118549208
An analytic Pade-motivated QCD coupling
We consider a modification of the Minimal Analytic (MA) coupling of Shirkov and Solovtsov. This modified MA (mMA) coupling reflects the desired analytic properties of the space‐like observables. We show that an approximation by Dirac deltas of its discontinuity function ρ is equivalent to a Pade (rational) approximation of the mMA coupling that keeps its analytic structure. We propose a modification to mMA that, as preliminary results indicate, could be an improvement in the evaluation of low‐energy observables compared with other analytic couplings.
117908138
COMPARING GALAXY POPULATIONS IN COMPACT AND LOOSEGROUPS OF GALAXIES
Aims. We compare the properties of galaxies in compact groups, loose groups, and the field to deepen our understanding of the physical mechanisms acting upon galaxy evolution in different environments. Methods. We select samples of galaxies in compact groups, loose groups, and field galaxies from the Sloan Digital Sky Survey. We compare the properties of the galaxy populations in these different environments: absolute magnitude, colour, size, surface brightness, stellar mass, and concentration. We also study the fraction of red and early-type galaxies, the luminosity function, the colourluminosity, and luminosity-size relations. Results. The population of galaxies in compact groups differ from that of loose groups and the field. The fraction of red and early-type galaxies is larger in compact groups. Galaxies in compact groups are, on average, systematically smaller in size, more concentrated, and have higher surface brightnesses than galaxies in the field and in loose groups. At a fixed absolute magnitude, or fixed surface brightness, galaxies in compact groups are smaller in size. Conclusions. The physical mechanisms that transform galaxies into earlier types could be more effective within compact groups, owing to the typically high densities and small velocity dispersions of these environments, which could explain the large fraction of red and early-type galaxies we found in compact groups. Galaxies inhabiting compact groups have undergone a major transformation compared to galaxies that inhabit loose groups.
119301581
Rational approximations in analytic QCD
We consider the 'modified minimal analytic' (mMA) coupling that involves an infrared cut to the standard MA coupling. The mMA coupling is a Stieltjes function and, as a consequence, the paradiagonal Pad? approximants converge to the coupling in the entire Q2-plane except on the timelike semiaxis below the cut. The equivalence between the narrow width approximation of the discontinuity function of the coupling, on the one hand, and this Pad? (rational) approximation of the coupling, on the other hand, is shown. We approximate the analytic analogs of the higher powers of mMA coupling by rational functions in such a way that the singularity region is respected by the approximants. Several comparisons, for real and complex arguments Q2, between the exact and approximate expressions are made and the speed of convergence is discussed. Motivated by the success of these approximants, an improvement of the mMA coupling is suggested and possible uses in the reproduction of experimental data are discussed.
17504603
Using the large scale quasar clustering to constrain flat quintessential universes
Aims. We search for the most suitable set of cosmological parameters that describes the observable universe. The search includes the possibility of quintessential flat universes, i.e., the analysis is restricted to the determination of the dimensionless matter density and the quintessential parameters, $\Omega_{\rm M}$ and w Q , respectively. Methods. Our study is focused on comparing the position of features at large scales in the density fluctuation field at different redshifts by analysing the evolution of the quasar two-point correlation function. We trace the density field fluctuations at large scales using a large and homogeneous sample of quasars (~38 000 objects with 0.3  ≲ z ≤  2.4 and a median z = 1.45) drawn from the Sloan Digital Sky Survey Data Release Six. The analysis relies on the assumption that, in the linear regime, the length scale of a particular feature should remain fixed at different times of the universe for the proper cosmological model. Our study does not assume any particular comoving length scale at which a feature should be found, but intends to perform a comparison for a wide range of scales instead. This is done by quantifying the amount of overlap among the quasar correlation functions at different times using a cross-correlation technique. Results. The most likely cosmological model is $\Omega_{\rm M}$ = 0.21 ± 0.02 and w Q = -0.93 ± 0.04, in agreement with previous studies. These constraints are the result of a good overall agreement of the correlation function at different redshifts over scales ~100–300 h -1 Mpc. Conclusions. Under the assumption of a flat cosmological model, our results indicate that we are living in a low density universe with a quintessential parameter greater than the one corresponding to a cosmological constant. This work also demonstrates that a large homogeneous quasar sample can be used to tighten the constraints upon cosmological parameters.
117776477
Luminosity function of galaxies in groups in the SDSS DR7: the dependence on mass, environment and galaxy type
We perform an analysis of the luminosities of galaxies in groups in the SDSS DR7. We analyse the luminosity function (LF) as a function of group mass for different photometric bands, galaxy populations, galaxy positions within the groups, and the group surrounding large scale density. We find that M* brightens and alpha becomes steeper as a function of mass in all SDSS photometric bands, in agreement with previous results. From the analysis of different galaxy populations, we observe that different methods to split galaxy populations, based on the concentration index or the colour-magnitude diagram, produce quite different behaviours in the luminosity trends, mainly for alpha. These discrepancies and the trends with mass mentioned above are explained when analysing the LF of galaxies classified simultaneously according to their concentrations and colours. We find that only the red spheroids have a LF that strongly depends on group mass. Late type galaxies, whether blue or red, have luminosity functions that do not depend on group mass. The intrinsic change in the LF of spheroids and the varying number contributions of the different types explain all the observed trends with group mass. On the other hand, dividing the galaxy members in the inner and outer regions of the groups do not introduce a significant difference in the Schechter parameter trends, except for the characteristic absolute magnitude in the high group virial mass range (M>1x10^13 M_sun/h) which is an indication of luminosity segregation in massive groups. Finally, we also analyse the possible influence of the large scale surrounding environment on the LF. We find that galaxies inhabiting groups at low density regions experience more pronounced variations on the Schechter parameters as a function of groups mass, while galaxies in groups at high density regions show an almost constant behaviour.
118533903
The dynamical state of galaxy groups and their luminosity content
We analyse the dependence of the luminosity function (LF) of galaxies in groups on group dynamical state. We use the Gaussianity of the velocity distribution of galaxy members as a measurement of the dynamical equilibrium of groups identified in the Sloan Digital Sky Survey Data Release 7 by Zandivarez & Martinez. We apply the Anderson–Darling goodness-of-fit test to distinguish between groups according to whether they have Gaussian or non-Gaussian velocity distributions, i.e. whether they are relaxed or not. For these two subsamples, we compute the 0.1r-band LF as a function of group virial mass and group total luminosity. For massive groups, , we find statistically significant differences between the LF of the two subsamples: the LFs of groups that have Gaussian velocity distributions have a brighter characteristic absolute magnitude (∼0.3 mag) and a steeper faint-end slope (∼0.25). We detect a similar effect when comparing the LF of bright [] Gaussian and non-Gaussian groups. Our results indicate that, for massive/luminous groups, the dynamical state of the system is directly related to the luminosity of its galaxy members.
122967003
Augmented reality aiding collimator exchange at the LHC
Novel Augmented Reality techniques have the potential to have a large positive impact on the way remote maintenance operations are carried out in hazardous areas, e.g. areas where radiation doses that imply careful planning and optimization of maintenance operations are present. This paper describes an Augmented Reality strategy, system and implementation for aiding the remote collimator exchange in the LHC, currently the world׳s largest and highest-energy particle accelerator. The proposed system relies on marker detection and multi-modal augmentation in real-time. A database system has been used to ensure flexibility. The system has been tested in a mock-up facility, showing real time performance and great potential for future use in the LHC. The technical-scientific difficulties identified during the development of the system and the proposed solutions described in this paper may help the development of future Augmented Reality systems for remote handling in scientific facilities.
56302496
Design, analysis, and fabrication of the APT cavities
The design for the superconducting cavities of the high-energy accelerator for the Accelerator Production of Tritium (APT) project has been extensively changed in the last two years. The original accelerator design incorporated 0.48 and 0.71 beta cavities with stiffeners, and a stainless-steel helium vessel. Today, the accelerator uses unstiffened 0.64 and 0.82 beta cavities, and a titanium helium vessel. This paper discusses the design process, including the supporting analyses, prototype cavities built, and the decisions made to support the current design. The design of the integrated cavity-helium vessel is presented. Future plans and testing for design validation are also discussed.
122910167
Implications of Yukawa textures in the neutral Higgs decays within the 2HDM–III
We discuss the implications of assuming a four–zero Yukawa ansatz for the neutral Higgs decays, within the context of the general 2–Higgs Doublet Model of type III. We begin by presenting a detailed analysis of the neutral Higgs boson couplings with fermions and gauge bosons and the resulting effects on its decays. In particular, we are interested on the possibility of the neutral Higgs boson production in current colliders.
14875226
Galaxy groups in the 2dF Galaxy Redshift Survey: a compactness analysis of groups
A comprehensive study on compactness has been carried out on the 2dF Galaxy Group Catalogue constructed by Merchan and Zandivarez. The compactness indices defined in this work take into account different geometrical constraints in order to explore a wide range of possibilities. Our results show that there is no clear distinction between groups with high and low levels of compactness when considering particular properties such as the radial velocity dispersion, the relative fraction of galaxies per spectral type, and the luminosity functions of their galaxy members. Studying the trend of the fraction of galaxies per spectral type as a function of the dimensionless crossing time, some signs of dynamical evolution are observed. From the comparison with previous works on compactness, we realize that special care should be taken for some compactness criteria definitions in order to avoid possible biases in the identification.
18387503
Galaxy groups in the 2dF Galaxy Redshift Survey: effects of environment on star formation
We estimate the fraction of star-forming galaxies in a catalogue of groups, constructed from the 2dF Galaxy Redshift Survey by Merchan & Zandivarez. We use the η spectral type parameter of galaxies and subdivide the sample of galaxies in groups into four types depending on the values of the η parameter following Madgwick et al. We obtain a strong correlation between the relative fraction of galaxies with high star formation and the parent group virial mass. We find that even in the environment of groups with low virial mass M∼1013 M⊙ the star formation of their member galaxies is significantly suppressed. The relation between the fraction of early-type galaxies and the group virial mass obeys a simple power law spanning over three orders of magnitude in virial mass. Our results show quantitatively the way that the presence of galaxies with high star formation rates is inhibited in massive galaxy systems.