Search

We present the first exploratory lattice quantum chromodynamics (QCD) calculation of the polarized gluon Ioffe-time pseudo-distribution in the nucleon. The Ioffe-time pseudo-distribution provides a frame-independent and gauge-invariant framework to determine the gluon helicity in the nucleon from first principles. We employ a high-statistics computation using a $32^3\times 64$ lattice ensemble characterized by a $358$ MeV pion mass and a $0.094$ fm lattice spacing. We establish the pseudo-distribution approach as a feasible method to address the proton spin puzzle with successive improvements in statistical and systematic uncertainties anticipated in the future. Within the statistical precision of our data, we find a good comparison between the lattice determined polarized gluon Ioffe-time distribution and the corresponding expectations from the state-of-the-art global analyses. We find a hint for a nonzero gluon spin contribution to the proton spin from the model-independent extraction of the gluon helicity pseudo-distribution over a range of Ioffe-time, $\nu\lesssim 9$., Comment: Version to be published in Phys. Rev. D, 24 pages, 13 figures

We present a determination of the non-singlet transversity parton distribution function (PDF) of the nucleon, normalized with respect to the tensor charge at $\mu^2=2$ GeV$^2$ from lattice quantum chromodynamics. We apply the pseudo-distribution approach, using a gauge ensemble with a lattice spacing of 0.094 fm and the light quark mass tuned to a pion mass of 358 MeV. We extract the transversity PDF from the analysis of the short-distance behavior of the Ioffe-time pseudo-distribution using the leading-twist next-to-leading order (NLO) matching coefficients calculated for transversity. We reconstruct the $x$-dependence of the transversity PDF through an expansion in a basis of Jacobi polynomials in order to reduce the PDF ansatz dependence. Within the limitations imposed by a heavier-than-physical pion mass and a fixed lattice spacing, we present a comparison of our estimate for the valence transversity PDF with the recent global fit results based on single transverse spin asymmetry. We find the intrinsic nucleon sea to be isospin symmetric with respect to transversity., Comment: 25 pages, 13 figures

38th International Symposium on Lattice Field Theory, LATTICE2021 , Online, United States, 26 Jul 2021 - 30 Jul 2021; Proceedings of Science / International School for Advanced Studies (LATTICE2021), 426 (2022). doi:10.22323/1.396.0426, Lattice QCD calculations of the nucleon electromagnetic form factors are of interest at both the high and low momentum transfer regions. For high momentum transfers especially there are open questions which require more intense study, such as the potential zero crossing in the proton’s electric form factor. We will present recent progress from the QCDSF/UKQCD/CSSM collaboration on the calculation of these form factors using the Feynman-Hellmann method in lattice QCD. The Feynman-Hellmann method allows for greater control over excited states which we take advantage of by going to high values of the momentum transfer. In this proceeding we present results of the form factors up to $6\ \textrm{GeV}^2$ , using $𝑁_f=2+1$ flavour fermions for three different pion masses in the range $310-470 \textrm{MeV}$. The results are extrapolated to the physical pion mass through the use of a flavour breaking expansion., Published by SISSA, Trieste

Journal of high energy physics 08(8), 220 (2022). doi:10.1007/JHEP08(2022)220, We compute the hadronic running of the electromagnetic and weak couplings in lattice QCD with N$_{f}$ = 2 + 1 flavors of $ \mathcal{O} $(a) improved Wilson fermions. Using two different discretizations of the vector current, we compute the quark-connected and –disconnected contributions to the hadronic vacuum polarization (HVP) functions $ \overline{\varPi} ^{γγ}$ and $ \overline{\varPi} ^{γZ}$ for Euclidean squared momenta Q$^{2}$ ≤ 7 GeV$^{2}$. Gauge field ensembles at four values of the lattice spacing and several values of the pion mass, including its physical value, are used to extrapolate the results to the physical point. The ability to perform an exact flavor decomposition allows us to present the most precise determination to date of the SU(3)-flavor-suppressed HVP function $ \overline{\varPi} ^{08}$ that enters the running of sin$^{2}$θ$_{W}$. Our results for $ \overline{\varPi} ^{γγ}$, $ \overline{\varPi} ^{γZ}$ and $ \overline{\varPi} ^{08}$ are presented in terms of rational functions for continuous values of Q$^{2}$ below 7 GeV$^{2}$. We observe a tension of up to 3.5 standard deviation between our lattice results for $ \Delta {\alpha}_{\mathrm{had}}^{(5)} $(−Q$^{2}$) and estimates based on the R-ratio for space-like momenta in the range 3–7 GeV$^{2}$. The tension is, however, strongly diminished when translating our result to the Z pole, by employing the Euclidean split technique and perturbative QCD, which yields $ \Delta {\alpha}_{\mathrm{had}}^{(5)}\left({M}_Z^2\right) $ = 0.02773(15) and agrees with results based on the R-ratio within the quoted uncertainties., Published by SISSA, [Trieste]

19th International Conference on Hadron Spectroscopy and Structure, HADRON 2021, Mexico City, Mexico, 26 Jul 2021 - 1 Aug 2021; Suplemento de la revista mexicana de física 3(3), 0308104 (2022). doi:10.31349/SuplRevMexFis.3.0308104, Momentum and spatial distributions of quarks and gluons inside hadrons are typically encoded in the so-called generalized parton distributions (GPDs). GPDs are multi-dimensional quantities that are very challenging to extract, both experimentally and within lattice QCD. We present the first lattice results on the $x$-dependence of isovector unpolarized, helicity and transversity GPDs of the proton, obtained from lattice QCD using an ensemble of $N_f=2+1+1$ maximally twisted mass fermions, with pion mass $M_\pi=260$ MeV and lattice spacing $a\simeq 0.093$ fm. Our calculations use the quasi-distribution formalism and the final distributions are presented in the MS-bar scheme at a renormalization scale of 2 GeV., Published by Sociedad Mexicana de Física, Ciudad de México

38th International Symposium on Lattice Field Theory, Lattice 2021, Online, United States, 26 Jul 2021 - 30 Jul 2021; Proceedings of Science / International School for Advanced Studies (LATTICE2021), 129 (2022). doi:10.22323/1.396.0129, Generalized parton distributions (GPDs) are among the most fundamental quantities for describing the internal structure of hadrons. In this work, we present results on isovector GPDs of the proton obtained within lattice Quantum Chromodynamics. We use the quasi-distribution formalism and perform the calculations on an ensemble of $N_f = 2 + 1 + 1$ twisted mass fermions, with pion mass $M_\pi=260$~MeV and lattice spacing $a\simeq 0.093$~fm. Results are presented for unpolarized, helicity, and transversity GPDs at zero and nonzero skewness with controlled statistical uncertainties. Comparisons with their forward limit show qualitative features anticipated from model calculations., Published by SISSA, Trieste

We consider three-flavor QCD and perform a determination of the low-energy coupling $\hat{g}_\chi$ of SU(2) Heavy Meson Chiral Perturbation Theory. It is the $B^*B\pi$ coupling in the limit of static heavy and chiral light quarks and has not been determined with precision thus far. The calculation is performed on a large set of the $2+1$ flavor CLS ensembles with pion masses from 420 MeV down to 130 MeV. This allows us to significantly reduce the systematic uncertainty from the chiral extrapolation compared to previous works. Only a weak dependence on the lattice spacing is visible in our results., Comment: 9 pages, 4 figures, The 38th International Symposium on Lattice Field Theory, LATTICE2021 26th-30th July, 2021, Zoom/Gather@Massachusetts Institute of Technology

Physical review / D 105(1), 014502 (2022). doi:10.1103/PhysRevD.105.014502, We determine the properties of generalized 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 parametrized 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, $t=-1.1,-2.2 GeV^2$, and a pion mass of $m_�����470 MeV$. 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., Published by Inst., Melville, NY

Physical review letters 127(25), 252001 (2021). doi:10.1103/PhysRevLett.127.252001, We perform the first full decomposition of the pion momentum into its gluon and quark contributions. We employ an ensemble generated by the Extended Twisted Mass Collaboration with $N_f=2+1+1$ Wilson twisted mass clover fermions at maximal twist tuned to reproduce the physical pion mass. We present our results in the $\overline{MS}$ scheme at 2 GeV. We find $���x���_{u+d}=0.601(28), ���x���_s=0.059(13), ���x���_c=0.019(05)$, and $���x���_g=0.52(11)$ for the separate contributions, respectively, whose sum saturates the momentum sum rule., Published by APS, College Park, Md.

Physical review / D 104(5), 054503 (2021). doi:10.1103/PhysRevD.104.054503, We present results on the quark unpolarized, helicity and transversity parton distributions functions of the nucleon. We use the quasi-parton distribution approach within the lattice QCD framework and perform the computation using an ensemble of twisted mass fermions with the strange and charm quark masses tuned to approximately their physical values and light quark masses giving pion mass of 260 MeV. We use hierarchical probing to evaluate the disconnected quark loops. We discuss identification of ground state dominance, the Fourier transform procedure and convergence with the momentum boost. We find non-zero results for the disconnected isoscalar and strange quark distributions. The determination of the quark parton distribution and in particular the strange quark contributions that are poorly known provide valuable input to the structure of the nucleon., Published by Inst., Melville, NY

In this work, we explore the predictive power of the recently proposed covariant chiral nuclear force. In particular, we focus on the $^3S_1$-$^3D_1$ coupled channel and show that it is capable to predict the $^3D_1$ phase shifts and mixing angle $\varepsilon_1$ by fitting to the $^3S_1$ phase shifts, or predict the $^3S_1$ phase shifts by fitting to the $^3D_1$ phase shifts and mixing angle $\varepsilon_1$. For the physical nucleon-nucleon phase shifts, one can achieve a reasonably good description up to $T_\mathrm{lab.}\approx 100$ MeV. Qualitative descriptions can be achieved up to even higher energies. On the other hand, for the lattice QCD nucleon-nucleon phase shfits obtained with $M_\pi=469$ MeV, the energy range for which a decent description can be achieved is much reduced, to only $T_\mathrm{lab.}\approx 10$ MeV. In addition, we show that with one more low energy constant, particularly, one for the mixing angle, the next-to-leading order heavy baryon chiral nuclear force can describe the lattice QCD data up to $T_\mathrm{lab.}\approx 40$ MeV, but the description of the physical nucleon-nucleon phase shifts is of similar quality to the leading order covariant chiral nuclear force. The present study is relevant to a better understanding of the lattice QCD nucleon-nucleon force or more general baryon-baryon interactions.

We present a calculation of the up, down, strange and charm quark masses performed within the lattice QCD framework. We use the twisted mass fermion action and carry out simulations that include in the sea two light mass-degenerate quarks, as well as the strange and charm quarks. In the analysis we use gauge ensembles simulated at three values of the lattice spacing and with light quarks that correspond to pion masses in the range from 350 MeV to the physical value, while the strange and charm quark masses are tuned approximately to their physical values. We use several quantities to set the scale in order to check for finite lattice spacing effects and in the continuum limit we get compatible results. The quark mass renormalization is carried out non-perturbatively using the RI'-MOM method converted into the $\overline{\rm MS}$ scheme. For the determination of the quark masses we use physical observables from both the meson and the baryon sectors, obtaining $m_{ud} = 3.636(66)(^{+60}_{-57})$~MeV and $m_s = 98.7(2.4)(^{+4.0}_{-3.2})$~MeV in the $\overline{\rm MS}(2\,{\rm GeV})$ scheme and $m_c = 1036(17)(^{+15}_{-8})$~MeV in the $\overline{\rm MS}(3\,{\rm GeV})$ scheme, where the first errors are statistical and the second ones are combinations of systematic errors. For the quark mass ratios we get $m_s / m_{ud} = 27.17(32)(^{+56}_{-38})$ and $m_c / m_s = 11.48(12)(^{+25}_{-19})$., 37 pages, 23 figures, 24 tables. One reference added

The European physical journal / C 81(7), 651 (2021). doi:10.1140/epjc/s10052-021-09455-4, We compute the hadronic light-by-light scattering contribution to the muon $g-2$ from the up, down, and strange-quark sector directly using lattice QCD. Our calculation features evaluations of all possible Wick-contractions of the relevant hadronic four-point function and incorporates several different pion masses, volumes, and lattice-spacings. We obtain a value of $a_\mu^{\text{Hlbl}} = 106.8(14.7) \times 10^{-11}$ (adding statistical and systematic errors in quadrature), which is consistent with current phenomenological estimates and a previous lattice determination. It now appears conclusive that the hadronic light-by-light contribution cannot explain the current tension between theory and experiment for the muon $g-2$., Published by Springer, Heidelberg

Physical review / D 104(11), 114514 (2021). doi:10.1103/PhysRevD.104.114514, We present a lattice analysis of the light pseudoscalar mesons with consideration for the mixing between the flavor-neutral states ��0, �� and �����. We extract the masses and flavor compositions of the pseudoscalar meson nonet in nf=1+1+1 lattice QCD+QED around an SU(3)-flavor symmetric point, and observe flavor-symmetry features of the extracted data, along with preliminary extrapolation results for the flavor compositions at the physical point. A key result of this work is the observed mass splitting between the ��0 and �� on our ensembles, which is found to exhibit behavior that is simply related to the corresponding flavor compositions., Published by Inst., Melville, NY

In this study, we present a determination of the unpolarized gluon Ioffe-time distribution in the nucleon from a first principles lattice quantum chromodynamics calculation. We carry out the lattice calculation on a $32^3\times 64$ ensemble with a pion mass of $358$ MeV and lattice spacing of $0.094$ fm. We construct the nucleon interpolating fields using the distillation technique, flow the gauge fields using the gradient flow, and solve the summed generalized eigenvalue problem to determine the glounic matrix elements. Combining these techniques allows us to provide a statistically well-controlled Ioffe-time distribution and unpolarized gluon PDF. We obtain the flow time independent reduced Ioffe-time pseudo-distribution, and calculate the light-cone Ioffe-time distribution and unpolarized gluon distribution function in the $\overline{\rm MS}$ scheme at $\mu = 2$ GeV, neglecting the mixing of the gluon operator with the quark singlet sector. Finally, we compare our results to phenomenological determinations., Comment: 23 pages, 12 figures, Phys Rev D accepted version

We present, for the first time, an ab initio calculation of the individual up, down, and strange quark helicity parton distribution functions for the proton. The calculation is performed within the twisted mass clover-improved fermion formulation of lattice QCD. The analysis is performed using one ensemble of dynamical up, down, strange, and charm quarks with a pion mass of 260 MeV. The lattice matrix elements are nonperturbatively renormalized and the final results are presented in the $\overline{MS}$ scheme at a scale of 2 GeV. We give results for $��u^+(x), ��d^+(x) ��u^-(x), ��d^-(x)$, including disconnected quark loop contributions, as well as for $��s^+(x)$ and $��s^-(x)$. For the latter we achieve unprecedented precision compared to the phenomenological estimates.

Physical review letters 126(10), 102003 (2021). doi:10.1103/PhysRevLett.126.102003, We present, for the first time, an ab initio calculation of the individual up, down, and strange quark helicity parton distribution functions for the proton. The calculation is performed within the twisted mass clover-improved fermion formulation of lattice QCD. The analysis is performed using one ensemble of dynamical up, down, strange, and charm quarks with a pion mass of 260 MeV. The lattice matrix elements are nonperturbatively renormalized and the final results are presented in the $\overline{MS}$ scheme at a scale of 2 GeV. We give results for $��u^+(x), ��d^+(x) ��u^-(x), ��d^-(x)$, including disconnected quark loop contributions, as well as for $��s^+(x)$ and $��s^-(x)$. For the latter we achieve unprecedented precision compared to the phenomenological estimates., Published by APS, College Park, Md.

Physical review / D 102(9), 094510 (1-21) (2020). doi:10.1103/PhysRevD.102.094510, We study the dependence of the electric conductivity on chemical potential in finite-density SU(2) gauge theory with Nf=2 flavors of rooted staggered sea quarks, in combination with Wilson-Dirac and domain-wall valence quarks. The pion mass is reasonably small with mπ/mρ≈0.4. We concentrate in particular on the vicinity of the chiral crossover, where we find the low-frequency electric conductivity to be most sensitive to small changes in fermion density. Working in the low-density QCD-like regime with spontaneously broken chiral symmetry, we obtain an estimate of the first nontrivial coefficient c(T) of the expansion of conductivity σ(T,μ)=σ(T,0)(1+c(T)(μ/T)2+O(μ4)) in powers of μ, which has rather weak temperature dependence and takes its maximal value c(T)≈0.10±0.07 around the critical temperature. At larger densities and lower temperatures, the conductivity quickly grows toward the diquark condensation phase and also becomes closer to the free-quark result. As a by-product of our study we confirm the conclusions of previous studies with heavier pion that for SU(2) gauge theory the ratio of crossover temperature to pion mass Tc/mπ≈0.4 at μ=0 is significantly smaller than in real QCD., Published by Inst., Melville, NY

Physical review / D D D101(9), 094513 (2020). doi:10.1103/PhysRevD.101.094513, We evaluate the gluon and quark contributions to the spin of the proton using an ensemble of gauge configurations generated at physical pion mass. We compute all valence and sea quark contributions to high accuracy. We perform a nonperturbative renormalization for both quark and gluon matrix elements. We find that the contribution of the up, down, strange, and charm quarks to the proton intrinsic spin is 12∑q=u,d,s,cΔΣq+=0.191(15) and to the total spin ∑q=u,d,s,cJq+=0.285(45)(10). The gluon contribution to the spin is Jg=0.187(46)(10) yielding J=Jq+Jg=0.473(71)(14) confirming the spin sum. The momentum fraction carried by quarks in the proton is found to be 0.618(60) and by gluons 0.427(92), the sum of which gives 1.045(118) confirming the momentum sum rule. All scale and scheme dependent quantities are given in the MS¯ scheme at 2 GeV., Published by Inst.302363, Melville, NY

Using lattice configurations for quantum chromodynamics (QCD) generated with three domain-wall fermions at a physical pion mass, we obtain a parameter-free prediction of QCD's renormalisation-group-invariant process-independent effective charge, $\hat\alpha(k^2)$. Owing to the dynamical breaking of scale invariance, evident in the emergence of a gluon mass-scale, this coupling saturates at infrared momenta: $\hat\alpha(0)/\pi=0.97(4)$. Amongst other things: $\hat\alpha(k^2)$ is almost identical to the process-dependent (PD) effective charge defined via the Bjorken sum rule; and also that PD charge which, employed in the one-loop evolution equations, delivers agreement between pion parton distribution functions computed at the hadronic scale and experiment. The diversity of unifying roles played by $\hat\alpha(k^2)$ suggests that it is a strong candidate for that object which represents the interaction strength in QCD at any given momentum scale; and its properties support a conclusion that QCD is a mathematically well-defined quantum field theory in four dimensions., Comment: 10 pages, 4 figures

Nucleon-nucleon interactions, both bare and effective, play an important role in our understanding of the non-perturbative strong interaction, as well as nuclear structure and reactions. In recent years, tremendous efforts have been seen in the lattice QCD community to derive nucleon-nucleon interactions from first principles. Because of the daunting computing resources needed, most of such simulations were still performed with larger than physical light quark masses. In the present work, employing the recently proposed covariant chiral effective field theory (ChEFT), we study the light quark mass dependence of the nucleon-nucleon interaction extracted by the HALQCD group. It is shown that the pion-full version of the ChEFT can describe the lattice QCD data with $m_\pi=469$ MeV and their experimental counterpart reasonably well, while the pion-less version can describe the lattice QCD data with $m_\pi=672, 837, 1015, 1171$ MeV, for both the $^1S_0$ and $^3S_1$-$^3D_1$ channels. The slightly better description of the single channel than the triplet channel indicates that higher order studies are necessary for the latter. Our results confirmed previous studies that the nucleon-nucleon interaction becomes more attractive for both the singlet and triplet channels as the pion mass decreases towards its physical value. It is shown that the virtual bound state in the $^1S_0$ channel remains virtual down to the chiral limit, while the deuteron only appears for a pion mass smaller than about 400 MeV. It seems that proper chiral extrapolations of nucleon-nucleon interaction are possible for pion masses smaller than 500 MeV, similar to the mesonic and one-baryon sectors., Comment: 7 pages, 5 figures, uncertainties generated by cutoff variations are added, and matched to the published version

Physical review letters 125(23), 232001 (2020). doi:10.1103/PhysRevLett.125.232001, The infamous strong CP problem in particle physics can in principle be solved by a massless up quark. In particular, it was hypothesized that topological effects could substantially contribute to the observed nonzero up-quark mass without reintroducing CP violation. Alternatively to previous work using fits to chiral perturbation theory, in this Letter, we bound the strength of the topological mass contribution with direct lattice QCD simulations, by computing the dependence of the pion mass on the dynamical strange-quark mass. We find that the size of the topological mass contribution is inconsistent with the massless up-quark solution to the strong CP problem., Published by APS, College Park, Md.

Physical review / D 103(9), 094512 (2021). doi:10.1103/PhysRevD.103.094512, The quasi-PDF approach provides a path to computing parton distribution functions (PDFs) using lattice QCD. This approach requires matrix elements of a power-divergent operator in a nucleon at high momentum and one generically expects discretization effects starting at first order in the lattice spacing $a$. Therefore, it is important to demonstrate that the continuum limit can be reliably taken and to understand the size and shape of lattice artifacts. In this work, we report a calculation of isovector unpolarized and helicity PDFs using lattice ensembles with $N_f=2+1+1$ Wilson twisted mass fermions, a pion mass of approximately 370 MeV, and three different lattice spacings. Our results show a significant dependence on $a$, and the continuum extrapolation produces a better agreement with phenomenology. The latter is particularly true for the antiquark distribution at small momentum fraction $x$, where the extrapolation changes its sign., Published by Inst., Melville, NY

We present results for the unpolarized parton distribution function of the nucleon computed in lattice QCD at the physical pion mass. This is the first study of its kind employing the method of Ioffe time pseudo-distributions. Beyond the reconstruction of the Bjorken-$x$ dependence we also extract the lowest moments of the distribution function using the small Ioffe time expansion of the Ioffe time pseudo-distribution. We compare our findings with the pertinent phenomenological determinations., Comment: v2, 8 pages, 6 figures, matches published version, to appear in Phys.Rev.Lett

Physical review / D D 102(1), 014508 (2020). doi:10.1103/PhysRevD.102.014508, We perform a first calculation for the unpolarized parton distribution function of the $\Delta^+$ baryon using lattice QCD simulations within the framework of large momentum effective theory. Two ensembles of $N_{f}=2+1+1$ twisted mass fermions are utilized with a pion mass of 270 and 360 MeV, respectively. The baryon, which is treated as a stable single-particle state, is boosted with momentum $P_3$ with values {$0.42,0.83,1.25$} $GeV$, and we utilize momentum smearing to improve the signal. The unpolarized parton distribution function of $\Delta^+$ is obtained using a nonperturbative renormalization and a one-loop formula for the matching, with encouraging precision. In particular, we compute the $\bar{d}(x)-\bar{u}(x)$ asymmetry and compare it with the same quantity in the nucleon, in a first attempt towards resolving the physical mechanism responsible for generating such asymmetry., Published by Inst.302363, Melville, NY

We report on the first computation of the strong running coupling at the physical point (physical pion mass) from the ghost-gluon vertex, computed from lattice simulations with three flavors of Domain Wall fermions. We find $\alpha_{\overline{\rm MS}}(m_Z^2)=0.1172(11)$, in remarkably good agreement with the world-wide average. Our computational bridge to this value is the Taylor-scheme strong coupling, which has been revealed of great interest by itself because it can be directly related to the quark-gluon interaction kernel in continuum approaches to the QCD bound-state problem., Comment: 6 pages, 3 figures, v2: references added

We calculate the scalar and tensor charges of the nucleon in 2+1-flavor lattice QCD, for which the systematics of the renormalization of the disconnected diagram is well controlled. Numerical simulations are performed at a single lattice spacing a = 0.11 fm. We simulate four pion masses, which cover a range of $m_\pi \sim$ 290 - 540 MeV, and a single strange quark mass close to its physical value. The statistical accuracy is improved by employing the so-called low-mode averaging technique and the truncated solver method. We study up, down, and strange quark contributions to the nucleon charges by calculating disconnected diagrams using the all-to-all quark propagator. Chiral symmetry is exactly preserved by using the overlap quark action to avoid operator mixing among different flavors, which complicates the renormalization of scalar and tensor matrix elements and leads to possibly large contamination to the small strange quark contributions. We also study the nucleon axial charge with contribution from the disconnected diagram. Our results are in reasonable agreement with experiments and previous lattice studies., Comment: 39 pages, 17 figures

We extend the prediction range of Pionless Effective Field Theory with an analysis of the ground state of $^{16}$O in leading order. To renormalize the theory, we use as input both experimental data and lattice QCD predictions of nuclear observables, which probe the sensitivity of nuclei to increased quark masses. The nuclear many-body Schr\"odinger equation is solved with the Auxiliary Field Diffusion Monte Carlo method. For the first time in a nuclear quantum Monte Carlo calculation, a linear optimization procedure, which allows us to devise an accurate trial wave function with a large number of variational parameters, is adopted. The method yields a binding energy of $^{4}$He which is in good agreement with experiment at physical pion mass and with lattice calculations at larger pion masses. At leading order we do not find any evidence of a $^{16}$O state which is stable against breakup into four $^4$He, although higher-order terms could bind $^{16}$O., Comment: 11 pages, 4 figures

We describe a procedure for extracting momentum derivatives of nucleon matrix elements on the lattice directly at $Q^2=0$. This is based on the Rome method for computing momentum derivatives of quark propagators. We apply this procedure to extract the nucleon isovector magnetic moment and charge radius as well as the isovector induced pseudoscalar form factor at $Q^2=0$ and the axial radius. For comparison, we also determine these quantities with the traditional approach of computing the corresponding form factors, i.e. $G^v_E(Q^2)$ and $G_M^v(Q^2)$ for the case of the vector current and $G_P^v(Q^2)$ and $G_A^v(Q^2)$ for the axial current, at multiple $Q^2$ values followed by $z$-expansion fits. We perform our calculations at the physical pion mass using a 2HEX-smeared Wilson-clover action. To control the effects of excited-state contamination, the calculations were done at three source-sink separations and the summation method was used. The derivative method produces results consistent with those from the traditional approach but with larger statistical uncertainties especially for the isovector charge and axial radii.

XXIV International Workshop on Deep-Inelastic Scattering and Related, Hamburg, Germany, 11 Apr 2016 - 15 Apr 2016 ; Proceedings of Science (DIS2016), 240(2016)., The exact decomposition of the proton spin has been a much debated topic, on the experimental as well as the theoretical side. In this talk we would like to report on recent non-perturbative results and ongoing efforts to explore the proton spin from lattice QCD. We present results for the relevant generalized form factors from gauge field ensembles that feature a physical value of the pion mass. These generalized form factors can be used to determine the total spin and angular momentum carried by the quarks. In addition we present first results for our ongoing effort to compute the angular momentum of the gluons in the proton., Published by SISSA, Trieste

Physical review / D 104(1), 014511 (2021). doi:10.1103/PhysRevD.104.014511, We study the chiral separation effect (CSE) in finite-density SU(2) lattice gauge theory with dynamical quarks. We find that the CSE is well described by the free quark result in the high-temperature quark-gluon plasma phase. As one enters the confinement regime with broken chiral symmetry at chemical potential smaller than half of the pion mass, the CSE response is gradually suppressed toward low temperatures in comparison to the free quark result. This suppression can be approximately described by assuming that the CSE current is proportional to the charge density, rather than the chemical potential, as suggested in the literature [Phys. Rev. D 97, 085020 (2018). We also provide an upper bound on the contribution of disconnected fermionic diagrams to the CSE, which is consistent with zero within our statistical errors and small compared to that of the connected diagrams. Our results are obtained mainly in the QCD-like regime of SU(2) gauge theory at low densities, and hence should be at least qualitatively applicable to QCD as well., Published by Inst., Melville, NY

Physical review / D 104(7), 074515 (2021). doi:10.1103/PhysRevD.104.074515, We present a calculation of the up, down, strange, and charm quark masses performed within the lattice QCD framework. We use the twisted-mass fermion action and carry out simulations that include in the sea two light mass-degenerate quarks, as well as the strange and charm quarks. In the analysis, we use gauge ensembles simulated at three values of the lattice spacing and with light quarks that correspond to pion masses in the range from 350 MeV to the physical value, while the strange and charm quark masses are tuned approximately to their physical values. We use several quantities to set the scale in order to check for finite lattice spacing effects, and in the continuum limit, we get compatible results. The quark mass renormalization is carried out nonperturbatively using the (modified) Regularization Independent Momentum Subtraction (RI���-MOM) method converted into the $\overline{MS}$ scheme. For the determination of the quark masses, we use physical observables from both the meson and the baryon sectors, obtaining $m_{ud}$=3.636(66)($_{-57}^{+60}$) MeV and $m_s$=98.7(2.4)($_{-3.2}^{+4.0}$) MeV in the $\overline{MS}$(2 GeV) scheme and $m_c$=1036(17)($_{-8}^{+15}$) MeV in the $\overline{MS}$(3 GeV) scheme, where the first errors are statistical and the second ones are combinations of systematic errors. For the quark mass ratios, we get $m_s/m_{ud}$=27.17(32)($_{-38}^{+56}$) and $m_c/m_s$=11.48(12)($_{-19}^{+25}$)., Published by Inst., Melville, NY