Local Operator Multipliers and Positivity

We establish an unbounded version of Stinespring's Theorem and a lifting result for Stinespring representations of completely positive modular maps defined on the space of all compact operators. We apply these results to study positivity for Schur multipliers. We characterise positive local Schur multipliers, and provide a description of positive local Schur multipliers of Toeplitz type. We introduce local operator multipliers as a non-commutative analogue of local Schur multipliers, and obtain a characterisation that extends earlier results concerning operator multipliers and local Schur multipliers. We provide a description of the positive local operator multipliers in terms of approximation by elements of canonical positive cones.Comment: 31 page

Housing subsidisation in the Netherlands; measuring its distortionary and distributional effects

This paper measures the distortionary and distributional effects of housing subsidies. The results are discussed in the light of the main justifications for subsidising housing, i.e. the merit-good argument, external effects and the distribution motive. Our measurements reveal some patterns of subsidisation that seem difficult to justify on these grounds. This applies especially to the differences between subsidisation of rental and owner-occupied housing, the differences between mortgage- and equity-financed ownership and the increase of relative subsidisation above a certain income level.

Constraints on the sound speed of dark energy

We have studied constraints on the equation of state, $w$, and speed of sound, c_s, of the dark energy from a joint analysis of data from the cosmic microwave background, large scale structure and type-Ia supernovae. We find that current observations have no significant sensitivity to c_s. However, there is a slight difference between models in which there are no dark energy perturbations and models in which dark energy behaves as a fluid. Assuming that there are no dark energy perturbations shifts the allowed region for $w$ to slightly higher values. At present models with and without dark energy perturbations provide roughly equally good fits to observations, but the difference is potentially important for future parameter estimations. Finally, we have also performed error forecasts for future measurements of c_s.Comment: 9 pages, 6 figures, Revte

Supernova Neutrino Opacity from Nucleon-Nucleon Bremsstrahlung and Related Processes

Elastic scattering on nucleons, \nu N -> N \nu, is the dominant supernova (SN) opacity source for \mu and \tau neutrinos. The dominant energy- and number-changing processes were thought to be \nu e^- -> e^- \nu and \nu\bar \nu e^+ e^- until Suzuki (1993) showed that the bremsstrahlung process \nu\bar \nu NN NN was actually more important. We find that for energy exchange, the related ``inelastic scattering process'' \nu NN NN \nu is even more effective by about a factor of 10. A simple estimate implies that the \nu_\mu and \nu_\tau spectra emitted during the Kelvin-Helmholtz cooling phase are much closer to that of \nu\bar_e than had been thought previously. To facilitate a numerical study of the spectra formation we derive a scattering kernel which governs both bremsstrahlung and inelastic scattering and give an analytic approximation formula. We consider only neutron-neutron interactions, we use a one-pion exchange potential in Born approximation, nonrelativistic neutrons, and the long-wavelength limit, simplifications which appear justified for the surface layers of a SN core. We include the pion mass in the potential and we allow for an arbitrary degree of neutron degeneracy. Our treatment does not include the neutron-proton process and does not include nucleon-nucleon correlations. Our perturbative approach applies only to the SN surface layers, i.e. to densities below about 10^{14} g cm^{-3}.Comment: 36 pages, LaTeX, 6 postscript figs included, matches version accepted for publication in Astrophysical Journa

Cosmology seeking friendship with sterile neutrinos

Precision cosmology and big-bang nucleosynthesis mildly favor extra radiation in the universe beyond photons and ordinary neutrinos, lending support to the existence of low-mass sterile neutrinos. We use the WMAP 7-year data, small-scale CMB observations from ACBAR, BICEP and QuAD, the SDSS 7th data release, and measurement of the Hubble parameter from HST observations to derive credible regions for the assumed common mass scale m_s and effective number N_s of thermally excited sterile neutrino states. Our results are compatible with the existence of one or perhaps two sterile neutrinos, as suggested by LSND and MiniBooNE, if m_s is in the sub-eV range.Comment: 4 pages, 1 figure, matches version published in PR

Cosmological axion bounds

We discuss current cosmological constraints on axions, as well as future sensitivities. Bounds on axion hot dark matter are discussed first, and subsequently we discuss both current and future sensitivity to models in which axions play the role as cold dark matter, but where the Peccei-Quinn symmetry is not restored during reheating.Comment: 4 pages, 2 figures, To appear in the proceedings of 5th Patras Workshop on Axions, WIMPs and WISPs, Durham 13-17 July 200

Achieving scalability in hierarchical location services

Services for locating mobile objects are often organized as a distributed search tree. A potential problem with this organization is that high-level nodes may become a bottleneck, affecting the scalability of the service. A traditional approach to handle such problems is to also distribute the location information managed by a single node across multiple machines

Pragmatics in legal interpretation

How should pragmatic dimensions of meaning be understood when they occur in the frequently normative use of language in law? In this chapter, referring principally to common law systems, we outline how pragmatic issues arise in the interpretation of legal texts; we describe how legal interpretation has treated indirect and implied meaning; and we ask how far dialogue between linguistic pragmatics and law can enrich thinking and practice in each of these fields

A Cosmological Three Level Neutrino Laser

We present a calculation of a neutrino decay scenario in the early Universe. The specific decay is \nu_{2} \to \nu_{1} + \phi, where \phi is a boson. If there is a neutrino mass hierarchy, m_{\nu_{e}} < m_{\nu_{\mu}} < m_{\nu_{\tau}}, we show that it is possible to generate stimulated decay and effects similar to atomic lasing without invoking new neutrinos, even starting from identical neutrino distributions. Under the right circumstances the decay can be to very low momentum boson states thereby producing something similar to a Bose condensate, with possible consequences for structure formation. Finally, we argue that this type of decay may also be important other places in early Universe physics.Comment: 7 pages, RevTex, due for publication in Phys. Rev. D, April 15 issu