The calibration of the Sudbury Neutrino Observatory using uniformly distributed radioactive sources

The production and analysis of distributed sources of 24Na and 222Rn in the Sudbury Neutrino Observatory (SNO) are described. These unique sources provided accurate calibrations of the response to neutrons, produced through photodisintegration of the deuterons in the heavy water target, and to low energy betas and gammas. The application of these sources in determining the neutron detection efficiency and response of the 3He proportional counter array, and the characteristics of background Cherenkov light from trace amounts of natural radioactivity is described.Comment: 24 pages, 13 figure

On the dust properties of high-redshift molecular clouds and the connection to the 2175 Å extinction bump

We present a study of the extinction and depletion-derived dust properties of gamma-ray burst (GRB) absorbers at $1<z<3$ showing the presence of neutral carbon (\ion{C}{I}). By modelling their parametric extinction laws, we discover a broad range of dust models characterizing the GRB \ion{C}{I} absorption systems. In addition to the already well-established correlation between the amount of \ion{C}{I} and visual extinction, $A_V$, we also observe a correlation with the total-to-selective reddening, $R_V$. All three quantities are also found to be connected to the presence and strength of the 2175\,{\AA} dust extinction feature. While the amount of \ion{C}{I} is found to be correlated with the SED-derived dust properties, we do not find any evidence for a connection with the depletion-derived dust content as measured from [Zn/Fe] and $N$(Fe)$_{\rm dust}$. To reconcile this, we discuss a scenario where the observed extinction is dominated by the composition of dust particles confined in the molecular gas-phase of the ISM. We argue that since the depletion level trace non-carbonaceous dust in the ISM, the observed extinction in GRB \ion{C}{I} absorbers is primarily produced by carbon-rich dust in the molecular cloud and is therefore only observable in the extinction curves and not in the depletion patterns. This also indicates that the 2175\,{\AA} dust extinction feature is caused by dust and molecules in the cold and molecular gas-phase. This scenario provides a possible resolution to the discrepancy between the depletion- and SED-derived amounts of dust in high-$z$ absorbers.Comment: 10 pages, 5 Figs. + Appendix. Accepted in MNRA

CutTools: a program implementing the OPP reduction method to compute one-loop amplitudes

We present a program that implements the OPP reduction method to extract the coefficients of the one-loop scalar integrals from a user defined (sub)-amplitude or Feynman Diagram, as well as the rational terms coming from the 4-dimensional part of the numerator. The rational pieces coming from the epsilon-dimensional part of the numerator are treated as an external input, and can be computed with the help of dedicated tree-level like Feynman rules. Possible numerical instabilities are dealt with the help of arbitrary precision routines, that activate only when needed.Comment: Version published in JHE

Local time and the pricing of time-dependent barrier options

A time-dependent double-barrier option is a derivative security that delivers the terminal value $\phi(S_T)$ at expiry $T$ if neither of the continuous time-dependent barriers b_\pm:[0,T]\to \RR_+ have been hit during the time interval $[0,T]$. Using a probabilistic approach we obtain a decomposition of the barrier option price into the corresponding European option price minus the barrier premium for a wide class of payoff functions $\phi$, barrier functions $b_\pm$ and linear diffusions $(S_t)_{t\in[0,T]}$. We show that the barrier premium can be expressed as a sum of integrals along the barriers $b_\pm$ of the option's deltas \Delta_\pm:[0,T]\to\RR at the barriers and that the pair of functions $(\Delta_+,\Delta_-)$ solves a system of Volterra integral equations of the first kind. We find a semi-analytic solution for this system in the case of constant double barriers and briefly discus a numerical algorithm for the time-dependent case.Comment: 32 pages, to appear in Finance and Stochastic

Magnetic Properties of YBa_2Cu_3O_{7-\delta} in a self-consistent approach: Comparison with Quantum-Monte-Carlo Simulations and Experiments

We analyze single-particle electronic and two-particle magnetic properties of the Hubbard model in the underdoped and optimally-doped regime of \YBCO by means of a modified version of the fluctuation-exchange approximation, which only includes particle-hole fluctuations. Comparison of our results with Quantum-Monte Carlo (QMC) calculations at relatively high temperatures ($T\sim 1000 K$) suggests to introduce a temperature renormalization in order to improve the agreement between the two methods at intermediate and large values of the interaction $U$. We evaluate the temperature dependence of the spin-lattice relaxation time $T_1$ and of the spin-echo decay time $T_{2G}$ and compare it with the results of NMR measurements on an underdoped and an optimally doped \YBCO sample. For $U/t=4.5$ it is possible to consistently adjust the parameters of the Hubbard model in order to have a good {\it semi-quantitative} description of this temperature dependence for temperatures larger than the spin gap as obtained from NMR measurements. We also discuss the case $U/t\sim 8$, which is more appropriate to describe magnetic and single-particle properties close to half-filling. However, for this larger value of $U/t$ the agreement with QMC as well as with experiments at finite doping is less satisfactory.Comment: Final version, to appear in Phys. Rev. B (sched. Feb. 99

Model-independent analysis of Higgs spin and CP properties in the process e+e−→ttˉΦe^+ e^- \to t \bar t \Phi

In this paper we investigate methods to study the $t\bar{t}$ Higgs coupling. The spin and CP properties of a Higgs boson are analysed in a model-independent way in its associated production with a $t\bar{t}$ pair in high-energy $e^+e^-$ collisions. We study the prospects of establishing the CP quantum numbers of the Higgs boson in the CP-conserving case as well as those of determining the CP-mixing if CP is violated. We explore in this analysis the combined use of the total cross section and its energy dependence, the polarisation asymmetry of the top quark and the up-down asymmetry of the antitop with respect to the top-electron plane. We find that combining all three observables remarkably reduces the error on the determination of the CP properties of the Higgs Yukawa coupling. Furthermore, the top polarisation asymmetry and the ratio of cross sections at different collider energies are shown to be sensitive to the spin of the particle produced in association with the top quark pair

Identifying an indoor air exposure limit for formaldehyde considering both irritation and cancer hazards

Formaldehyde is a well-studied chemical and effects from inhalation exposures have been extensively characterized in numerous controlled studies with human volunteers, including asthmatics and other sensitive individuals, which provide a rich database on exposure concentrations that can reliably produce the symptoms of sensory irritation. Although individuals can differ in their sensitivity to odor and eye irritation, the majority of authoritative reviews of the formaldehyde literature have concluded that an air concentration of 0.3 ppm will provide protection from eye irritation for virtually everyone. A weight of evidence-based formaldehyde exposure limit of 0.1 ppm (100 ppb) is recommended as an indoor air level for all individuals for odor detection and sensory irritation. It has recently been suggested by the International Agency for Research on Cancer (IARC), the National Toxicology Program (NTP), and the US Environmental Protection Agency (US EPA) that formaldehyde is causally associated with nasopharyngeal cancer (NPC) and leukemia. This has led US EPA to conclude that irritation is not the most sensitive toxic endpoint and that carcinogenicity should dictate how to establish exposure limits for formaldehyde. In this review, a number of lines of reasoning and substantial scientific evidence are described and discussed, which leads to a conclusion that neither point of contact nor systemic effects of any type, including NPC or leukemia, are causally associated with exposure to formaldehyde. This conclusion supports the view that the equivocal epidemiology studies that suggest otherwise are almost certainly flawed by identified or yet to be unidentified confounding variables. Thus, this assessment concludes that a formaldehyde indoor air limit of 0.1 ppm should protect even particularly susceptible individuals from both irritation effects and any potential cancer hazard