Wed·Nov 23, 2022Wednesday·November 23, 2022

1. 01*

   Inclusive semileptonic $B$-decays from lattice QCD

   Paolo Gambino🇮🇹 · Shoji Hashimoto🇯🇵 · Sandro Mächler🇮🇹 · Marco Panero🇮🇹 · Francesco Sanfilippo🇮🇹 · Silvano Simula🇮🇹 · Antonio Smecca🇮🇹 · Nazario Tantalo🇮🇹

   We present the lattice QCD calculation of inclusive semileptonic $B_s$-meson decays. We follow a recently proposed method, which is based on the extraction of smeared spectral densities from Euclidean correlation functions and on the numerical reconstruction of the integration kernel relevant for the inclusive decay rate calculation. We compute four-point Euclidean correlation functions using JLQCD and ETM gauge ensembles with unphysically light $b$-quark masses, and apply two different methods for the integration kernel reconstruction. Finally, we show that the lattice results obtained in this work are in good agreement with the analytic predictions of the operator-product-expansion. This opens the path for a future full lattice QCD calculation to be used as theoretical input for the determination of the magnitude of the CKM element $V_{cb}$.

   hep-lathep-phPoS(2023)·4 citations
2. 02*

   The muon anomalous magnetic moment: is the lattice spacing small enough?

   Christopher Aubin🇺🇸 · Thomas Blum🇺🇸 · Maarten Golterman🇺🇸 · Santiago Peris🇪🇸

   We present new results for the light-quark connected part of the leading order hadronic-vacuum-polarization (HVP) contribution to the muon anomalous magnetic moment, using $2+1+1$ staggered fermions. We have collected more statistics on previous ensembles, and we added two new ensembles. This allows us to reduce statistical errors on the HVP contribution and related window quantities significantly. We also calculated the current-current correlator to next-to-next-to-leading order (NNLO) in staggered chiralperturbation theory, so that we can correct to NNLO for finite-volume, pion-mass mistuning and taste-breaking effects. We discuss the applicability of NNLO chiral perturbation theory, emphasizing that it provides a systematic EFT approach to the HVP contribution, but not to short- or intermediate-distance window quantities. This makes it difficult to assess systematic errors on the standard intermediate-distance window quantity that is now widely considered in the literature. In view of this, we investigate a longer-distance window, for which EFT methods should be more reliable. Our most important conclusion is that new high-statistics computations at lattice spacings significantly smaller than 0.06 fm are indispensable. The ensembles we use have been generously provided by MILC and CalLat.

   hep-lathep-phPoS(2023)·4 citations
3. 03*

   Non-perturbative insights into the spectral properties of QCD at finite temperature

   Peter Lowdon🇩🇪 · Owe Philipsen🇩🇪

   In quantum field theories at finite temperature spectral functions describe how particle systems behave in the presence of a thermal medium. Although data from lattice simulations can in principle be used to determine spectral function characteristics, existing methods rely on the extraction of these quantities from temporal correlators, which requires one to circumvent an ill-posed inverse problem. In these proceedings we report on a recent approach that instead utilises the non-perturbative constraints imposed by field locality to extract spectral function information directly from spatial correlators. In particular, we focus on the application of this approach to lattice QCD data of the spatial pseudo-scalar meson correlator in the temperature range $220-960\text{MeV}$, and outline why this data supports the conclusion that there exists a distinct pion state above the chiral pseudo-critical temperature $T_{\text{pc}}$.

   hep-lathep-phhep-thnucl-thEPJ Web Conf.(2022)·5 citations
4. 04*

   Phase diagram of QCD in strong background magnetic field

   Massimo D'Elia🇮🇹 · Lorenzo Maio🇮🇹 · Francesco Sanfilippo🇮🇹 · Alfredo Stanzione🇮🇹

   We discuss the phase diagram of QCD in the presence of a strong background magnetic field, providing numerical evidence, based on lattice simulations of QCD with $2+1$ flavours and physical quark masses, that the QCD crossover turns into a first order phase transition for large enough magnetic field, with a critical endpoint located between $eB=4$ GeV${}^2$ (where we found an analytic crossover at a pseudo-critical temperature $T_c=(98\pm 3)$ MeV) and $eB=9$ GeV${}^2$ (where the measured critical temperature is $T_c=(63\pm 5)$ MeV).

   hep-latPoS·7 citations
5. 05*

   Mass Renormalization of the Schwinger Model with Wilson and Staggered Fermions in the Hamiltonian Lattice Formulation

   Takis Angelides🇩🇪 · Lena Funcke🇺🇸 · Karl Jansen🇩🇪 · Stefan Kühn🇩🇪

   Lattice computations in the Hamiltonian formulation have so far mainly focused on staggered fermions. In these proceedings, we study Wilson fermions in the Hamiltonian formulation and propose a new method to determine the resulting mass shift. As a benchmark study, we examine the one-flavour Schwinger model with Wilson fermions and a topological $\theta$-term using matrix product states. Wilson fermions explicitly break chiral symmetry; thus, the bare mass of the lattice model receives an additive renormalization. In order to measure this mass shift directly, we develop a method that is suitable for the Hamiltonian formulation, which relies on the fact that the vacuum expectation value of the electric field density vanishes when the renormalized mass is zero. We examine the dependence of the mass shift on the lattice spacing, the lattice volume, the $\theta$-parameter, and the Wilson parameter. Using the mass shift, we then perform the continuum extrapolation of the electric field density and compare the resulting mass dependence to the analytical predictions of mass perturbation theory. We demonstrate that incorporating the mass shift significantly improves the continuum extrapolation. Finally, we apply our method to the same model using staggered fermions instead of Wilson fermions and compare the resulting mass shift to recent theoretical predictions.

   hep-latquant-phPoS(2023)·10 citations
6. 06*

   Three-gluon vertex in Landau-gauge from quenched-lattice QCD in general kinematics

   F. Pinto-Gomez🇪🇸 · F. de Soto🇪🇸

   We report on a novel and extensive lattice QCD analysis for the three-gluon vertex from quenched lattice-QCD simulations. Using standard Wilson action, we have computed the three-gluon vertex beyond the usual kinematic restriction to the symmetric $(q^2=r^2=p^2)$ and soft-gluon $(p=0)$ cases where it depends on a single momentum scale. The so-dubbed bisectoral case $(r^2=q^2\ne p^2)$, where the transversely projected vertex can be cast in terms of three independent tensors, have been the object of a recent exhaustive scrutiny, also shown in this communication. Herein, beyond this special case, results for kinematic configurations with three different squared momenta are also presented. All data considered, the lattice estimate of the three-gluon vertex exhibits a clear dominance of the tree-level tensor form factor.

   hep-lathep-phEPJ Web Conf.(2022)·5 citations
7. 07*

   Toward $N$ to $N\pi$ matrix elements from lattice QCD

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

   QCD matrix elements of axial and vector currents between nucleons are required for the Monte Carlo reconstruction of the energy of neutrinos that are detected in long baseline oscillation experiments in the quasi-elastic regime. The cleanest approach for determining the axial matrix elements is lattice QCD. However, the extraction of these from the corresponding correlation functions is complicated by very large excited state contributions, that are related to transitions from the nucleon to a nucleon-pion pair. In this pilot study with a pion mass $m_{\pi }=429\mathrm{MeV}$, we demonstrate for the first time that these contributions can be removed by including five-(anti)quark operators into the basis of interpolators used to create the nucleon. The same techniques will be needed to compute transition matrix elements between the nucleon and nucleon-pion scattering states that are relevant in the resonance production regime.

   hep-latPRD(2023)·43 citations
8. 08*

   Confined Charged Particles in C-periodic Volumes

   G. Kanwar🇨🇭 · A. Mariani🇨🇭 · J. C. Pinto Barros🇨🇭 · U. J. Wiese🇨🇭

   Charged particles in an Abelian Coulomb phase are non-local infraparticles that are surrounded by a cloud of soft photons which extends to infinity. Gauss' law prevents the existence of charged particles in a periodic volume. In a $C$-periodic volume, which is periodic up to charge conjugation, on the other hand, charged particles can exist. This includes vortices in the $3$-d XY-model, magnetic monopoles in $4$-d $\mathrm{U}(1)$ gauge theory, as well as protons and other charged particles in QCD coupled to QED. In four dimensions non-Abelian charges are confined. Hence, in an infinite volume non-Abelian infraparticles cost an infinite amount of energy. However, in a $C$-periodic volume non-Abelian infraparticles (whose energy increases linearly with the box size) can indeed exist. Investigating these states holds the promise of deepening our understanding of confinement.

   hep-latPoS(2023)·0 citations
9. 09*

   Gradient flow scale setting with tree-level improvement

   Christian Schneider🇦🇹 · Anna Hasenfratz🇺🇸 · Oliver Witzel🇩🇪

   Lattice scales defined using gradient flow are typically very precise, while also easy to calculate. However, different definitions of flows and operators can differ significantly, suggesting possible systematical effects. Using a subset of RBC-UKQCD's 2+1 flavor domain wall fermion and Iwasaki gauge action ensembles, we explore differences between $\sqrt{t_0}$ and $w_0$ gradient flow scales, compare the impact of different operators to define the energy density, and study the effect of using tree-level improvement for the gradient flow. We find that for this set of gauge field ensembles Zeuthen flow with Symanzik operators has the most consistent approach to the continuum limit and exhibit very small cutoff corrections. Tree-level improvement, traditionally used in step-scaling studies, significantly reduces the spread between different operators, but does not lead to an overall improvement when it comes to reducing cutoff effects for gradient flow scales $\sqrt{t_0}$ or $w_0$.

   hep-latPoS(2023)·2 citations
10. 10*

    $QQqq\bar{q}$ Quark System, Compact Pentaquark, and Gauge/String Duality

    Oleg Andreev🇩🇪

    For the case of two light flavors we propose the stringy description of the system consisting of two heavy and three light quarks, with the aim of exploring the quark organization inside the system and its low-lying Born-Oppenheimer potentials as a function of the heavy quark separation. Our analysis reveals several critical separations related to the processes of string reconnection, breaking and junction annihilation. We find that a compact pentaquark configuration makes the dominant contribution to the potential of the first excited state at small separations, and for separations larger than $0.1\text{fm}$, the antiquark-diquark-diquark structure emerges. Moreover, it turns out that the length scale of string junction annihilation is the same as that for the $QQ\bar{q}\bar{q}$ system. We also discuss the relation to the potential of the $QQq$ system and some relations among the masses of hadrons in the heavy quark limit.

    ↳ hep-phhep-lathep-thnucl-thPRD(2023)·13 citations
11. 11*

    Cornering Large-$N_c$ QCD with Positivity Bounds

    Clara Fernandez🇪🇸 · Alex Pomarol🇪🇸 · Francesco Riva🇨🇭 · Francesco Sciotti🇪🇸

    The simple analytic structure of meson scattering amplitudes in the large-$N_c$ limit, combined with positivity of the spectral density, provides precise predictions on low-energy observables. Building upon previous studies, we explore the allowed regions of chiral Lagrangian parameters and meson couplings to pions. We reveal a structure of kinks at all orders in the chiral expansion and develop analytical tools to show that kinks always correspond to amplitudes with a single light pole. We build (scalar- and vector-less) deformations of the Lovelace-Shapiro and Coon UV-complete amplitudes, and show that they lie close to the boundaries. Moreover, constraints from crossing-symmetry imply that meson couplings to pions become smaller as their spin increases, providing an explanation for the success of Vector Meson Dominance and holographic QCD. We study how these conclusions depend on assumptions about the high-energy behavior of amplitudes. Finally, we emphasize the complementarity between our results and Lattice computations in the exploration of large-$N_c$ QCD.

    ↳ hep-thhep-lathep-phJHEP(2023)·75 citations
12. 12*

    Width effects of broad new resonances in loop observables and application to $(g-2{)}_{\mu }$

    Andreas Crivellin🇨🇭 · Martin Hoferichter🇨🇭

    In the phenomenology of strong interactions most physical states acquire a substantial width, and thus can only be defined in a model-independent way by pole positions and residues of the $S$-matrix. This information is incorporated in the Källén-Lehmann representation, whose spectral function characterizes the shape of the resonance and can be constrained by the dominant decay channels. Here, we argue that similar effects become important whenever beyond-the-Standard-Model particles possess a sizable decay width - as possible for instance in cases with a large branching fraction to a dark sector or strongly coupled scenarios - and show how their widths can be incorporated in the calculation of loop observables. As an application, we consider the anomalous magnetic moment of the muon, including both the direct effect of new physics and the possible indirect impact of a broad light $Z^{\prime }$ on $e^{+}{e}^{-}\to \text{hadrons}$ cross sections. Throughout, we provide results for a general spectral function and its reconstruction from the one-loop imaginary part, where the latter captures the leading two-loop effects.

    ↳ hep-phhep-exhep-latnucl-thPRD(2023)·29 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.