Neutron star - white dwarf mergers: Early evolution, physical properties, and outcomes

Neutron-star (NS) - white-dwarf (WD) mergers may give rise to observable explosive transients, but have been little explored. We use 2D coupled hydrodynamical-thermonuclear FLASH-code simulations to study the evolution of WD debris-disks formed following WD-disruptions by NSs. We use a 19-elements nuclear-network and a detailed equation-of-state to follow the evolution, complemented by a post-process analysis using a larger 125-isotopes nuclear-network. We consider a wide range of initial conditions and study the dependence of the results on the NS/WD masses ($1.4-2{\rm M_{\odot}}$;$\,{\rm 0.375-0.7\,M_{\odot}}$, respectively), WD-composition (CO/He/hybrid-He-CO) and the accretion-disk structure. We find that viscous inflow in the disk gives rise to continuous wind-outflow of mostly C/O material mixed with nuclear-burning products arising from a weak detonation occurring in the inner-region of the disk. We find that such transients are energetically weak ($10^{48}-10^{49}$ergs) compared with thermonuclear-supernovae (SNe), and are dominated by the (gravitational) accretion-energy. Although thermonuclear-detonations occur robustly in all of our simulations (besides the He-WD) they produce only little energy $(1-10\%$ of the kinetic energy) and $^{56}{\rm Ni}$ ejecta (few$\times10^{-4}-10^{-3}{\rm M_{\odot}})$, with overall low ejecta masses of $\sim0.01-0.1{\rm M_{\odot}}$. Such explosions may produce rapidly-evolving transients, much shorter and fainter than regular type-Ia SNe. The composition and demographics of such SNe appear to be inconsistent with those of Ca-rich type Ib SNe. Though they might be related to the various classes of rapidly evolving SNe observed in recent years, they are likely to be fainter than the typical ones, and may therefore give rise a different class of potentially observable transients.Comment: MNRAS final versio

Coping with the legacies of subsidized mortgage credit in Hungary

The authors examine alternatives for dealing with the initial conditions of housing finance facing countries making the transition to a market economy and moving toward a more efficient and equitable system. They focus on the problem of restructuring the stock of housing loans that exist at the time a new regime is implemented. Almost without exception, the stock of housing loans is yielding heavily subsidized rates, and its market value is significantly below its book value. Hungary makes an interesting case study. The mortgage portfolio inherited from past regimes makes especially clear the perverse implications of housing finance systems based on across-the-board subsidized interest rates. The authors propose a general approach to finding options to reduce the fiscal burden implicit in the subsidized housing loan portfolio. They identify mechanisms to reduce the interest subsidy embodied in that portfolio as well as mechanisms to spread the associated losses among those benefiting from the subsidies as well as among other parties. Clearly any residual subsidy must be absorbed by the government and ultimately by the population in the form of increased taxation or decreased availability of public services. The problem is complex and no obvious, easily implementable solutions emerge. But delaying action could hardly improve the situation.Banks&Banking Reform,Economic Theory&Research,Public Sector Economics&Finance,Housing Finance,Urban Economics

Understanding the performance of the low energy neutrino factory: the dependence on baseline distance and stored-muon energy

Motivated by recent hints of large {\theta}13 from the T2K, MINOS and Double Chooz experiments, we study the physics reach of a Low Energy Neutrino Factory (LENF) and its dependence on the chosen baseline distance, L, and stored-muon energy, E_{\mu}, in order to ascertain the configuration of the optimal LENF. In particular, we study the performance of the LENF over a range of baseline distances from 1000 km to 4000 km and stored-muon energies from 4 GeV to 25 GeV, connecting the early studies of the LENF (1300 km, 4.5 GeV) to those of the conventional, high-energy neutrino factory design (4000 km and 7000 km, 25 GeV). Three different magnetized detector options are considered: a Totally-Active Scintillator Detector (TASD) and two models of a liquid-argon detector distinguished by optimistic and conservative performance estimates. In order to compare the sensitivity of each set-up, we compute the full {\delta}-dependent discovery contours for the determination of non-zero {\theta}13, CP-violating values of {\delta} and the mass hierarchy. In the case of large {\theta}13 with sin^2(2*{\theta}13) = (few)*10^{-3}, the LENF provides a strong discovery potential over the majority of the L-E_{\mu} parameter space and is a promising candidate for the future generation of long baseline experiments aimed at discovering CP-violation and the mass hierarchy, and at making a precise determination of the oscillation parameters.Comment: 14 pages, 5 figure

Hungary : financial sector reform in a socialist economy

Financial reforms in formerly centrally planned economies take a different form than in market economies because they imply not only liberalizing the system but also reshaping the structure and functioning of financial markets. And the reforms must be designed to facilitate the conduct of monetary policy under rapidly changing economic circumstances. To fulfill this role, financial reforms should: (1) provide the authorities with monetary policy instruments that contribute to short-term stabilization; and (2) provide the incentives for inducing a more efficient intermediation of savings though the financial markets. In this context, the authors identify the main tasks and targets of financial reform and comment on the key development of the Hungarian process. Hungary has made substantial progress, they conclude, but macrofinancial indicators suggest that administrative and technical obstacles remain and that supporting measures must be deepened. The four steps needed are: (1) the ability of the monetary authority to conduct monetary policy must be enhanced; (2) the operating and financial condition of financial intermediaries must be improved; (3) healthy competition among financial intermediaries must be encouraged; and (4) a prudential regulatory framework that does not discriminate against the development of securities market must be established.Banks&Banking Reform,Financial Intermediation,Environmental Economics&Policies,Economic Theory&Research,Financial Crisis Management&Restructuring

A viability theory approach to a two-stage optimal control problem of technology adoption

A new technology adoption problem can be modelled as a two-stage control problem, in which model parameters ("technology") might be altered at some time. An optimal solution to utility maximisation for this class of problems needs to contain information on the time, at which the change will take place (0, finite or never), along with the optimal control strategies before and after the change. For the change, or switch, to occur the "new technology" value function needs to dominate the "old technology" value function, after the switch. We charaterise the value function using the fact that its hypograph is a viability kernel of an auxiliary problem and we study when the graphs can intersect. If they do not, the switch cannot occur at a positive time. Using this characterisation we analyse a technology adoption problem and showmodels, for which the switch will occur at time zero or never.technology adoption, value function, viability kernel, viscosity solutions