Publications

Order by: publication date number of citations

• An algorithm to parallelise parton showers on a GPU

  Michael H. Seymour, Siddharth Sule

  SciPost Phys. Codebases 33 (2024) · published 12 August 2024 | Toggle abstract · pdf

  The Single Instruction, Multiple Thread (SIMT) paradigm of GPU programming does not support the branching nature of a parton shower algorithm by definition. However, modern GPUs are designed to schedule threads with diverging processes independently, allowing them to handle such branches. With regular thread synchronisation and careful treatment of the individual steps, one can simulate a parton shower on a GPU. We present a Sudakov veto algorithm designed to simulate parton branching on multiple events in parallel. We also release a CUDA C++ program that generates matrix elements, showers partons and computes jet rates and event shapes for LEP at 91.2 GeV on a GPU. To benchmark its performance, we also provide a near-identical C++ program designed to simulate events serially on a CPU. While the consequences of branching are not absent, we demonstrate that a GPU can provide the throughput of a many-core CPU. As an example, we show that the time taken to shower $10^6$ events on one NVIDIA TESLA V100 GPU is equivalent to that of 295 Intel Xeon E5-2620 CPU cores.

  1 citation

• Codebase release 0.5 for divERGe

  Jonas B. Profe, Dante M. Kennes, Lennart Klebl

  SciPost Phys. Codebases 26-r0.5 (2024) · published 8 February 2024 | Toggle abstract · src

  We present divERGe, an open source, high-performance C/C++/Python library for functional renormalization group (FRG) calculations on lattice fermions. The versatile model interface is tailored to real materials applications and seamlessly integrates with existing, standard tools from the ab-initio community. The code fully supports multi-site, multi-orbital, and non-SU(2) models in all of the three included FRG variants: TU$^2$FRG, N-patch FRG, and grid FRG. With this, the divERGe library paves the way for widespread application of FRG as a tool in the study of competing orders in quantum materials.

  1 citation

• Implementing Transverse Momentum Dependent splitting functions in Parton Branching evolution equations

  Lissa Keersmaekers

  SciPost Phys. Proc. 8, 127 (2022) · published 13 July 2022 | Toggle abstract · pdf

  The Parton Branching (PB) approach describes the evolution of transverse momentum dependent (TMD) parton densities. We propose to extend the PB method by including TMD splitting functions, instead of the DGLAP splitting functions which assume strong ordering in transverse momentum. We present the evolution equations and their numerical solution, which is the first Monte Carlo implementation including TMD splitting functions.

  1 citation

• A somewhat random walk through nuclear and particle physics

  Thomas D. Cohen, Nicholas R. Poniatowski

  SciPost Phys. Lect. Notes 34 (2021) · published 20 September 2021 | Toggle abstract · pdf

  These notes are an outgrowth of an advanced undergraduate course taught at the University of Maryland, College Park. They are intended as an introduction to various aspects of particle and nuclear physics with an emphasis on the role of symmetry. The basic philosophy is to introduce many of the fundamental ideas in nuclear and particle physics using relatively sophisticated mathematical tools -- but to do so in as a simplified a context to explain the underlying ideas. Thus, for example, the Higgs mechanism is discussed in terms of an Abelian Higgs model. The emphasis is largely, but not entirely theoretical in orientation. The goal is for readers to develop an understanding of many of the underlying issues in a relatively sophisticated way.

  1 citation

• Comparative analysis of tight-binding models for transition metal dichalcogenides

  Bert Jorissen, Lucian Covaci, Bart Partoens

  SciPost Phys. Core 7, 004 (2024) · published 6 February 2024 | Toggle abstract · pdf

  We provide a comprehensive analysis of the prominent tight-binding (TB) models for transition metal dichalcogenides (TMDs) available in the literature. We inspect the construction of these TB models, discuss their parameterization used and conduct a thorough comparison of their effectiveness in capturing important electronic properties. Based on these insights, we propose a novel TB model for TMDs designed for enhanced computational efficiency. Utilizing $MoS_2$ as a representative case, we explain why specific models offer a more accurate description. Our primary aim is to assist researchers in choosing the most appropriate TB model for their calculations on TMDs.

  1 citation

• Constraints on heavy dark matter annihilation and decay from electron and positron cosmic ray spectra

  Holger Motz

  SciPost Phys. Proc. 12, 035 (2023) · published 4 July 2023 | Toggle abstract · pdf

  Annihilation or decay of dark matter (DM) could contribute to the electron and positron cosmic-ray flux, allowing for constraints on DM parameters from its measurement. CALET is directly measuring the energy spectrum of electron+positron cosmic rays up into the TeV region most important for studying heavy DM, while AMS-02 provides a positron-only spectrum below the TeV range. Limits on DM annihilation and decay well into the TeV mass range have been derived from a combined analysis of both data-sets with an astrophysical background model including pulsars as the origin of the positron excess and individual nearby supernova remnant sources.

  1 citation

• The $g$-function and defect changing operators from wavefunction overlap on a fuzzy sphere

  Zheng Zhou, Davide Gaiotto, Yin-Chen He, Yijian Zou

  SciPost Phys. 17, 021 (2024) · published 25 July 2024 | Toggle abstract · pdf

  Defects are common in physical systems with boundaries, impurities or extensive measurements. The interaction between bulk and defect can lead to rich physical phenomena. Defects in gapless phases of matter with conformal symmetry usually flow to a defect conformal field theory (dCFT). Understanding the universal properties of dCFTs is a challenging task. In this paper, we propose a computational strategy applicable to a line defect in arbitrary dimensions. Our main assumption is that the defect has a UV description in terms of a local modification of the Hamiltonian so that we can compute the overlap between low-energy eigenstates of a system with or without the defect insertion. We argue that these overlaps contain a wealth of conformal data, including the $g$-function, which is an RG monotonic quantity that distinguishes different dCFTs, the scaling dimensions of defect creation operators $\Delta^{+0}_\alpha$ and changing operators $\Delta^{+-}_\alpha$ that live on the intersection of different types of line defects, and various OPE coefficients. We apply this method to the fuzzy sphere regularization of 3D CFTs and study the magnetic line defect of the 3D Ising CFT. Using exact diagonalization and DMRG, we report the non-perturbative results $g=0.602(2),\Delta^{+0}_0=0.108(5)$ and $\Delta^{+-}_0=0.84(5)$ for the first time. We also obtain other OPE coefficients and scaling dimensions. Our results have significant physical implications. For example, they constrain the possible occurrence of spontaneous symmetry breaking at line defects of the 3D Ising CFT. Our method can be potentially applied to various other dCFTs, such as plane defects and Wilson lines in gauge theories.

  1 citation

• Gapful electrons in a vortex core in granular superconductors

  Dmitry E. Kiselov, Mikhail A. Skvortsov, Mikhail V. Feigel'man

  SciPost Phys. 15, 008 (2023) · published 12 July 2023 | Toggle abstract · pdf

  We calculate the quasiparticle density of states (DoS) inside the vortex core in a granular superconductor, generalizing the classical solution applicable for dirty superconductors. A discrete version of the Usadel equation for a vortex is derived and solved numerically for a broad range of parameters. Electron DoS is found to be gapful when the coherence length $\xi$ becomes comparable to the distance between neighboring grains $l$. Minigap magnitude $E_g$ grows from zero at $\xi \approx 1.4 l$ to third of superconducting gap $\Delta_0 $ at $\xi \approx 0.5 l$. The absence of low-energy excitations is the main ingredient needed to understand strong suppression of microwave dissipation recently observed in a mixed state of granular Al.

  1 citation

• Search for ultralight axion dark matter in a side-band analysis of a ${}^{199}$Hg free-spin precession signal

  C. Abel, N. J. Ayres, G. Ban, G. Bison, K. Bodek, V. Bondar, E. Chanel, C. B. Crawford, M. Daum, B. Dechenaux, S. Emmenegger, P. Flaux, W. C. Griffith, P. G. Harris, Y. Kermaidic, K. Kirch, S. Komposch, P. A. Koss, J. Krempel, B. Lauss, T. Lefort, Prajwal MohanMurthy, Oscar Naviliat Cuncic, D. Pais, F. M. Piegsa, Guillaume Pignol, M. Rawlik, D. Ries, Stephanie Roccia, D. Rozpedzik, Philipp Schmidt-Wellenburg, N. Severijns, Y. V. Stadnik, J. A. Thorne, A. Weis, E. Wursten, Jacek Zejma, Geza Zsigmond

  SciPost Phys. 15, 058 (2023) · published 9 August 2023 | Toggle abstract · pdf

  Ultra-low-mass axions are a viable dark matter candidate and may form a coherently oscillating classical field. Nuclear spins in experiments on Earth might couple to this oscillating axion dark-matter field, when propagating on Earth's trajectory through our Galaxy. This spin coupling resembles an oscillating pseudo-magnetic field which modulates the spin precession of nuclear spins. Here we report on the null result of a demonstration experiment searching for a frequency modulation of the free spin-precession signal of \magHg in a 1 $\mu$T magnetic field. Our search covers the axion mass range $10^{-16}$ eV $\lesssim m_a \lesssim 10^{-13}$ eV and achieves a peak sensitivity to the axion-nucleon coupling of $g_{aNN} \approx 3.5 \times 10^{-6}$ GeV$^{-1}$.

  1 citation

• Testing the mean field theory of scalar field dark matter

  Andrew Eberhardt, Alvaro Zamora, Michael Kopp, Tom Abel

  SciPost Phys. Proc. 12, 058 (2023) · published 5 July 2023 | Toggle abstract · pdf

  Scalar field dark matter offers an interesting alternative to the traditional WIMP dark matter picture. Astrophysical and cosmological simulations are useful to constraining the mass of the dark matter particle in this model. This is particularly true at low mass where the wavelike nature of the dark matter particle manifests on astrophysical scales. These simulations typical use a classical field approximation. In this work, we look at extending these simulations to include quantum corrections. We look into both the ways in which large corrections impact the predictions of scalar field dark matter, and the timescales on which these corrections grow large. Corrections tend to lessen density fluctuations and increase the effect of "quantum pressure". During collapse, these corrections grow exponentially, quantum corrections would become important in about $\sim 30$ dynamical times. This implies that the predictions of classical field simulations may differ from those with quantum corrections for systems with short dynamical times.

  1 citation