4,323 research outputs found

    An Angular Correlation Test of Time Reversal Invariance

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    Gamma-ray angular correlation experiment of time reversal invarianc

    Angular Correlation of Cascade Gamma Rays in 94nb

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    Angular correlation of cascade gamma rays in niobiu

    Formation of Black Holes from Collapsed Cosmic String Loops

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    The fraction of cosmic string loops which collapse to form black holes is estimated using a set of realistic loops generated by loop fragmentation. The smallest radius sphere into which each cosmic string loop may fit is obtained by monitoring the loop through one period of oscillation. For a loop with invariant length LL which contracts to within a sphere of radius RR, the minimum mass-per-unit length μmin\mu_{\rm min} necessary for the cosmic string loop to form a black hole according to the hoop conjecture is μmin=R/(2GL)\mu_{\rm min} = R /(2 G L). Analyzing 25,57625,576 loops, we obtain the empirical estimate fBH=104.9±0.2(Gμ)4.1±0.1f_{\rm BH} = 10^{4.9\pm 0.2} (G\mu)^{4.1 \pm 0.1} for the fraction of cosmic string loops which collapse to form black holes as a function of the mass-per-unit length μ\mu in the range 10−3≲Gμ≲3×10−210^{-3} \lesssim G\mu \lesssim 3 \times 10^{-2}. We use this power law to extrapolate to Gμ∼10−6G\mu \sim 10^{-6}, obtaining the fraction fBHf_{\rm BH} of physically interesting cosmic string loops which collapse to form black holes within one oscillation period of formation. Comparing this fraction with the observational bounds on a population of evaporating black holes, we obtain the limit Gμ≤3.1(±0.7)×10−6G\mu \le 3.1 (\pm 0.7) \times 10^{-6} on the cosmic string mass-per-unit-length. This limit is consistent with all other observational bounds.Comment: uuencoded, compressed postscript; 20 pages including 7 figure

    Bounds on Dark Matter from the ``Atmospheric Neutrino Anomaly''

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    Bounds are derived on the cross section, flux and energy density of new particles that may be responsible for the atmospheric neutrino anomaly. 4.6×10−45cm2<σ<2.4×10−34cm24.6 \times 10^{-45} cm^2 < \sigma <2.4 \times 10^{-34} cm^2 Decay of primordial homogeneous dark matter can be excluded.Comment: 10 pages, TeX (revtex

    Analytic Results for the Gravitational Radiation from a Class of Cosmic String Loops

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    Cosmic string loops are defined by a pair of periodic functions a{\bf a} and b{\bf b}, which trace out unit-length closed curves in three-dimensional space. We consider a particular class of loops, for which a{\bf a} lies along a line and b{\bf b} lies in the plane orthogonal to that line. For this class of cosmic string loops one may give a simple analytic expression for the power γ\gamma radiated in gravitational waves. We evaluate γ\gamma exactly in closed form for several special cases: (1) b{\bf b} a circle traversed MM times; (2) b{\bf b} a regular polygon with NN sides and interior vertex angle π−2πM/N\pi-2\pi M/N; (3) b{\bf b} an isosceles triangle with semi-angle θ\theta. We prove that case (1) with M=1M=1 is the absolute minimum of γ\gamma within our special class of loops, and identify all the stationary points of γ\gamma in this class.Comment: 15 pages, RevTex 3.0, 7 figures available via anonymous ftp from directory pub/pcasper at alpha1.csd.uwm.edu, WISC-MILW-94-TH-1

    A Closed-Form Expression for the Gravitational Radiation Rate from Cosmic Strings

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    We present a new formula for the rate at which cosmic strings lose energy into gravitational radiation, valid for all piecewise-linear cosmic string loops. At any time, such a loop is composed of NN straight segments, each of which has constant velocity. Any cosmic string loop can be arbitrarily-well approximated by a piecewise-linear loop with NN sufficiently large. The formula is a sum of O(N4)O(N^4) polynomial and log terms, and is exact when the effects of gravitational back-reaction are neglected. For a given loop, the large number of terms makes evaluation ``by hand" impractical, but a computer or symbolic manipulator yields accurate results. The formula is more accurate and convenient than previous methods for finding the gravitational radiation rate, which require numerical evaluation of a four-dimensional integral for each term in an infinite sum. It also avoids the need to estimate the contribution from the tail of the infinite sum. The formula has been tested against all previously published radiation rates for different loop configurations. In the cases where discrepancies were found, they were due to errors in the published work. We have isolated and corrected both the analytic and numerical errors in these cases. To assist future work in this area, a small catalog of results for some simple loop shapes is provided.Comment: 29 pages TeX, 16 figures and computer C-code available via anonymous ftp from directory pub/pcasper at alpha1.csd.uwm.edu, WISC-MILW-94-TH-10, (section 7 has been expanded, two figures added, and minor grammatical changes made.

    (5S,6S)-4,5-Dimethyl-3-methyl­acryloyl-6-phenyl-1,3,4-oxadiazinan-2-one

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    The title compound, C15H18N2O3, is an example of an oxadiazinan-2-one with significant inter­action between the N3-acyl and N4-methyl groups. These steric inter­actions result in a large torsion angle between the two carbonyl groups, not present with acyl substituents with less steric demand

    Off-diagonal structure of neutrino mass matrix in see-saw mechanism and electron-muon-tau lepton universality

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    By a simple extension of the standard model in which (e−μ−τe-\mu -\tau ) universality is not conserved, we present a scenario within the framework of see-saw mechanism in which the neutrino mass matrix is strictly off-diagonal in the flavor basis. We show that a version of this scenario can accomodate the atmospheric νμ−ντ\nu_\mu -\nu_\tau neutrino oscillations and νμ−νe\nu_\mu -\nu_e oscillations claimed by the LSND collaboration. PACS: 14.60.Pq; 14.60.St;13.15.+gComment: 5 pages, Revtex, 1 figure: The model accomodate another version which explains atmospheric neutrino data and the observed solar neutrino oscillations (large angle solution). In the previous version the value of \lambda parameter is changed to the expected one. This version now accomodates LSND result and solar neutrino oscillations (small angle MSW solution
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