5,686 research outputs found
Supersymmetric Electroweak Baryogenesis in the WKB approximation
We calculate the baryon asymmetry generated at the electroweak phase
transition in the minimal supersymmetric standard model, treating the particles
in a WKB approximation in the bubble wall background. A set of diffusion
equations for the particle species relevant to baryon generation, including
source terms arising from the CP violation associated with the complex phase
of the parameter, are derived from Boltzmann equations, and
solved. The conclusion is that must be \gsim 0.1 to generate a
baryon asymmetry consistent with nucleosynthesis. We compare our results to
several other recent computations of the effect, arguing that some are
overestimates.Comment: 12 pages, 1 figure, corrected some criticisms of hep-ph/9702409; to
appear in Phys. Lett.
Testing for Features in the Primordial Power Spectrum
Well-known causality arguments show that events occurring during or at the
end of inflation, associated with reheating or preheating, could contribute a
blue component to the spectrum of primordial curvature perturbations, with the
dependence k^3. We explore the possibility that they could be observably large
in CMB, LSS, and Lyman-alpha data. We find that a k^3 component with a cutoff
at some maximum k can modestly improve the fits (Delta chi^2=2.0, 5.4) of the
low multipoles (l ~ 10 - 50) or the second peak (l ~ 540) of the CMB angular
spectrum when the three-year WMAP data are used. Moreover, the results from
WMAP are consistent with the CBI, ACBAR, 2dFGRS, and SDSS data when they are
included in the analysis. Including the SDSS galaxy clustering power spectrum,
we find weak positive evidence for the k^3 component at the level of Delta chi'
= 2.4, with the caveat that the nonlinear evolution of the power spectrum may
not be properly treated in the presence of the k^3 distortion. To investigate
the high-k regime, we use the Lyman-alpha forest data (LUQAS, Croft et al., and
SDSS Lyman-alpha); here we find evidence at the level Delta chi^2' = 3.8.
Considering that there are two additional free parameters in the model, the
above results do not give a strong evidence for features; however, they show
that surprisingly large bumps are not ruled out. We give constraints on the
ratio between the k^3 component and the nearly scale-invariant component, r_3 <
1.5, over the range of wave numbers 0.0023/Mpc < k < 8.2/Mpc. We also discuss
theoretical models which could lead to the k^3 effect, including ordinary
hybrid inflation and double D-term inflation models. We show that the
well-motivated k^3 component is also a good representative of the generic
spikelike feature in the primordial perturbation power spectrum.Comment: 23 pages, 6 figures; added new section on theoretical motivation for
k^3 term, and discussion of double D-term hybrid inflation models; title
changed, added a new section discussing the generic spikelike features,
published in IJMP
The protein import apparatus of chloroplasts
Routing of cytosolically synthesized precursor proteins into chloroplasts is a specific process which involves a multitude of soluble and membrane components. In this review we wil1 focus on early events of the translocation pathway of nuclear coded plastidic precursor proteins and compare import routes for polypeptide of the outer chloroplast envelope to that of internal chloroplast compartments. A number of proteins housed in the chloroplast envelopes have been implied to be involved in the translocation process, but so far a certain function has not been assigned to any of these proteins. The only exception could be an envelope localized hsc 70 homologue which could retain the import competence of a precursor protein in transit into the organelle
Supersymmetric electroweak phase transition: beyond perturbation theory
We compute the three-dimensional effective action for the minimal supersymmetric standard model, which describes the light modes of the theory near the finite-temperature electroweak phase transition, keeping the one-loop corrections from the third generation quarks and squarks. Using the lattice results of Kajantie et al. for the phase transition in the same class of 3-D models, we find that the strength of the phase transition is sufficient for electroweak baryogenesis, in much broader regions of parameter space than have been indicated by purely perturbative analyses. In particular we find that, while small values of \tan\beta are favored, positive results persist even for arbitrarily large values of \tan\beta if the mass of the A^0 boson is between 40 and 100 GeV, a region of parameters which has not been previously identified as being favorable for electroweak baryogenesis
Status of Electroweak Phase Transition and Baryogenesis
I review recent progress on the electroweak phase transition and
baryogenesis, focusing on the minimal supersymmetric standard model as the
source of new physics.Comment: 10 pp, 6 figures; plenary talk given at 6th Workshop on High Energy
Physics Phenomenology, 4 Jan. 2000, Chennai, India. v.2: added reference
Spontaneous Symmetry Breaking in General Relativity. Vector Order Parameter
Gravitational properties of a hedge-hog type topological defect in two extra
dimensions are considered in General Relativity employing a vector as the order
parameter. All previous considerations were done using the order parameter in
the form of a multiplet in a target space of scalar fields. The difference of
these two approaches is analyzed and demonstrated in detail. Regular solutions
of the Einstein equations are studied analytically and numerically. It is shown
that the existence of a negative cosmological constant is sufficient for the
spontaneous symmetry breaking of the initially plain bulk. Regular
configurations have a growing gravitational potential and are able to trap the
matter on the brane. If the energy of spontaneous symmetry breaking is high,
the gravitational potential has several points of minimum. Identical in the
uniform bulk spin-less particles, being trapped within separate minima, acquire
different masses and appear to the observer on brane as different particles
with integer spins.Comment: 23 pages, 6 figure
Narrow-line Laser Cooling by Adiabatic Transfer
We propose and demonstrate a novel laser cooling mechanism applicable to
particles with narrow-linewidth optical transitions. By sweeping the frequency
of counter-propagating laser beams in a sawtooth manner, we cause adiabatic
transfer back and forth between the ground state and a long-lived optically
excited state. The time-ordering of these adiabatic transfers is determined by
Doppler shifts, which ensures that the associated photon recoils are in the
opposite direction to the particle's motion. This ultimately leads to a robust
cooling mechanism capable of exerting large forces via a weak transition and
with reduced reliance on spontaneous emission. We present a simple intuitive
model for the resulting frictional force, and directly demonstrate its efficacy
for increasing the total phase-space density of an atomic ensemble. We rely on
both simulation and experimental studies using the 7.5~kHz linewidth S
to P transition in Sr. The reduced reliance on spontaneous
emission may allow this adiabatic sweep method to be a useful tool for cooling
particles that lack closed cycling transitions, such as molecules.Comment: 5 pages, 4 figure
Phosphoproteins and protein-kinase activity in isolated envelopes of pea (Pisum sativum L.) chloroplasts
A protein kinase was found in envelope membranes of purified pea (Pisum sativum L.) chloroplasts. Separation of the two envelope membranes showed that most of the enzyme activity was localized in the outer envelope. The kinase was activated by Mg2+ and inhibited by ADP and pyrophosphate. It showed no response to changes in pH in the physiological range (pH 7-8) or conventional protein substrates. Up to ten phosphorylated proteins could be detected in the envelope-membrane fraction. The molecular weights of these proteins, as determined by polyacrylamide-gel electrophoresis were: two proteins higher than 145 kDa, 97, 86, 62, 55, 46, 34 and 14 kDa. The 86-kDa band being the most pronounced. Experiments with separated inner and outer envelopes showed that most labeled proteins are also localized in the outer-envelope fraction. The results indicate a major function of the outer envelope in the communication between the chloroplast and the parent cell
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