720 research outputs found

    Radiative corrections to low energy neutrino reactions

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    We show that the radiative corrections to charged current (CC) nuclear reactions with an electron(positron) in the final state are described by a universal function. The consistency of our treatment of the radiative corrections with the procedure used to extract the value of the axial coupling constant gAg_A is discussed. To illustrate we apply our results to (anti)neutrino deuterium disintegration and to pppp fusion in the sun. The limit of vanishing electron mass is considered, and a simple formula valid for E_{obs}\gsim 1 MeV is obtained. The size of the nuclear structure-dependent effects is also discussed. Finally, we consider CC transitions with an electron(positron) in the initial state and discuss some applications to electron capture reactions.Comment: 23 pages, 5 figure

    Multipath Modeling of Automotive Power Line Communication Channels

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    In this paper an in-vehicle power line channel mathematical multipath representation is proposed. The selected approach aims at describing the transmission of a signal on a possibly complex power network by means of a finite number of delayed echoes. Model parameters are computed via a welldefined step-by-step procedure from frequency-domain channel characteristics. The feasibility and strength of the method are demonstrated by means of a measurement campaign. Two-port scattering measurements have been carried out on a commercial automobile and the effect of the measurement setup has been considered in the analysis

    Effects of site dilution on the magnetic properties of geometrically frustrated antiferromagnets

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    The effect of site dilution by non magnetic impurities on the susceptibility of geometrically frustrated antiferromagnets (kagome and pyrochlore lattices) is discussed in the framework of the Generalized Constant Coupling model, for both classical and quantum Heisenberg spins. For the classical diluted pyrochlore lattice, excellent agreement is found when compared with Monte Carlo data. Results for the quantum case are also presented and discussed.Comment: 5 pages, 3 figure

    SELEX RICH Performance and Physics Results

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    SELEX took data in the 1996/7 Fixed Target Run at Fermilab. The excellent performance parameters of the SELEX RICH Detector had direct influence on the quality of the obtained physics results.Comment: Contributed talk at the Fourth Workshop on RICH Detectors, June 5-10, 2002, Pylos, Greece. Accepted for publication in NIM

    Bubble fluctuations in Ω<1\Omega<1 inflation

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    In the context of the open inflationary universe, we calculate the amplitude of quantum fluctuations which deform the bubble shape. These give rise to scalar field fluctuations in the open Friedman-Robertson-Walker universe which is contained inside the bubble. One can transform to a new gauge in which matter looks perfectly smooth, and then the perturbations behave as tensor modes (gravitational waves of very long wavelength). For (1Ω)<<1(1-\Omega)<<1, where Ω\Omega is the density parameter, the microwave temperature anisotropies produced by these modes are of order δT/TH(R0μl)1/2(1Ω)l/2\delta T/T\sim H(R_0\mu l)^{-1/2} (1-\Omega)^{l/2}. Here, HH is the expansion rate during inflation, R0R_0 is the intrinsic radius of the bubble at the time of nucleation, μ\mu is the bubble wall tension and ll labels the different multipoles (l>1l>1). The gravitational backreaction of the bubble has been ignored. In this approximation, GμR0<<1G\mu R_0<<1, and the new effect can be much larger than the one due to ordinary gravitational waves generated during inflation (unless, of course, Ω\Omega gets too close to one, in which case the new effect disappears).Comment: 17 pages, 3 figs, LaTeX, epsfig.sty, available at ftp://ftp.ifae.es/preprint/ft/uabft387.p

    On random flights with non-uniformly distributed directions

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    This paper deals with a new class of random flights Xd(t),t>0,\underline{\bf X}_d(t),t>0, defined in the real space Rd,d2,\mathbb{R}^d, d\geq 2, characterized by non-uniform probability distributions on the multidimensional sphere. These random motions differ from similar models appeared in literature which take directions according to the uniform law. The family of angular probability distributions introduced in this paper depends on a parameter ν0\nu\geq 0 which gives the level of drift of the motion. Furthermore, we assume that the number of changes of direction performed by the random flight is fixed. The time lengths between two consecutive changes of orientation have joint probability distribution given by a Dirichlet density function. The analysis of Xd(t),t>0,\underline{\bf X}_d(t),t>0, is not an easy task, because it involves the calculation of integrals which are not always solvable. Therefore, we analyze the random flight Xmd(t),t>0,\underline{\bf X}_m^d(t),t>0, obtained as projection onto the lower spaces Rm,m<d,\mathbb{R}^m,m<d, of the original random motion in Rd\mathbb{R}^d. Then we get the probability distribution of Xmd(t),t>0.\underline{\bf X}_m^d(t),t>0. Although, in its general framework, the analysis of Xd(t),t>0,\underline{\bf X}_d(t),t>0, is very complicated, for some values of ν\nu, we can provide some results on the process. Indeed, for ν=1\nu=1, we obtain the characteristic function of the random flight moving in Rd\mathbb{R}^d. Furthermore, by inverting the characteristic function, we are able to give the analytic form (up to some constants) of the probability distribution of Xd(t),t>0.\underline{\bf X}_d(t),t>0.Comment: 28 pages, 3 figure

    Energy Transfer between Throats from a 10d Perspective

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    Strongly warped regions, also known as throats, are a common feature of the type IIB string theory landscape. If one of the throats is heated during cosmological evolution, the energy is subsequently transferred to other throats or to massless fields in the unwarped bulk of the Calabi-Yau orientifold. This energy transfer proceeds either by Hawking radiation from the black hole horizon in the heated throat or, at later times, by the decay of throat-localized Kaluza-Klein states. In both cases, we calculate in a 10d setup the energy transfer rate (respectively decay rate) as a function of the AdS scales of the throats and of their relative distance. Compared to existing results based on 5d models, we find a significant suppression of the energy transfer rates if the size of the embedding Calabi-Yau orientifold is much larger than the AdS radii of the throats. This effect can be partially compensated by a small distance between the throats. These results are relevant, e.g., for the analysis of reheating after brane inflation. Our calculation employs the dual gauge theory picture in which each throat is described by a strongly coupled 4d gauge theory, the degrees of freedom of which are localized at a certain position in the compact space.Comment: 25 pages; a comment adde

    Scalar field in the Bianchi I: Non commutative classical and Quantum Cosmology

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    Using the ADM formalism in the minisuperspace, we obtain the commutative and noncommutative exact classical solutions and exact wave function to the Wheeler-DeWitt equation with an arbitrary factor ordering, for the anisotropic Bianchi type I cosmological model, coupled to a scalar field, cosmological term and barotropic perfect fluid. We introduce noncommutative scale factors, considering that all minisuperspace variables qi\rm q^i do not commute, so the symplectic structure was modified. In the classical regime, it is shown that the anisotropic parameter β±nc\rm \beta_{\pm nc} and the field ϕ\phi, for some value in the λeff\lambda_{eff} cosmological term and noncommutative θ\theta parameter, present a dynamical isotropization up to a critical cosmic time tct_{c}; after this time, the effects of isotropization in the noncommutative minisuperspace seems to disappear. In the quantum regimen, the probability density presents a new structure that corresponds to the value of the noncommutativity parameter.Comment: 17 pages, 6 figures, Acepted in IJT
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