596 research outputs found
Chiral freedom and electroweak symmetry breaking
Antisymmetric tensor fields with chiral couplings to quarks and leptons may
induce spontaneous electroweak symmetry breaking in a model without a
``fundamental'' Higgs scalar. No microscopic local mass term for the chiral
tensors or ``chirons'' is allowed by the symmetries and our model exhibits only
dimensionless couplings. However, the chiral couplings are asymptotically free
and therefore generate a mass scale where they grow large. We argue that at
this scale mass terms for the chiral tensor fields are generated
non-perturbatively - the chirons appear as new massive spin one particles.
Furthermore a scalar top-antitop condensate forms, giving mass to the weak
gauge bosons and fermions. In this scenario the longstanding gauge hierarchy
problem finds a solution similar to the mass generation in QCD. We compute the
general form of the effective action for the chiral tensors and sketch several
possibilities of their detection at LHC or through precision tests of the
electroweak standard model.Comment: 30 pages, 7 figure
Alternative evolutionary paths to bacterial antibiotic resistance cause distinct collateral effects.
Published onlineJournal ArticleThis is the author accepted manuscript. The final version is available from Oxford University Press via the DOI in this record.When bacteria evolve resistance against a particular antibiotic, they may simultaneously gain increased sensitivity against a second one. Such collateral sensitivity may be exploited to develop novel, sustainable antibiotic treatment strategies aimed at containing the current, dramatic spread of drug resistance. To date, the presence and molecular basis of collateral sensitivity has only been studied in few bacterial species and is unknown for opportunistic human pathogens such as Pseudomonas aeruginosa. In the present study, we assessed patterns of collateral effects by experimentally evolving 160 independent populations of P. aeruginosa to high levels of resistance against eight commonly used antibiotics. The bacteria evolved resistance rapidly and expressed both collateral sensitivity and cross-resistance. The pattern of such collateral effects differed to those previously reported for other bacterial species, suggesting inter-specific differences in the underlying evolutionary trade-offs. Intriguingly, we also identified contrasting patterns of collateral sensitivity and cross-resistance among the replicate populations adapted to the same drug. Whole-genome sequencing of 81 independently evolved populations revealed distinct evolutionary paths of resistance to the selective drug, which determined whether bacteria became cross-resistant or collaterally sensitive towards others. Based on genomic and functional genetic analysis, we demonstrate that collateral sensitivity can result from resistance mutations in regulatory genes such as nalC or mexZ, which mediate aminoglycoside sensitivity in β-lactam-adapted populations, or the two-component regulatory system gene pmrB, which enhances penicillin sensitivity in gentamicin-resistant populations. Our findings highlight substantial variation in the evolved collateral effects among replicates, which in turn determine their potential in antibiotic therapy.We thank Anette Friedrichs, Lutz Becks, and the Schulenburg group for valuable advice and Melanie Vollstedt for technical support during genome sequencing. We are grateful for financial support from the German Science Foundation (DFG grant SCHU 1415/12-1) and the International Max-Planck Research School for Evolutionary Biology at the University of Kiel. We acknowledge infrastructural support by the DFG excellence cluster Inflammation at Interfaces
Status of a DEPFET pixel system for the ILC vertex detector
We have developed a prototype system for the ILC vertex detector based on
DEPFET pixels. The system operates a 128x64 matrix (with ~35x25 square micron
large pixels) and uses two dedicated microchips, the SWITCHER II chip for
matrix steering and the CURO II chip for readout. The system development has
been driven by the final ILC requirements which above all demand a detector
thinned to 50 micron and a row wise read out with line rates of 20MHz and more.
The targeted noise performance for the DEPFET technology is in the range of
ENC=100 e-. The functionality of the system has been demonstrated using
different radioactive sources in an energy range from 6 to 40keV. In recent
test beam experiments using 6GeV electrons, a signal-to-noise ratio of S/N~120
has been achieved with present sensors being 450 micron thick. For improved
DEPFET systems using 50 micron thin sensors in future, a signal-to-noise of 40
is expected.Comment: Invited poster at the International Symposium on the Development of
Detectors for Particle, AstroParticle and Synchrotron Radiation Experiments,
Stanford CA (SNIC06) 6 pages, 12 eps figure
On the quantum analogue of Galileo's leaning tower experiment
The quantum analogue of Galileo's leaning tower experiment is revisited using
wave packets evolving under the gravitational potential. We first calculate the
position detection probabilities for particles projected upwards against
gravity around the classical turning point and also around the point of initial
projection, which exhibit mass dependence at both these points. We then compute
the mean arrival time of freely falling particles using the quantum probability
current, which also turns out to be mass dependent. The mass dependence of both
the position detection probabilities and the mean arrival time vanish in the
limit of large mass. Thus, compatibility between the weak equivalence principle
and quantum mechanics is recovered in the macroscopic limit of the latter.Comment: Latex, 12 pages, 1 figure, uses IOP style, clarifications and
references adde
Relativistic Aharonov-Casher Phase in Spin One
The Aharonov-Casher (AC) phase is calculated in relativistic wave equations
of spin one. The AC phase has previously been calculated from the Dirac-Pauli
equation using a gauge-like technique \cite{MK1,MK2}. In the spin-one case, we
use Kemmer theory (a Dirac-like particle theory) to calculate the phase in a
similar manner. However the vector formalism, the Proca theory, is more widely
known and used. In the presence of an electromagnetic field, the two theories
are `equivalent' and may be transformed into one another. We adapt these
transformations to show that the Kemmer theory results apply to the Proca
theory. Then we calculate the Aharonov-Casher phase for spin-one particles
directly in the Proca formalism.Comment: 12 page
Quantum Mechanics of Proca Fields
We construct the most general physically admissible positive-definite inner
product on the space of Proca fields. Up to a trivial scaling this defines a
five-parameter family of Lorentz invariant inner products that we use to
construct a genuine Hilbert space for the quantum mechanics of Proca fields. If
we identify the generator of time-translations with the Hamiltonian, we obtain
a unitary quantum system that describes first-quantized Proca fields and does
not involve the conventional restriction to the positive-frequency fields. We
provide a rather comprehensive analysis of this system. In particular, we
examine the conserved current density responsible for the conservation of the
probabilities, explore the global gauge symmetry underlying the conservation of
the probabilities, obtain a probability current density, construct position,
momentum, helicity, spin, and angular momentum operators, and determine the
localized Proca fields. We also compute the generalized parity (\cP),
generalized time-reversal (\cT), and generalized charge or chirality (\cC)
operators for this system and offer a physical interpretation for its
\cP\cT-, \cC-, and \cC\cP\cT-symmetries.Comment: Published version, typos fixed, a change in symbol, 1 fi
Proposal for chiral bosons search at LHC via their unique new signature
The resonance production of new chiral spin-1 bosons and their detection
through the Drell--Yan process at the CERN LHC is considered. Quantitative
evaluations of various differential cross-sections of the chiral bosons
production are made within the CalcHEP package. The new neutral chiral bosons
can be observed as a Breit--Wigner resonance peak in the invariant dilepton
mass distribution, as usual. However, unique new signatures of the chiral
bosons exist. First, there is no Jacobian peak in the lepton transverse
momentum distribution. Second, the lepton angular distribution in the
Collins-Soper frame for the high on-peak invariant masses of the lepton pairs
has a peculiar "swallowtail" shape.Comment: 4 pages, 5 figure
Approximate solution of the Duffin-Kemmer-Petiau equation for a vector Yukawa potential with arbitrary total angular momenta
The usual approximation scheme is used to study the solution of the
Duffin-Kemmer-Petiau (DKP) equation for a vector Yukawa potential in the
framework of the parametric Nikiforov-Uvarov (NU) method. The approximate
energy eigenvalue equation and the corresponding wave function spinor
components are calculated for arbitrary total angular momentum in closed form.
Further, the approximate energy equation and wave function spinor components
are also given for case. A set of parameter values is used to obtain the
numerical values for the energy states with various values of quantum levelsComment: 17 pages; Communications in Theoretical Physics (2012). arXiv admin
note: substantial text overlap with arXiv:1205.0938, and with
arXiv:quant-ph/0410159 by other author
Anomalously interacting new extra vector bosons and their first LHC constraints
In this review phenomenological consequences of the Standard Model extension
by means of new spin-1 chiral fields with the internal quantum numbers of the
electroweak Higgs doublets are summarized. The prospects for resonance
production and detection of the chiral vector and bosons at
the LHC energies are considered. The boson can be observed as a
Breit-Wigner resonance peak in the invariant dilepton mass distributions in the
same way as the well-known extra gauge bosons. However, the bosons
have unique signatures in transverse momentum, angular and pseudorapidity
distributions of the final leptons, which allow one to distinguish them from
other heavy neutral resonances. In 2010, with 40 pb of the LHC
proton-proton data at the energy 7 TeV, the ATLAS detector was used to search
for narrow resonances in the invariant mass spectrum of and
final states and high-mass charged states decaying to a charged
lepton and a neutrino. No statistically significant excess above the Standard
Model expectation was observed. The exclusion mass limits of 1.15 TeV and
1.35 TeV were obtained for the chiral neutral and charged
bosons, respectively. These are the first direct limits on the and
boson production. For almost all currently considered exotic models the
relevant signal is expected in the central dijet rapidity region. On the
contrary, the chiral bosons do not contribute to this region but produce an
excess of dijet events far away from it. For these bosons the appropriate
kinematic restrictions lead to a dip in the centrality ratio distribution over
the dijet invariant mass instead of a bump expected in the most exotic models.Comment: 24 pages, 34 figure, based on talk given by V.A.Bednyakov at 15th
Lomonosov conference, 22.08.201
Cross-linked amylose bio-plastic: A transgenic-based compostable plastic alternative
Bio-plastics and bio-materials are composed of natural or biomass derived polymers, offering solutions to solve immediate environmental issues. Polysaccharide-based bio-plastics represent important alternatives to conventional plastic because of their intrinsic biodegradable nature. Amylose-only (AO), an engineered barley starch with 99% amylose, was tested to produce cross-linked all-natural bioplastic using normal barley starch as a control. Glycerol was used as plasticizer and citrate cross-linking was used to improve the mechanical properties of cross-linked AO starch extrudates. Extrusion converted the control starch from A-type to Vh- and B-type crystals, showing a complete melting of the starch crystals in the raw starch granules. The cross-linked AO and control starch specimens displayed an additional wide-angle diffraction reflection. Phospholipids complexed with Vh-type single helices constituted an integrated part of the AO starch specimens. Gas permeability tests of selected starch-based prototypes demonstrated properties comparable to that of commercial Mater-Bi© plastic. The cross-linked AO prototypes had composting characteristics not different from the control, indicating that the modified starch behaves the same as normal starch. The data shows the feasibility of producing all-natural bioplastic using designer starch as raw material
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