A new look at microlensing limits on dark matter in the Galactic halo

The motivation for this paper is to review the limits set on the MACHO content of the Galactic halo by microlensing experiments in the direction of the Large Magellanic Cloud. This has been prompted by recent measurements of the Galactic rotation curve, which suggest that the limits have been biassed by the assumption of an over-massive halo. The paper first discusses the security of the detection efficiency calculations which are central to deriving the MACHO content of the Galactic halo. It then sets out to compare the rotation curves from various halo models with recent observations, with a view to establishing what limits can be put on an all-MACHO halo. The main thrust of the paper is to investigate whether lighter halo models which are consistent with microlensing by an all-MACHO halo are also consistent with recent measures of the Galactic rotation curve. In this case the population of bodies discovered by the MACHO collaboration would make up the entire dark matter content of the Galactic halo. The main result of this paper is that it is easy to find low mass halo models consistent with the observed Galactic rotation curve, which also imply an optical depth to microlensing similar to that found by the MACHO collaboration. This means that all-MACHO halos cannot be ruled out on the basis of their observations. In conclusion, limits placed on the MACHO content of the Galactic halo from microlensing surveys in the Magellanic Clouds are inconsistent and model dependent, and do not provide a secure basis for rejecting an all-MACHO halo.Comment: 8 pages, 4 figures, accepted for publication in A&

Accretion onto Seed Black Holes in the First Galaxies

The validity of the hypothesis that the massive black holes in high redshift quasars grew from stellar-sized "seeds" is contingent on a seed's ability to double its mass every few ten million years. This requires that the seed accrete at approximately the Eddington-limited rate. In the specific case of radiatively efficient quasiradial accretion in a metal-poor protogalactic medium, for which the Bondi accretion rate is often prescribed in cosmological simulations of massive black hole formation, we examine the effects of the radiation emitted near the black hole's event horizon on the structure of the surrounding gas flow. We find that the radiation pressure from photoionization significantly reduces the steady-state accretion rate and renders the quasiradial accretion flow unsteady and inefficient. The time-averaged accretion rates are a small fraction of the Eddington-limited accretion rate for Thomson scattering. The pressure of Ly-alpha photons trapped near the HII region surrounding the black hole may further attenuate the inflow. These results suggest that an alternative to quasiradial, radiatively efficient Bondi-like accretion should be sought to explain the rapid growth of quasar-progenitor seed black holes.Comment: replaced with significantly revised and expanded version; 14 pages, 2 figure

Proposal for SPS beam time for the baby MIND and TASD neutrino detector prototypes

The design, construction and testing of neutrino detector prototypes at CERN are ongoing activities. This document reports on the design of solid state baby MIND and TASD detector prototypes and outlines requirements for a test beam at CERN to test these, tentatively planned on the H8 beamline in the North Area, which is equipped with a large aperture magnet. The current proposal is submitted to be considered in light of the recently approved projects related to neutrino activities with the SPS in the North Area in the medium term 2015-2020

Combining WMAP and SDSS Quasar Data on Reionization Constrains Cosmological Parameters and the Star Formation Efficiency

We present constraints on cosmological and star formation parameters based on combining observations of the Wilkinson Microwave Anisotropy Probe (WMAP) and high-redshift quasars from the Sloan Digital Sky Survey (SDSS). We use a semi-analytic model for reionization (Chiu and Ostriker 2000) that takes into account a number of important physical processes both within collapsing halos and in the intergalactic medium. Assuming that the efficiency of producing UV photons per baryon is constant, we derive a constraint of the form sigma_8 Omega_0^0.5~0.33 in a flat, Lambda-dominated universe with h=0.72, n=0.99, and Omega_b h^2=0.024. However, the calculated optical depth to electron scattering of tau_es~0.06 is well below the value found by WMAP of 0.17+/-(0.04~0.07) (Spergel et al 2003). Since the WMAP constraints on tau_es are somewhat degenerate with the value of the spectral index n, we then permit the primordial spectral index n to float and fix Omega_0 h^2=0.14, while normalizing the power spectrum using WMAP. In addition, we allow the UV-efficiency to have time-dependence. Combining the WMAP constraints with the quasar transmission data, our analysis then favors a model with tau_es=0.11^{+0.02}_{-0.03}, n=0.96^{+0.02}_{-0.03}$, implying sigma_8=0.83^{+0.03}_{-0.05} (95% confidence), and an effective UV-efficiency that was at least ~10x greater at z >> 6. These results indicate that the quasar and WMAP observations are consistent. If future observations confirm an optical depth to electron scattering tau_es~0.1, then it would appear that no more "exotic" sources of UV-photons, such as mini-quasars or AGNs, are necessary; but our analysis indicates that a determination of tau_es>~0.17 would require a more radical solution.Comment: 31 pages, 7 figures, 5 table

Femtosecond laser ablation-ICP-mass spectrometry analysis of a heavy metallic matrix : determination of platinum group metals and gold in lead fire-assay buttons as a case study

Owing to the shorter time interval during which energy is delivered to the sample material, femtosecond (fs) laser ablation is preferable over nanosecond laser ablation for metallic samples. In this project, the influence of various laser parameters-beam diameter, repetition rate and laser fluence-on the ablation of Pb as a heavy metallic matrix using an infrared (lambda = 795 nm) fs-LA system (150 fs pulse duration) was studied. The merits of Ar and He as carrier gases were compared and as He did not provide a substantial improvement in the limits of detection, while deposition of sample material on the window of the ablation chamber was more pronounced, Ar was selected for all further measurements. The effect on the ICP caused by the introduction of various amounts of sample aerosol was studied by monitoring the signal intensity for Ar-38(+). It was shown that maximizing the amount of sample ablated and thus, the amount of sample aerosol introduced into the ICP, did not result in maximum sensitivity, which was rather obtained under 'compromise' conditions. Subsequently, femtosecond LA-quadrupole-based ICP-mass spectrometry (ICP-MS) was used for the determination of traces of the platinum group metals (PGMs) Rh, Pd, Ru, Ir and Pt and of Au in Pb buttons obtained by fire assay of platiniferous ore reference materials. The signal of Pb-204(+) was used as an internal reference, correcting for variations in the laser ablation and transport efficiencies and in the instrument's sensitivity. The spectral interferences established for some of the target nuclides due to the occurrence of Pb2+ ions were successfully overcome by pressurizing the reaction cell with NH3. Quantification versus a calibration curve constructed on the basis of the results obtained for matrix-matched standards (>99% Pb) provided excellent accuracy, superior to those obtained using nanosecond LA-ICP-MS. Also the limits of detection were improved by a factor ranging between 3 and 10 and are <0.010 mu g g(-1) for the most important PGMs (Rh, Pd, Pt) and Au. Several measures, such as the use of a large ablation cell and housing up to 10 Pb buttons, were taken to increase the sample throughput. In the same context, day-to-day reproducibility of the calibration curve was also examined. When recording a 'fresh' calibration curve every day, the average bias between the experimental results and the corresponding reference values was established to be <2.5% for every target element. When using one calibration curve during three consecutive days, the bias still remains <10%, while the sample throughput is increased and analysis of several tens of buttons per day is feasible (10-15 min total analysis time per sample)

A first search of excited states double beta and double electron capture decays of Pd110 and Pd102

A search for double beta decays of the palladium isotopes 110Pd and 102Pd into excited states of their daughters was performed and first half-life limits for the 2{\nu}{\beta}{\beta} and 0{\nu}{\beta}{\beta} decays into first excited 0+ and 2+ states of 5.89e19 yr and 4.40e19 yr (95% CL) for the 110Pd decay were obtained. The half-life limits for the corresponding double electron capture transition of 102Pd are 7.64e18 yr and 2.68e18 yr (95% CL) respectively. These are the first measurements for 102Pd.Comment: Updated to published version. Refined analysis and minor text changes. Half-life limits change

Firms, Courts, and Reputation Mechanisms: Towards a Positive Theory of Private Ordering

This Essay formulates a positive model that predicts when commercial parties will employ private ordering to enforce their agreements. The typical enforcement mechanism associated with private ordering is the reputation mechanism, in which a merchant community punishes parties in breach of contract by denying them future business. The growing private ordering literature argues that these private enforcement mechanisms can be superior to the traditional, less efficient enforcement measures provided by public courts. However, previous comparisons between public and private contractual enforcement have presented a misleading dichotomy by failing to consider a third enforcement mechanim: the vertically integrated firm. This Essay develops a model that comprehensively addresses three distinct types of enforcement mechanisms--firms, courts, and reputation-based private ordering. The model rests on a synthesis of transaction cost economics, which compares the efficiencies of firms versus markets, and the private ordering literature, which compares the efficiencies of public courts versus private ordering. It hypothesizes that private ordering will arise when agreements present enforcement difficulties, high-powered market incentives are important, and the costs of entry barriers are low. The Essay then conducts an illustrative test by comparing the model\u27s predictions to documented instances of private ordering

Diagnosis for ecological intensification of maize-based smallholder farming systems in the Costa Chica, Mexico

Enhanced utilization of ecological processes for food and feed production as part of the notion of ecological intensification starts from location-specific knowledge of production constraints. A diagnostic systems approach which combined social-economic and production ecological methods at farm and field level was developed and applied to diagnose extent and causes of the perceived low productivity of maize-based smallholder systems in two communities of the Costa Chica in South West Mexico. Social-economic and production ecological surveys were applied and complemented with model-based calculations. The results demonstrated that current nutrient management of crops has promoted nutrition imbalances, resulting in K- and, less surprisingly N-limited production conditions, reflected in low yields of the major crops maize and roselle and low resource use efficiencies. Production on moderate to steep slopes was estimated to result in considerable losses of soil and organic matter. Poor crop production, lack of specific animal fodder production systems and strong dependence on animal grazing within communal areas limited recycling of nutrients through manure. In combination with low prices for the roselle cash crop, farmers are caught in a vicious cycle of cash shortage and resource decline. The production ecological findings complemented farmers opinions by providing more insight in background and extent of livelihood constraints. Changing fertilizer subsidies and rethinking animal fodder production as well as use of communal lands requires targeting both formal and informal governance structures. The methodology has broader applicability in smallholder systems in view of its low demand on capital intensive resource

The OGLE View of Microlensing towards the Magellanic Clouds. II. OGLE-II SMC data

The primary goal of this paper is to provide the evidence that can either prove or falsify the hypothesis that dark matter in the Galactic halo can clump into stellar-mass compact objects. If such objects existed, they would act as lenses to external sources in the Magellanic Clouds, giving rise to an observable effect of microlensing. We present the results of our search for such events, based on the data from the second phase of the OGLE survey (1996-2000) towards the SMC. The data set we used is comprised of 2.1 million monitored sources distributed over an area of 2.4 square degrees. We found only one microlensing event candidate, however its poor quality light curve limited our discussion on the exact distance to the lensing object. Given a single event, taking the blending (crowding of stars) into account for the detection efficiency simulations, and deriving the HST-corrected number of monitored stars, the microlensing optical depth is tau=(1.55+-1.55)10e-7. This result is consistent with the expected SMC self-lensing signal, with no need of introducing dark matter microlenses. Rejecting the unconvincing event leads to the upper limit on the fraction of dark matter in the form of MACHOs to f<20 per cent for deflectors' masses around 0.4 Msun and f<11 per cent for masses between 0.003 and 0.2 Msun (95 per cent confidence limit). Our result indicates that the Milky Way's dark matter is unlikely to be clumpy and form compact objects in the sub-solar-mass range.Comment: Accepted for publication in MNRAS. Data in electronic form are available on the OGLE's website: http://ogle.astrouw.edu.pl