The neutron and its role in cosmology and particle physics

Experiments with cold and ultracold neutrons have reached a level of precision such that problems far beyond the scale of the present Standard Model of particle physics become accessible to experimental investigation. Due to the close links between particle physics and cosmology, these studies also permit a deep look into the very first instances of our universe. First addressed in this article, both in theory and experiment, is the problem of baryogenesis ... The question how baryogenesis could have happened is open to experimental tests, and it turns out that this problem can be curbed by the very stringent limits on an electric dipole moment of the neutron, a quantity that also has deep implications for particle physics. Then we discuss the recent spectacular observation of neutron quantization in the earth's gravitational field and of resonance transitions between such gravitational energy states. These measurements, together with new evaluations of neutron scattering data, set new constraints on deviations from Newton's gravitational law at the picometer scale. Such deviations are predicted in modern theories with extra-dimensions that propose unification of the Planck scale with the scale of the Standard Model ... Another main topic is the weak-interaction parameters in various fields of physics and astrophysics that must all be derived from measured neutron decay data. Up to now, about 10 different neutron decay observables have been measured, much more than needed in the electroweak Standard Model. This allows various precise tests for new physics beyond the Standard Model, competing with or surpassing similar tests at high-energy. The review ends with a discussion of neutron and nuclear data required in the synthesis of the elements during the "first three minutes" and later on in stellar nucleosynthesis.Comment: 91 pages, 30 figures, accepted by Reviews of Modern Physic

Quasi-Atomistic Approach to Modeling of Liposomes

Small-angle X-ray scattering is an important structural tool for studying biological membranes; however, interpretation of scattering data remains a challenging problem. In most cases, analysis makes it possible to determine some structural parameters and the electron density profile of lipid bilayers, but no methods providing more detailed information (e.g., about the structural organization of vesicles) have been proposed yet. An approach making it possible to determine the main integral characteristics of liposomes using small-angle scattering is presented in this study. Within this approach a quasi-atomic model of liposome is built from individual lipid molecules, which form a sphere or a hollow ellipsoid. The method has been implemented in a computer program, verified on experimental small-angle X-ray scattering data, and proposed to analyze the structure of lipid vesicles and their interactions with proteins