Chemical evolution of classical and ultra-faint dwarf spheroidal galaxies

This article has been accepted for publication in Monthly Notices of the Royal Astronomical Society ©: 2014 The Author(s). Published by Oxford University Press on behalf of the Royal Astronomical Society. All rights reservedPeer reviewedFinal Published versio

Chemical evolution of local galaxies in a hierarchical model

We investigate the chemical properties of local galaxies within a cosmological framework in the hierarchical picture of galaxy formation. To this aim, we use a hierarchical semi-analytic model which includes the contribution from (i) low and intermediate mass stars, (ii) type Ia Supernovae (SNe) and (iii) massive stars. - Abridged - We compare our predictions with available observations in the Milky Way (MW), in local dwarf galaxies and in local ellipticals. For Milky-Way-like galaxies, we can successfully reproduce the [O-Fe] vs [Fe/H] relation observed in disc stars and the stellar metallicity distribution (SMD). For dwarf galaxies, the stellar metallicity vs mass relation is reproduced by assuming that a substantial fraction of the heavy elements is lost through metal-enhanced outflows and a type Ia SN realization probability lower than the one of MW-like galaxies. - Abridged - In ellipticals, the observations indicate higher [alpha/Fe] values in larger galaxies. - Abridged - Our results computed with a standard Salpeter initial mass function (IMF) indicate a flat [alpha/Fe]-sigma relation. However, we suggest a possible solution to this problem and show how, by assuming a star formation-dependent IMF with a slope x=1.35 in systems with star formation rates < 100 M_sun/yr and slightly flatter (i.e. with x=1) in object with stronger star formation, the observed correlation between [alpha/Fe] and sigma can be accounted for on a large velocity dispersion range. Fundamental roles are played also by interaction-triggered starbursts and AGN.Comment: MNRAS, accepted, 27 pages, 22 figure

Measurement of the KL meson lifetime with the KLOE detector

We present a measurement of the KL lifetime using the KLOE detector. From a sample of 4 x 10^8 KS KL pairs following the reaction e+ e- -> phi -> KS KL we select 15 x 10^6 KL -> p0 p0 p0 decays tagged by KS -> pi+ pi- events. From a fit of the proper time distribution we find tau_L = (50.92 +- 0.17{stat} +- 0.25{syst})$ ns. This is the most precise measurement of the KL lifetime performed to date.Comment: 14 pages, 14 figure

Study of the a_0(980) meson via the radiative decay phi->eta pi^0 gamma with the KLOE detector

We have studied the phi->a_0(980) gamma process with the KLOE detector at the Frascati phi-factory DAPhNE by detecting the phi->eta pi^0 gamma decays in the final states with eta->gamma gamma and eta->pi^+ pi^- pi^0. We have measured the branching ratios for both final states: Br(phi->eta pi^0 gamma)=(7.01 +/- 0.10 +/- 0.20)x10^-5 and (7.12 +/- 0.13 +/- 0.22)x10^-5 respectively. We have also extracted the a_0(980) mass and its couplings to eta pi^0, K^+ K^-, and to the phi meson from the fit of the eta pi^0 invariant mass distributions using different phenomenological models.Comment: 17 pages, 6 figures, submitted to Physics Letters B. Corrected typos in eq.

Study of the process e+e- -> omega pi0 in the phi-meson mass region with the KLOE detector

We have studied the e+e- -> omegapi0 cross section in the sqrt(s) interval 1000-1030 MeV using the pi+pi-pi0pi0 and pi0pi0gamma final states with a sample of ~600 pb^-1 collected with the KLOE detector at DAFNE. By fitting the observed interference pattern around M_phi for both final states, we extract the ratio of the decay widths Gamma(omega->pi0gamma)/Gamma(omega->pi+pi-pi0) = 0.0897 +- 0.0016 and derive the branching fractions BR(omega -> pi+pi-pi0)= (90.24 +- 0.19)%, BR(omega -> pi0gamma) = (8.09 +- 0.14)%. The parameters describing the e+e- -> omegapi0 reaction around M_\phi are also used to extract the branching fraction for the OZI and G-parity violating phi -> omegapi0 decay: BR(phi->omegapi0) = (4.4 +- 0.6)x10^-5.Comment: 12 Pages, 4 figures, submitted to Physics Letter

Search for the K_S -> e+e- decay with the KLOE detector

We present the result of a direct search for the decay K_S -> e+e-, obtained with a sample of e+e- -> phi -> K_S K_L events produced at DAFNE, the Frascati phi-factory, for an integrated luminosity of 1.9 fb^-1. The search has been performed using a pure K_S beam tagged by the simultaneous detection of a K_L interaction in the calorimeter. Background rejection has been optimized by using both kinematic and particle identification cuts. We find BR(K_S -> e+e-) < 9x10^-9 at 90% CL, which improves by an order of magnitude on the previous best limit.Comment: 13 pages, 11 figures, submitted to Physics Letters

A Study of the Radiative Ke3 Decay and Search for Direct Photon Emission with the KLOE Detector

We present a measurement of the ratio R = \Gamma(\keg;\Estar>30\mev,\qstar>20^\circ)$/$\Gamma(\kegf)$and a first measurement of the direct emission contribution in KL semileptonic decays. The measurement is done at the DAFNE phi-factory selecting phi->KL KS decays with the KLOE detector. We use 328 pb^{-1}$ of data corresponding to about 3.5 million Ke3(g) events and about 9000 radiative events. Our result is R=(924 +/- 23(stat) +/-16(syst)10^{-5} for the branching ratio and X=-2.3 +/- 1.3(stat) +/- 1.4(syst) for the parameter describing direct emission.Comment: 8 pages, 7 figure

A global fit to determine the pseudoscalar mixing angle and the gluonium content of the eta' meson

We update the values of the eta-eta' mixing angle and of the eta' gluonium content by fitting our measurement R_phi = BR(phi to eta' gamma)/ BR(phi to eta gamma) together with several vector meson radiative decays to pseudoscalars (V to P gamma), pseudoscalar mesons radiative decays to vectors (P to V gamma) and the eta' to gamma gamma, pi^0 to gamma gamma widths. From the fit we extract a gluonium fraction of Z^2_G = 0.12 +- 0.04, the pseudoscalar mixing angle psi_P = (40.4 +- 0.6) degree and the phi-omega mixing angle psi_V = (3.32 +- 0.09) degree. Z^2_G and psi_P are fairly consistent with those previously published. We also evaluate the impact on the eta' gluonium content determination of future experimental improvements of the eta' branching ratios and decay width.Comment: 13 pages, 7 figures to submit to JHE

Cardiac overexpression of melusin protects from dilated cardiomyopathy due to long-standing pressure overload.

We have previously shown that genetic ablation of melusin, a muscle specific beta 1 integrin interacting protein, accelerates left ventricle (LV) dilation and heart failure in response to pressure overload. Here we show that melusin expression was increased during compensated cardiac hypertrophy in mice subjected to 1 week pressure overload, but returned to basal levels in LV that have undergone dilation after 12 weeks of pressure overload. To better understand the role of melusin in cardiac remodeling, we overexpressed melusin in heart of transgenic mice. Echocardiography analysis indicated that melusin over-expression induced a mild cardiac hypertrophy in basal conditions (30% increase in interventricular septum thickness) with no obvious structural and functional alterations. After prolonged pressure overload (12 weeks), melusin overexpressing hearts underwent further hypertrophy retaining concentric LV remodeling and full contractile function, whereas wild-type LV showed pronounced chamber dilation with an impaired contractility. Analysis of signaling pathways indicated that melusin overexpression induced increased basal phosphorylation of GSK3beta and ERK1/2. Moreover, AKT, GSK3beta and ERK1/2 were hyper-phosphorylated on pressure overload in melusin overexpressing compared with wild-type mice. In addition, after 12 weeks of pressure overload LV of melusin overexpressing mice showed a very low level of cardiomyocyte apoptosis and stromal tissue deposition, as well as increased capillary density compared with wild-type. These results demonstrate that melusin overexpression allows prolonged concentric compensatory hypertrophy and protects against the transition toward cardiac dilation and failure in response to long-standing pressure overload