Inert Doublet Model and LEP II Limits

The inert doublet model is a minimal extension of the standard model introducing an additional SU(2) doublet with new scalar particles that could be produced at accelerators. While there exists no LEP II analysis dedicated for these inert scalars, the absence of a signal within searches for supersymmetric neutralinos can be used to constrain the inert doublet model. This translation however requires some care because of the different properties of the inert scalars and the neutralinos. We investigate what restrictions an existing DELPHI collaboration study of neutralino pair production can put on the inert scalars and discuss the result in connection with dark matter. We find that although an important part of the inert doublet model parameter space can be excluded by the LEP II data, the lightest inert particle still constitutes a valid dark matter candidate.Comment: 12 pages, 9 figures; v2: published versio

Disentangling the Hercules stream

Using high-resolution spectra of nearby F and G dwarf stars, we have investigated the detailed abundance and age structure of the Hercules stream. We find that the stars in the stream have a wide range of stellar ages, metallicities, and element abundances. By comparing to existing samples of stars in the solar neighbourhood with kinematics typical of the Galactic thin and thick disks we find that the properties of the Hercules stream distinctly separate into the abundance and age trends of the two disks. Hence, we find it unlikely that the Hercules stream is a unique Galactic stellar population, but rather a mixture of thin and thick disk stars. This points toward a dynamical origin for the Hercules stream, probably caused by the Galactic bar.Comment: Accepted for publication in ApJ Letter

Neutron electric form factor at large momentum transfer

Based on the recent, high precision data for elastic electron scattering from protons and deuterons, at relatively large momentum transfer $Q^2$, we determine the neutron electric form factor up to $Q^2=3.5$ GeV$^2$. The values obtained from the data (in the framework of the nonrelativistic impulse approximation) are larger than commonly assumed and are in good agreement with the Gari-Kr\"umpelmann parametrization of the nucleon electromagnetic form factors.Comment: 11 pages 2 figure

A pure S-wave covariant model for the nucleon

Using the manifestly covariant spectator theory, and modeling the nucleon as a system of three constituent quarks with their own electromagnetic structure, we show that all four nucleon electromagnetic form factors can be very well described by a manifestly covariant nucleon wave function with zero orbital angular momentum. Since the concept of wave function depends on the formalism, the conclusions of light-cone theory requiring nonzero angular momentum components are not inconsistent with our results. We also show that our model gives a qualitatively correct description of deep inelastic scattering, unifying the phenomenology at high and low momentum transfer. Finally we review two different definitions of nuclear shape and show that the nucleon is spherical in this model, regardless of how shape is defined.Comment: 20 pages and 10 figures; greatly expanded version with new fits and discussion of DIS; similar to published versio

Chemical abundance patterns -- fingerprints of nucleosynthesis in the first stars

The interstellar medium of low-metallicity systems undergoing star formation will show chemical abundance inhomogeneities due to supernova events enriching the medium on a local scale. If the star formation time-scale is shorter than the time-scale of mixing of the interstellar matter, the inhomogeneities are reflected in the surface abundances of low-mass stars and thereby detailed information on the nucleosynthesis in the first generations of supernovae is preserved. Characteristic patterns and substructures are therefore expected to be found, apart from the large scatter behaviour, in the distributions of stars when displayed in diagrams relating different element abundance ratios. These patterns emerge from specific variations with progenitor stellar mass of the supernova yields and it is demonstrated that the patterns are insensitive to the initial mass function (IMF) even though the relative density of stars within the patterns may vary. An analytical theory of the formation of patterns is presented and it is shown that from a statistical point of view the abundance ratios can trace the different nucleosynthesis sites even when mixing of the interstellar medium occurs. Using these results, it should be possible to empirically determine supernova yields from the information on relative abundance ratios of a large, homogeneous sample of extremely metal-poor Galactic halo stars.Comment: 20 pages, minor typos corrected to match the published version in A&A. Includes the corrected Figs. 17 and 18 (erratum

The Invisible Power of MacHines Revisiting the Proposed Flash Order Ban in the Wake of the Flash Crash

Technological innovation continues to make trading and markets more efficient, generally benefitting market participants and the investing public. But flash trading, a practice that evolved from high-frequency trading, benefits only a select few sophisticated traders and institutions with the resources necessary to view and respond to flashed orders. This practice undermines the basic principles of fairness and transparency in securities regulation, exacerbates information asymmetries and harms investor confidence. This iBrief revisits the Securities and Exchange Commission\u27s proposed ban on the controversial practice of flash trading and urges the Securities and Exchange Commission and the Commodity Futures Trading Commission to implement the ban across the securities and futures markets. Banning flash trading will not impact high-frequency trading or other advantageous innovative trading practices, and will benefit all market participants by making prices and liquidity more transparent. In the wake of the May 6, 2010 flash crash and the passage of the Dodd-Frank Wall Street Reform and Consumer Protection Act, now is an opportune time for the Securities and Exchange Commission and Commodity Futures Trading Commission to implement the ban

Would You Choose to be Happy? Tradeoffs Between Happiness and the Other Dimensions of Life in a Large Population Survey

A large literature documents the correlates and causes of subjective well-being, or happiness. But few studies have investigated whether people choose happiness. Is happiness all that people want from life, or are they willing to sacrifice it for other attributes, such as income and health? Tackling this question has largely been the preserve of philosophers. In this article, we find out just how much happiness matters to ordinary citizens. Our sample consists of nearly 13,000 members of the UK and US general populations. We ask them to choose between, and make judgments over, lives that are high (or low) in different types of happiness and low (or high) in income, physical health, family, career success, or education. We find that people by and large choose the life that is highest in happiness but health is by far the most important other concern, with considerable numbers of people choosing to be healthy rather than happy. We discuss some possible reasons for this preference

Fragmentation and the formation of primordial protostars: the possible role of Collision Induced Emission

The mechanisms which could lead to chemo-thermal instabilities and fragmentation during the formation of primordial protostars are investigated analytically. We introduce approximations for H2 cooling rates bridging the optically thin and thick regimes. These allow us to discuss instabilities up to densities when protostars become optically thick to continuum radiation (n~10^16 cm^-3). During the collapse, instability arises at two different stages: at low density (n~10^8-10^11 cm^-3), it is due to fast 3-body reactions converting H into H2; at high density (n>10^13 cm^-3), it is due to Collisional Induced Emission (CIE). In agreement with the 3D simulations, we find that the instability at low densities cannot lead to fragmentation, because fluctuations do not survive turbulent mixing, and because their growth is slow. The situation at high density is similar. The CIE-induced instability is as weak as the low density one, with similar ratios of growth and dynamical time scales. Fluctuation growth time is longer than free fall time, and fragmentation seems unlikely. One then expects the first stars to be massive, not to form binaries nor harbour planets. Nevertheless, full 3D simulations are required. They could become possible using simplified estimates of radiative transfer effects, which we show to work very well in the 1D case. This indicates that the effects of radiative transfer during the initial stages of formation of primordial protostars can be treated as local corrections to cooling. (Abridged)Comment: 17 pages, 9 figures; accepted for publication in MNRA