Wed·Nov 17, 2021Wednesday·November 17, 2021

1. 01*

   The scalar, vector and tensor form factors for the pion and kaon from lattice QCD

   Constantia Alexandrou🇨🇾 · Simone Bacchio🇨🇾 · Ian Cloet🇺🇸 · Martha Constantinou🇺🇸 · Joseph Delmar🇺🇸 · Kyriakos Hadjiyiannakou🇨🇾 · Giannis Koutsou🇨🇾 · Colin Lauer🇺🇸 · Alejandro Vaquero🇺🇸

   We present a calculation of the scalar, vector, and tensor form factors for the pion and kaon in lattice QCD. We use an ensemble of two degenerate light, a strange and a charm quark ($N_f=2+1+1$) of maximally twisted mass fermions with clover improvement. The corresponding pion and kaon masses are about 265 MeV and 530 MeV, respectively. The calculation is done in both rest and boosted frames obtaining data for four-vector momentum transfer squared up to $-q^2=2.5$ GeV${}^2$ for the pion and 3 GeV${}^2$ for the kaon. The excited-states effects are studied by analyzing six values of the source-sink time separation for the rest frame ($1.12-2.23$ fm) and for four values for the boosted frame ($1.12-1.67$ fm). The lattice data are renormalized non-perturbatively and the results for the scheme- and scale-dependent scalar and tensor form factors are presented in the $\overline{\mathrm{MS}}$ scheme at a scale of 2 GeV. We apply different parametrizations to describe $q^2$-dependence of the form factors to extract the scalar, vector, and tensor radii, as well as the tensor anomalous magnetic moment. We compare the pion and kaon form factors to study SU(3) flavor symmetry breaking effects. By combining the data for the vector and tensor form factors we also obtain the lowest moment of the densities of transversely polarized quarks in the impact parameter space. Finally, we give an estimate for the average transverse shift in the $y$ direction for polarized quarks in the $x$ direction.

   hep-lathep-exhep-phPRD(2022)·35 citations
2. 02*

   Confinement/Deconfinement in 4D compact QED on the lattice

   Lee C. Loveridge🇵🇹 · Orlando Oliveira🇵🇹 · Paulo J. Silva🇵🇹

   It has long been known that there is a phase transition between confined and unconfined phases of compact pure gauge QED on the lattice. In this work we report three manifestations of this phase change as seen in the Landau gauge photon propagator, the static potential, and distribution of Dirac Strings in the gauge fixed configurations. Each of these was calculated with large lattices with volumes: $32^4$, $48^4$ and $96^4$. We show that the confined phase manifests with a Yukawa type propagator with a dynamically generated mass gap, a linearly increasing potential, and a significant concentration of Dirac strings while the unconfined phase appears consistent with the continuum results: a free propagator, a near constant long-distance potential, and a small concentration of Dirac strings trending towards zero. Furthermore, the photon propagator is investigated in detail near the transition between the two phases.

   hep-latPoS(2022)·1 citation
3. 03*

   Lattice results for the longitudinal spin structure and color forces on quarks in a nucleon

   S. Bürger🇩🇪 · T. Wurm🇩🇪 · M. Löffler🇩🇪 · M. Göckeler🇩🇪 · G. Bali🇩🇪 · S. Collins🇩🇪 · A. Schäfer🇩🇪 · A. Sternbeck🇩🇪

   Using lattice QCD, we calculate the twist-2 contribution $a_2$ to the third Mellin moment of the spin structure functions $g_1$ and $g_2$ in the nucleon. In addition we evaluate the twist-3 contribution $d_2$. Our computations make use of $N_f=2+1$ gauge field ensembles generated by the Coordinated Lattice Simulations (CLS) effort. Neglecting quark-line disconnected contributions we obtain as our best estimates $a_2^{(p)}=0.069(17)$, $d_2^{(p)}=0.0105(68)$ and $a_2^{(n)}=0.0068(88)$, $d_2^{(n)}=-0.0009(70)$ for the proton and the neutron, respectively, where we use the normalizations given in Eqs. (58) and (59). While the $a_2$ results have been converted to the $\overline{\mathrm{MS}}$ scheme using three-loop perturbation theory, the numbers for $d_2$ are given in the regularization independent momentum subtraction (RI${}^{\prime }$-MOM) scheme, i.e., the conversion has been performed only in tree-level perturbation theory. The $d_2$ results can be interpreted as corresponding to a transverse color Lorentz force on a quark in a transversely polarized proton of size $F^{(u)}=116(61)$ MeV/fm and $F^{(d)}=-38(66)$ MeV/fm for $u$ and $d$ quarks, respectively. The error estimates quoted include statistical and systematic uncertainties added in quadrature.

   hep-lathep-phPRD(2022)·27 citations
4. 04*

   QMC study of the chiral Heisenberg Gross-Neveu universality class

   Yuichi Otsuka🇯🇵 · Kazuhiro Seki🇯🇵 · Sandro Sorella🇧🇷 · Seiji Yunoki🇯🇵

   We investigate a quantum criticality of an antiferromagnetic phase transition in the Hubbard model on a square lattice with a $d$-wave pairing field by large-scale auxiliary-field quantum Monte Carlo simulations. Since the $d$-wave pairing filed induces Dirac cones in the non-interacting single-particle spectrum, the quantum criticality should correspond to the chiral Heisenberg universality class in terms of the Gross-Neveu theory, which is the same as those expected in the Hubbard model on the honeycomb lattice, despite the unit cells being different (e.g., they contain one and two sites, respectively). We show that both the two phase transitions, expected to occur on the square and on the honeycomb lattices, indeed have the same quantum criticality. We also argue that details of the models, i.e., the way of counting the total number $N$ of fermion components and the anisotropy of the Dirac cones, do not change the critical exponents.

   ↳ cond-mat.str-elhep-latJ.Phys.Conf.Ser.(2022)·2 citations
5. 05*

   Using classical bit-flip correction for error mitigation including 2-qubit correlations

   Constantia Alexandrou🇨🇾 · Lena Funcke🇺🇸 · Tobias Hartung🇬🇧 · Karl Jansen🇩🇪 · Stefan Kuehn🇨🇭 · Georgios Polykratis🇨🇾 · Paolo Stornati🇩🇪 · Xiaoyang Wang🇨🇳

   We present an error mitigation scheme which corrects readout errors on Noisy Intermediate-Scale Quantum (NISQ) computers [1,2]. After a short review of applying the method to one qubit, we proceed to discuss the case when correlations between different qubits occur. We demonstrate how the readout error can be mitigated in this case. By performing experiments on IBMQ hardware, we show that such correlations do not have a strong effect on the results, justifying to neglect them.

   ↳ quant-phhep-latPoS(2022)·9 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.