9,572 research outputs found

    Flavor Delta(54) in SU(5) SUSY Model

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    We design a supersymmetric SU (5) GUT model using \Delta (54), a finite non-abelian subgroup of SU (3)f . Heavy right handed neutrinos are introduced which transform as three-dimensional repre-sentation of our chosen family group. The model successfully reproduces the mass hierarchical mass structures of the Standard Model, and the CKM mixing matrix. It then provides predictions for the light neutrino with a normal hierarchy and masses such that m{\nu},1 \approx 5\times10-3 eV, m{\nu}, 2 \approx 1\times 10-2 eV, and m{\nu},3 \approx 5 \times 10-2 eV. We also provide predictions for masses of the heavy neutrinos, and correc- tions to the tri-bimaximal matrix that fit within experimental limits, e.g. a reactor angle of -7.31o. A simple modification to our model is introduced at the end and is shown to also produce predictions that fall well within those limits.Comment: 22 page

    Investigation of HNCO isomers formation in ice mantles by UV and thermal processing: an experimental approach

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    Current gas phase models do not account for the abundances of HNCO isomers detected in various environments, suggesting a formation in icy grain mantles. We attempted to study a formation channel of HNCO and its possible isomers by vacuum-UV photoprocessing of interstellar ice analogues containing H2_2O, NH3_3, CO, HCN, CH3_3OH, CH4_4, and N2_2 followed by warm-up, under astrophysically relevant conditions. Only the H2_2O:NH3_3:CO and H2_2O:HCN ice mixtures led to the production of HNCO species. The possible isomerization of HNCO to its higher energy tautomers following irradiation or due to ice warm-up has been scrutinized. The photochemistry and thermal chemistry of H2_2O:NH3_3:CO and H2_2O:HCN ices was simulated using the Interstellar Astrochemistry Chamber (ISAC), a state-of-the-art ultra-high-vacuum setup. The ice was monitored in situ by Fourier transform mid-infrared spectroscopy in transmittance. A quadrupole mass spectrometer (QMS) detected the desorption of the molecules in the gas phase. UV-photoprocessing of H2_2O:NH3_3:CO/H2_2O:HCN ices lead to the formation of OCN^- as main product in the solid state and a minor amount of HNCO. The second isomer HOCN has been tentatively identified. Despite its low efficiency, the formation of HNCO and the HOCN isomers by UV-photoprocessing of realistic simulated ice mantles, might explain the observed abundances of these species in PDRs, hot cores, and dark clouds

    Bose-Einstein Condensation of 88^{88}Sr Through Sympathetic Cooling with 87^{87}Sr

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    We report Bose-Einstein condensation of 88^{88}Sr, which has a small, negative s-wave scattering length (a88=2a_{88}=-2\,a0a_0). We overcome the poor evaporative cooling characteristics of this isotope by sympathetic cooling with 87^{87}Sr atoms. 87^{87}Sr is effective in this role in spite of the fact that it is a fermion because of the large ground state degeneracy arising from a nuclear spin of I=9/2I=9/2, which reduces the impact of Pauli blocking of collisions. We observe a limited number of atoms in the condensate (Nmax104N_{max}\approx 10^4) that is consistent with the value of a88a_{88} and the optical dipole trap parameters.Comment: 4 pages, 4 figure

    Casimir effect in presence of spontaneous Lorentz symmetry breaking

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    The Casimir effect is one of the most remarkable consequences of the nonzero vacuum energy predicted by quantum field theory. In this contribution we study the Lorentz-violation effects of the minimal standard-model extension on the Casimir force between two parallel conducting plates in the vacuum. Using a perturbative method, we compute the relevant Green's function which satisfies given boundary conditions. The standard point-splitting technique allow us to express the vacuum expectation value of the stress-energy tensor in terms of this Green's function. Finally, we study the Casimir energy and the Casimir force paying particular attention to the quantum effects as approaching the plates.Univ. Algarve; Inst. Super Técnico Lisboa, Multidisciplinary Ctr Astrophys; Fundação Ciência Tecnologia; Centro Multidisciplinar Astrofisica. CONACyT Posdoctoral Grant 234745info:eu-repo/semantics/publishedVersio

    Degenerate Fermi Gas of 87^{87}Sr

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    We report quantum degeneracy in a gas of ultra-cold fermionic 87^{87}Sr atoms. By evaporatively cooling a mixture of spin states in an optical dipole trap for 10.5\,s, we obtain samples well into the degenerate regime with T/TF=0.26.06+.05T/T_F=0.26^{+.05}_{-.06}. The main signature of degeneracy is a change in the momentum distribution as measured by time-of-flight imaging, and we also observe a decrease in evaporation efficiency below T/TF0.5T/T_F \sim 0.5.Comment: 4 pages, 3 figure

    Inelastic and elastic collision rates for triplet states of ultracold strontium

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    We report measurement of the inelastic and elastic collision rates for ^{88}Sr atoms in the (5s5p)^3P_0 state in a crossed-beam optical dipole trap. This is the first measurement of ultracold collision properties of a ^3P_0 level in an alkaline-earth atom or atom with similar electronic structure. Since the (5s5p)^3P_0 state is the lowest level of the triplet manifold, large loss rates indicate the importance of principle-quantum-number-changing collisions at short range. We also provide an estimate of the collisional loss rates for the (5s5p){^3P_2} state.Comment: 4 pages 5 figure

    Runaway evaporation for optically dressed atoms

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    Forced evaporative cooling in a far-off-resonance optical dipole trap is proved to be an efficient method to produce fermionic- or bosonic-degenerated gases. However in most of the experiences, the reduction of the potential height occurs with a diminution of the collision elastic rate. Taking advantage of a long-living excited state, like in two-electron atoms, I propose a new scheme, based on an optical knife, where the forced evaporation can be driven independently of the trap confinement. In this context, the runaway regime might be achieved leading to a substantial improvement of the cooling efficiency. The comparison with the different methods for forced evaporation is discussed in the presence or not of three-body recombination losses

    Repumping and spectroscopy of laser-cooled Sr atoms using the (5s5p)3P2 - (5s4d)3D2 transition

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    We describe repumping and spectroscopy of laser-cooled strontium (Sr) atoms using the (5s5p)3P2 - (5s4d)3D2 transition. Atom number in a magneto-optical trap is enhanced by driving this transition because Sr atoms that have decayed into the (5s5p)3P2 dark state are repumped back into the (5s2)1S0 ground state. Spectroscopy of 84Sr, 86Sr, 87Sr, and 88Sr improves the value of the (5s5p)3P2 - (5s4d)3D2 transition frequency for 88Sr and determines the isotope shifts for the transition.Comment: 4 pages, 5 figure

    Lazy AC-Pattern Matching for Rewriting

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    We define a lazy pattern-matching mechanism modulo associativity and commutativity. The solutions of a pattern-matching problem are stored in a lazy list composed of a first substitution at the head and a non-evaluated object that encodes the remaining computations. We integrate the lazy AC-matching in a strategy language: rewriting rule and strategy application produce a lazy list of terms.Comment: In Proceedings WRS 2011, arXiv:1204.531
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