arXiv subjects

Andrea Shindler

Publications and source records attributed to Andrea Shindler.

At least 37 records · Page 2Linked to original sources

arXiv2023

Opportunities for Fundamental Physics Research with Radioactive Molecules

Molecules containing short-lived, radioactive nuclei are uniquely positioned to enable a wide range of scientific discoveries in the areas of fundamental symmetries, astrophysics, nuclear structure, and chemistry. Recent advances in the ability to create, cool, and control complex molecules down to the quantum level, along with recent and upcoming advances in radioactive species production at several facilities around the world, create a compelling opportunity to coordinate and combine these efforts to bring precision measurement and control to molecules containing extreme nuclei. In this manuscript, we review the scientific case for studying radioactive molecules, discuss recent atomic, molecular, nuclear, astrophysical, and chemical advances which provide the foundation for their study, describe the facilities where these species are and will be produced, and provide an outlook for the future of this nascent field.

nucl-ex↗

arXiv2023

Cutoff effects of the gradient flow for fermions

I analyze cutoff effects of the gradient flow for Wilson-type fermions. I show that with a proper choice of the higher dimensional fields in the Symanzik effective theory, O($a$) improvement of the action is achieved changing the initial conditions of the gradient flow equation.

hep-lat↗

arXiv2023

Gradient Flow: Perturbative and Non-Perturbative Renormalization

We review the gradient flow for gauge and fermion fields and its applications to lattice gauge theory computations. Using specific examples, we discuss the interplay between perturbative and non-perturbative calculations in the context of renormalization with the gradient flow.

hep-lat↗

arXiv2022

One-loop matching for quark dipole operators in a gradient-flow scheme

The quark chromoelectric dipole (qCEDM) operator is a CP-violating operator describing, at hadronic energies, beyond-the-standard-model contributions to the electric dipole moment of particles with nonzero spin. In this paper we define renormalized dipole operators in a regularization-independent scheme using the gradient flow, and we perform the matching at one loop in perturbation theory to renormalized operators of the same and lower dimension in the more familiar MS scheme. We also determine the matching coefficients for the quark chromomagnetic dipole operator (qCMDM), which contributes, for example, to matrix elements relevant to CP-violating and CP-conserving kaon decays. The calculation provides a basis for future lattice QCD computations of hadronic matrix elements of the qCEDM and qCMDM operators.

hep-lat↗

arXiv2022

A novel nonperturbative renormalization scheme for local operators

The gradient flow exponentially suppresses ultraviolet field fluctuations and removes ultraviolet divergences (up to a multiplicative fermionic wavefunction renormalization). It can be used to describe real-space Wilsonian renormalization group transformations and determine the corresponding beta function. We propose a new nonperturbative renormalization scheme for local composite fermionic operators that uses the gradient flow and is amenable to lattice QCD calculations. We present preliminary nonperturbative results for the running of quark bilinear operators in this scheme and outline the calculation of perturbative matching to the MS-bar scheme.

hep-lat↗

arXiv2022

Properties, ensembles and hadron spectra with Stabilised Wilson Fermions

In this joint contribution we announce the formation of the "OPEN LATtice initiative", https://openlat1.gitlab.io, to study Stabilised Wilson Fermions (SWF). They are a new avenue for QCD calculations with Wilson-type fermions and we report results on our continued study of this framework: Tuning the clover improvement coefficient, and extending the reach of lattice spacings to $a=0.12$ fm. We fix the flavor symmetric points $m_π=m_K=412$ MeV at $a=0.055,0.064, 0.077, 0.094, 0.12$ fm and define the trajectories to the physical point by fixing the trace of the quark mass matrix. Currently our pion mass range extends down to $m_π\sim200$ MeV. We outline our tuning goals and strategy as well as our future planned ensembles. First scaling studies are performed on $f_π$ and $m_π$. Additionally results of a preliminary continuum extrapolation of $m_N$ at the flavor symmetric point are presented. Going further a first determination of the light and strange hadron spectrum chiral dependence is shown, which serves to check the quality of the action for precision measurements. We also investigate other quantities such as flowed gauge observables to study how the continuum limit is approached. Taken together we observe the SWF enable us to perform stable lattice simulations across a large range of parameters in mass, volume and lattice spacing. Pooling resources our new initiative has made our reported progress possible and through it we will share generated gauge ensembles under an open science philosophy.

hep-lat↗

arXiv2021

Nonperturbative Renormalization of the Quark Chromoelectric Dipole Moment with the Gradient Flow:Power Divergences

The CP-violating quark chromoelectric dipole moment (qCEDM) operator, contributing to the electric dipole moment (EDM), mixes under renormalization and particularly on the lattice with the pseudoscalar density. The mixing coefficient is power-divergent with the inverse lattice spacing squared, $1/a^2$, regardless of the lattice action used. We use the gradient flow to define a multiplicatively renormalized qCEDM operator and study its behavior at small flow time. We determine nonperturbatively the linearly divergent coefficient with the flow time, $1/t$, up to subleading logarithmic corrections, and compare it with the 1-loop perturbative expansion in the bare and renormalized strong coupling. We also discuss the O($a$) improvement of the qCEDM defined at positive flow time.

hep-lat↗

arXiv2021

Quantum State Preparation for the Schwinger Model

It is not possible, using standard lattice techniques in Euclidean space, to calculate the complete fermionic spectrum of a quantum field theory. Algorithms running on quantum computers have the potential to access the theory with real-time evolution, enabling a direct computation. As a testing ground we consider the 1 + 1-dimensional Schwinger model with the presence of a θ term using a staggered fermions discretization. We study the convergence properties of two different algorithms - adiabatic evolution and the Quantum Approximate Optimization Algorithm - with an emphasis on their cost in terms of CNOT gates. This is crucial to understand the feasibility of these algorithms, because calculations on near-term quantum devices depend on their rapid convergence. We also propose a blocked algorithm that has the first indications of a better scaling behavior with the dimensionality of the problem.

hep-lat↗

arXiv2020

Short flow-time coefficients of CP-violating operators

Measurements of a permanent neutron electric dipole moment (EDM) potentially probe Beyond-the-Standard Model (BSM) sources of CP-violation. At low energy the CP-violating BSM interactions are parametrized by flavor-conserving CP-violating operators of dimension higher than four. QCD calculations of the nucleon matrix elements of these operators are required to fully reconstruct the sources and magnitudes of the different CP-violating contributions to the nucleon EDM. Herein we study the quark-chromo electric dipole moment (qCEDM) operator and the three-gluon Weinberg operator. The non-perturbative determination, using lattice QCD, of the nucleon matrix elements of these CP-violating operators is hampered by their short-distance behavior. Under renormalization these operators mix with lower dimensional operators, which induces power divergences in the lattice spacing, as the continuum limit is approached. We study the short-distance behavior of the qCEDM and the Weinberg operators using the gradient flow. We perform a short flow time expansion and determine, in perturbation theory, the expansion coefficients of the linearly-divergent terms stemming from the mixing with the pseudoscalar density and the topological charge, confirming the expectations of the operator product expansion. We introduce a new method to perform calculations at non-zero flow-time for arbitrary values of the external momenta. This method allows us to work in four dimensions for most of the calculations described in this paper, avoiding the complications associated with defining $γ_5$ in generic d dimensions. We show that leading contributions in the external momenta can be reproduced by defining $γ_5$ using the 't Hooft-Veltman-Breitenlohner-Maison scheme.

hep-lat↗

arXiv2019

Confirming the Existence of the strong CP Problem in Lattice QCD with the Gradient Flow

We calculate the electric dipole moment of the nucleon induced by the QCD theta term. We use the gradient flow to define the topological charge and use $N_f = 2+1$ flavors of dynamical quarks corresponding to pion masses of $700$, $570$, and $410$ MeV, and perform an extrapolation to the physical point based on chiral perturbation theory. We perform calculations at $3$ different lattice spacings in the range of $0.07~{\rm fm} < a < 0.11$ fm at a single value of the pion mass, to enable control on discretization effects. We also investigate finite size effects using $2$ different volumes. A novel technique is applied to improve the signal-to-noise ratio in the form factor calculations. The very mild discretization effects observed suggest a continuum-like behavior of the nucleon EDM towards the chiral limit. Under this assumption our results read $d_{n}=-0.00152(71)\ \barθ e~\text{fm}$ and $d_{p}=0.0011(10)\ \barθ e~\text{fm}$. Assuming the theta term is the only source of CP violation, the experimental bound on the neutron electric dipole moment limits $\left|\barθ\right| < 1.98\times 10^{-10}$ ($90\%$ CL). A first attempt at calculating the nucleon Schiff moment in the continuum resulted in $S_{p} = 0.50(59)\times 10^{-4}\ \barθ e~\text{fm}^3$ and $S_{n} = -0.10(43)\times 10^{-4}\ \barθ e~\text{fm}^3$.

hep-lat↗

arXiv2018

Three neutrons from Lattice QCD

We present a study on ab-initio calculations of three-neutron correlators from Lattice QCD. We extend the method of baryon blocks to systems of three spacially displaced baryons. This allows the measurement of three-neutron $p$-wave correlators with total spin $S=1/2$ and $3/2$. In addition, we use automatic code generation that has high flexibility and allows for easy inclusion of additional channels in the future while optimizing the evaluation of contractions. Our measurements were performed on a newly generated $96\times 48^3$ Clover-Wilson gauge field ensemble with $m_π \approx 370\,\text{MeV}$. We present preliminary results of our calculations of one pion and nucleon as well as two nucleon ($2N$) and three neutron ($3n$) correlators.

hep-lat↗

arXiv2018

Towards a determination of the nucleon EDM from the quark chromo-EDM operator with the gradient flow

In this proceedings, we lay the foundation for computing the contribution of quark chromo-electric dipole moment (qCEDM) operator to the nucleon electric dipole moment. By applying the gradient flow technique, we can parameterize the renormalization and operator mixing issues associated with the qCEDM operator on the lattice. As the nucleon mixing angle $α_N$ is a key component for determining the neutron and proton electric dipole moments induced by the qCEDM operator, we present the formalism and preliminary results for $α_N$ with respect to the gradient flow time $t_f$. The results are computed on $N_f=2+1$ Wilson-clover lattices provided by PACS-CS. The 3 ensembles have lattice spacing values of $a=\lbrace 0.1095,\,0.0936,\,0.0684\rbrace $fm, whilst keeping a similar $m_π\approx701$MeV, and a fixed box size of $L\approx1.9$fm.

hep-lat↗

arXiv2018

Renormalization of CP-Violating Pure Gauge Operators in Perturbative QCD Using the Gradient Flow

We use the Yang-Mills gradient flow to study the mixing of CP-violating pure gauge operators in continuum QCD with special attention to Weinberg's d=6 purely gluonic operator. The gradient flow allows for a relatively clear derivation of the Wilson coefficients of the CP-violating effective Hamiltonian. This calculation is the first step towards a high-energy matching of matrix elements involving the CP-violating operators between the perturbative and lattice regimes.

hep-lat↗

arXiv2018

Improvements to Nucleon Matrix Elements within a $θ$ Vacuum from Lattice QCD

Using the gradient flow, we calculated the nucleon mixing angle $α_{N}$ and the nucleon electric dipole moment (EDM) induced by the QCD $θ$-term. To do so, we computed the topological charge, and the nucleon two-point and three-point correlation functions. The purpose of these proceedings is to explore how the topological charge density interacts with the nucleon interpolation operators. By understanding this relation, we can try to suppress noise contributions to the $α_{N}$ and EDM signals by selecting specific regions where the signal dominates. Using gauge fields provided by PACS-CS at $N_{f}=2+1$, a first collection of ensembles were selected at a fixed lattice spacing $a=0.0907$ fm ($β=1.90$), fixed dimensions $32^{3}\times 64$ and varying $m_π\approx\lbrace 411,\,570,\,701\rbrace$ MeV. A second collection was selected at fixed $m_π\approx701$ MeV, fixed box size of $L\approx1.9$ fm and varying $a=\lbrace 0.1215,\,0.0980,\,0.0685\rbrace $ fm.

hep-lat↗

arXiv2017

Electric Dipole Moment Results from lattice QCD

We utilize the gradient flow to define and calculate electric dipole moments induced by the strong QCD $θ$-term and the dimension-6 Weinberg operator. The gradient flow is a promising tool to simplify the renormalization pattern of local operators. The results of the nucleon electric dipole moments are calculated on PACS-CS gauge fields (available from the ILDG) using $N_{f}=2+1$, of discrete size $32^{3}\times 64$ and spacing $a \simeq 0.09$ fm. These gauge fields use a renormalization-group improved gauge action and a non-perturbatively $O(a)$ improved clover quark action at $β= 1.90$, with $c_{SW} = 1.715$. The calculation is performed at pion masses of $m_π \simeq 411,701$ MeV.

hep-lat↗

arXiv2016

Massive photons: an infrared regularization scheme for lattice QCD+QED

Standard methods for including electromagnetic interactions in lattice quantum chromodynamics calculations result in power-law finite-volume corrections to physical quantities. Removing these by extrapolation requires costly computations at multiple volumes. We introduce a photon mass to alternatively regulate the infrared, and rely on effective field theory to remove its unphysical effects. Electromagnetic modifications to the hadron spectrum are reliably estimated with a precision and cost comparable to conventional approaches that utilize multiple larger volumes. A significant overall cost advantage emerges when accounting for ensemble generation. The proposed method may benefit lattice calculations involving multiple charged hadrons, as well as quantum many-body computations with long-range Coulomb interactions.

hep-lat↗

arXiv2015

Photon mass term as an IR regularization for QCD+QED on the lattice

Inclusion of QED in lattice QCD calculations can lead to power-law volume artifacts as a consequence of the long-range nature of the interaction. Such artifacts must be removed by extrapolation in order to attain reliable infinite volume estimates of observables and quantities derived from them. As an alternative to this methodology, we consider the use of a photon mass term as an infrared regulator for QCD+QED, and explore the viability of its use in determining hadron mass shifts and splittings.

hep-lat↗

arXiv2015

The nucleon electric dipole moment with the gradient flow: the $θ$-term contribution

We propose a new method to calculate electric dipole moments induced by the strong QCD $θ$-term. The method is based on the gradient flow for gauge fields and is free from renormalization ambiguities. We test our method by computing the nucleon electric dipole moments in pure Yang-Mills theory at several lattice spacings, enabling a first-of-its-kind continuum extrapolation. The method is rather general and can be applied for any quantity computed in a $θ$ vacuum. This first application of the gradient flow has been successful and demonstrates proof-of-principle, thereby providing a novel method to obtain precise results for nucleon and light nuclear electric dipole moments.

hep-lat↗