Behavioral and Network Origins of Wealth Inequality: Insights from a Virtual World

Almost universally, wealth is not distributed uniformly within societies or economies. Even though wealth data have been collected in various forms for centuries, the origins for the observed wealth-disparity and social inequality are not yet fully understood. Especially the impact and connections of human behavior on wealth could so far not be inferred from data. Here we study wealth data from the virtual economy of the massive multiplayer online game (MMOG) Pardus. This data not only contains every player's wealth at every point in time, but also all actions of every player over a timespan of almost a decade. We find that wealth distributions in the virtual world are very similar to those in western countries. In particular we find an approximate exponential for low wealth and a power-law tail. The Gini index is found to be $g=0.65$, which is close to the indices of many Western countries. We find that wealth-increase rates depend on the time when players entered the game. Players that entered the game early on tend to have remarkably higher wealth-increase rates than those who joined later. Studying the players' positions within their social networks, we find that the local position in the trade network is most relevant for wealth. Wealthy people have high in- and out-degree in the trade network, relatively low nearest-neighbor degree and a low clustering coefficient. Wealthy players have many mutual friendships and are socially well respected by others, but spend more time on business than on socializing. We find that players that are not organized within social groups with at least three members are significantly poorer on average. We observe that high `political' status and high wealth go hand in hand. Wealthy players have few personal enemies, but show animosity towards players that behave as public enemies.Comment: 22 pages, 8 figures, 8 pages S

Casimir-Polder Potential of a Driven Atom

We investigate theoretically the Casimir-Polder potential of an atom which is driven by a laser field close to a surface. This problem is addressed in the framework of macroscopic quantum electrodynamics using the Green's tensor formalism and we distinguish between two different approaches, a perturbative ansatz and a method based on Bloch equations. We apply our results to a concrete example, namely an atom close to a perfectly conducting mirror, and create a scenario where the tunable Casimir-Polder potential becomes similar to the respective potential of an undriven atom due to fluctuating field modes. Whereas the perturbative approach is restricted to large detunings, the ansatz based on Bloch equations is exact and yields an expression for the potential which does not exceed 1/2 of the undriven Casimir-Polder potential.Comment: 13 pages, 8 figure

CP\mathcal{CP}-violating effects on MSSM Higgs searches

We study the effects of $\mathcal{CP}$-violating phases on the phenomenology of the Higgs sector of the MSSM. Complex parameters in the MSSM lead to $\mathcal{CP}$-violating mixing between the tree-level $\mathcal{CP}$-even and $\mathcal{CP}$-odd neutral Higgs states, leading to three new loop-corrected mass eigenstates $h_a$, $a \in \lbrace 1,2,3\rbrace$. For scenarios where a light Higgs boson at about 125 GeV can be identified with the observed signal and where the other Higgs states are significantly heavier, a large admixture of the heavy neutral Higgs bosons occurs as a generic feature if $\mathcal{CP}$-violating effects are taken into account. Including interference contributions in the predictions for cross sections times branching ratios of the Higgs bosons is essential in this case. As a first step, we present the gluon-fusion and bottom-quark annihilation cross sections for $h_a$ for the general case of arbitrary complex parameters, and we demonstrate that squark effects strongly depend on the phases of the complex parameters. We then study the effects of interference between $h_2$ and $h_3$ for the example of the process $b\bar{b} \to \tau^+\tau^-$. We show that large destructive interference effects modify LHC exclusion bounds such that parts of the parameter space that would be excluded by MSSM Higgs searches under the assumption of $\mathcal{CP}$-conservation open up when the possibility of $\mathcal{CP}$-violation in the Higgs sector is accounted for.Comment: 11 pages, 4 figures, contribution to the HiggsTools Final Meeting, Durha

Active Learning of Points-To Specifications

When analyzing programs, large libraries pose significant challenges to static points-to analysis. A popular solution is to have a human analyst provide points-to specifications that summarize relevant behaviors of library code, which can substantially improve precision and handle missing code such as native code. We propose ATLAS, a tool that automatically infers points-to specifications. ATLAS synthesizes unit tests that exercise the library code, and then infers points-to specifications based on observations from these executions. ATLAS automatically infers specifications for the Java standard library, and produces better results for a client static information flow analysis on a benchmark of 46 Android apps compared to using existing handwritten specifications