Lattice Quantum Chromodynamics on Intel Xeon Phi based supercomputers

Preface The aim of this master\u2019s thesis project was to expand the QPhiX library for twisted-mass fermions with and without clover term. To this end, I continued work initiated by Mario Schr\uf6ck et al. [63]. In writing this thesis, I was following two main goals. Firstly, I wanted to stress the intricate interplay of the four pillars of High Performance Computing: Algorithms, Hardware, Software and Performance Evaluation. Surely, algorithmic development is utterly important in Scientific Computing, in particular in LQCD, where it even outweighed the improvements made in Hardware architecture in the last decade\u2014cf. the section about computational costs of LQCD. It is strongly influenced by the available hardware\u2014think of the advent of parallel algorithms\u2014but in turn also influenced the design of hardware itself. The IBM BlueGene series is only one of many examples in LQCD. Furthermore, there will be no benefit from the best algorithms, when one cannot implement the ideas into correct, performant, user-friendly, read- and maintainable (sometimes over several decades) software code. But again, truly outstanding HPC software cannot be written without a profound knowledge of its target hardware. Lastly, an HPC software architect and computational scientist has to be able to evaluate and benchmark the performance of a software program, in the often very heterogeneous environment of supercomputers with multiple software and hardware layers. My second goal in writing this thesis was to produce a self-contained introduction into the computational aspects of LQCD and in particular, to the features of QPhiX, so the reader would be able to compile, read and understand the code of one truly amazing pearl of HPC [40]. It is a pleasure to thank S. Cozzini, R. Frezzotti, E. Gregory, B. Jo\uf3, B. Kostrzewa, S. Krieg, T. Luu, G. Martinelli, R. Percacci, S. Simula, M. Ueding, C. Urbach, M. Werner, the Intel company for providing me with a copy of [55], and the J\ufclich Supercomputing Center for granting me access to their KNL test cluster DEE

Matter fields in asymptotically safe quantum field theories of gravity

In this doctoral thesis we present the research of Refs. [1\u20134] concerning the asymptotic safety scenario in quantum gravity. We motivate the theoretical and conceptual need for the existence of a theory of quantum gravity, and explain how such a theory might be realised through the construction of an ultraviolet complete quantum field theory defined via a high-energy interacting fixed point. In particular, we give a pedagogical introduction to the functional renormalisation group, as well as fixed points and critical phenomena. Thereafter we investigate the issue of background independence, which is introduced when constructing a scale-dependent effective action of a gauge theory using the background field formalism through the introduction of an infrared cutoff operator and the gauge fixing procedure. To this end we study simultaneous solutions of the flow equation combined with so-called modified split Ward identities in a conformally truncated theory in the derivative expansion. In the main part of this thesis we study the dynamics of a gravitational system coupled to a number of scalar fields. In doing so, we find scaling solutions in a fully functional truncation using the derivative expansion and background field approximation on a d-dimensional sphere. We then study a similar system using the vertex expansion in a fully dynamical fluctuation field calculation. This is done in the exponential as well as the linear parametrisation of the metric, using different gauge fixing procedures. We find that the overall behaviour is very similar in both cases. We furthermore find however that the contribution of the scalar fields to the gravitational coupling differs in its sign compared to older results obtained in a background field approximation. To correct this behaviour, we supplement the background field equations with modified split Ward identities, with the aim to obtain the fluctuation field behaviour from a background approximation. This seems to give satisfactory results in the case of the cosmological constant, whilst the running of Newton\u2019s constant still differs significantly

Extracting the Single-Particle Gap in Carbon Nanotubes with Lattice Quantum Monte Carlo

We show how lattice Quantum Monte Carlo simulations can be used to calculate electronic properties of carbon nanotubes in the presence of strong electron-electron correlations. We employ the path integral formalism and use methods developed within the lattice QCD community for our numerical work and compare our results to empirical data of the Anti-Ferromagnetic Mott Insulating gap in large diameter tubes.Comment: 8 pages, 5 figures, Lat2017 proceedin

Gradient-flow scale setting with Nf=2+1+1N_f=2+1+1 Wilson-clover twisted-mass fermions

We present a determination of the gradient flow scales w0 , t0‾‾√ and t0/w0 in isosymmetric QCD, making use of the gauge ensembles produced by the Extended Twisted Mass Collaboration (ETMC) with Nf=2+1+1 flavours of Wilson-clover twisted-mass quarks including configurations close to the physical point for all dynamical flavours. The simulations are carried out at three values of the lattice spacing and the scale is set through the PDG value of the pion decay constant, yielding w0=0.17383(63) fm, t0‾‾√=0.14436(61) fm and t0/w0=0.11969(62) fm. Finally, fixing the kaon mass to its isosymmetric value, we determine the ratio of the kaon and pion leptonic decay constants to be fK/fπ=1.1995(44)

Asymptotic safety in O(N) scalar models coupled to gravity

We extend recent results on scalar-tensor theories to the case of an O( N)-invariant multiplet. Some exact fixed point solutions of the RG flow equations are discussed. We find that also in the functional context, on employing a standard "type-I" cutoff, too many scalars destroy the gravitational fixed point. For d= 3 we show the existence of the gravitationally dressed Wilson-Fisher fixed point also for N> 1. We discuss also the results of the analysis for a different, scalar-free, coarse-graining scheme. \ua9 2015 The Authors

Gastrointestinal specific anxiety in irritable bowel syndrome: validation of the Japanese version of the visceral sensitivity index for university students

Objective: The visceral sensitivity index (VSI) is a useful self-report measure of the gastrointestinal symptom-specific anxiety (GSA) of patients with irritable bowel syndrome (IBS). Previous research has shown that worsening GSA in IBS patients is related to the severity of GI symptoms, suggesting that GSA is an important endpoint for intervention. However, there is currently no Japanese version of the VSI. We therefore translated the VSI into Japanese (VSI-J) and verified its reliability and validity.Material and methods: Participants were 349 university students aged 18 and 19 years and recruited from an academic class. We analyzed data from the VSI-J, Anxiety Sensitivity Index (ASI), Hospital Anxiety and Depression scale (HAD), and Irritable Bowel Syndrome Severity Index (IBS-SI). The internal consistency, stability, and factor structure of the VSI-J and its associations with anxiety, depression and severity measures were investigated.Results: The factor structure of the VSI-J is unidimensional and similar to that of the original VSI (Cronbach\u27s α = 0.93). Construct validity was demonstrated by significant correlations with ASI (r = 0.43, p < 0.0001), HAD-ANX (r = 0.19, p = 0.0003), and IBS-SI scores (r = 0.45, p < 0.0001). Furthermore, the VSI-J was a significant predictor of severity scores on the IBS-SI and demonstrated good discriminant (p < 0.0001) and incremental (p < 0.0001) validity.Conclusion: These findings suggest that the VSI-J is a reliable and valid measure of visceral sensitivity

Background independence in a background dependent renormalization group

Within the derivative expansion of conformally reduced gravity, the modified split Ward identities are shown to be compatible with the flow equations if and only if either the anomalous dimension vanishes or the cutoff profile is chosen to have a power-law form. No solutions exist if the Ward identities are incompatible. In the compatible case, a clear reason is found for why Ward identities can still forbid the existence of fixed points; however, for any cutoff profile, a background independent (and parametrization independent) flow equation is uncovered. Finally, expanding in vertices, the combined equations are shown generically to become either overconstrained or highly redundant beyond the six-point level