Collide and Conquer: Constraints on Simplified Dark Matter Models using Mono-X Collider Searches

The use of simplified models as a tool for interpreting dark matter collider searches has become increasingly prevalent, and while early Run II results are beginning to appear, we look to see what further information can be extracted from the Run I dataset. We consider three `standard' simplified models that couple quarks to fermionic singlet dark matter: an $s$-channel vector mediator with vector or axial-vector couplings, and a $t$-channel scalar mediator. Upper limits on the couplings are calculated and compared across three alternate channels, namely mono-jet, mono-$Z$ (leptonic) and mono-$W/Z$ (hadronic). The strongest limits are observed in the mono-jet channel, however the computational simplicity and absence of significant $t$-channel model width effects in the mono-boson channels make these a straightforward and competitive alternative. We also include a comparison with relic density and direct detection constraints.Comment: 32 pages, 8 figures; v2: minor changes, conclusion unchanged, matches published versio

The Mirage of Triangular Arbitrage in the Spot Foreign Exchange Market

We investigate triangular arbitrage within the spot foreign exchange market using high-frequency executable prices. We show that triangular arbitrage opportunities do exist, but that most have short durations and small magnitudes. We find intra-day variations in the number and length of arbitrage opportunities, with larger numbers of opportunities with shorter mean durations occurring during more liquid hours. We demonstrate further that the number of arbitrage opportunities has decreased in recent years, implying a corresponding increase in pricing efficiency. Using trading simulations, we show that a trader would need to beat other market participants to an unfeasibly large proportion of arbitrage prices to profit from triangular arbitrage over a prolonged period of time. Our results suggest that the foreign exchange market is internally self-consistent and provide a limited verification of market efficiency

Analytical Representation of the Relationship Between Generator Design and System Fault Behavior

This paper presents the development and application of an analytical method for formalizing the dependence of the behavior of a large power system under fault conditions on the equivalent impedance presented by a single generator. After selecting an appropriate generator model, it is demonstrated that network-wide fault behavior can be expressed as a rational function of the equivalent impedance presented by a single generator under fault conditions. This representation simplifies the identification and depiction of constraints imposed by system configuration on the ability of a generator replacement or augmentation to affect fault behavior. The effectiveness of the proposed method is confirmed by considering the three-phase fault currents produced in a six-bus test system. In addition, the new analytical method is extended to obtain a numerical estimate of the maximum possible change in fault behavior that could result from a generator replacement or augmentation. Overall, the new approach aids in the evaluation of the suitability of generator modification or augmentation schemes

A Sensitivity Method for Assessing the Impact of Generator/Transformer Impedance upon Power System Fault Behaviour

An analytical method is presented for determining the potential impact that the connection of a single new generator may have upon the performance of a transmission system under balanced three-phase fault conditions. Expressions are derived that demonstrate the dependence of the system-wide fault behaviour of the modified network upon both the sub-transient or short circuit impedance of the new generator/transformer and the configuration of the original network. From these expressions sensitivity factors are developed that characterise the potential impact that the connection of the new generator can have upon network fault behaviour. The procedure is derived in general terms and verified with results from simulation of a 17-bus test system. The results emphasize that the impact of the generator/transformer is often more contingent upon the network characteristics at the point of connection rather than the subtransient/ short circuit impedances of the new elements

Selection of Generator Fault Impedances for Enhancement of Network-Wide Fault Behaviour

This paper presents the development and application of a method for illustrating graphically the range of suitable generator designs for achieving a desired performance of a network under either balanced or single line-to-ground fault conditions. After derivation of its theoretical basis, the effectiveness of the method is verified by examination of the impact of generator design on either balanced or single line-to-ground fault currents produced in a small test system. The results demonstrate the ability of the technique to provide a clear representation of the range of generator designs that could enhance or degrade network-wide fault behaviour, aiding in the selection of generator parameters for suitable fault performance