Mon·Oct 25, 2021Monday·October 25, 2021

1. 01*

   Generalised parton distributions from the off-forward Compton amplitude in lattice QCD

   Alec Hannaford-Gunn🇦🇺 · Kadir Utku Can🇦🇺 · Roger Horsley🇬🇧 · Yoshifumi Nakamura🇯🇵 · Holger Perlt🇩🇪 · Paul E. L. Rakow🇬🇧 · Hinnerk Stüben🇩🇪 · Gerrit Schierholz🇩🇪 · Ross D. Young🇦🇺 · James M. Zanotti🇦🇺

   We determine the properties of generalised parton distributions (GPDs) from a lattice QCD calculation of the off-forward Compton amplitude (OFCA). By extending the Feynman-Hellmann relation to second-order matrix elements at off-forward kinematics, this amplitude can be calculated from lattice propagators computed in the presence of a background field. Using an operator product expansion, we show that the deeply-virtual part of the OFCA can be parameterised in terms of the low-order Mellin moments of the GPDs. We apply this formalism to a numerical investigation for zero-skewness kinematics at two values of the soft momentum transfer, $t=-1.1,-2.2{\text{GeV}}^2$, and a pion mass of $m_{\pi }\approx 470\text{MeV}$. The form factors of the lowest two moments of the nucleon GPDs are determined, including the first lattice QCD determination of the $n=4$ moments. Hence we demonstrate the viability of this method to calculate the OFCA from first principles, and thereby provide novel constraint on the $x$- and $t$-dependence of GPDs.

   hep-latPRD(2022)·42 citations
2. 02*

   State mixing and masses of the ${\pi }^0$, $\eta$ and ${\eta }^{\prime }$ mesons from $n_f=1+1+1$ lattice QCD+QED

   Z. R. Kordov🇦🇺 · R. Horsley🇬🇧 · W. Kamleh🇦🇺 · Z. Koumi🇦🇺 · Y. Nakamura🇯🇵 · H. Perlt🇩🇪 · P. E. L. Rakow🇬🇧 · G. Schierholz🇩🇪 · H. Stüben🇩🇪 · R. D. Young🇦🇺 · J. M. Zanotti🇦🇺

   We present a lattice analysis of the light pseudoscalar mesons with consideration for the mixing between the flavour-neutral states ${\pi }^0$, $\eta$ and ${\eta }^{\prime }$. We extract the masses and flavour compositions of the pseudoscalar meson nonet in $n_f=1+1+1$ lattice QCD+QED around an SU(3)-flavour symmetric point, and observe flavour-symmetry features of the extracted data, along with preliminary extrapolation results for the flavour compositions at the physical point. A key result of this work is the observed mass splitting between the ${\pi }^0$ and $\eta$ on our ensembles, which is found to exhibit behaviour that is simply related to the corresponding flavour compositions.

   hep-lathep-phnucl-thPRD(2021)·14 citations
3. 03*

   Static quark anti-quark interactions at non-zero temperature from lattice QCD

   Dibyendu Bala🇩🇪 · Olaf Kaczmarek🇩🇪 · Rasmus Larsen🇳🇴 · Swagato Mukherjee🇺🇸 · Gaurang Parkar🇳🇴 · Peter Petreczky🇺🇸 · Alexander Rothkopf🇳🇴 · Johannes Heinrich Weber🇩🇪

   We study the interactions of a static quark antiquark pair at non-zero temperature using realistic 2+1 flavor lattice QCD calculations. The study consists of two parts: the first investigates the properties of Wilson line correlators in Coulomb gauge and compares to predictions of hard-thermal loop perturbation theory. As a second step we extract the spectral functions underlying the correlators using four conceptually different methods: spectral function fits, a HTL inspired fit for the correlation function, Padé rational approximation and the Bayesian BR spectral reconstruction. We find that our high statistics Euclidean lattice data are amenable to different hypotheses for the shapes of the spectral function and we compare the implications of each analysis method for the existence and properties of a well defined ground state spectral peak.

   hep-lathep-phnucl-thPRD(2022)·80 citations
4. 04*

   Investigating $\mathbf{N}\to \mathbf{N}\pi$ axial matrix elements

   Lorenzo Barca🇩🇪 · Gunnar S. Bali🇩🇪 · Sara Collins🇩🇪

   Excited state contamination is one of the most challenging sources of systematics to tackle in the determination of nucleon matrix elements and form factors. The signal-to-noise problem prevents one from considering large source-sink time separations for the three-point functions to ensure ground state dominance. Instead, relevant analyses consider multi-state fits. Excited state contributions are particularly significant in the axial channel. In this work, we confront the problem directly. Since the major source of contamination is understood to be related to pion production, we consider three-point correlation functions with a nucleon operator at the source and a nucleon-pion interpolating operator at the sink, which allows studies of $N\to N\pi$ matrix elements. We discuss the construction of these three-point correlation functions and we solve the generalized eigenvalue problem (GEVP) using different sets of nucleon and nucleon-pion interpolators. The analysis is performed on the CLS ensemble A653 with $m_{\pi }\approx 420$ MeV. Results were generated with valence quark masses corresponding to $m_{\pi }\approx 1750$ MeV and $m_{\pi }\approx 420$ MeV.

   hep-latPoS(2022)·6 citations
5. 05*

   Hybrid stochastic method for the tensor renormalization group

   Hiroshi Ohki🇯🇵 · Erika Arai🇯🇵 · Masaaki Tomii🇺🇸

   We propose a hybrid stochastic method for the tensor renormalization group (TRG) approach. TRG is known as a powerful tool to study the many-body systems and quantum field theory on the lattice. It is based on a low-rank approximation of the tensor using the truncated singular value decomposition (SVD), whose computational cost increases as the bond dimension increases, so that efficient cost reduction techniques are highly demanded. We use noise vectors for the low-rank approximation with the truncated SVD, by which the truncation error is replaced with a statistical error due to noise, and an error estimation could be improved. We test this method in the classical Ising model and observe a better accuracy than TRG. We also discuss a cross contamination issue in a multiple use of the same noise vectors, and to remove this systematic error we consider position-dependent noise vectors.

   hep-latcond-mat.str-elPoS(2022)·0 citations
6. 06*

   A First-Quantized Model For Unparticles and Gauge Theories Around Conformal Window

   N. Boulanger🇧🇪 · F. Buisseret🇧🇪 · G. Lhost🇧🇪

   We first quantize the action proposed by Casalbuoni and Gomis in [Phys. Rev. D \textbf{90}, 026001 (2014)], an action that describes two massless relativistic scalar particles interacting via a conformally invariant potential. The spectrum is a continuum of massive states that may be interpreted as unparticles. We then obtain in a similar way the mass operator for a deformed action in which two terms are introduced that break the conformal symmetry: a mass term and an extra position-dependent coupling constant. A simple Ansatz for the latter leads to a mass operator with linear confinement in terms of an effective string tension $\sigma$. The quantized model is confining when $\sigma \ne 0$ and its mass spectrum shows Regge trajectories. We propose a tensionless limit in which highly excited confined states reduce to (gapped) unparticles. Moreover, the low-lying confined bound states become massless in the latter limit as a sign of conformal symmetry restoration and the ratio between their masses and $\sqrt{\sigma }$ stays constant. The originality of our approach is that it applies to both confining and conformal phases via an effective interacting model.

   ↳ hep-thhep-latUniverse(2021)·0 citations

* Reconstructed cohort: no mailing for this day survives in the archive. Papers are grouped by their submission times and arXiv's announcement cut-off, assuming announcement without delay; positions follow identifier order. Validated at ~91% exact-day agreement against the archived era.