Theoretical Constraints and Systematic Effects in the Determination of the Proton Form Factors

We calculate the two-photon exchange corrections to electron-proton scattering with nucleon and $\Delta$ intermediate states. The results show a dependence on the elastic nucleon and nucleon-$\Delta$-transition form factors used as input which leads to significant changes compared to previous calculations. We discuss the relevance of these corrections and apply them to the most recent and precise data set and world data from electron-proton scattering. Using this, we show how the form factor extraction from these data is influenced by the subsequent inclusion of physical constraints. The determination of the proton charge radius from scattering data is shown to be dominated by the enforcement of a realistic spectral function. Additionally, the third Zemach moment from the resulting form factors is calculated. The obtained radius and Zemach moment are shown to be consistent with Lamb shift measurements in muonic hydrogen.Comment: minor changes, added references, version to appear in PR

Benchmark calculations for elastic fermion-dimer scattering

We present continuum and lattice calculations for elastic scattering between a fermion and a bound dimer in the shallow binding limit. For the continuum calculation we use the Skorniakov-Ter-Martirosian (STM) integral equation to determine the scattering length and effective range parameter to high precision. For the lattice calculation we use the finite-volume method of L\"uscher. We take into account topological finite-volume corrections to the dimer binding energy which depend on the momentum of the dimer. After subtracting these effects, we find from the lattice calculation kappa a_fd = 1.174(9) and kappa r_fd = -0.029(13). These results agree well with the continuum values kappa a_fd = 1.17907(1) and kappa r_fd = -0.0383(3) obtained from the STM equation. We discuss applications to cold atomic Fermi gases, deuteron-neutron scattering in the spin-quartet channel, and lattice calculations of scattering for nuclei and hadronic molecules at finite volume.Comment: 16 pages, 5 figure

Few-body physics in effective field theory

Effective Field Theory (EFT) provides a powerful framework that exploits a separation of scales in physical systems to perform systematically improvable, model-independent calculations. Particularly interesting are few-body systems with short-range interactions and large two-body scattering length. Such systems display remarkable universal features. In systems with more than two particles, a three-body force with limit cycle behavior is required for consistent renormalization already at leading order. We will review this EFT and some of its applications in the physics of cold atoms and nuclear physics. In particular, we will discuss the possibility of an infrared limit cycle in QCD. Recent extensions of the EFT approach to the four-body system and N-boson droplets in two spatial dimensions will also be addressed.Comment: 10 pages, 5 figures, Proceedings of the INT Workshop on "Nuclear Forces and the Quantum Many-Body Problem", Oct. 200

A Semantic Framework for the Security Analysis of Ethereum smart contracts

Smart contracts are programs running on cryptocurrency (e.g., Ethereum) blockchains, whose popularity stem from the possibility to perform financial transactions, such as payments and auctions, in a distributed environment without need for any trusted third party. Given their financial nature, bugs or vulnerabilities in these programs may lead to catastrophic consequences, as witnessed by recent attacks. Unfortunately, programming smart contracts is a delicate task that requires strong expertise: Ethereum smart contracts are written in Solidity, a dedicated language resembling JavaScript, and shipped over the blockchain in the EVM bytecode format. In order to rigorously verify the security of smart contracts, it is of paramount importance to formalize their semantics as well as the security properties of interest, in particular at the level of the bytecode being executed. In this paper, we present the first complete small-step semantics of EVM bytecode, which we formalize in the F* proof assistant, obtaining executable code that we successfully validate against the official Ethereum test suite. Furthermore, we formally define for the first time a number of central security properties for smart contracts, such as call integrity, atomicity, and independence from miner controlled parameters. This formalization relies on a combination of hyper- and safety properties. Along this work, we identified various mistakes and imprecisions in existing semantics and verification tools for Ethereum smart contracts, thereby demonstrating once more the importance of rigorous semantic foundations for the design of security verification techniques.Comment: The EAPLS Best Paper Award at ETAP

Potential Energy Surface for H_2 Dissociation over Pd(100)

The potential energy surface (PES) of dissociative adsorption of H_2 on Pd(100) is investigated using density functional theory and the full-potential linear augmented plane wave (FP-LAPW) method. Several dissociation pathways are identified which have a vanishing energy barrier. A pronounced dependence of the potential energy on ``cartwheel'' rotations of the molecular axis is found. The calculated PES shows no indication of the presence of a precursor state in front of the surface. Both results indicate that steering effects determine the observed decrease of the sticking coefficient at low energies of the H_2 molecules. We show that the topology of the PES is related to the dependence of the covalent H(s)-Pd(d) interactions on the orientation of the H_2 molecule.Comment: RevTeX, 8 pages, 5 figures in uufiles forma

Recursive self-organizing map as a contractive iterative function system

Recently, there has been a considerable research activity in extending topographic maps of vectorial data to more general data structures, such as sequences or trees. However, the representational capabilities and internal representations of the models are not well understood. We rigorously analyze a generalization of the Self-Organizing Map (SOM) for processing sequential data, Recursive SOM (RecSOM [1]), as a non-autonomous dynamical system consisting off a set of fixed input maps. We show that contractive fixed input maps are likely to produce Markovian organizations of receptive fields o the RecSOM map. We derive bounds on parameter $\beta$ (weighting the importance of importing past information when processing sequences) under which contractiveness of the fixed input maps is guaranteed

Strange chiral nucleon form factors

We investigate the strange electric and magnetic form factors of the nucleon in the framework of heavy baryon chiral perturbation theory to third order in the chiral expansion. All counterterms can be fixed from data. In particular, the two unknown singlet couplings can be deduced from the parity-violating electron scattering experiments performed by the SAMPLE and the HAPPEX collaborations. Within the given uncertainties, our analysis leads to a small and positive electric strangeness radius, $= (0.05 \pm 0.09) fm^2$. We also deduce the consequences for the upcoming MAMI A4 experiment.Comment: 7 pp, REVTeX, uses epsf, minor correction

The size of the proton - closing in on the radius puzzle

We analyze the recent electron-proton scattering data from Mainz using a dispersive framework that respects the constraints from analyticity and unitarity on the nucleon structure. We also perform a continued fraction analysis of these data. We find a small electric proton charge radius, r_E^p = 0.84_{-0.01}^{+0.01} fm, consistent with the recent determination from muonic hydrogen measurements and earlier dispersive analyses. We also extract the proton magnetic radius, r_M^p = 0.86_{-0.03}^{+0.02} fm, consistent with earlier determinations based on dispersion relations.Comment: 4 pages, 2 figures, fit improved, small modifications, section on continued fractions modified, conclusions on the proton charge radius unchanged, version accepted for publication in European Physical Journal

Reduction of Acetylmethylcarbinol and Diacetyl to 2,3-Butylene Glycol by the citric acid fermenting streptococci of butter cultures

When acetylmethylcarbinol or diacetyl was added to a tomato bouillon culture of one of the citric acid fermenting streptococci normally present in butter cultures, there was a rapid disappearance of the added reagent and an increase in 2,3-butylene glycol. The amount of the glycol produced accounted, in a general way, for the acetylmethylcarbinol or diacetyl that disappeared. The added reagent did not usually disappear completely. In trials with acetylmethylcarbinol the change of the carbinol to the glycol was delayed when sulfuric acid was added in amounts to yield a pH of from 3.8 to 4.0. There was also a change of acetylmethylcarbinol or diacetyl to 2,3-butylene glycol when one of these reagents was added to a milk culture of one of the organisms. With the diacetyl there was an increase in the acetylmethylcarbinol as well as in the 2,3-butylene glycol, and the increase in the carbinol was greater than the increase in the glycol. The added reagent did not disappear completely in any of the trials. When various amounts of sulfuric acid were added to milk cultures of the organisms, acetylmethylcarbinol was not produced at the higher pH values but was produced at the lower values, while 2,3-butylene glycol was produced at both the higher and lower pH values. There was less of the glycol formed at the lower pH values than at the higher ones. The total molarities of acetylmethylcarbinol and 2,3-butylene glycol showed an increase as the pH was lowered, although there were some irregularities in the increase with one of the organisms. The addition of 0.65 percent citric acid to a milk culture of one of the organisms resulted in an increase in both acetylmethylcarbinol and 2,3-butylene glycol. The reduction of acetylmethylcarbinol, which had been added to a milk culture of one of the organisms, to 2,3-butylene glycol was not delayed by potassium nitrate in the quantity used but was delayed by the largest amount of hydrogen peroxide employed. In pure cultures of the citric acid fermenting streptococci which had been acidified with sulfuric acid to a pH of about 3.9, the addition of acetaldehyde or propionaldehyde increased the amount of acetylmethylcarbinol present after 96 hours at 21 °C. but decreased the amount of 2,3-butylene glycol and also commonly decreased the total molarities of the two compounds. These results suggest that the increased production of acetylmethylcarbinol is accounted for by a decrease in the reduction of the carbinol to the corresponding glycol, rather than to an aldehyde condensation involving, in part, the added aldehyde. In butter cultures the decrease in acetylmethylcarbinol was accompanied by an increase in 2,3-butylene glycol, and there was commonly an increase, from one examination to the next, in the total molarities of the two compounds. When ripened butter cultures were neutralized to a low acidity there was a rapid decrease in the acetylmethylcarbinol, and in some of the trials this was followed by an increase. The decrease in the carbinol was accompanied by a rapid increase in 2,3-butylene glycol, and there was also an increase in the total molarities of the two compounds. Hydrogen peroxide, in certain concentrations, delayed the reduction of acetylmethylcarbinol to 2,3-butylene glycol as did also 1 percent sodium fumarate or 12 percent sodium chloride. Ice water temperatures also delayed the reduction in either neutralized or unneutralized cultures, but the reduction was more rapid with neutralization than without