Hadron Masses From Novel Fat-Link Fermion Actions

The hadron mass spectrum is calculated in lattice QCD using a novel fat-link clover fermion action in which only the irrelevant operators in the fermion action are constructed using smeared links. The simulations are performed on a 16^3 x 32 lattice with a lattice spacing of a=0.125 fm. We compare actions with n=4 and 12 smearing sweeps with a smearing fraction of 0.7. The n=4 Fat-Link Irrelevant Clover (FLIC) action provides scaling which is superior to mean-field improvement, and offers advantages over nonperturbative 0(a) improvement, including a reduced exceptional configuration problem.Comment: 12 pages, 4 figures, new simulation with mean-field improved clover, further discussion of actio

Investigation of slowing down and charge-exchange of nickel and uranium ions in gases and solids in the energy range (60 - 200) MeV/u

In this thesis new slowing down and charge-state measurements will be presented in the energy range of (60 - 200) MeV/u. These measurements were done using the Fragment Separator (FRS) facility at GSI in Darmstadt. The presented data were taken during two experimental runs. The experiments were divided into two parts. In the first part a 200 MeV/u Ni27+ beam was used. The evolution of charge states as a function of the target thickness was investigated covering both the non-equilibrium and equilibrium region. This was done with various mono-atomic materials (Z2 = 6, 7, 10, 13, 18, 22) and compound materials (ethylene, polyethylene and polypropylene). From the measured charge-state distributions the one-electron ionization and capture cross sections have been extracted. A 40 % gas-solid difference is observed in the ionization cross sections for the mono-atomic materials. In the compound materials a 30 % difference is observed between ethylene and the polymers. The experimental cross sections for the mono-atomic materials have been compared with theoretical calculations [1, 2]. The theoretical ionization cross sections agree quite well with the corresponding experimental ionization cross sections. In the gaseous targets the agreement between experiment and theory is better than 3 %. For the capture cross sections the agreement between experiment and theory is also very good for the lighter target materials (Z2 <= 7). For the heavier targets large deviations up to one order of magnitude are observed. These deviations are due to the increasing importance of the non-radiative capture channel in heavier target materials which is quite difficult to calculate accurately. The results motivate for further refinement of the theory in this energy region. In the second part 3 different uranium beams were used with initial energies of 61 MeV/u (U86+ incident), 85 MeV/u (U73+ incoming) and 200 MeV/u (U81+ incident) to measure the evolution of the charge states again and the energy loss as a function of the target thickness in the same materials as used in the first part plus some additional mono-atomic materials Z2 = 29, 36, 47, 54. From the measured charge-state distributions and energy losses the mean charges and stopping forces have been extracted. At 61 MeV/u we observe a gas-solid difference in the mean charge of up to 4 charge states for the mono-atomic materials. The corresponding stopping powers (forces) at the same specific energy only show a gas-solid difference for light materials (Z2 <= 7). The stopping forces are compared with calculations done with the PASS code [3, 4], ATIMA code [5] and the Hubert et al. tables [6]. The agreement is quite good between experiment and theory. The PASS code predicts by using the experimental mean charges a gas-solid difference in the stopping force for the heavier target materials. In the data at 200 MeV/u there is a gas-solid difference in the ionization rate for U81+ ions similar to the Ni27+ results.In dieser Dissertation werden neue Ladungsverteilungen und Energieverlustmessungen präsentiert. Diese Messungen wurden am Fragment Separator (FRS) bei der GSI in Darmstadt durchgeführt. Die Daten, die hier vorgestellt werden, wurden in zwei Experimenten aufgenommen. Die Experimente bestanden aus zwei Teilen. Im ersten Teil wurde mit einem 200 MeV/u Ni27+ Strahl gemessen. Ziel dieser Messung war die Entwicklung der Ladungsverteilung als Funktion der Targetdicke vom Nichtgleichgewicht bis Gleichgewicht zu untersuchen. Dies wurde mit verschiedenen Targets gemacht (Z2 = 6, 7, 10, 13, 18, 22, Äthylen, Polyäthylen und Polypropylen). Von den gemessenen Ladungsverteilung konnten die Umladungsquerrschnitte für Elektroneneinfang und -verlust extrahiert werden. Ein Gas-Festkörper Effekt von 40 % wurde im Ionizationsquerrschnitt für die monoatomaren (reinen Elemente) Targets gemessen. Im Äthylen und den Polymeren (Polyäthylen und Polypropylen) war ein Effekt von 30 % zu sehen. Die experimentellen Umladungsquerrschnitte für die monoatomaren Targets wurden mit theoretischen Rechnungen von A. Surzhykov und S. Fritzsche [1] und V. P. Shevelko [2] verglichen. In der Ionization stimmen die theoretischen Rechnungen mit den experimentellen Werten gut überein. In den Gastargets ist die Übereinstimmung besser als 3 %. Im Elektroneneinfang gibt es gute Übereinstimmung zwischen Experiment und Theorie bei den leichten Targets (Z2 <= 7), bei den schweren Targets gibt es grosse Abweichungen bis zu einer Grössenordnung. Diese Abweichung kommt zustande, weil der nicht-radiative Querrschnitt einen grösseren Anteil hat bei den schweren Targets und dieser Teil sehr schwer theoretisch zu rechnen ist. Die Ergebnisse sind eine Motivation für Verbesserungen in der Theorie im diesen Energiebereich. Im zweiten Teil wurde ein Uranstrahl bei drei verschiedenen Energien benutzt, diese waren 61 MeV/u mit 86+ als Eingangsladungszustand, 85 MeV/u mit 73+ als Eingangsladungszustand und 200 MeV/u mit 81+ als Eingangsladungszustand. Ziel dieser Messung war es wiederum, die Entwicklung der Ladungsverteilung zu untersuchen und auch Energieverluste zu messen. Dieselben Targets wurden benutzt und zusätzlich wurden folgende Targets vermessen Z2 = 29, 36, 47, 54. Von den gemessenen Ladungsverteilungen und Energieverlusten wurde die mittlere Ladung und das Bremsvermögen bestimmt. Bei 61 MeV/u ist ein Gas-Festkörper Effekt in der mittleren Ladung bei den monoatomaren Targets zu sehen. Der Effekt hat eine Grösse von fast 4 Ladungen. Das dazu gehörige Bremsvermögen zeigt nur einen Gas-Festkörper Effekt bei den leichteren Targets (Z2 <= 7). Die experimentellen Werte wurden mit dem PASS Programm [3, 4], dem ATIMA Programm [5] und den Hubert et al. Tabellen [6] verglichen. Die theoretischen Rechnungen von den Programmen stimmen mit den experimentellen Werten gut überein. PASS sagt einen Gas-Festkörper Effekt bei den schwereren Targets voraus, weil experimentelle Ladungen als Eingangsparameter benutzt wurden. Bei der 200 MeV/u Messung wurde ein Gas-Festkörper Unterschied in der Ionizationsrate in der Entwicklung des U81+ Ladungszustand beobachtet, ähnlich wie in der Ni27+ Messung

Can a supernova be located by its neutrinos?

A future core-collapse supernova in our Galaxy will be detected by several neutrino detectors around the world. The neutrinos escape from the supernova core over several seconds from the time of collapse, unlike the electromagnetic radiation, emitted from the envelope, which is delayed by a time of order hours. In addition, the electromagnetic radiation can be obscured by dust in the intervening interstellar space. The question therefore arises whether a supernova can be located by its neutrinos alone. The early warning of a supernova and its location might allow greatly improved astronomical observations. The theme of the present work is a careful and realistic assessment of this question, taking into account the statistical significance of the various neutrino signals. Not surprisingly, neutrino-electron forward scattering leads to a good determination of the supernova direction, even in the presence of the large and nearly isotropic background from other reactions. Even with the most pessimistic background assumptions, SuperKamiokande (SK) and the Sudbury Neutrino Observatory (SNO) can restrict the supernova direction to be within circles of radius $5^\circ$ and $20^\circ$, respectively. Other reactions with more events but weaker angular dependence are much less useful for locating the supernova. Finally, there is the oft-discussed possibility of triangulation, i.e., determination of the supernova direction based on an arrival time delay between different detectors. Given the expected statistics we show that, contrary to previous estimates, this technique does not allow a good determination of the supernova direction.Comment: 11 pages including 2 figures. Revised version corrects typos, adds some brief comment

Evolution of the Schr\"odinger--Newton system for a self--gravitating scalar field

Using numerical techniques, we study the collapse of a scalar field configuration in the Newtonian limit of the spherically symmetric Einstein--Klein--Gordon (EKG) system, which results in the so called Schr\"odinger--Newton (SN) set of equations. We present the numerical code developed to evolve the SN system and topics related, like equilibrium configurations and boundary conditions. Also, we analyze the evolution of different initial configurations and the physical quantities associated to them. In particular, we readdress the issue of the gravitational cooling mechanism for Newtonian systems and find that all systems settle down onto a 0--node equilibrium configuration.Comment: RevTex file, 19 pages, 26 eps figures. Minor changes, matches version to appear in PR

Geophysical constraints on mirror matter within the Earth

We have performed a detailed investigation of geophysical constraints on the possible admixture of mirror matter inside the Earth. On the basis of the Preliminary Reference Earth Model (PREM) -- the `Standard Model' of the Earth's interior -- we have developed a method which allows one to compute changes in various quantities characterising the Earth (mass, moment of inertia, normal mode frequencies etc.)due to the presence of mirror matter. As a result we have been able to obtain for the first time the direct upper bounds on the possible concentration of the mirror matter in the Earth. In terms of the ratio of the mirror mass to the Earth mass a conservative upper bound is $3.8\times 10^{-3}$. We then analysed possible mechanisms (such as lunar and solar tidal forces, meteorite impacts and earthquakes) of exciting mirror matter oscillations around the Earth centre. Such oscillations could manifest themselves through global variations of the gravitational acceleration at the Earth's surface. We conclude that such variations are too small to be observed. Our results are valid for other types of hypothetical matter coupled to ordinary matter by gravitation only (e.g. the shadow matter of superstring theories).Comment: 25 pages, in RevTeX, to appear in Phys.Rev.

Excited Baryons in Lattice QCD

We present first results for the masses of positive and negative parity excited baryons calculated in lattice QCD using an O(a^2)-improved gluon action and a fat-link irrelevant clover (FLIC) fermion action in which only the irrelevant operators are constructed with APE-smeared links. The results are in agreement with earlier calculations of N^* resonances using improved actions and exhibit a clear mass splitting between the nucleon and its chiral partner. An correlation matrix analysis reveals two low-lying J^P=(1/2)^- states with a small mass splitting. The study of different Lambda interpolating fields suggests a similar splitting between the lowest two Lambda1/2^- octet states. However, the empirical mass suppression of the Lambda^*(1405) is not evident in these quenched QCD simulations, suggesting a potentially important role for the meson cloud of the Lambda^*(1405) and/or a need for more exotic interpolating fields.Comment: Correlation matrix analysis performed. Increased to 400 configurations. 22 pages, 13 figures, 15 table

Exclusive processes in position space and the pion distribution amplitude

We suggest to carry out lattice calculations of current correlators in position space, sandwiched between the vacuum and a hadron state (e.g. pion), in order to access hadronic light-cone distribution amplitudes (DAs). In this way the renormalization problem for composite lattice operators is avoided altogether, and the connection to the DA is done using perturbation theory in the continuum. As an example, the correlation function of two electromagnetic currents is calculated to the next-to-next-to-leading order accuracy in perturbation theory and including the twist-4 corrections. We argue that this strategy is fully competitive with direct lattice measurements of the moments of the DA, defined as matrix elements of local operators, and offers new insight in the space-time picture of hard exclusive reactions.Comment: 15 pages, 10 figure

A finite element approach for the acoustic modelling of perforated dissipative mufflers with non-homogeneous properties

[EN] In this work, a finite element approach is presented for modeling sound propagation in perforated dissipative mufflers with non-homogeneous properties. The spatial variations of the acoustic properties can arise, for example, from uneven filling processes during manufacture and degradation associated with the flow of soot particles within the absorbent material. First, the finite element method is applied to the wave equation for a propagation medium with variable properties (outer chamber with absorbent material) and a homogeneous medium (central passage). For the case of a dissipative muffler, the characterization of the absorbent material is carried out by means of its equivalent complex density and speed of sound. To account for the spatial variations of these properties, a coordinate-dependent function is proposed for the filling density of the absorbent material. The coupling between the outer chamber and the central passage is achieved by using the acoustic impedance of the perforated central pipe, that relates the acoustic pressure jump and the normal velocity through the perforations. The acoustic impedance of the perforated central duct includes the influence of the absorbent material and therefore a spatial variation of the impedance is also taken into account. A detailed study is then presented to assess the influence of the heterogeneous properties and the perforated duct porosity on the acoustic attenuation performance of the muffler.The authors gratefully acknowledge the financial support of Ministerio de Ciencia e Innovacion and the European Regional Development Fund by means of the projects DPI2007-62635 and DPI2010-15412.Antebas, A.; Denia Guzmán, FD.; Pedrosa Sanchez, AM.; Fuenmayor Fernández, FJ. (2013). A finite element approach for the acoustic modelling of perforated dissipative mufflers with non-homogeneous properties. Mathematical and Computer Modelling. 57(7):1970-1978. https://doi.org/10.1016/j.mcm.2012.01.021S1970197857

Post-Newtonian SPH calculations of binary neutron star coalescence. II. Binary mass ratio, equation of state, and spin dependence

Using our new Post-Newtonian SPH (smoothed particle hydrodynamics) code, we study the final coalescence and merging of neutron star (NS) binaries. We vary the stiffness of the equation of state (EOS) as well as the initial binary mass ratio and stellar spins. Results are compared to those of Newtonian calculations, with and without the inclusion of the gravitational radiation reaction. We find a much steeper decrease in the gravity wave peak strain and luminosity with decreasing mass ratio than would be predicted by simple point-mass formulae. For NS with softer EOS (which we model as simple $\Gamma=2$ polytropes) we find a stronger gravity wave emission, with a different morphology than for stiffer EOS (modeled as $\Gamma=3$ polytropes as in our previous work). We also calculate the coalescence of NS binaries with an irrotational initial condition, and find that the gravity wave signal is relatively suppressed compared to the synchronized case, but shows a very significant second peak of emission. Mass shedding is also greatly reduced, and occurs via a different mechanism than in the synchronized case. We discuss the implications of our results for gravity wave astronomy with laser interferometers such as LIGO, and for theoretical models of gamma-ray bursts (GRBs) based on NS mergers.Comment: RevTeX, 38 pages, 24 figures, Minor Corrections, to appear in Phys. Rev.

What Drives Fitness Apps Usage? An Empirical Evaluation

Part 3: Creating Value through ApplicationsInternational audienceThe increased health problems associated with lack of physical activity is of great concern around the world. Mobile phone based fitness applications appear to be a cost effective promising solution for this problem. The aim of this study is to develop a research model that can broaden understanding of the factors that influence the user acceptance of mobile fitness apps. Drawing from Unified Theory of Acceptance and Use of Technology (UTAUT) and Elaboration Likelihood Model (ELM), we conceptualize the antecedents and moderating factors of fitness app use. We validate our model using field survey. Implications for research and practice are discussed