Design of NbN Superconducting Nanowire Single-Photon Detectors with Enhanced Infrared Detection Efficiency

Quantum Matter and Optic

The Implications of Sequential Investment in the Property Rights Theory of the Firm

In the property rights theory of the firm, control over assets (ownership) affords bargaining power in the case of re-negotiation, providing incentives for parties to make relationship specific investments. The models predict that property rights will be allocated so as to maximise surplus generated from investment. However, these models assume that investments are made simultaneously. In this thesis I extend the standard property-rights framework to allow for sequential investment; the model allows for two investment periods. If a party invests first (ex-ante), they sink their investment before any contracting is possible. The parties that invest second (ex-post) do so after some aspects of the project are tangible, so that they can contract on (at least some) of their investment costs. As well as being empirically relevant, sequencing has several important theoretical implications. First, if a party gets to invest second, then – ceteris paribus – it has a greater incentive to invest. Second, the investment of parties that invest first are affected by a more than one influence. Anticipating higher ex-post investment, they can have a greater incentive to increase their investments. However, higher ex-post investment leads to greater costs being borne by the ex-ante investors (via the cost sharing contracts); this reduces ex-ante incentives to invest. Overall either effect can dominate so that ex-ante investment can either increase or decrease as a result of sequential investment. Third, as noted, sequencing of investment provides the possibility to (partially) contract on ex-post investment and costs. This is an additional method of providing incentives to invest, beyond the allocation of property rights themselves. Consequently, ex-post investors can be protected (and be provided incentives to invest) via these contracts, whereas ex-ante investors –who can not contract on their investments at all – are more likely to require the protection of property rights (through the allocation of asset ownership). The addition of sequential investment alters some of the predictions of the standard models. For example, previously the literature found that if all assets are complements at the margin all agents should have access to all assets (Bel (2005)). However, when investment sequencing is possible, making a control structure more inclusive (increasing the number of agents who have access to assets) can reduce the incentives of the ex-ante investors, decreasing overall surplus; this is because increasing the property rights of ex-post investors increases the marginal costs borne by ex-ante investors, effectively reducing their claim on surplus, diminishing their incentives to invest. This result contradicts Bel (2005), and shows that even when all assets are complimentary at the margin allocating access rights can be detrimental to incentives. Furthermore, if assets are substitutes at the margin then transfer of assets from ex-ante investors to ex-post investors can increase ex-ante investment and surplus. This counter intuitive result can occur in the case when decreasing ex-post investment is necessary to provide an incentive to ex-ante investors to increase their investments.Discipline of Economic

Tracing very high energy neutrinos from cosmological distances in ice

Astrophysical sources of ultrahigh energy neutrinos yield tau neutrino fluxes due to neutrino oscillations. We study in detail the contribution of tau neutrinos with energies above PeV relative to the contribution of the other flavors. We consider several different initial neutrino fluxes and include tau neutrino regeneration in transit through the Earth and energy loss of charged leptons. We discuss signals of tau neutrinos in detectors such as IceCube, RICE and ANITA.Comment: 27 pages, 19 figure

The modulation effect for supersymmetric dark matter detection with asymmetric velocity dispersion

The detection of the theoretically expected dark matter is central to particle physics cosmology. Current fashionable supersymmetric models provide a natural dark matter candidate which is the lightest supersymmetric particle (LSP). Such models combined with fairly well understood physics like the quark substructure of the nucleon and the nuclear form factor and the spin response function of the nucleus, permit the evaluation of the event rate for LSP-nucleus elastic scattering. The thus obtained event rates are, however, very low or even undetectable. So it is imperative to exploit the modulation effect, i.e. the dependence of the event rate on the earth's annual motion. In this review we study such a modulation effect in directional and undirectional experiments. We calculate both the differential and the total rates using symmetric as well as asymmetric velocity distributions. We find that in the symmetric case the modulation amplitude is small, less than 0.07. There exist, however, regions of the phase space and experimental conditions such that the effect can become larger. The inclusion of asymmetry, with a realistic enhanced velocity dispersion in the galactocentric direction, yields the bonus of an enhanced modulation effect, with an amplitude which for certain parameters can become as large as 0.46.Comment: 35 LATEX pages, 7 Tables, 8 PostScript Figures include

Energy, interaction, and photoluminescence of spin-reversed quasielectrons in fractional quantum Hall systems

The energy and photoluminescence spectra of a two-dimensional electron gas in the fractional quantum Hall regime are studied. The single-particle properties of reversed-spin quasielectrons (QE$_{\rm R}$'s) as well as the pseudopotentials of their interaction with one another and with Laughlin quasielectrons (QE's) and quasiholes (QH's) are calculated. Based on the short-range character of the QE$_{\rm R}$--QE$_{\rm R}$ and QE$_{\rm R}$--QE repulsion, the partially unpolarized incompressible states at the filling factors $\nu={4\over11}$ and ${5\over13}$ are postulated within Haldane's hierarchy scheme. To describe photoluminescence, the family of bound $h($QE$_{\rm R})_n$ states of a valence hole $h$ and $n$ QE$_{\rm R}$'s are predicted in analogy to the found earlier fractionally charged excitons $h$QE$_n$. The binding energy and optical selection rules for both families are compared. The $h$QE$_{\rm R}$ is found radiative in contrast to the dark $h$QE, and the $h($QE$_{\rm R})_2$ is found non-radiative in contrast to the bright $h$QE$_2$.Comment: 9 pages, 6 figure

Dynamical coupled-channel approaches on a momentum lattice

Dynamical coupled-channel approaches are a widely used tool in hadronic physics that allow to analyze different reactions and partial waves in a consistent way. In such approaches the basic interactions are derived within an effective Lagrangian framework and the resulting pseudo-potentials are then unitarized in a coupled-channel scattering equation. We propose a scheme that allows for a solution of the arising integral equation in discretized momentum space for periodic as well as twisted boundary conditions. This permits to study finite size effects as they appear in lattice QCD simulations. The new formalism, at this stage with a restriction to S-waves, is applied to coupled-channel models for the sigma(600), f0(980), and a0(980) mesons, and also for the Lambda(1405) baryon. Lattice spectra are predicted.Comment: 7 pages, 4 figure

Limits on spin-dependent WIMP-nucleon cross-sections from the first ZEPLIN-II data

The first underground data run of the ZEPLIN-II experiment has set a limit on the nuclear recoil rate in the two-phase xenon detector for direct dark matter searches. In this paper the results from this run are converted into the limits on spin-dependent WIMP-proton and WIMP-neutron cross-sections. The minimum of the curve for WIMP-neutron cross-section corresponds to 0.07 pb at a WIMP mass of around 65 GeV.Comment: 12 pages, 2 figures, to be published in Physics Letters

Measurement of the production of charged pions by protons on a tantalum target

A measurement of the double-differential cross-section for the production of charged pions in proton--tantalum collisions emitted at large angles from the incoming beam direction is presented. The data were taken in 2002 with the HARP detector in the T9 beam line of the CERN PS. The pions were produced by proton beams in a momentum range from 3 \GeVc to 12 \GeVc hitting a tantalum target with a thickness of 5% of a nuclear interaction length. The angular and momentum range covered by the experiment (100 \MeVc \le p < 800 \MeVc and 0.35 \rad \le \theta <2.15 \rad) is of particular importance for the design of a neutrino factory. The produced particles were detected using a small-radius cylindrical time projection chamber (TPC) placed in a solenoidal magnet. Track recognition, momentum determination and particle identification were all performed based on the measurements made with the TPC. An elaborate system of detectors in the beam line ensured the identification of the incident particles. Results are shown for the double-differential cross-sections ${{\mathrm{d}^2 \sigma}} / {{\mathrm{d}p\mathrm{d}\theta}}$ at four incident proton beam momenta (3 \GeVc, 5 \GeVc, 8 \GeVc and 12 \GeVc). In addition, the pion yields within the acceptance of typical neutrino factory designs are shown as a function of beam momentum. The measurement of these yields within a single experiment eliminates most systematic errors in the comparison between rates at different beam momenta and between positive and negative pion production.Comment: 49 pages, 31 figures. Version accepted for publication on Eur. Phys. J.