Heterotic GUT and Standard Model Vacua from simply connected Calabi-Yau Manifolds

We consider four-dimensional supersymmetric compactifications of the E8 x E8 heterotic string on Calabi-Yau manifolds endowed with vector bundles with structure group SU(N) x U(1) and five-branes. After evaluating the Green-Schwarz mechanism and deriving the generalized Donaldson-Uhlenbeck-Yau condition including the five-brane moduli, we show that this construction can give rise to GUT models containing U(1) factors like flipped SU(5) or directly the Standard Model even on simply connected Calabi-Yau manifolds. Concrete realizations of three-generation models on elliptically fibered Calabi-Yau manifolds are presented. They exhibit the most attractive features of flipped SU(5) models such as doublet-triplet splitting and proton stability. In contrast to conventional GUT string models, the tree level relations among the Standard Model gauge couplings at the GUT scale are changed.Comment: 46 pages, 2 figures, 6 tables; v2: references added, typos corrected; v3: typos corrected, final version published in Nucl.Phys.

String GUT Scenarios with Stabilised Moduli

Taking into account the recently proposed poly-instanton corrections to the superpotential and combining the race-track with a KKLT respectively LARGE Volume Scenario in an intricate manner, we show that we gain exponential control over the parameters in an effective superpotential. This allows us to dynamically stabilise moduli such that a conventional MSSM scenario with the string scale lowered to the GUT scale is realised. Depending on the cycles wrapped by the MSSM branes, two different scenarios for the hierarchy of soft masses arise. The first one is a supergravity mediated model with M_3/2=1TeV while the second one features mixed anomaly-supergravity mediation with M_3/2=10^10GeV and split supersymmetry. We also comment on dynamically lowering the scales such that the tree-level cosmological constant is of the order \Lambda=(10^-3eV)^4.Comment: 22 pages, 13 figures; v2: refs. and explanation adde

Clustering Constraints on the Relative Sizes of Central and Satellite Galaxies

We empirically constrain how galaxy size relates to halo virial radius using new measurements of the size- and stellar mass-dependent clustering of galaxies in the Sloan Digital Sky Survey. We find that small galaxies cluster much more strongly than large galaxies of the same stellar mass. The magnitude of this clustering difference increases on small scales, and decreases with increasing stellar mass. Using Halotools to forward model the observations, we test an empirical model in which present-day galaxy size is proportional to the size of the virial radius at the time the halo reached its maximum mass. This simple model reproduces the observed size-dependence of galaxy clustering in striking detail. The success of this model provides strong support for the conclusion that satellite galaxies have smaller sizes relative to central galaxies of the same halo mass. Our findings indicate that satellite size is set prior to the time of infall, and that a remarkably simple, linear size--virial radius relation emerges from the complex physics regulating galaxy size. We make quantitative predictions for future measurements of galaxy-galaxy lensing, including dependence upon size, scale, and stellar mass, and provide a scaling relation of the ratio of mean sizes of satellites and central galaxies as a function of their halo mass that can be used to calibrate hydrodynamical simulations and semi-analytic models.Comment: 12 pages plus an appendix. Submitted to MNRAS. Figure 5 shows that a simple empirical model, with R50 = 0.01Rvir, can accurately reproduce new measurements of size-dependent clustering of SDSS galaxies. Figure 9 shows predictions for the size-dependence of future lensing measurements. Figure 10 provides a diagnostic for hydro sims and SAM

USING HYBRID SCRUM TO MEET WATERFALL PROCESS DELIVERABLES

System Development Life Cycles (SDLCs) for organizations are often based upon traditional software development models such as the waterfall model. These processes are complex, heavy in documentation deliverables, and are rigid and less flexible than other methods being used in modern software development. Consider by contrast, agile methods for software development. In essence, agile methods recommend lightweight documentation and simplified process. The focus shifts to completed software as the "measure of success" for delivery of product in software projects, versus accurate and comprehensive documentation, and the accomplishment of static milestones in a work breakdown structure. This thesis implements, explores, and recommends a hybrid agile approach to Scrum in order to satisfy the rigid, document-laden deliverables of a waterfall-based SDLC process. This hybrid Scrum is a balance of having enough documentation and process - but not too much - to meet SDLC deliverables, while at the same time focusing on timely product delivery and customer interactions that come from an agile approach to software development.M.S

The Mass Profile of the Galaxy to 80 kpc

The Hypervelocity Star survey presents the currently largest sample of radial velocity measurements of halo stars out to 80 kpc. We apply spherical Jeans modeling to these data in order to derive the mass profile of the Galaxy. We restrict the analysis to distances larger than 25 kpc from the Galactic center, where the density profile of halo stars is well approximated by a single power law with logarithmic slope between -3.5 and -4.5. With this restriction, we also avoid the complication of modeling a flattened Galactic disk. In the range 25 < r < 80 kpc, the radial velocity dispersion declines remarkably little; a robust measure of its logarithmic slope is between -0.05 and -0.1. The circular velocity profile also declines remarkably little with radius. The allowed range of V_c(80 kpc) lies between 175 and 231 km/s, with the most likely value 193 km/s. Compared with the value at the solar location, the Galactic circular velocity declines by less than 20% over an order of magnitude in radius. Such a flat profile requires a massive and extended dark matter halo. The mass enclosed within 80 kpc is 6.9(+3.0-1.2) 10^11 Msun. Our sample of radial velocities is large enough that the biggest uncertainty in the mass is not statistical but systematic, dominated by the density slope and anisotropy of the tracer population. Further progress requires modeling observed datasets within realistic simulations of galaxy formation.Comment: matches version accepted to ApJ Letter

A Cosmic Variance Cookbook

Deep pencil beam surveys (<1 deg^2) are of fundamental importance for studying the high-redshift universe. However, inferences about galaxy population properties are in practice limited by 'cosmic variance'. This is the uncertainty in observational estimates of the number density of galaxies arising from the underlying large-scale density fluctuations. This source of uncertainty can be significant, especially for surveys which cover only small areas and for massive high-redshift galaxies. Cosmic variance for a given galaxy population can be determined using predictions from cold dark matter theory and the galaxy bias. In this paper we provide tools for experiment design and interpretation. For a given survey geometry we present the cosmic variance of dark matter as a function of mean redshift z and redshift bin size Dz. Using a halo occupation model to predict galaxy clustering, we derive the galaxy bias as a function of mean redshift for galaxy samples of a given stellar mass range. In the linear regime, the cosmic variance of these galaxy samples is the product of the galaxy bias and the dark matter cosmic variance. We present a simple recipe using a fitting function to compute cosmic variance as a function of the angular dimensions of the field, z, Dz and stellar mass m*. We also provide tabulated values and a software tool. We find that for GOODS at z=2 and with Dz=0.5 the relative cosmic variance of galaxies with m*>10^11 Msun is ~38%, while it is ~27% for GEMS and ~12% for COSMOS. For galaxies of m*~10^10 Msun the relative cosmic variance is ~19% for GOODS, ~13% for GEMS and ~6% for COSMOS. This implies that cosmic variance is a significant source of uncertainty at z=2 for small fields and massive galaxies, while for larger fields and intermediate mass galaxies cosmic variance is less serious.Comment: 8 pages, 4 figures, 5 tables, submitted to Ap