467 research outputs found

    <VAP> Green Function in the Resonance Region

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    We analyse the three-point function of vector, axial-vector and pseudoscalar currents. In the spirit of large N_C, a resonance dominated Green function is confronted with the leading high-energy behaviour from the operator product expansion. The matching is shown to be fully compatible with a chiral resonance Lagrangian and it allows to determine some of the chiral low-energy constants of O(p^6).Comment: 13 pages, 2 figures. Published version. Results and conclusions unchange

    V(us) Determination from Hyperon Semileptonic Decays

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    We analyze the numerical determination of the quark mixing factor V(us) from hyperon semileptonic decays. The discrepancies between the results obtained in two previous studies are clarified. Our fits indicate sizeable SU(3) breaking corrections, which unfortunately can only be fully determined from the data at the first order. The lack of a reliable theoretical calculation of second-order symmetry breaking effects translates into a large systematic uncertainty, which has not been taken into account previously. Our final result, V(us) = 0.226 +/- 0.005, is not competitive with the existing determinations from K(l3), K(l2) and \tau decays.Comment: 16 pages, no figures. References added and other minor change

    Neutrinoless Double Beta Decay and Lepton Flavor Violation

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    We point out that extensions of the Standard Model with low scale (~TeV) lepton number violation (LNV) generally lead to a pattern of lepton flavor violation (LFV) experimentally distinguishable from the one implied by models with GUT scale LNV. As a consequence, muon LFV processes provide a powerful diagnostic tool to determine whether or not the effective neutrino mass can be deduced from the rate of neutrinoless double beta decay. We discuss the role of \mu -> e \gamma and \mu -> e conversion in nuclei, which will be studied with high sensitivity in forthcoming experiments.Comment: 4 pages, 3 figure

    The Human SLC25A33 and SLC25A36 Genes of Solute Carrier Family 25 Encode Two Mitochondrial Pyrimidine Nucleotide Transporters

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    The human genome encodes 53 members of the solute carrier family 25 (SLC25), also called the mitochondrial carrier family, many of which have been shown to transport inorganic anions, amino acids, carboxylates, nucleotides, and coenzymes across the inner mitochondrial membrane, thereby connecting cytosolic and matrix functions. Here two members of this family, SLC25A33 and SLC25A36, have been thoroughly characterized biochemically. These proteins were overexpressed in bacteria and reconstituted in phospholipid vesicles. Their transport properties and kinetic parameters demonstrate that SLC25A33 transports uracil, thymine, and cytosine (deoxy)nucleoside di- and triphosphates by an antiport mechanism and SLC25A36 cytosine and uracil (deoxy)nucleoside mono-, di-, and triphosphates by uniport and antiport. Both carriers also transported guanine but not adenine (deoxy)nucleotides. Transport catalyzed by both carriers was saturable and inhibited by mercurial compounds and other inhibitors of mitochondrial carriers to various degrees. In confirmation of their identity (i) SLC25A33 and SLC25A36 were found to be targeted to mitochondria and (ii) the phenotypes of Saccharomyces cerevisiae cells lacking RIM2, the gene encoding the well characterized yeast mitochondrial pyrimidine nucleotide carrier, were overcome by expressing SLC25A33 or SLC25A36 in these cells. The main physiological role of SLC25A33 and SLC25A36 is to import/export pyrimidine nucleotides into and from mitochondria, i.e. to accomplish transport steps essential for mitochondrial DNA and RNA synthesis and breakdown

    Monitoring urban heat island through google earth engine. Potentialities and difficulties in different cities of the United States

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    The aim of this work is to exploit the large-scale analysis capabilities of the innovative Google Earth Engine platform in order to investigate the temporal variations of the Urban Heat Island phenomenon as a whole. A intuitive methodology implementing a large-scale correlation analysis between the Land Surface Temperature and Land Cover alterations was thus developed. The results obtained for the Phoenix MA are promising and show how the urbanization heavily affects the magnitude of the UHI effects with significant increases in LST. The proposed methodology is therefore able to efficiently monitor the UHI phenomenon

    pi/K -> e nu branching ratios to O(e^2 p^4) in Chiral Perturbation Theory

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    We calculate the ratios R_{e/mu}^{(P)} = Gamma(P -> e nu)/Gamma (P -> mu nu) (P=pi,K) in Chiral Perturbation Theory to order e^2 p^4. We complement the one- and two-loop effective theory results with a matching calculation of the local counterterm, performed within the large-NCN_C expansion. We find R_{e/mu}^{(\pi)} = (1.2352 \pm 0.0001)*10^{-4} and R_{e/mu}^{(K)} = (2.477 \pm 0.001)*10^{-5}, with uncertainty induced by the matching procedure and chiral power counting. Given the sensitivity of upcoming new measurements, our results provide a clean baseline to detect or constrain effects from weak-scale new physics in these rare decays. As a by-product, we also update the theoretical analysis of the individual pi/K -> \ell nu modes.Comment: 40 pages, 4 figures, 3 table

    New limits on top squark NLSP from ATLAS 4.7 fb1fb^{-1} data

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    Using the ATLAS 4.7 fb1fb^{-1} data on new physics search in the jets + \met channel, we obtain new limits on the lighter top squark (t~1\tilde t_1) considering all its decay modes assuming that it is the next to lightest supersymmetric particle (NLSP). If the decay \lstop \ra c \lspone dominates and the production of dark matter relic density is due to NLSP - LSP co-annihilation then the lower limit on \mlstop is 240 GeV. The limit changes to 200 GeV if the decay \lstop \ra b W \lspone dominates. Combining these results it follows that \lstop NLSP induced baryogenesis is now constrained more tightly.Comment: 9 pages, 2 figures, published in MPL

    Comment on `Analysis of O(p^2) Corrections to <2pi|Q_{7,8}|K>'

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    We extend in several respects our earlier work on O(p^2) corrections to matrix elements of the electroweak penguin operator O_{ewp}. First, to facilitate comparison with certain lattice studies we calculate O(p^2) corrections to in the SU(3) limit of equal light quark masses. Next, we demonstrate how an apparent disagreement in the literature regarding whether higher order chiral contributions increase or decrease is simply a consequence of how the leading order chiral amplitude is defined. Finally, we address an aspect of the epsilon'/epsilon problem by estimating O(p^2) corrections to recent determinations of which were carried out in the chiral limit.Comment: 6 pages, Reference added and typo correcte

    An updated analysis of eps'/eps in the standard model with hadronic matrix elements from the chiral quark model

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    We discuss the theoretical and experimental status of the CP violating ratio eps'/eps. We revise our 1997 standard-model estimate-based on hadronic matrix elements computed in the chiral quark model up to O(p^4) in the chiral expansion-by including an improved statistical analysis of the uncertainties and updated determination of the Cabibbo-Kobayashi-Maskawa elements and other short-distance parameters. Using normal distributions for the experimental input data we find Re eps'/eps = (2.2 \pm 0.8) x 10^{-3}, whereas a flat scanning gives 0.9 x 10^{-3} < Re eps'/eps < 4.8 x 10^{-3}. Both results are in agreement with the current experimental data. The key element in our estimate is, as before, the fit of the Delta I=1/2 rule, which allows us to absorb most of the theoretical uncertainties in the determination of the model-dependent parameters in the hadronic matrix elements. Our semi-phenomenological approach leads to numerical stability against variations of the renormalization scale and scheme dependence of the short- and long-distance components. The same dynamical mechanism at work in the selection rule also explains the larger value obtained for \ratio with respect to other estimates. A coherent picture of K -> pi pi decays is thus provided.Comment: 15 pages, 11 figures, RevTeX, discussion updated, refs adde

    Lepton Flavor Violation without Supersymmetry

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    We study the lepton flavor violating (LFV) processes mu -> e gamma, mu -> 3e, and mu -> e conversion in nuclei in the left-right symmetric model without supersymmetry and perform the first complete computation of the LFV branching ratios B(mu -> f) to leading non-trivial order in the ratio of left- and right-handed symmetry breaking scales. To this order, B(mu -> e gamma) and B(mu -> e) are governed by the same combination of LFV violating couplings, and their ratio is naturally of order unity. We also find B(mu -> 3 e)/B(mu -> e) \sim 100 under slightly stronger assumptions. Existing limits on the branching ratios already substantially constrain mass splittings and/or mixings in the heavy neutrino sector. When combined with future collider studies and precision electroweak measurements, improved limits on LFV processes will test the viability of low-scale, non-supersymmetric LFV scenarios.Comment: 24 pages, 7 figures, 2 table
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