914 research outputs found
Experimental probes of axions
Experimental searches for axions or axion-like particles rely on
semiclassical phenomena resulting from the postulated coupling of the axion to
two photons. Sensitive probes of the extremely small coupling constant can be
made by exploiting familiar, coherent electromagnetic laboratory techniques,
including resonant enhancement of transitions using microwave and optical
cavities, Bragg scattering, and coherent photon-axion oscillations. The axion
beam may either be astrophysical in origin as in the case of dark matter axion
searches and solar axion searches, or created in the laboratory from laser
interactions with magnetic fields. This note is meant to be a sampling of
recent experimental results.Comment: 6 pages, 7 figures, proceedings of XXIX Physics in Collision
Conference, Kobe, Japan, August 30-September 2, 2009. An incorrect file was
accidentally submitted as V1. V2 is the version in the actual proceedings.
Difference: axion-fermion scattering is always suppressed by the Yukawa
coupling m_f/f_a. High kinetic energies do not overcome this suppressio
Designing dark energy afterglow experiments
Chameleon fields, which are scalar field dark energy candidates, can evade
fifth force constraints by becoming massive in high-density regions. However,
this property allows chameleon particles to be trapped inside a vacuum chamber
with dense walls. Afterglow experiments constrain photon-coupled chameleon
fields by attempting to produce and trap chameleon particles inside such a
vacuum chamber, from which they will emit an afterglow as they regenerate
photons. Here we discuss several theoretical and systematic effects underlying
the design and analysis of the GammeV and CHASE afterglow experiments. We
consider chameleon particle interactions with photons, Fermions, and other
chameleon particles, as well as with macroscopic magnetic fields and matter.
The afterglow signal in each experiment is predicted, and its sensitivity to
various properties of the experimental apparatus is studied. Finally, we use
CHASE data to exclude a wide range of photon-coupled chameleon dark energy
models.Comment: 29 pages, 31 figures, 1 tabl
On the anomalous afterglow seen in a chameleon afterglow search
We present data from our investigation of the anomalous orange-colored
afterglow that was seen in the GammeV Chameleon Afterglow Search (CHASE). These
data includes information about the broad band color of the observed glow, the
relationship between the glow and the temperature of the apparatus, and other
data taken prior to and during the science operations of CHASE. While differing
in several details, the generic properties of the afterglow from CHASE are
similar to luminescence seen in some vacuum compounds. Contamination from this,
or similar, luminescent signatures will likely impact the design of
implementation of future experiments involving single photon detectors and high
intensity light sources in a cryogenic environment.Comment: 6 pages, 5 figures, submitted to PR
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Search for chameleon particles via photon regeneration
We report the first results from the GammeV search for chameleon particles, which may be created via photon-photon interactions within a strong magnetic field. The chameleons are assumed to have matter effects sufficiently strong that they reflect from all solid surfaces of the apparatus, thus evading detection in our previous search for weakly-interacting axion-like particles. We implement a novel technique to create and trap the reflective particles within a jar and to detect them later via their afterglow as they slowly convert back into photons. These measurements provide the first experimental constraints on the couplings of chameleons to photons
Deep shower interpretation of the cosmic ray events observed in excess of the Greisen-Zatsepin-Kuzmin energy
We consider the possibility that the ultra-high-energy cosmic ray flux has a
small component of exotic particles which create showers much deeper in the
atmosphere than ordinary hadronic primaries. It is shown that applying the
conventional AGASA/HiRes/Auger data analysis procedures to such exotic events
results in large systematic biases in the energy spectrum measurement. SubGZK
exotic showers may be mis-reconstructed with much higher energies and mimick
superGZK events. Alternatively, superGZK exotic showers may elude detection by
conventional fluorescence analysis techniques.Comment: 22 pages, 5 figure
First measurements of high frequency cross-spectra from a pair of large Michelson interferometers
Measurements are reported of the cross-correlation of spectra of differential
position signals from the Fermilab Holometer, a pair of co-located 39 m long,
high power Michelson interferometers with flat, broadband frequency response in
the MHz range. The instrument obtains sensitivity to high frequency correlated
signals far exceeding any previous measurement in a broad frequency band
extending beyond the 3.8 MHz inverse light crossing time of the apparatus. The
dominant but uncorrelated shot noise is averaged down over
independent spectral measurements with 381 Hz frequency resolution to obtain
sensitivity to stationary
signals. For signal bandwidths kHz, the sensitivity to strain
or shear power spectral density of classical or exotic origin surpasses a
milestone where
is the Planck time.Comment: 5 pages, 3 figure
Interferometric Constraints on Quantum Geometrical Shear Noise Correlations
Final measurements and analysis are reported from the first-generation
Holometer, the first instrument capable of measuring correlated variations in
space-time position at strain noise power spectral densities smaller than a
Planck time. The apparatus consists of two co-located, but independent and
isolated, 40 m power-recycled Michelson interferometers, whose outputs are
cross-correlated to 25 MHz. The data are sensitive to correlations of
differential position across the apparatus over a broad band of frequencies up
to and exceeding the inverse light crossing time, 7.6 MHz. By measuring with
Planck precision the correlation of position variations at spacelike
separations, the Holometer searches for faint, irreducible correlated position
noise backgrounds predicted by some models of quantum space-time geometry. The
first-generation optical layout is sensitive to quantum geometrical noise
correlations with shear symmetry---those that can be interpreted as a
fundamental noncommutativity of space-time position in orthogonal directions.
General experimental constraints are placed on parameters of a set of models of
spatial shear noise correlations, with a sensitivity that exceeds the
Planck-scale holographic information bound on position states by a large
factor. This result significantly extends the upper limits placed on models of
directional noncommutativity by currently operating gravitational wave
observatories.Comment: Matches the journal accepted versio
MHz gravitational wave constraints with decameter Michelson interferometers
A new detector, the Fermilab Holometer, consists of separate yet identical 39-meter Michelson interferometers. Strain sensitivity achieved is better than 10[superscript -21]/√Hz between 1 to 13 MHz from a 130-h data set. This measurement exceeds the sensitivity and frequency range made from previous high frequency gravitational wave experiments by many orders of magnitude. Constraints are placed on a stochastic background at 382 Hz resolution. The 3σ upper limit on Ω[subscript GW], the gravitational wave energy density normalized to the closure density, ranges from 5.6×10[superscript 12] at 1 MHz to 8.4×10[superscript 15] at 13 MHz. Another result from the same data set is a search for nearby primordial black hole binaries (PBHB). There are no detectable monochromatic PBHBs in the mass range 0.83–3.5×10[superscript 21]  g between the Earth and the Moon. Projections for a chirp search with the same data set increase the mass range to 0.59-2.5×10[superscript 25]  g and distances out to Jupiter. This result presents a new method for placing limits on a poorly constrained mass range of primordial black holes. Additionally, solar system searches for PBHBs place limits on their contribution to the total dark matter fraction.United States. Dept. of Energy (Contract DE-AC02-07CH11359)United States. Dept. of Energy (Early Career Research Program FNAL FWP 11-03)Templeton FoundationNational Science Foundation (U.S.) (Grants PHY- 1205254 and DGE-1144082)National Aeronautics and Space Administration (Grant NNX09AR38G)Fermi Research AllianceUniversity of Chicago. Kavli Institute for Cosmological PhysicsUniversity of Chicago. Fermilab Strategic Collaborative InitiativesScience Support ConsortiumNational Science Foundation (U.S.). Graduate Research Fellowship Program (Grant DGE-0638477)Universities Research Association (U.S.). Visiting Scholars Progra
Characterization of the role of BGS13 in the secretory mechanism of Pichia pastoris
The methylotrophic yeast Pichia pastoris has been utilized for heterologous protein expression for over 30 years. Because P. pastoris secretes few of its own proteins, the exported recombinant protein is the major polypeptide in the extracellular medium, making purification relatively easy. Unfortunately, some recombinant proteins intended for secretion are retained within the cell. A mutant strain isolated in our laboratory, containing a disruption of the BGS13 gene, displayed elevated levels of secretion for a variety of reporter proteins. The Bgs13 peptide (Bgs13p) is similar to the Saccharomyces cerevisiae protein kinase C 1 protein (Pkc1p), but its specific mode of action is currently unclear. To illuminate differences in the secretion mechanism between the wild-type (wt) strain and the bgs13 strain, we determined that the disrupted bgs13 gene expressed a truncated protein that had reduced protein kinase C activity and a different location in the cell, compared to the wt protein. Because the Pkc1p of baker’s yeast plays a significant role in cell wall integrity, we investigated the sensitivity of the mutant strain’s cell wall to growth antagonists and extraction by dithiothreitol, determining that the bgs13 strain cell wall suffered from inherent structural problems although its porosity was normal. A proteomic investigation of the bgs13 strain secretome and cell wall-extracted peptides demonstrated that, compared to its wt parent, the bgs13 strain also displayed increased release of an array of normally secreted, endogenous proteins, as well as endoplasmic reticulum-resident chaperone proteins, suggesting that Bgs13p helps regulate the unfolded protein response and protein sorting on a global scale. IMPORTANCE The yeast Pichia pastoris is used as a host system for the expression of recombinant proteins. Many of these products, including antibodies, vaccine antigens, and therapeutic proteins such as insulin, are currently on the market or in late stages of development. However, one major weakness is that sometimes these proteins are not secreted from the yeast cell efficiently, which impedes and raises the cost of purification of these vital proteins. Our laboratory has isolated a mutant strain of Pichia pastoris that shows enhanced secretion of many proteins. The mutant produces a modified version of Bgs13p. Our goal is to understand how the change in the Bgs13p function leads to improved secretion. Once the Bgs13p mechanism is illuminated, we should be able to apply this understanding to engineer new P. pastoris strains that efficiently produce and secrete life-saving recombinant proteins, providing medical and economic benefits
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