12,906 research outputs found

    Extended Modified Observable Technique for a Multi-Parametric Trilinear Gauge Coupling Estimation at LEP II

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    This paper describes the extension of the Modified Observables technique in estimating simultaneously more than one Trilinear Gauge Couplings. The optimal properties, unbiasedness and consistent error estimation of this method are demonstrated by Monte Carlo experimentation using νjj\ell \nu jj four-fermion final state topologies. Emphasis is given in the determination of the expected sensitivities in estimating the λγΔg1z\lambda_{\gamma} - \Delta g_{1}^{z} and ΔkγΔg1z\Delta k_{\gamma} - \Delta g_{1}^{z} pair of couplings with data from the 183 GeV LEPII run.Comment: (17 pages, 8 figures

    Bar pattern speed evolution over the last 7 Gyr

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    The tumbling pattern of a bar is the main parameter characterising its dynamics. From numerical simulations, its evolution since bar formation is tightly linked to the dark halo in which the bar is formed through dynamical friction and angular momentum exchange. Observational measurements of the bar pattern speed with redshift can restrict models of galaxy formation and bar evolution. We aim to determine, for the first time, the bar pattern speed evolution with redshift based on morphological measurements. We have selected a sample of 44 low inclination ringed galaxies from the SDSS and COSMOS surveys covering the redshift range 0 <z< 0.8 to investigate the evolution of the bar pattern speed. We have derived morphological ratios between the deprojected outer ring radius (R_{ring}) and the bar size (R_{bar}). This quantity is related to the parameter {\cal R}=R_{CR}/R_{bar} used for classifiying bars in slow and fast rotators, and allow us to investigate possible differences with redshift. We obtain a similar distribution of RR at all redshifts. We do not find any systematic effect that could be forcing this result. The results obtained here are compatible with both, the bulk of the bar population (~70%) being fast-rotators and no evolution of the pattern speed with redshift. We argue that if bars are long-lasting structures, the results presented here imply that there has not been a substantial angular momentum exchange between the bar and halo, as predicted by numerical simulations. In consequence, this might imply that the discs of these high surface-brightness galaxies are maximal.Comment: Accepted for publication in A&

    The stellar host in star-forming low-mass galaxies: Evidence for two classes

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    The morphological evolution of star-forming galaxies provides important clues to understand their physical properties, as well as the triggering and quenching mechanisms of star formation. We aim at connecting morphology and star-formation properties of low-mass galaxies (median stellar mass \sim 108.5^{8.5} M_{\odot}) at low redshift (z<0.36z<0.36). We use a sample of medium-band selected star-forming galaxies from the GOODS-North field. Hα\alpha images for the sample are created combining both spectral energy distribution fits and HST data. Using them, we mask the star forming regions to obtain an unbiased two-dimensional model of the light distribution of the host galaxies. For this purpose we use PHI\texttt{PHI}, a new Bayesian photometric decomposition code. We apply it independently to 7 HST bands assuming a S\'ersic surface brightness model. Star-forming galaxy hosts show low S\'ersic index (with median nn \sim 0.9), as well as small sizes (median ReR_e \sim 1.6 kpc), and negligible change of the parameters with wavelength (except for the axis ratio, which grows with wavelength). Using a clustering algorithm, we find two different classes of star-forming galaxies: A more compact, redder, and high-nn (class A) and a more extended, bluer and lower-nn one (class B). We also find evidence that the first class is more spheroidal-like. In addition, we find that 48% of the analyzed galaxies present negative color gradients (only 5% are positive). The host component of low-mass star-forming galaxies at z<0.36z<0.36 separates into two different classes, similar to what has been found for their higher mass counterparts. The results are consistent with an evolution from class B to class A. Several mechanisms from the literature, like minor and major mergers, and violent disk instability, can explain the physical process behind the likely transition between the classes. [abridged]Comment: Accepted for publication in Astronomy & Astrophysics. 13 pages, 11 figure

    Home Country Bias: Does Domestic Experience Help Investors Enter Foreign Markets?

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    This paper investigates whether investors' domestic experience helps them enter foreign markets. We show that investors first invest in domestic securities and only some time later they invest abroad in foreign securities. We also show that investors who trade more often in the domestic market start to invest abroad earlier. Our findings suggest that the experience investors acquire while they trade in the domestic market is a key reason why active investors enter the foreign market earlier. A reason is that highly educated investors as well as investors with more financial knowledge, arguably those for whom learning by trading is the least important, do not need to trade as much in the domestic market before they start investing in foreign securities. Another reason is that investors who start investing in foreign securities are able to improve on their performance afterwards. This improvement in performance constitutes further evidence that the home country bias is costly, thereby confirming that there are gains for investors from investing abroad.Learning, home country bias, duration analysis.
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