3,987 research outputs found
Galaxy clusters and microwave background anisotropy
Previous estimates of the microwave background anisotropies produced by
freely falling spherical clusters are discussed. These estimates are based on
the Swiss-Cheese and Tolman-Bondi models. It is proved that these models give
only upper limits to the anisotropies produced by the observed galaxy clusters.
By using spherically symmetric codes including pressureless matter and a hot
baryonic gas, new upper limits are obtained. The contributions of the hot gas
and the pressureless component to the total anisotropy are compared. The
effects produced by the pressure are proved to be negligible; hence,
estimations of the cluster anisotropies based on N-body simulations are
hereafter justified. After the phenomenon of violent relaxation, any realistic
rich cluster can only produce small anisotropies with amplitudes of order
. During the rapid process of violent relaxation, the anisotropies
produced by nonlinear clusters are expected to range in the interval
. The angular scales of these anisotropies are discussed.Comment: 31 pages, 3 postscript figures, accepted MNRA
Securitization and Lending Standards: Evidence from the Wholesale Loan Market
securitization;bank risk taking;syndicated loans;financial crisis
Tadpole versus anomaly cancellation in D=4,6 compact IIB orientifolds
It is often stated in the literature concerning D=4,6 compact Type IIB
orientifolds that tadpole cancellation conditions i) uniquely fix the gauge
group (up to Wilson lines and/or moving of branes) and ii) are equivalent to
gauge anomaly cancellation. We study the relationship between tadpole and
anomaly cancellation conditions and qualify both statements. In general the
tadpole cancellation conditions imply gauge anomaly cancellation but are
stronger than the latter conditions in D=4, N=1 orientifolds. We also find that
tadpole cancellation conditions in Z_N D=4,6 compact orientifolds do not
completely fix the gauge group and we provide new solutions different from
those previously reported in the literature.Comment: 28 pages, Latex. Minor corrections, updated reference
Inverse tri-bimaximal type-III seesaw and lepton flavor violation
We present a type-III version of inverse seesaw or, equivalently an inverse
version of type-III seesaw. Naturally small neutrino masses arise at low-scale
from the exchange of neutral fermions transforming as hyperchargeless SU(2)
triplets. In order to implement tri-bimaximal lepton mixing we supplement the
minimal SU(3)xSU(2)xU(1) gauge symmetry with an A4-based flavor symmetry. Our
scenario induces lepton flavour violating (LFV) three body decays that can
proceed at the tree level, while radiative li to lj gamma decays and mu-e
conversion in nuclei are also expected to be sizeable. LFV decays are related
by the underlying flavor symmetry and the new fermions are also expected to be
accessible for study at the Large Hadron Collider (LHC)
Twisted Sector Yukawa Couplings For The Orbifolds
The moduli dependent Yukawa couplings between twisted sectors of Coxeter orbifolds are studied.Comment: 40 pages, SUSX-TH-92/1
Zirconium stable isotope analysis of zircon by MC-ICP-MS: Methods and application to evaluating intra-crystalline zonation in a zircon megacryst
Zirconium (Zr) plays a key role in the development of phases like zircon (ZrSiO₄) and baddeleyite (ZrO₂) in magmatic systems. These minerals are crucial for the study of geologic time and crustal evolution, and their high resistivity to weathering and erosion results in their preservation on timescales of billions of years. Although zircon and baddeleyite may also preserve a robust record of Zr isotope behavior in high-temperature terrestrial environments, little is known about the factors that control Zr isotope partitioning in magmatic systems, the petrogenetic significance of fractionated compositions, or how these variations are recorded in Zr-rich accessory phases. Here, we describe a new analytical protocol for accurately determining the Zr stable isotope composition of zircon by multicollector-inductively coupled plasma-mass spectrometry (MC-ICP-MS), using the double-spike method to correct for procedural and instrumental mass bias. We apply this technique to test whether zircon crystallization in carbonatite magmatic systems is a driver of Zr isotope fractionation by interrogating the internal zonation of a zircon megacryst from the Mud Tank carbonatite (MTUR1). We find the MTUR1 megacryst to lack internal zoning within analytical uncertainties with a mean μ⁹⁴/⁹⁰Zr_(NIST) = −55 ± 28 ppm (2 SD, n = 151), which suggests that zircon crystallization is not a driver of Zr isotope fractionation in carbonatite magmas. This observation is in stark contrast with those made in silicate magmatic systems, raising the possibility that the bonding environment of Zr⁴⁺ ions may be fundamentally different in carbonatite vs. silicate melts. Because of its remarkable homogeneity, the MTUR1 megacryst is an ideal natural reference material for Zr isotopic analysis of zircon using both solution and spatially resolved methods. The reproducibility of a pure Zr solution and our chemically purified zircon fractions indicate that the external reproducibility of our method is on the order of ±28 ppm for μ⁹⁴/⁹⁰Zr, or ±7 ppm per amu, at 95% confidence
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