of an explicit metric allows analytic expressions for the gauge bundle and for the chiral matter wavefunctions through solving the Dirac and Laplace equations. The triple overlap of the normalised matter wavefunctions generates the physical Yukawa couplings. Our main examples are the cases of D7 branes on P1xP1 and P2. We consider both supersymmetric and non-supersymmetric gauge backgrounds and both Abelian and non-Abelian gauge bundles. We briefly outline potential phenomenological applications of our results.Comment: 50 pages, 1 figur

The Impacts of Payments for Watershed Services in Ecuador: Emerging Lessons from Pimampiro and Cuenca

The project set out to engage stakeholders in the evaluation of this emerging "market" for watershed services and its social impact. The study consists of two documents that are separate but also complement each other. The first document, called Markets or Metaphors? A Sustainable Livelihoods Approach to the Management of Environmental Services: two Cases from Ecuador, written by Dr Joseph Vogel, is at the centre of the research. This document presents the results of the development of a methodology and its application in the field. It also includes an economic and legal analysis that demonstrates the importance of understanding and including social and cultural implications when developing a market for watershed service

A Note on the Magnitude of the Flux Superpotential

The magnitude of the flux superpotential $W_{flux}$ plays a crucial role in determining the scales of IIB string compactifications after moduli stabilisation. It has been argued that values of $W_{flux}$ much less than one are preferred, and even required for physical and consistency reasons. This note revisits these arguments. We establish that the coupling (g) of heavy Kaluza-Klein modes to light states scales as ${M_{KK} / M_{Pl}}$ (hence is suppressed by two third powers of the inverse volume of compactification) and argue that consistency of the superspace derivative expansion requires $gF/M^2 \sim m_{3/2}/ M_{KK} << 1$, where $F$ is the auxiliary field of the light fields and $M$ the ultraviolet cutoff. This gives only a mild constraint on the flux superpotential, $W_{flux} << V^{1/3}$ (where V is the volume of the compactification), which can be easily satisfied for order one values of $W_{flux}$. This regime is also statistically favoured and makes the Bousso-Polchinski mechanism for the vacuum energy hierarchically more efficient.Comment: 14 page

Crop Insurance, Disaster Payments and Land Use Change: The Effect of Sodsaver on Incentives for Grassland Conversion

Subsidized crop insurance may encourage conversion of native grassland to cropland. The Sodsaver provision of the 2008 farm bill could deny crop insurance on converted land in the Prairie Pothole states for 5 years. Supplemental Revenue Assistance payments, which are linked to crop insurance purchases, could also be withheld. Using representative farms, we estimate that Sodsaver would reduce expected crop revenue by up to 8% and expected net return by up to 20%, while increasing the standard deviation of revenue by as much as 6% of market revenue. Analysis based on elasticities from the literature suggests that Sodsaver would reduce grassland conversion by 9% or less.bootstrap, crop insurance, grassland, joint densities, Sodsaver, Supplemental Revenue Assistance, Agricultural and Food Policy, Production Economics, Risk and Uncertainty, Q2,

Crop Insurance, Disaster Payments, and Incentives for Land Use Change in Agriculture: A Preliminary Assessment

Crop Insurance, Disaster Payments, Supplemental Revenue Assistance, corn, wheat, Agricultural and Food Policy, Research Methods/ Statistical Methods, Risk and Uncertainty,

Soft SUSY Breaking Terms for Chiral Matter in IIB String Compactifications

This paper develops the computation of soft supersymmetry breaking terms for chiral D7 matter fields in IIB Calabi-Yau flux compactifications with stabilised moduli. We determine explicit expressions for soft terms for the single-modulus KKLT scenario and the multiple-moduli large volume scenario. In particular we use the chiral matter metrics for Calabi-Yau backgrounds recently computed in hep-th/0609180. These differ from the better understood metrics for non-chiral matter and therefore give a different structure of soft terms. The soft terms take a simple form depending explicitly on the modular weights of the corresponding matter fields. For the large-volume case we find that in the simplest D7 brane configuration, scalar masses, gaugino masses and A-terms are very similar to the dilaton-dominated scenario. Although all soft masses are suppressed by ln(M_P/m_{3/2}) compared to the gravitino mass, the anomaly-mediated contributions do not compete, being doubly suppressed and thus subdominant to the gravity-mediated tree-level terms. Soft terms are flavour-universal to leading order in an expansion in inverse Kahler moduli. They also do not introduce extra CP violating phases to the effective action. We argue that soft term flavour universality should be a property of the large-volume compactifications, and more generally IIB flux models, in which flavour is determined by the complex structure moduli while supersymmetry is broken by the Kahler moduli. For the simplest large-volume case we run the soft terms to low energies and present some sample spectra and a basic phenomenological analysis.Comment: 40 pages, 9 figures, JHEP style; v2. sentence rephrase