DSpace Community:
http://hdl.handle.net/2445/7503
2019-01-24T04:25:51ZGalaxy and mass assembly (GAMA): refining the local galaxy merger rate using morphological information
http://hdl.handle.net/2445/127513
Title: Galaxy and mass assembly (GAMA): refining the local galaxy merger rate using morphological information
Author: Casteels, Kevin R. V; Conselice, Christopher J.; Bamford, Steven P.; Salvador Solé, Eduard; Norberg, Peder R.; Agius, Nicola K.; Baldry, Ivan; Brough, Sarah; Brown, Michael J. I.; Drinkwater, Michael J.; Driver, Simon P; Graham, Alister W.; Bland Hawthorn, Joss; Hopkins, Andrew M.; Kelvin, Lee S.; López Sánchez, Angel R.; Loveday, Jon; Robotham, Aaron S. G.; Vázquez Mata, José A.
Abstract: We use the Galaxy And Mass Assembly (GAMA) survey to measure the local Universe mass dependent merger fraction and merger rate using galaxy pairs and the CAS structural method, which identifies highly asymmetric merger candidate galaxies. Our goals are to determine which types of mergers produce highly asymmetrical galaxies, and to provide a new measurement of the local galaxy major merger rate. We examine galaxy pairs at stellar mass limits down to $M_{*} = 10^{8}M_{\odot}$ with mass ratios of $<$100:1 and line of sight velocity differences of $\Delta V<500$ km s$^{-1}$. We find a significant increase in mean asymmetries for projected separations less than the sum of the individual galaxy's Petrosian 90 radii. For systems in major merger pairs with mass ratios of $<$4:1 both galaxies in the pair show a strong increase in asymmetry, while in minor merger systems (with mass ratios of $>$4:1) the lower mass companion becomes highly asymmetric, while the larger galaxy is much less affected. The fraction of highly asymmetric paired galaxies which have a major merger companion is highest for the most massive galaxies and drops progressively with decreasing mass. We calculate that the mass dependent major merger fraction is fairly constant at $\sim1.3-2\%$ between $10^{9.5}<M_{*}<10^{11.5} M_{\odot}$, and increases to $\sim4\%$ at lower masses. When the observability time scales are taken into consideration, the major merger rate is found to approximately triple over the mass range we consider. The total co-moving volume major merger rate over the range $10^{8.0}<M_{*}<10^{11.5} M_{\odot}$ is $(1.2 \pm 0.5) \times 10^{-3}$ $h^{3}_{70}$ Mpc$^{-3}$ Gyr$^{-1}$.2019-01-22T12:32:26ZSelf-bound ultradilute Bose mixtures within local density approximation
http://hdl.handle.net/2445/126725
Title: Self-bound ultradilute Bose mixtures within local density approximation
Author: Ancilotto, Francesco; Barranco Gómez, Manuel; Guilleumas, Montserrat; Pi Pericay, Martí
Abstract: We have investigated self-bound ultradilute bosonic binary mixtures at zero temperature within density functional theory using a local density approximation. We provide the explicit expression of the Lee-Huang-Yang correction in the general case of heteronuclear mixtures, and investigate the general thermodynamic conditions which lead to the formation of self-bound systems. We have determined the conditions for stability against the evaporation of one component, as well as the mechanical and diffusive spinodal lines. We have also calculated the surface tension of the self-bound state as a function of the interspecies interaction strength. We find that relatively modest variations of the latter result in order-of-magnitude changes in the calculated surface tension. We suggest experimental realizations which might display the metastability and phase separation of the mixture when entering regions of the phase diagram characterized by negative pressures. Finally, we show that these droplets may sustain stable vortex and vortex pairs.2018-12-04T16:46:37ZTransport peak in thermal spectral function of N=4 supersymmetric Yang-Mills plasma at intermediate coupling
http://hdl.handle.net/2445/126144
Title: Transport peak in thermal spectral function of N=4 supersymmetric Yang-Mills plasma at intermediate coupling
Author: Casalderrey Solana, Jorge; Grozdanov, Saso; Starinets, Andrei O.
Abstract: We study the structure of thermal spectral function of the stress-energy tensor in N=4 supersymmetric Yang-Mills theory at intermediate 't Hooft coupling and infinite number of colors. In gauge-string duality, this analysis reduces to the study of classical bulk supergravity with higher-derivative corrections, which correspond to (inverse) coupling corrections on the gauge theory side. We extrapolate the analysis of perturbative leading-order corrections to intermediate coupling by nonperturbatively solving the equations of motion of metric fluctuations dual to the stress-energy tensor at zero spatial momentum. We observe the emergence of a separation of scales in the analytic structure of the thermal correlator associated with two types of characteristic relaxation modes. As a consequence of this separation, the associated spectral function exhibits a narrow structure in the small frequency region which controls the dynamics of transport in the theory and may be described as a transport peak typically found in perturbative, weakly interacting thermal field theories. We compare our results with generic expectations drawn from perturbation theory, where such a structure emerges as a consequence of the existence of quasiparticles.2018-11-15T14:43:36ZGaia Data Release 1: Summary of the astrometric, photometric and survey properties
http://hdl.handle.net/2445/125903
Title: Gaia Data Release 1: Summary of the astrometric, photometric and survey properties
Author: Gaia Collaboration; Mor Crespo, Roger; Romero Gómez, Mercè; González Vidal, Juan José; Portell i de Mora, Jordi; Jordi i Nebot, Carme; Luri Carrascoso, Xavier; Masana Fresno, Eduard; Torra Roca, Jorge; Balaguer Núñez, María de los Dolores; Fabricius, Claus; Figueras Siñol, Francesca; Fries, Aidan; Castañeda Pons, Javier Bernardo; Carrasco Martínez, José Manuel; Gràcia Abril, G.; Antiche Garzón, Erika; Borrachero, R.; Clotet Altarriba Marcial; Farràs Casas, M.; Garralda, N.; Gúrpide Lasheras, Andrés; Soria Nieto Sergio; Voss, H.; Weiler, Michael; Anglada Escudé, G.; Gallardo, E.; Isasi Parache, Y.; Julbe, F.; Molina Martínez, Daniel; Gebran, M.; Martínez Rubí, O.; Palmer, Max; Peralta, J.; Valles, P.
Abstract: Context. At about 1000 days after the launch of Gaia we present the first Gaia data release, Gaia DR1, consisting of astrometry and photometry for over 1 billion sources brighter than magnitude 20.7. Aims. A summary of Gaia DR1 is presented along with illustrations of the scientific quality of the data, followed by a discussion on the limitations due to the preliminary nature of this release. Methods. The raw data collected by Gaia during the first 14 months of the mission have been processed by the Gaia Data Processing and Analysis Consortium (DPAC) and turned into an astrometric and photometric catalogue. Results. Gaia DR1 consists of three components: a primary astrometric data set which contains the positions, parallaxes, and mean proper motions for about 2 million of the brightest stars in common with the Hipparcos and Tycho-2 catalogues - a realisation of the Tycho-Gaia Astrometric Solution (TGAS) - and a secondary astrometric data set containing the positions for an additional 1.1 billion sources. The second component is the photometric data set, consisting of mean G-band magnitudes for all sources. The G-band light curves and the characteristics of ∼ 3000 Cepheid and RR-Lyrae stars, observed at high cadence around the south ecliptic pole, form the third component. For the primary astrometric data set the typical uncertainty is about 0.3 mas for the positions and parallaxes, and about 1 mas yr−1for the proper motions. To the parallax uncertainties a systematic component of ∼ 0.3 mas should be added. For the subset of ∼ 94 000 Hipparcos stars in the primary data set the proper motions are much more precise, at about 0.06 mas yr−1 . For the secondary astrometric data set the typical uncertainty of the positions is ∼ 10 mas. The median uncertainties on the mean G-band magnitudes range from the mmag level to ∼ 0.03 mag over the magnitude range 5 to 20.7. Conclusions. Gaia DR1 is an important milestone ahead of the next Gaia data release, which will feature 5-parameter astrometry for all sources. Extensive validation shows that Gaia DR1 represents a major advance in the mapping of the heavens and the availability of basic stellar data that underpin observational astrophysics. Nevertheless the very preliminary nature of this first Gaia data release does lead to a number of important limitations to the data quality which should be carefully considered before drawing conclusions from the data.2018-11-08T12:13:32ZAn Extension of Poincaré group based on generalized Fermi-Walker coordinates
http://hdl.handle.net/2445/125474
Title: An Extension of Poincaré group based on generalized Fermi-Walker coordinates
Author: Llosa, Josep
Abstract: The class of accelerated and rotating reference frames has been studied on the basis of generalized Fermi-Walker coordinates. We obtain the infinitesimal transformations connecting any two of these frames and also their commutation relations. We thus have an infinite dimensional extension of the Poincaré algebra and, although it turns out to be Abelian extension, and hence trivial, it is noteworthy that, contrarily to Lorentz boosts, acceleration and rotational boost generators commute with each other and with the generators of Poincaré group as well2018-10-19T17:04:53ZBound states of dark solitons and vortices in trapped multidimensional Bose-Einstein condensates
http://hdl.handle.net/2445/125441
Title: Bound states of dark solitons and vortices in trapped multidimensional Bose-Einstein condensates
Author: Morera Navarro, I.; Guilleumas, M.; Mayol, R.; Muñoz Mateo, A.
Abstract: We report on the existence and stability of multidimensional bound solitonic states in harmonically trapped scalar Bose-Einstein condensates. Their equilibrium separation, as a measure of the strength of the soliton- soliton or the solitonic vortex-vortex interaction, is provided for varying chemical potential μ. Static bound dark solitons are shown to be dynamically stable in elongated condensates within a range of intermediate (repulsive) interparticle-interaction strength. Beyond this range the snaking instability manifests during the time evolution of the planar solitons and produces the decay into nonstationary vortex states. A subsequent dynamical recurrence of solitons and vortices can be observed at low μ. At equilibrium, the bifurcations of bound dark solitons are bound solitonic vortices. Among them, both two-open and two-ring vortex lines are demonstrated to exist with both counter- and co-rotating steady velocity fields. The latter flow configurations evolve, for high chemical potential, into a stationary three-dimensional (3D)-chain-shaped vortex and a three vortex-antivortex-vortex ring sequence that arrest the otherwise increasing angular or linear momentum respectively. As a feature common to the bifurcated families of vortex states, their excitation spectra present unstable modes with associated oscillatory dynamics. In spite of this, the family of two-open counter-rotating vortices support dynamically stable 3D states.2018-10-18T16:38:00ZPrecise measurement of the e+e−→π+π−(γ) cross section with the initial state radiation method at BABAR
http://hdl.handle.net/2445/125031
Title: Precise measurement of the e+e−→π+π−(γ) cross section with the initial state radiation method at BABAR
Author: Aubert, B.; Graugés Pous, Eugeni; BABAR Collaboration
Abstract: A precise measurement of the cross section of the process eþe ! þ ðÞ from threshold to an energy of 3 GeV is obtained with the initial state radiation (ISR) method using 232 fb 1 of data collected with the BABAR detector at eþe center-of-mass energies near 10.6 GeV. The ISR luminosity is determined from a study of the leptonic process eþe ! þ ðÞ. The leading-order hadronic contribution to the muon magnetic anomaly calculated using the cross section measured from threshold to 1.8 GeV is ð514:1 2:2ðstatÞ 3:1ðsystÞÞ 10 10.2018-10-03T12:22:17ZMeasurement of B→K∗(892)γ branching fractions and CP and isospin asymmetry
http://hdl.handle.net/2445/125030
Title: Measurement of B→K∗(892)γ branching fractions and CP and isospin asymmetry
Author: BABAR Collaboration; Aubert, B.; Graugés Pous, Eugeni
Abstract: We present an analysis of the decays B0→K*0(892)γ and B+→K*+(892)γ using a sample of about 383×106 B¯¯¯B events collected with the BABAR detector at the PEP-II symmetric energy B factory. We measure the branching fractions B(B0→K*0γ)=(4.47±0.10±0.16)×1− 5 and B (B+→K*+γ)=(4.22±0.14±0.16)×10−5. We constrain the direct CP asymmetry to be −0.033<A(B→K∗γ)<0.028 and the isospin asymmetry to be 0.017<Δ0−<0.116, where the limits are determined by the 90% confidence interval and include both the statistical and systematic uncertainties.2018-10-03T12:12:53ZSearches for lepton flavor violation in the decays tau+- --> e+- gamma and tau+- --> mu+- gamma
http://hdl.handle.net/2445/124892
Title: Searches for lepton flavor violation in the decays tau+- --> e+- gamma and tau+- --> mu+- gamma
Author: Garra Tico, J.; Graugés Pous, Eugeni; BABAR Collaboration
Abstract: Searches for lepton flavor violating decay of a tau lepton to a lighter mass lepton and a photon have been performed with the full dataset of (963 +- 7) x 10^6 tau decays collected by the BaBar detector near the Upsilon(4S), Upsilon(3S) and Upsilon(2S) resonances. The searches yield no evidence of signals and we set upper limits on the branching fractions of BR(tau -> e gamma) < 3.3 x 10^-8 and BR(tau -> mu gamma) < 4.4 x 10^-8 at 90% confidence level.2018-09-27T15:26:33ZTest of lepton universality in Upsilon(1S) decays at BaBar
http://hdl.handle.net/2445/124889
Title: Test of lepton universality in Upsilon(1S) decays at BaBar
Author: Garra Tico, J.; Graugés Pous, Eugeni; BABAR Collaboration
Abstract: The ratio Rtau mu(Υ(1S))=ΓΥ(1S)-->tau+tau-/GammaΥ(1S)-->mu+mu- is measured using a sample of (121.8±1.2)×10[superscript 6]Υ(3S) events recorded by the BABAR detector. This measurement is intended as a test of lepton universality and as a search for a possible light pseudoscalar Higgs boson. In the standard model (SM) this ratio is expected to be close to 1. Any significant deviations would violate lepton universality and could be introduced by the coupling to a light pseudoscalar Higgs boson. The analysis studies the decays Υ(3S)-->Υ(1S)pi+pi-, Υ(1S)→l+l-, where l=mu, tau. The result, Rtau mu(Υ(1S))=1.005±0.013(stat)±0.022(syst), shows no deviation from the expected SM value, while improving the precision with respect to previous measurements.2018-09-27T15:11:03Z