2,069 research outputs found
Vector Meson Exchanges and CP Asymmetry in
Using a current algebra framework, we discuss the contribution of vector
meson exchanges to the CP violating asymmetry in the decay
, resulting from the interference of the
amplitude with the radiative correction
.Comment: 9 pages (plain-TEX), IC/93/186, UTS-DFT-93-18, (two figures not
included
Spectroscopic Confirmation of a Protocluster at z=3.786
We present new observations of the field containing the z=3.786 protocluster,
PC217.96+32.3. We confirm that it is one of the largest and most overdense
high-redshift structures known. Such structures are rare even in the largest
cosmological simulations. We used the Mayall/MOSAIC1.1 imaging camera to image
a 1.2x0.6 deg area (~150x75 comoving Mpc) surrounding the protocluster's core
and discovered 165 candidate Lyman Alpha emitting galaxies (LAEs) and 788
candidate Lyman Break galaxies (LBGs). There are at least 2 overdense regions
traced by the LAEs, the largest of which shows an areal overdensity in its core
(i.e., within a radius of 2.5 comoving Mpc) of 14+/-7 relative to the average
LAE spatial density in the imaged field. Further, the average LAE spatial
density in the imaged field is twice that derived by other field LAE surveys.
Spectroscopy with Keck/DEIMOS yielded redshifts for 164 galaxies (79 LAEs and
85 LBGs); 65 lie at a redshift of 3.785+/-0.010. The velocity dispersion of
galaxies near the core is 350+/-40 km/s, a value robust to selection effects.
The overdensities are likely to collapse into systems with present-day masses
of >10^{15} solar masses and >6x10^{14} solar masses. The low velocity
dispersion may suggest a dynamically young protocluster. We find a weak trend
between narrow-band (Lyman Alpha) luminosity and environmental density: the
Lyman Alpha luminosity is enhanced on average by 1.35X within the protocluster
core. There is no evidence that the Lyman Alpha equivalent width depends on
environment. These suggest that star-formation and/or AGN activity is enhanced
in the higher density regions of the structure. PC217.96+32.3 is a Coma cluster
analog, witnessed in the process of formation.Comment: Accepted for publication in the Astrophysical Journal (March 27,
2016
Locality, Causality and Noncommutative Geometry
We analyse the causality condition in noncommutative field theory and show
that the nonlocality of noncommutative interaction leads to a modification of
the light cone to the light wedge. This effect is generic for noncommutative
geometry. We also check that the usual form of energy condition is violated and
propose that a new form is needed in noncommutative spacetime. On reduction
from light cone to light wedge, it looks like the noncommutative dimensions are
effectively washed out and suggests a reformulation of noncommutative field
theory in terms of lower dimensional degree of freedom. This reduction of
dimensions due to noncommutative geometry could play a key role in explaining
the holographic property of quantum gravity.Comment: 16 pages, LaTeX, 4 figure
Constraints on Light Top Squark from - mixing
We discuss the constraints on the mass of the lighter top squark from \bbbar\
mixing in the minimal supersymmetric standard model. A light top squark whose
mass is less than half of the -boson mass has not yet been excluded from
direct search experiments at LEP. However, the existence of the light top
squark may exceedingly enhance \bbbar\ mixing, owing to the box diagrams
exchanging the charginos and the up-type squarks. We show that for a sizable
region of parameter space the light top squark contribution to \bbbar\ mixing
becomes the same order of magnitude as the standard -boson contribution.
Taking into account the experimental results for \bbbar\ and \kkbar\ mixings,
the existence of the light top squark is excluded in an appreciable region of
the parameter space which LEP experiments have not ruled out.Comment: 8 pages latex file, 2 figure
Decay in Extensions of the Standard Model
The rare radiative decay is studied in extensions of the Standard Model. Matching conditions for
coefficients of operators appearing in the low energy effective Hamiltonian for
this process are derived, and QCD corrections to these coefficients are
analyzed. The decay rate is then calculated and compared with
the corresponding Standard Model result. We find that observable deviations
from Standard Model predictions can occur in theories for a reasonable range of parameter values.Comment: 17 pages with 5 figures not included but available upon request,
CALT-68-1893, TUM-T31-52/9
Quark and Lepton Masses in 5D SO(10)
We construct a five dimensional supersymmetric SO(10)D grand
unified model with an orbifold as the extra
dimension. The orbifold breaks half of the supersymmetry and breaks the SO(10)
gauge symmetry down to . The Higgs mechanism is used to break the remaining gauge symmetry
the rest of the way to the Standard Model. We place matter fields variously in
the bulk and on the orbifold fixed points and the resulting massless fields are
mixtures between these brane and bulk fields. A chiral adjoint field in the
bulk gets a U(1) vacuum expectation value, resulting in an -dependent
localization of the bulk matter fields and the Standard Model Higgs field. This
Higgs field localization allows us to simultaneously explain the hierarchies
and . The model uses 11 parameters to fit the 13
independent low energy observables of the quark and charged lepton Yukawa
matrices. The model predicts the values of two quark mass combinations,
\f{m_u}{m_c} and , each of which are predicted to be
approximately above their experimental values. The remaining
observables are successfully fit at the 5% level.Comment: 52 pages, published version, includes more discussion of 6D version
of mode
Mixing in the Presence of Isosinglet Quarks
We analyse transitions in the framework of a minimal extension
of the Standard Model where either a or a isosinglet quark is
added to the standard quark spectrum. In the case of a isosinglet
quark, it is shown that there is a significant region of parameter space where
mixing is sufficiently enhanced to be observed at the next
round of experiments. On the contrary, in the case of a isosinglet
quark, it is pointed out that obtaining a substancial enhancement of mixing, while complying with the experimental constraints on rare
kaon decays, requires a contrived choice of parameters.Comment: 10 pages plus four figures. The figures are not included but are
available upon reques
Rare Kaon Decay K^+ --> \pi^+ \nu \bar{\nu} in SU(3)_C X SU(3)_L X U(1)_N Models
The rare kaon decay K^+ --> \pi^+ \nu \bar{\nu} is considered in the
framework of the models based on the SU(3)_C X SU(3)_L X U(1)_N (3 - 3 - 1)
gauge group. It is shown that a lower bound of the Z' mass in the 3 - 3 - 1
model with right-handed neutrinos at a value of 3 TeV is derived, while that in
the minimal version -- 1.7 TeV.Comment: 7 pages, 1 figure, late
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