Fri·Dec 16, 2022Friday·December 16, 2022

1. 01*

   Charm mass effects in the static energy computed in 2+1+1 flavor lattice QCD

   Johannes Heinrich Weber🇩🇪 · Nora Brambilla🇩🇪 · Rafael L. Delgado🇪🇸 · Andreas Kronfeld🇺🇸 · Viljami Leino🇩🇪 · Peter Petreczky🇺🇸 · Sebastian Steinbeißer🇩🇪 · Antonio Vairo🇩🇪

   We report our analysis for the static energy in (2+1+1)-flavor QCD over a wide range of lattice spacings and several quark masses. We obtain results for the static energy out to distances of nearly 1 fm, allowing us to perform a simultaneous determination of the lattice scales $r_2$, $r_1$ and $r_0$ as well as the string tension, $\sigma$. While our results for $r_0/r_1$ and $r_0$ $\sqrt{\sigma }$ agree with published (2+1)-flavor results, our result for $r_1/r_2$ differs significantly from the value obtained in the (2+1)-flavor case, likely due to the effect of the charm quark. We study in detail the effect of the charm quark on the static energy by comparing our results on the finest lattices with the previously published (2+1)-flavor QCD results at similar lattice spacing. The lattice results agree well with the two-loop perturbative expression of the static energy incorporating finite charm mass effects.

   hep-lathep-phPoS(2023)·0 citations
2. 02*

   Non-perturbative renormalization of quark and gluon operators using a gauge-invariant scheme

   G. Spanoudes🇨🇾 · C. Alexandrou🇨🇾 · J. Finkenrath🇨🇾 · K. Hadjiyiannakou🇨🇾 · H. Panagopoulos🇨🇾 · S. Yamamoto🇨🇾

   We present preliminary results for the renormalization functions (RFs) of a number of quark and gluon operators studied in lattice QCD using a gauge-invariant renormalization scheme (GIRS). GIRS is a variant of the coordinate-space renormalization prescription, in which Green's functions of gauge-invariant operators are calculated in position space. A novel aspect is that summations over different time slices of the positions of the operators are employed in order to reduce the statistical noise in lattice simulations. We test the reliability of this scheme by calculating RFs for the vector one-derivative quark bilinear operator, which enters the average momentum fraction of the nucleon. We use $N_f=4$ degenerate twisted mass clover-improved fermion ensembles of different volumes and lattice spacings. We also present first results of applying GIRS when operator mixing occurs: the mixing coefficients of the gluon and quark singlet energy-momentum tensor operators are evaluated by imposing appropriate renormalization conditions on the lattice.

   hep-latPoS(2023)·2 citations
3. 03*

   Tetraquarks and pentaquarks in lattice QCD with light and heavy quarks

   Pedro Bicudo🇵🇹

   We review how lattice QCD can contribute to the prediction and the comprehension of tetraquarks, pentaquarks and related exotic hadrons, with at least one heavy quark. We include all families of exotic hadrons, except for the quarkless glueballs and the hexaquarks which are related to nuclear physics. Since the discovery of quarks and the development of the QCD theory, there has been a large interest in exotic hadrons, initiated by the tetraquark models developed by Jaffe in 1977. Lattice QCD, being a first principle approach to solve non-perturbative QCD, has been crucial not only to compute precise results, but also to inspire research in hadronic physics. In the new millennium, this interest exploded with several experimental discoveries of tetraquark and pentaquark resonances with heavy quarks, starting with the Zc and Zb. Lattice QCD has not yet been able to comprehend this Z class of tetraquarks, and is developing new methods to determine their masses, decay widths and decay processes. The interest in tetraquarks was also fuelled by the lattice QCD prediction of a second class of tetraquarks such as the Tbb, boundstates in the sense of having no strong decays. Recently, the Tcc tetraquark, first predicted with quark models in 1982 by Richard et al, was observed experimentally. We expect the lattice QCD community will be able to explore this T class of tetraquarks in more detail and with very precise results. We report on all the different direct and indirect approaches that lattice QCD, with more focus on tetraquarks, has been employing to study exotic hadrons with at least one heavy quark. We also briefly review the experimental progress in observing tetraquarks and pentaquarks, and some of the theoretical paradigms of tetraquarks, including three different types of mechanisms (diquark, molecular and s pole), comparing them with the results of lattice QCD.

   hep-lathep-exhep-phPhys.Rept.(2023)·63 citations
4. 04*

   Kernel controlled real-time Complex Langevin simulation

   Daniel Alvestad🇳🇴 · Rasmus Larsen🇳🇴 · Alexander Rothkopf🇳🇴

   This study explores the utility of a kernel in complex Langevin simulations of quantum real-time dynamics on the Schwinger-Keldysh contour. We give several examples where we use a systematic scheme to find kernels that restore correct convergence of complex Langevin. The schemes combine prior information we know about the system and the correctness of convergence of complex Langevin to construct a kernel. This allows us to simulate up to $1.5\beta$ on the real-time Schwinger-Keldysh contour with the 0+1 dimensional anharmonic oscillator using $m=1$, $\lambda =24$, which was previously unattainable using the complex Langevin equation.

   hep-latPoS(2023)·0 citations
5. 05*

   Fits of finite-volume smeared spectral densities

   Luigi Del Debbio🇬🇧 · Alessandro Lupo🇬🇧 · Marco Panero🇮🇹 · Nazario Tantalo🇮🇹

   Motivated by recent progress in the numerical inversion of the Laplace transform, we investigate applications of finite-volume smeared spectral densities. These include the tuning of operator smearing, and the study of the finite-volume spectrum.

   hep-latPoS(2023)·8 citations
6. 06*

   Can the two-pole structure of the $D_0^{\ast }(2300)$ be understood from recent lattice data?

   Anuvind Asokan🇩🇪 · Meng-Na Tang🇨🇳 · Feng-Kun Guo🇨🇳 · Christoph Hanhart🇩🇪 · Yuki Kamiya🇩🇪 · Ulf-G. Meißner🇩🇪

   It was demonstrated in a series of papers employing unitarized chiral perturbation theory that the phenomenology of the scalar open-charm state, the $D_0^{\ast }(2300)$, can be understood as the interplay of two poles, corresponding to two scalar-isospin doublet states with different SU(3) flavor content. Within this formalism the lightest open charm positive parity states emerge as being dynamically generated from the scattering of the Goldstone-boson octet off $D$ mesons, a picture that at the same time solves various problems that the experimental observations posed. However, in recent lattice studies of $D\pi$ scattering at different pion masses only one pole was reported in the $D_0^{\ast }$ channel, while it was not possible to extract reliable parameters of a second pole from the lattice data. In this paper we demonstrate how this seeming contradiction can be understood and that imposing SU(3) constraints on the fitting amplitudes allows one to extract information on the second pole from the lattice data with minimal bias. The results may also be regarded as a showcase how approximate symmetries can be imposed in the $K$-matrix formalism to reduce the number of parameters.

   ↳ hep-phhep-exhep-latnucl-thEPJC(2023)·26 citations
7. 07*

   Phase transitions and light scalars in bottom-up holography

   Daniel Elander🇫🇷 · Ali Fatemiabhari🇬🇧 · Maurizio Piai🇬🇧

   Within the bottom-up approach to holography, we construct a class of six-dimensional gravity models, and discuss solutions that can be interpreted, asymptotically in the far UV, in terms of dual five-dimensional conformal field theories deformed by a single scalar operator. We treat the scaling dimension of such operator, related to the mass of the one scalar field in the gravity theory, as a free parameter. One dimension in the regular geometry is compactified on a shrinking circle, hence mimicking confinement in the resulting dual four-dimensional theories. We study the mass spectrum of bosonic states. The lightest state in this spectrum is a scalar particle. Along the regular (confining) branch of solutions, we find the presence of a tachyonic instability in part of the parameter space, reached by a smooth deformation of the mass spectrum, as a function of the boundary value of the background scalar field in the gravity theory. In a region of parameter space nearby the tachyonic one, the lightest scalar particle can be interpreted as an approximate dilaton, sourced by the trace of the stress-energy tensor, and its mass is parametrically suppressed. We also compute the free energy, along several branches of gravity solutions. We find that both the dilatonic and tachyonic regions of parameter space, identified along the branch of confining solutions, are hidden behind a first-order phase transition, so that they are not realised as stable solutions, irrespectively of the scaling dimension of the deforming field-theory operator. The (approximate) dilaton, in particular, appears in metastable solutions. Yet, the mass of the lightest state, computed close to the phase transition, is (mildly) suppressed. This feature is amplified when the (free) parameter controlling the scaling dimension of the deformation is 5/2, half the dimension of space-time in the field theory.

   ↳ hep-thhep-lathep-phPRD(2023)·15 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.