Topological charge unfreezing with AMReX

A new approach to the problem of topological freezing in gauge theories is introduced in which a physical volume preserving coarsening of the lattice induces sufficient energy variation in the Hamiltonian to overcome large topological barriers. Though the process is not reversible, the physical volume preserving aspect minimises the time spent rethermalisating the lattice after coarsening periods, which we then treat as a new ensemble disjoint from previous runs. We have tested this technique on the pure gauge 2D Schwinger model and find that topological sampling rates are improved. We also demonstrate that autocorrelation times for extensive observables are restored to their pre-coarsening values after coarsening periods over a acceptably short simulation time.Comment: 12 pages, 6 figure

Investigating volume effects for Nf_f=2 twisted clover fermions at the physical point

In this work we present preliminary results on the nucleon axial and tensor charges, the quark momentum fraction and the first moment of the helicity distribution. The simulations have been performed using two $N_f{=}2$ and $N_f{=}2{+}1{+}1$ ensembles. Both ensembles have a twisted mass action with a clover term with the quark masses fixed at their physical values (physical point) and volumes of $64^3{\times}128$. The extracted quantities are compared with results from an existing $N_f{=}2$ ($48^3{\times}96$) ensemble. This comparison allows one to address volume and quenching effects.Comment: 6 pages, Proceedings of the 36th Annual International Symposium on Lattice Field Theory - LATTICE201

Multigrid for Chiral Lattice Fermions: Domain Wall

Critical slowing down for the Krylov Dirac solver presents a major obstacle to further advances in lattice field theory as it approaches the continuum solution. We propose a new multi-grid approach for chiral fermions, applicable to both the 5-d domain wall or 4-d Overlap operator. The central idea is to directly coarsen the 4-d Wilson kernel, giving an effective domain wall or overlap operator on each level. We provide here an explicit construction for the Shamir domain wall formulation with numerical tests for the 2-d Schwinger prototype, demonstrating near ideal multi-grid scaling. The framework is designed for a natural extension to 4-d lattice QCD chiral fermions, such as the M\"obius, Zolotarev or Borici domain wall discretizations or directly to a rational expansion of the 4-d Overlap operator. For the Shamir operator, the effective overlap operator is isolated by the use of a Pauli-Villars preconditioner in the spirit of the K\"ahler-Dirac spectral map used in a recent staggered MG algorithm [1].Comment: 39 pages, 13 figure

Radial Lattice Quantization of 3D ϕ4\phi^4 Field Theory

The quantum extension of classical finite elements, referred to as quantum finite elements ({\bf QFE})~\cite{Brower:2018szu,Brower:2016vsl}, is applied to the radial quantization of 3d $\phi^4$ theory on a simplicial lattice for the $\mathbb R \times \mathbb S^2$ manifold. Explicit counter terms to cancel the one- and two-loop ultraviolet defects are implemented to reach the quantum continuum theory. Using the Brower-Tamayo~\cite{Brower:1989mt} cluster Monte Carlo algorithm, numerical results support the QFE ansatz that the critical conformal field theory (CFT) is reached in the continuum with the full isometries of $\mathbb R \times \mathbb S^2$ restored. The Ricci curvature term, while technically irrelevant in the quantum theory, is shown to dramatically improve the convergence opening, the way for high precision Monte Carlo simulation to determine the CFT data: operator dimensions, trilinear OPE couplings and the central charge.Comment: 8 pages, 7 figure

Lattice setup for quantum field theory in AdS2

Holographic conformal field theories (CFTs) are usually studied in a limit where the gravity description is weakly coupled. By contrast, lattice quantum field theory can be used as a tool for doing computations in a wider class of holographic CFTs where nongravitational interactions in AdS become strong, and gravity is decoupled. We take preliminary steps for studying such theories on the lattice by constructing the discretized theory of a scalar field in AdS 2 and investigating its approach to the continuum limit in the free and perturbative regimes. Our main focus is on finite sublattices of maximally symmetric tilings of hyperbolic space. Up to boundary effects, these tilings preserve the triangle group as a large discrete subgroup of AdS 2 , but have a minimum lattice spacing that is comparable to the radius of curvature of the underlying spacetime. We quantify the effects of the lattice spacing as well as the boundary effects, and find that they can be accurately modeled by modifications within the framework of the continuum limit description. We also show how to do refinements of the lattice that shrink the lattice spacing at the cost of breaking the triangle group symmetry of the maximally symmetric tilings.Published versio

Temperature-controlled laminar airflow in severe asthma for exacerbation reduction (The LASER Trial): study protocol for a randomised controlled trial

BackgroundAsthma affects more than 5 million patients in the United Kingdom. Nearly 500,000 of these patients have severe asthma with severe symptoms and frequent exacerbations that are inadequately controlled with available treatments. The burden of severe asthma on the NHS is enormous, accounting for 80 % of the total asthma cost (£1 billion), with frequent exacerbations and expensive medications generating much of this cost.Of those patients with severe asthma, 70 % are sensitised to indoor aeroallergens, and the level of exposure to allergens determines the symptoms; patients exposed to high levels are therefore most at risk of exacerbations and hospital admissions.The LASER trial aims to assess whether a new treatment, temperature controlled laminar airflow (TLA) delivered by the Airsonett™ device, can reduce the frequency of exacerbations in patients with severe allergic asthma by reducing exposure to aeroallergens overnight.MethodsThis multicentre study is a placebo-controlled, blinded, randomised controlled, parallel group trial. A total of 222 patients with a new or current diagnosis of severe allergic asthma will be assigned with a random element in a 1:1 ratio to receive either an active device for one year or a placebo device. The primary outcome is the frequency of severe asthma exacerbations occurring over a 12-month period, defined in accordance with the American Thoracic Society/European Respiratory Society (ATS/ERS) guidelines. Secondary outcomes include changes in asthma control, lung function, asthma-specific and global quality of life for participants and their carers, adherence to intervention, healthcare resource use and costs, and cost-effectiveness. Qualitative interviews will be conducted to elicit participant’s and their partner’s perceptions of the treatment.DiscussionEffective measures of allergen avoidance have, to date, proved elusive. The LASER trial aims to address this. The study will ascertain whether home-based nocturnal TLA usage over a 12-month period can reduce the frequency of exacerbations and improve asthma control and quality of life as compared to placebo, whilst being cost-effective and acceptable to adults with poorly controlled, severe allergic asthma. The results of this study will be widely applicable to the many patients with allergic asthma both in the UK and internationally.Trial registrationCurrent controlled trials ISRCTN46346208 (Date assigned 22 January 2014)

Jurassic sedimentation in the Cleveland Basin : a review

This review combines two Presidential Addresses (2005, 2006) and aims to provides an up-to-date overview of the stratigraphy and sedimentation of the Jurassic sequence of the Cleveland Basin (Yorkshire), including poorly known data from the western outcrop. These fascinating rocks have been the focus of geological research since the 18th Century and have had a profound influence on the development of the geological sciences. Throughout the 20th Century, the excellent coastal exposures have acted as a magnet for palaeontologists, stratigraphers, sedimentologists and geochemists, as a natural geological laboratory, and in recent decades, the coastal exposures received increased scientific interest as a result of their analogy with hydrocarbon source and reservoir rocks in the North Sea. Designation of the international Global Stratotype Section and Point (GSSP) for the Sinemurian–Pliensbachian stage boundary in Robin Hood's Bay, the establishment of the Dinosaur Coast, and development of the Rotunda Museum in Scarborough have all given the regional geology additional importance. The Lias Group (Hettangian–Toarcian age; 199.6–175.6 Ma), exposed in the well known coastal sections, is illustrated by the fully cored Felixkirk Borehole, located at the western margin of the outcrop, and is one of the best examples of shallow marine sedimentation in an epeiric shelf-sea setting. It comprises two large-scale, upward coarsening cycles, namely the Redcar Mudstone to Staithes Sandstone cycle, followed by the Cleveland Ironstone to Blea Wyke Sandstone cycle. Within this broad pattern, smaller scale transgressive–regressive cycles are described from stratigraphically expanded and reduced successions. Detailed ammonite biostratigraphy provides a finely calibrated temporal framework to study the variations in sedimentation, which include storm-generated limestones and sandstones (‘tempestites’) interbedded with mudstone deposited during fair-weather periods. Hemipelagic mud, occasionally organic-rich, reflects deeper-water anoxic events that may indicate a response to global climate change. In cores, the tempestite beds (Hettangian–Sinemurian) are characterized by sharp bases that, at outcrop, are often masked by downward penetrating burrows. Cyclicity on a centimetre scale in the overlying Pliensbachian ‘Banded Shales’ may be the result of orbitally induced, climatic cycles. Gradational upward coarsening to the Staithes Sandstone Formation marks a transition to sand-rich tempestite deposits, characterized by low angle and swaley cross-lamination, interbedded with sand-starved units (striped siltstones). The sands were probably deposited from sediment-laden, storm-surge and ebb currents in inner- and mid-shelf settings; the sandy substrate was, at some levels, extensively bioturbated by deposit feeding organisms that produced a spectacular range of trace fossil assemblages characteristic of shoreface, inner-, mid-, and outer-shelf settings. Intrabasinal tectonics was a controlling factor during deposition of both the Staithes Sandstone and the overlying Cleveland Ironstone (Late Pliensbachian). The influx of sand is attributed to hinterland uplift and increased sediment flux. More marked intraformational uplift during deposition of the Cleveland Ironstone is manifested in a much attenuated succession in the west of the basin (Felixkirk); southwards, towards the Market Weighton High, the Pecten/Main Seam of the ironstone oversteps unconformably onto progressively older beds to rest on the lower part of the Redcar Mudstone Formation. Ironstone, in the form of berthierine ooids and sideritic mud, was deposited during 5–6 cycles (in coastal exposures) of high sea-level stands that cut off siliciclastic influx from the low-gradient hinterland; regressive, upward-shoaling intervals are marked by interbedded, bioturbated siltstone and fine-grained sandstone. The Toarcian succession (Whitby Mudstone and Blea Wyke Sandstone formations) continues the second upward coarsening cycle in response to increased subsidence, rising sea-level, and an influx of siliciclastic sand. Oxygenated, open marine mud was deposited during the initial deepening phase, followed by bituminous mud, attributed to ocean-water stratification and the establishment of anoxic bottom conditions; in the west of the basin an upward shoaling sequence suggests that water depths were not as great. Recent research on the geochemistry and stable isotope signatures across this early Toarcian interval indicates a widespread, global anoxic event, possibly attributed to the release of methane hydrate on the ocean floor. The Alum Shale Member represents increasingly oxygenated bottom conditions and an upward coarsening motif with passage to the Blea Wyke Sandstone Formation, which is preserved only in the Peak Trough, an actively subsiding graben. Basin uplift accompanied by gentle folding in late Toarcian to Aalenian times removed much of the late Toarcian succession so that the Middle Jurassic Dogger Formation (Aalenian), a complex, condensed, shallow water unit rests unconformably on beds as low as the Alum Shale over much of the basin. Deep boreholes and revision mapping by the British Geological Survey (BGS) in the west of the outcrop have allowed a fuller, basin-wide synthesis of the palaeoenvironments and the influence of intra-Jurassic tectonics during Mid- to Late Jurassic times. During Mid-Jurassic times the low-lying, paralic coastal plain, typified by braided and meandering fluvial systems and lacustrine deposits was invaded by marine incursions from the south and east. Each transgressive event was different in its geographical penetration across the coastal plain, resulting in varied lithofacies and palaeoenvironments including ooidal ironstone and lime mud (Eller Beck Formation), peloid and ooid carbonate shoals (Lebberston Member), and tidal sand bars, pelloidal limestones and nearshore marine muds (Scarborough Formation). Trace fossils, including dinosaur footprints, and macro-plant fossils tell us much about the palaeoenvironments on the coastal plain, during this time interval (175.6–164.7 Ma) that was characterized by a warm, seasonal climate. The basin wide transgression and marked global sea-level rise represented by the Cornbrash Formation, marks deposition in a shallow marine environment during the Callovian, followed by sand (Osgodby Formation) and deeper water muds (Oxford Clay Formation) that spread northwards from the East Midlands over the Market Weighton High during the Oxfordian. Subsequent shallowing of the basin resulted in the establishment of a carbonate/siliciclastic platform typified by ooidal shoals, coral patch reefs and sponge spicule-rich marine sands (Corallian Group). Their complex sedimentation pattern was influenced by local infra-Oxfordian tectonics related to the Howardian–Flamborough Fault Belt. Although the Ampthill Clay and Kimmeridge Clay formations, the latter representing the most important regional hydrocarbon source rock, are not well-exposed, recent boreholes in the Cleveland Basin have allowed a much better understanding of the hemi-pelagic marine environment (both oxic and anoxic) during this phase of sedimentation which marks a global sea-level rise. Although well-studied by world standards, the Jurassic sediments of the Cleveland Basin continue to throw up surprises and advances in our understanding of the Earth as a dynamic system over a period of c. 30 million years. These studies have directly and indirectly influenced our understanding of the Earth as a system, and have played an important role in educating non-specialists, undergraduates and professional geologists over many decades

Scale setting the M\"obius Domain Wall Fermion on gradient-flowed HISQ action using the omega baryon mass and the gradient-flow scales t0t_0 and w0w_0

We report on a sub-percent scale determination using the omega baryon mass and gradient-flow methods. The calculations are performed on 22 ensembles of $N_f=2+1+1$ highly improved, rooted staggered sea-quark configurations generated by the MILC and CalLat Collaborations. The valence quark action used is M\"obius Domain-Wall fermions solved on these configurations after a gradient-flow smearing is applied with a flowtime of $t_{\rm gf}=1$ in lattice units. The ensembles span four lattice spacings in the range $0.06 \lesssim a \lesssim 0.15$ fm, six pion masses in the range $130 \lesssim m_\pi \lesssim 400$ MeV and multiple lattice volumes. On each ensemble, the gradient-flow scales $t_0/a^2$ and $w_0/a$ and the omega baryon mass $a m_\Omega$ are computed. The dimensionless product of these quantities is then extrapolated to the continuum and infinite volume limits and interpolated to the physical light, strange and charm quark mass point in the isospin limit, resulting in the determination of $\sqrt{t_0}=0.1422(14)$ fm and $w_0 = 0.1709(11)$ fm with all sources of statistical and systematic uncertainty accounted for. The dominant uncertainty in this result is the stochastic uncertainty, providing a clear path for a few-per-mille uncertainty, as recently obtained by the Budapest-Marseille-Wuppertal Collaboration.Comment: v3: Published version; v2: Added determination of t_0 as well as w_0; v1: 13 pages plus appendices. The correlation function data, mass results and analysis code accompanying this publication can be found at this github repository: https://github.com/callat-qcd/project_scale_setting_mdwf_his