Muon g-2: Review of Theory and Experiment

A review of the experimental and theoretical determinations of the anomalous magnetic moment of the muon is given. The anomaly is defined by a=(g-2)/2, where the Land\'e g-factor is the proportionality constant that relates the spin to the magnetic moment. For the muon, as well as for the electron and tauon, the anomaly a differs slightly from zero (of order 10^{-3}) because of radiative corrections. In the Standard Model, contributions to the anomaly come from virtual `loops' containing photons and the known massive particles. The relative contribution from heavy particles scales as the square of the lepton mass over the heavy mass, leading to small differences in the anomaly for e, \mu, and \tau. If there are heavy new particles outside the Standard Model which couple to photons and/or leptons, the relative effect on the muon anomaly will be \sim (m_\mu/ m_e)^2 \approx 43\times 10^3 larger compared with the electron anomaly. Because both the theoretical and experimental values of the muon anomaly are determined to high precision, it is an excellent place to search for the effects of new physics, or to constrain speculative extensions to the Standard Model. Details of the current theoretical evaluation, and of the series of experiments that culminates with E821 at the Brookhaven National Laboratory are given. At present the theoretical and the experimental values are known with a similar relative precision of 0.5 ppm. There is, however, a 3.4 standard deviation difference between the two, strongly suggesting the need for continued experimental and theoretical studyComment: 103 pages, 57 figures, submitted to Reports on Progress in Physics Final version as published, several minor clarifications to text and a number of references were correcte

Spontaneous alloying in binary metal microclusters - A molecular dynamics study -

Microcanonical molecular dynamics study of the spontaneous alloying(SA), which is a manifestation of fast atomic diffusion in a nano-sized metal cluster, is done in terms of a simple two dimensional binary Morse model. Important features observed by Yasuda and Mori are well reproduced in our simulation. The temperature dependence and size dependence of the SA phenomena are extensively explored by examining long time dynamics. The dominant role of negative heat of solution in completing the SA is also discussed. We point out that a presence of melting surface induces the diffusion of core atoms even if they are solid-like. In other words, the {\it surface melting} at substantially low temperature plays a key role in attaining the SA.Comment: 15 pages, 12 fgures, Submitted to Phys.Rev.

Semi-analytic modeling of the EBL and consequences for extragalactic gamma-ray spectra

Attenuation of high-energy gamma rays by pair-production with UV, optical and IR extragalactic background light (EBL) photons provides a link between the history of galaxy formation and high-energy astrophysics. We present results from our latest semi-analytic models (SAMs), which employ the main ingredients thought to be important to galaxy formation and evolution, as well as an improved model for reprocessing of starlight by dust to mid- and far-IR wavelengths. These SAMs are based upon a Lambda-CDM hierarchical structural formation scenario, and are successful in reproducing a large variety of observational constraints such as number counts, luminosity and mass functions, and color bimodality. Our fiducial model is based upon a WMAP5 cosmology, and treats dust emission using empirical templates. This model predicts a background flux considerably lower than optical and near-IR measurements that rely on subtraction of zodiacal and galactic foregrounds, and near the lower bounds set by number counts of resolvable sources at a large number of wavelengths. We also show the results of varying cosmological parameters and dust attenuation model used in our SAM. For each EBL prediction, we show how the optical depth due to electron-positron pair-production is affected by redshift and gamma-ray energy, and the effect of gamma-ray absorption on the spectra of a variety of extragalactic sources. We conclude with a discussion of the implications of our work, comparisons to other models and key measurements of the EBL and a discussion of how the burgeoning science of gamma-ray astronomy will continue to help constrain cosmology. The low EBL flux predicted by our fiducial model suggests an optimistic future for further studies of distant gamma-ray sources.Comment: 23 pages, 11 figures, 3 tables, accepted by MNRAS; this preprint matches accepted versio

Ultradiscrete kinks with supersonic speed in a layered crystal with realistic potentials

We develop a dynamical model of the propagating nonlinear localized excitations, supersonic kinks, in the cation layer in a silicate mica crystal. We start from purely electrostatic Coulomb interaction and add the Ziegler-Biersack-Littmark short-range repulsive potential and the periodic potential produced by other atoms of the lattice. This approach allows the construction of supersonic kinks which can propagate in the lattice within a large range of energies and velocities. The interparticle distances in the lattice kinks with high energy are physically reasonable values. The introduction of the periodic lattice potential results in the important feature that the kinks propagate with a single velocity and a single energy which are independent on the excitation conditions. The found kinks are ultra-discrete and can be described with the "magic wave number" $q\simeq 2\pi/3a$, which was previously revealed in the nonlinear sinusoidal waves and supersonic kinks in the Fermi-Pasta-Ulam lattice. The extreme discreteness of the supersonic kinks, with basically two particles moving at the same time, allows the interpretation of their double-kink structure. The energy of the supersonic kinks is between the possible source of $^{40}$K recoil in beta decay and the energy necessary for the ejection of an atom at the border as has been found experimentally.Comment: 14 pages, 15 figure

Collectivity of neutron-rich Ti isotopes

The structure of the neutron-rich nucleus 58Ti was investigated via proton inelastic scattering in inverse kinematics at a mean energy of 42.0 MeV/nucleon. By measuring the deexcitation γ rays, three transitions with the energies of 1046(11) keV, 1376(18) keV, and 1835(27) keV were identified. The angle-integrated cross section for the 1046-keV excitation, which corresponds to the decay from the first 2+ state, was determined to be 13(7) mb. The deformation length δp,p′ was extracted from the cross section to be 0.83−0.30+0.22 fm. The energy of the first 2+ state and the δp,p′ value are comparable to the ones of 56Ti, which indicates that the collectivity of the Ti isotopes does not increase significantly with neutron number until N=36. This fact indicates that 58Ti is outside of the region of the deformation known in the neutron-rich nuclei around N=40

Dirac fermions and flat bands in the ideal kagome metal FeSn.

A kagome lattice of 3d transition metal ions is a versatile platform for correlated topological phases hosting symmetry-protected electronic excitations and magnetic ground states. However, the paradigmatic states of the idealized two-dimensional kagome lattice-Dirac fermions and flat bands-have not been simultaneously observed. Here, we use angle-resolved photoemission spectroscopy and de Haas-van Alphen quantum oscillations to reveal coexisting surface and bulk Dirac fermions as well as flat bands in the antiferromagnetic kagome metal FeSn, which has spatially decoupled kagome planes. Our band structure calculations and matrix element simulations demonstrate that the bulk Dirac bands arise from in-plane localized Fe-3d orbitals, and evidence that the coexisting Dirac surface state realizes a rare example of fully spin-polarized two-dimensional Dirac fermions due to spin-layer locking in FeSn. The prospect to harness these prototypical excitations in a kagome lattice is a frontier of great promise at the confluence of topology, magnetism and strongly correlated physics

Injustice and Balance in Pervasive Video Games

Sendo um meio artistico intimamente relacionado com o avanço da tecnologia, alguns dos video-jogos mais interessantes são feitos através da expansão dos limites técnicos do que é considerado um jogo. Tal como o salto de gráficos em 2D para 3D, o impacto da internet em jogos multi-player e a inter-conectividade entre jogadores, ou a forma como a realidade virtual e a realidade aumentada têm mudado o que é possível dentro de um mundo virtual, há um outro género que tem aumentado em popularidade com a chegada de tecnologia nova - jogos pervasivos. O género de jogos pervasivos engloba jogos que misturam o mundo virtual do jogo e o mundo real através dos dados contextuais e de localização do jogador, servindo-se dos novos avanços tecnológicos acerca de tecnologia móvel. O fenómeno de Pokémon GO liderou a quebra do género para o mainstream, permitindo a que muitos outros jogos semelhantes tenham sucesso e obtendo para si uma audiência mundial considerável. Ao contrário de jogos de realidade aumentada - que esperam que o jogador veja o mundo através de uma câmara e a ela aplica os elementos do mundo virtual - os jogos pervasivos usam dados do mundo real como a sua base de construção. Existe bastante junção entre estes dois géneros de jogo, como vendo os dinossauros do Jurassic Park Alive através do telemóvel após os encontrar num parque local. Um grande problema presente nos jogos pervasivos é central ao aspeto que os torna únicos: devido a serem tão dependentes do contexto e localização do jogador, jogos pervasivos têm maior tendência para perconceitos que tornam alguns contextos melhores que outros. Um exemplo relevante é como no Pokémon GO, jogadores em zonas rurais têm uma quantidade reduzida ou nula de geração de Pokémons, enquanto jogadores em grandes cidades têm uma enchente constante de novos monstros para apanhar. Para resolver este problema, esta dissertação tem como objetivo desenvolver uma plataforma de análise de dados para jogos pervasivos que permita aos desenvolvedores obter um parecer relativamente ao balanço do seu jogo. Este objetivo será alcançado fazendo um cruzamento entre os dados do jogador e os contextuais, servindo-se de técnicas de aprendizagem automática para entender o que está a funcionar no jogo e o que não está. Esta tese não tem apenas a finalidade de oferecer aos desenvolvedores uma ferramenta que permita melhorar o balanço de jogos pré-existentes, mas sim resolver um problema significativo que tem estado a impedir o avanço e a experimentação de jogos pervasivos com experiências mais complexas e profundas.Being an art medium closely tied with the advancement of technology, some of the most interesting video games get made by expanding the technical limits of play in many new ways. Just like the jump from 2D graphics to 3D, how the internet shaped multiplayer games and inter-connectivity between players, and the way that now Virtual Reality and Augmented Reality are changing what is possible in a virtual world, another game genre has grown in popularity with the advent of new, exciting technology - pervasive games. The genre of pervasive games encompasses games that merge the game's virtual world and the real world together by taking advantage of the player's location data and contextual information, using the new leaps in technology regarding mobile internet. The phenomenon of Pokémon GO spearheaded the genre's break into the mainstream, allowing many other similar games to thrive and carving for itself a really large audience worldwide. Unlike augmented reality games - that expect you to see the world through a camera, that it then applies elements of the virtual world to - pervasive games uses the data from the real world as its base. There is a lot of cross-over between these two genres, like seeing the dinosaurs in Jurassic Park Alive through your phone after finding them in a local park. A big issue with pervasive games is central to its claim-to-fame: due to being so context and location-dependent, pervasive games are bound to have biases that make some contexts much better than others. A prime example of this is how in Pokémon GO, players in rural areas have nearly no Pokémon spawns, while players in cities have a constant stream of new monsters to catch. To solve this, this dissertation aims to develop an analytics platform for pervasive games that allows developers to obtain feedback on their game's balance. This goal will be achieved by cross-referencing player data and context data, using machine learning techniques to discover what works and what doesn't. This work's goal isn't simply to offer a tool to developers that help balance their games but also to help solve a significant issue holding pervasive games back from experimenting with more complex and deep experiences