5,630 research outputs found
Exotic QQ\qbar\qbar States in QCD
We show that QCD contains stable four-quark QQ\qbar\qbar hadronic states in
the limit where the heavy quark mass goes to infinity. (Here Q denotes a heavy
quark, \qbar a light antiquark and the stability refers only to the strong
interactions.) The long range binding potential is due to one pion exchange
between ground state Q\qbar mesons, and is computed using chiral perturbation
theory. For the Q=b, this long range potential may be sufficiently attractive
to produce a weakly bound two meson state.Comment: (21 pages, 1 figure; uses harvmac.tex, tables.tex and uufiles),
CERN-TH.6744/92, CALT-68-186
Flavor Changing Neutral Currents, an Extended Scalar Sector, and the Higgs Production Rate at the LHC
We study extensions of the standard model with additional colored scalar
fields which can couple directly to quarks. Natural suppression of flavor
changing neutral currents implies minimal flavor violation, and fixes the
scalars to transform as (8,2)_1/2 under the SU(3) X SU(2) X U(1) gauge
symmetry. We explore the phenomenology of the standard model with one
additional (8,2)_1/2 scalar, and discuss how this extension can modify flavor
physics and the Higgs boson production rate at the LHC. Custodial SU(2)
symmetry can be implemented for the octet scalars since they transform as a
real color representation. Additional weak scale degrees of freedom needed for
gauge unification are discussed.Comment: Minor change
Renormalization of the Vector Current in QED
It is commonly asserted that the electromagnetic current is conserved and
therefore is not renormalized. Within QED we show (a) that this statement is
false, (b) how to obtain the renormalization of the current to all orders of
perturbation theory, and (c) how to correctly define an electron number
operator. The current mixes with the four-divergence of the electromagnetic
field-strength tensor. The true electron number operator is the integral of the
time component of the electron number density, but only when the current
differs from the MSbar-renormalized current by a definite finite
renormalization. This happens in such a way that Gauss's law holds: the charge
operator is the surface integral of the electric field at infinity. The theorem
extends naturally to any gauge theory.Comment: 9 pages. Corresponds to published version (Phys. Rev. D), including
appendix about Weeks's parado
Magnetic Moments of Dirac Neutrinos
The existence of a neutrino magnetic moment implies contributions to the
neutrino mass via radiative corrections. We derive model-independent
"naturalness" upper bounds on the magnetic moments of Dirac neutrinos,
generated by physics above the electroweak scale. The neutrino mass receives a
contribution from higher order operators, which are renormalized by operators
responsible for the neutrino magnetic moment. This contribution can be
calculated in a model independent way. In the absence of fine-tuning, we find
that current neutrino mass limits imply that Bohr
magnetons. This bound is several orders of magnitude stronger than those
obtained from solar and reactor neutrino data and astrophysical observations.Comment: 3 pages. Talk given at PANIC'0
Criteria for the experimental observation of multi-dimensional optical solitons in saturable media
Criteria for experimental observation of multi-dimensional optical solitons
in media with saturable refractive nonlinearities are developed. The criteria
are applied to actual material parameters (characterizing the cubic
self-focusing and quintic self-defocusing nonlinearities, two-photon loss, and
optical-damage threshold) for various glasses. This way, we identify operation
windows for soliton formation in these glasses. It is found that two-photon
absorption sets stringent limits on the windows. We conclude that, while a
well-defined window of parameters exists for two-dimensional solitons (spatial
or spatiotemporal), for their three-dimensional spatiotemporal counterparts
such a window \emph{does not} exist, due to the nonlinear loss in glasses.Comment: 8 pages, to appear in Phys. Rev.
Translational Invariance and the Anisotropy of the Cosmic Microwave Background
Primordial quantum fluctuations produced by inflation are conventionally
assumed to be statistically homogeneous, a consequence of translational
invariance. In this paper we quantify the potentially observable effects of a
small violation of translational invariance during inflation, as characterized
by the presence of a preferred point, line, or plane. We explore the imprint
such a violation would leave on the cosmic microwave background anisotropy, and
provide explicit formulas for the expected amplitudes of
the spherical-harmonic coefficients.Comment: Notation improve
Historical antecedents shaping corporate reporting in Iran
This research paper examines the evolution of corporate reporting and governance in Iran over the last century. The approach adopted was to provide an historical perspective to examine the environment within which Iranian corporate reporting has emerged and been shaped. An historical framework allows the study to focus on the evolution and development of corporate reporting practice in Iran. By adopting an historical framework, this study is able to inform future research based on models that adopt an evolutionary approach to the assessment of environmental factors on economic systems. The conclusion reached in this study is that socio-economic and political changes during the century have been opportune as drivers of corporate reporting in Iran. The study makes an incremental contribution to the existing accounting history literature for Asia / Middle East / developing countries
A right-handed isotropic medium with a negative refractive index
The sign of the refractive index of any medium is soley determined by the
requirement that the propagation of an electromagnetic wave obeys Einstein
causality. Our analysis shows that this requirement predicts that the real part
of the refractive index may be negative in an isotropic medium even if the
electric permittivity and the magnetic permeability are both positive. Such a
system may be a route to negative index media at optical frequencies. We also
demonstrate that the refractive index may be positive in left-handed media that
contain two molecular species where one is in its excited state.Comment: 4.1 pages, 4 figures, submitted to Physical Review Letter
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