54 research outputs found
Physics Opportunities of e+e- Linear Colliders
We describe the anticipated experimental program of an e+e- linear collider
in the energy range 500 GeV -- 1.5 TeV. We begin with a description of current
collider designs and the expected experimental environment. We then discuss
precision studies of the W boson and top quark. Finally, we review the range of
models proposed to explain the physics of electroweak symmetry breaking and
show, for each case, the central role that the linear collider experiments will
play in elucidating this physics. (to appear in Annual Reviews of Nuclear and
Particle Science)Comment: 93 pages, latex + 23 figures; typos corrections + 1 reference adde
Probing the Vertex in e^\pm p\to\nu\gammaX
We study the prospects of testing the vertex in and at HERA and LEP/LHC. Destructive interference
effects between the Standard Model and the anomalous contributions to the
amplitude severely limit the sensitivity of both processes to non-standard
couplings. Sensitivity limits for the anomalous couplings
and at HERA and LEP/LHC are derived, taking into account
experimental cuts and uncertainties, and the form factor behaviour of
nonstandard couplings. These limits are found to be significantly weaker than
those which can be expected from other collider processes within the next few
years. At HERA, they are comparable to bounds obtained from -matrix
unitarity.Comment: 13 pages, 4 figures (not included
High-Energy Vector-Boson Scattering with Non-Standard Interactions and the Role of a Scalar Sector
The high-energy behavior of vector-boson scattering amplitudes is examined
within an effective theory for non-standard self-interactions of electroweak
vector-bosons. Irrespectively of whether this theory is brought into a gauge
invariant form by including non-standard interactions of a Higgs particle I
find that terms that grow particularly strongly with increasing scattering
energy are absent. Different theories are compared concerning their high-energy
behavior and the appearance of divergences at the one-loop level.Comment: 21 pages LaTeX, condensed version of BI-TP 93/5
Single-photon events in e^+ e^- collisions
We provide a detailed investigation of single-photon production processes in
collisions with missing momenta carried by neutrinos or neutralinos.
The transition amplitudes for both processes can be organized into a generic
simplified, factorized form; each neutral VA vector current of missing
energy carriers is factorized out and all the characteristics of the reaction
is solely included in the electron vector current. Firstly, we apply the
generic form to give a unified description of a single-photon production with a
Dirac-type or Majorana-type neutrino-pair and to confirm their identical
characteristics as suggested by the so-called Practical Dirac-Majorana
Confusion Theorem. Secondly, we show that the generic amplitude form is
maintained with the anomalous P- and C-invariant WW couplings in the
neutrino-associated process and it enables us to easily understand large
contributions of the anomalous WW couplings at higher energies and, in
particular, at the points away from the Z-resonance peak. Finally, the
neutralino-associated process, which receives modifications in both the
left-handed and right-handed electron currents due to the exchanges of the
left-handed and right-handed selectrons, can be differentiated from the
neutrino-associated ones through the left-right asymmetries and/or the circular
polarization of the outgoing photon.Comment: 20 pages, REVTeX, epsfig.sty, 7 figures (7 eps files
W ANOMALOUS MOMENTS AND THE POLARIZATION ASYMMETRY ZERO IN gamma e --> W nu
We show from general principles that there must be a center of mass energy,
, where the polarization asymmetry for circularly-polarized photon and
electron beams vanishes. In the case of the Standard Model, the crossing point
where the asymmetry changes sign occurs in Born approximation at GeV. We demonstrate the sensitivity
of the position of the polarization asymmetry zero to modifications of the SM
trilinear coupling. Given reasonable assumptions for the
luminosity and energy range for the Next Linear Collider(NLC) with a
backscattered laser beam, we show that the zero point, , of the
polarization asymmetry may be determined with sufficient precision to constrain
the anomalous couplings of the to better than the 1\% level at CL.
In addition to the fact that only a limited range of energy is required, the
polarization asymmetry measurements have the important advantage that many of
the systematic errors cancel in taking cross section ratios. The position of
the zero thus provides an additional weapon in the arsenal used to probe
anomalous trilinear gauge couplings.Comment: 21 pages, uuencoded postscript file. For hard copy, send e-mail to
[email protected]
The PNPase, exosome and RNA helicases as the building components of evolutionarily-conserved RNA degradation machines
Impact of Methimazole Treatment on Magnesium Concentration and Lymphocytes Activation in Adolescents with Graves’ Disease
Ion homeostasis in the Chloroplast
peer reviewedThe chloroplast is an organelle of high demand for macro- and micro-nutrient ions, which are required for the maintenance of the photosynthetic process. To avoid deficiency while preventing excess, homeostasis mechanisms must be tightly regulated. Here, we describe the needs for nutrient ions in the chloroplast and briefly highlight their functions in the chloroplastidial metabolism. We further discuss the impact of nutrient deficiency on chloroplasts and the acclimation mechanisms that evolved to preserve the photosynthetic apparatus. We finally present what is known about import and export mechanisms for these ions. Whenever possible, a comparison between cyanobacteria, algae and plants is provided to add an evolutionary perspective to the description of ion homeostasis mechanisms in photosynthesis
Integration of Chloroplast Nucleic Acid Metabolism into the Phosphate Deprivation Response in Chlamydomonas reinhardtii
Cell survival depends on the cell's ability to acclimate to phosphorus (P) limitation. We studied the chloroplast ribonuclease polynucleotide phosphorylase (PNPase), which consumes and generates phosphate, by comparing wild-type Chlamydomonas reinhardtii cells with strains with reduced PNPase expression. In the wild type, chloroplast RNA (cpRNA) accumulates under P limitation, correlating with reduced PNPase expression. PNPase-deficient strains do not exhibit cpRNA variation under these conditions, suggesting that in the wild type PNPase limits cpRNA accumulation under P stress. PNPase levels appear to be mediated by the P response regulator PHOSPHORUS STARVATION RESPONSE1 (PSR1), because in psr1 mutant cells, cpRNA declines under P limitation and PNPase expression is not reduced. PNPase-deficient cells begin to lose viability after 24 h of P depletion, suggesting that PNPase is important for cellular acclimation. PNPase-deficient strains do not have enhanced sensitivity to other physiological or nutrient stresses, and their RNA and cell growth phenotypes are not observed under P stress with phosphite, a phosphate analog that blocks the stress signal. In contrast with RNA metabolism, chloroplast DNA (cpDNA) levels declined under P deprivation, suggesting that P mobilization occurs from DNA rather than RNA. This unusual phenomenon, which is phosphite- and PSR1-insensitive, may have evolved as a result of the polyploid nature of cpDNA and the requirement of P for cpRNA degradation by PNPase
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