32 research outputs found
An Extended Model for the Evolution of Prebiotic Homochirality: A Bottom-Up Approach to the Origin of Life
A generalized autocatalytic model for chiral polymerization is investigated
in detail. Apart from enantiomeric cross-inhibition, the model allows for the
autogenic (non-catalytic) formation of left and right-handed monomers from a
substrate with reaction rates and , respectively. The
spatiotemporal evolution of the net chiral asymmetry is studied for models with
several values of the maximum polymer length, N. For N=2, we study the validity
of the adiabatic approximation often cited in the literature. We show that the
approximation obtains the correct equilibrium values of the net chirality, but
fails to reproduce the short time behavior. We show also that the autogenic
term in the full N=2 model behaves as a control parameter in a chiral symmetry-
breaking phase transition leading to full homochirality from racemic initial
conditions. We study the dynamics of the N -> infinity model with symmetric
() autogenic formation, showing that it only achieves
homochirality for , where is an N-dependent
critical value. For we investigate the behavior of
models with several values of N, showing that the net chiral asymmetry grows as
tanh(N). We show that for a given symmetric autogenic reaction rate, the net
chirality and the concentrations of chirally pure polymers increase with the
maximum polymer length in the model. We briefly discuss the consequences of our
results for the development of homochirality in prebiotic Earth and possible
experimental verification of our findings
Prebiotic Homochirality as a Critical Phenomenon
The development of prebiotic homochirality on early-Earth or another
planetary platform may be viewed as a critical phenomenon. It is shown, in the
context of spatio-temporal polymerization reaction networks, that environmental
effects -- be them temperature surges or other external disruptions -- may
destroy any net chirality previously produced. In order to understand the
emergence of prebiotic homochirality it is important to model the coupling of
polymerization reaction networks to different planetary environments.Comment: 6 Pages, 1 Figure, In Press: Origins of Life and Evolution of
Biosphere
Search for electric dipole moments at storage rings
Permanent electric dipole moments (EDMs) violate parity and time reversal
symmetry. Within the Standard Model (SM) they are many orders of magnitude
below present experimental sensitivity. Many extensions of the SM predict much
larger EDMs, which are therefore an excellent probe for the existence of "new
physics". Until recently it was believed that only electrically neutral systems
could be used for sensitive searches of EDMs. With the introduction of a novel
experimental method, high precision for charged systems will be within reach as
well. The features of this method and its possibilities are discussed.Comment: Proc. EXA2011, 6 pages;
http://www.springerlink.com/content/45l35376832vhrg0
Chiral Polymerization in Open Systems From Chiral-Selective Reaction Rates
We investigate the possibility that prebiotic homochirality can be achieved
exclusively through chiral-selective reaction rate parameters without any other
explicit mechanism for chiral bias. Specifically, we examine an open network of
polymerization reactions, where the reaction rates can have chiral-selective
values. The reactions are neither autocatalytic nor do they contain explicit
enantiomeric cross-inhibition terms. We are thus investigating how rare a set
of chiral-selective reaction rates needs to be in order to generate a
reasonable amount of chiral bias. We quantify our results adopting a
statistical approach: varying both the mean value and the rms dispersion of the
relevant reaction rates, we show that moderate to high levels of chiral excess
can be achieved with fairly small chiral bias, below 10%. Considering the
various unknowns related to prebiotic chemical networks in early Earth and the
dependence of reaction rates to environmental properties such as temperature
and pressure variations, we argue that homochirality could have been achieved
from moderate amounts of chiral selectivity in the reaction rates.Comment: 15 pages, 6 figures, accepted for publication in Origins of Life and
Evolution of Biosphere
Ultracold dense gas of deeply bound heteronuclear molecules
Recently, the quest for an ultracold and dense ensemble of polar molecules
has attracted strong interest. Polar molecules have bright prospects for novel
quantum gases with long-range and anisotropic interactions, for quantum
information science, and for precision measurements. However, high-density
clouds of ultracold polar molecules have so far not been produced. Here, we
report a key step towards this goal. Starting from an ultracold dense gas of
heteronuclear 40K-87Rb Feshbach molecules with typical binding energies of a
few hundred kHz and a negligible dipole moment, we coherently transfer these
molecules into a vibrational level of the ground-state molecular potential
bound by >10 GHz. We thereby increase the binding energy and the expected
dipole moment of the 40K-87Rb molecules by more than four orders of magnitude
in a single transfer step. Starting with a single initial state prepared with
Feshbach association, we achieve a transfer efficiency of 84%. While dipolar
effects are not yet observable, the presented technique can be extended to
access much more deeply bound vibrational levels and ultimately those
exhibiting a significant dipole moment. The preparation of an ultracold quantum
gas of polar molecules might therefore come within experimental reach.Comment: 5 pages, 5 figure
Punctuated Chirality
Most biomolecules occur in mirror, or chiral, images of each other. However,
life is homochiral: proteins contain almost exclusively levorotatory (L) amino
acids, while only dextrorotatory (R) sugars appear in RNA and DNA. The
mechanism behind this fundamental asymmetry of life remains an open problem.
Coupling the spatiotemporal evolution of a general autocatalytic polymerization
reaction network to external environmental effects, we show through a detailed
statistical analysis that high intensity and long duration events may drive
achiral initial conditions towards chirality. We argue that life's
homochirality resulted from sequential chiral symmetry breaking triggered by
environmental events, thus extending the theory of punctuated equilibrium to
the prebiotic realm. Applying our arguments to other potentially life-bearing
planetary platforms, we predict that a statistically representative sampling
will be racemic on average.Comment: 13 pages, 4 color figures. Final version published in Origins of Life
and Evolution of Biospheres. Typos corrected, figures improved, and a few
definitions and word usage clarifie
QCD and strongly coupled gauge theories : challenges and perspectives
We highlight the progress, current status, and open challenges of QCD-driven physics, in theory and in experiment. We discuss how the strong interaction is intimately connected to a broad sweep of physical problems, in settings ranging from astrophysics and cosmology to strongly coupled, complex systems in particle and condensed-matter physics, as well as to searches for physics beyond the Standard Model. We also discuss how success in describing the strong interaction impacts other fields, and, in turn, how such subjects can impact studies of the strong interaction. In the course of the work we offer a perspective on the many research streams which flow into and out of QCD, as well as a vision for future developments.Peer reviewe