Electromagnetic corrections to light hadron masses

At the precision reached in current lattice QCD calculations, electromagnetic effects are becoming numerically relevant. We will present preliminary results for electromagnetic corrections to light hadron masses, based on simulations in which a $\mathrm{U}(1)$ degree of freedom is superimposed on $N_f=2+1$ QCD configurations from the BMW collaboration.Comment: 7 pages, 2 figures, The XXVIII International Symposium on Lattice Field Theory, June 14-19,2010, Villasimius, Sardinia Ital

Non-Gaussian Resistance Noise near Electrical Breakdown in Granular Materials

The distribution of resistance fluctuations of conducting thin films with granular structure near electrical breakdown is studied by numerical simulations. The film is modeled as a resistor network in a steady state determined by the competition between two biased processes, breaking and recovery. Systems of different sizes and with different levels of internal disorder are considered. Sharp deviations from a Gaussian distribution are found near breakdown and the effect increases with the degree of internal disorder. However, we show that in general this non-Gaussianity is related to the finite size of the system and vanishes in the large size limit. Nevertheless, near the critical point of the conductor-insulator transition, deviations from Gaussianity persist when the size is increased and the distribution of resistance fluctuations is well fitted by the universal Bramwell-Holdsworth-Pinton distribution.Comment: 8 pages, 6 figures; accepted for publication on Physica

The "Multimat" experiment at CERN HiRadMat facility: advanced testing of novel materials and instrumentation for HL-LHC collimators

The increase of the stored beam energy in future particle accelerators, such as the HL-LHC and the FCC, calls for a radical upgrade in the design, materials and instrumentation of Beam Intercepting Devices (BID), such as collimators Following successful tests in 2015 that validated new composite materials and a novel jaw design conceived for the HL-LHC collimators, a new HiRadMat experiment, named “HRMT36-MultiMat”, is scheduled for autumn 2017. Its objective is to determine the behaviour under high intensity proton beams of a broad range of materials relevant for collimators and beam intercepting devices, thin-film coatings and advanced equipment. The test bench features 16 separate target stations, each hosting various specimens, allowing the exploration of complex phenomena such as dynamic strength, internal damping, nonlinearities due to anisotropic inelasticity and inhomogeneity, effects of energy deposition and radiation on coatings. This paper details the main technical solutions and engineering calculations for the design of the test bench and of the specimens, the candidate target materials and the instrumentation system

Universal Magnetic Fluctuations with a Field Induced Length Scale

We calculate the probability density function for the order parameter fluctuations in the low temperature phase of the 2D-XY model of magnetism near the line of critical points. A finite correlation length, \xi, is introduced with a small magnetic field, h, and an accurate expression for \xi(h) is developed by treating non-linear contributions to the field energy using a Hartree approximation. We find analytically a series of universal non-Gaussian distributions with a finite size scaling form and present a Gumbel-like function that gives the PDF to an excellent approximation. We propose the Gumbel exponent, a(h), as an indirect measure of the length scale of correlations in a wide range of complex systems.Comment: 7 pages, 4 figures, 1 table. To appear in Phys. Rev.

Ab initio calculation of the neutron-proton mass difference

The existence and stability of atoms rely on the fact that neutrons are more massive than protons. The measured mass difference is only 0.14% of the average of the two masses. A slightly smaller or larger value would have led to a dramatically different universe. Here, we show that this difference results from the competition between electromagnetic and mass isospin breaking effects. We performed lattice quantum-chromodynamics and quantum-electrodynamics computations with four nondegenerate Wilson fermion flavors and computed the neutron-proton mass-splitting with an accuracy of 300 kilo-electron volts, which is greater than 0 by 5 standard deviations. We also determine the splittings in the Sigma, Xi, D, and Xi(cc) isospin multiplets, exceeding in some cases the precision of experimental measurements

Up and Down Quark Masses and Corrections to Dashen's Theorem from Lattice QCD and Quenched QED

In a previous letter (arXiv:1306.2287) we determined the isospin mass splittings of the baryon octet from a lattice calculation based on quenched QED and $N_f{=}2{+}1$ QCD simulations with 5 lattice spacings down to $0.054~\mathrm{fm}$, lattice sizes up to $6~\mathrm{fm}$ and average up-down quark masses all the way down to their physical value. Using the same data we determine here the corrections to Dashen's theorem and the individual up and down quark masses. For the parameter which quantifies violations to Dashens's theorem, we obtain $\epsilon=0.73(2)(5)(17)$, where the first error is statistical, the second is systematic, and the third is an estimate of the QED quenching error. For the light quark masses we obtain, $m_u=2.27(6)(5)(4)~\mathrm{MeV}$ and $m_d=4.67(6)(5)(4)~\mathrm{MeV}$ in the $\bar{\mathrm{MS}}$ scheme at $2~\mathrm{GeV}$ and the isospin breaking ratios $m_u/m_d=0.485(11)(8)(14)$, $R=38.2(1.1)(0.8)(1.4)$ and $Q=23.4(0.4)(0.3)(0.4)$. Our results exclude the $m_u=0$ solution to the strong CP problem by more than $24$ standard deviations

Light Hadron Masses from Lattice QCD

This article reviews lattice QCD results for the light hadron spectrum. We give an overview of different formulations of lattice QCD, with discussions on the fermion doubling problem and improvement programs. We summarize recent developments in algorithms and analysis techniques, that render calculations with light, dynamical quarks feasible on present day computer resources. Finally, we summarize spectrum results for ground state hadrons and resonances using various actions.Comment: 53 pages, 24 figures, one table; Rev.Mod.Phys. (published version); v2: corrected typ

The Hidden Curriculum of Veterinary Education: Mediators and Moderators of Its Effects

The “hidden curriculum” has long been supposed to have an effect on students' learning during their clinical education, and in particular in shaping their ideas of what it means to be a professional. Despite this, there has been little evidence linking specific changes in professional attitudes to the individual components of the hidden curriculum. This study aimed to recognize those components that led to a change in students' professional attitudes at a UK veterinary school, as well as to identify the attitudes most affected. Observations were made of 11 student groups across five clinical rotations, followed by semi-structured interviews with 23 students at the end of their rotation experience. Data were combined and analyzed thematically, taking both an inductive and deductive approach. Views about the importance of technical competence and communication skills were promoted as a result of students' interaction with the hidden curriculum, and tensions were revealed in relation to their attitudes toward compassion and empathy, autonomy and responsibility, and lifestyle ethic. The assessment processes of rotations and the clinical service organization served to communicate the messages of the hidden curriculum, bringing about changes in student professional attitudes, while student-selected role models and the student rotation groups moderated the effects of these influences