Wed·Oct 27, 2021Wednesday·October 27, 2021

1. 01*

   Controlling unwanted exponentials in lattice calculations of radiative leptonic decays

   Christopher Kane🇺🇸 · Davide Giusti🇩🇪 · Christoph Lehner🇩🇪 · Stefan Meinel🇺🇸 · Amarjit Soni🇺🇸

   Two important sources of systematic errors in lattice QCD calculations of radiative leptonic decays are unwanted exponentials in the sum over intermediate states and unwanted excited states created by the meson interpolating field. Performing the calculation using a 3d sequential propagator allows for better control over the systematic uncertainties from intermediate states, while using a 4d sequential propagator allows for better control over the systematic uncertainties from excited states. We calculate form factors using both methods and compare how reliably each controls these systematic errors. We also employ a hybrid approach involving global fits to data from both methods.

   hep-lathep-phPoS(2022)·8 citations
2. 02*

   QCD viscosity by combining the gradient flow and sparse modeling methods

   Etsuko Itou🇯🇵 · Yuki Nagai🇯🇵

   We give a new description to obtain the shear viscosity in QCD at finite temperature. Firstly, we obtain the correlation function of the renormalized energy-momentum tensor using the gradient flow method. Secondly, we estimate the spectral function from the smeared correlation functions using the sparse modeling method. The combination of these two methods looks promising to determine the shear viscosity precisely.

   hep-lathep-phnucl-thPoS(2022)·4 citations
3. 03*

   Continuum limit of two-dimensional multiflavor scalar gauge theories

   Claudio Bonati🇮🇹 · Alessio Franchi🇮🇹 · Andrea Pelissetto🇮🇹 · Ettore Vicari🇮🇹

   We address the interplay between local and global symmetries by analyzing the continuum limit of two-dimensional multicomponent scalar lattice gauge theories, endowed by non-Abelian local and global invariance. These theories are asymptotically free. By exploiting Monte Carlo simulations and finite-size scaling techniques, we provide numerical results concerning the universal behavior of such models in the critical regime. Our results support the conjecture that two-dimensional multiflavor scalar models have the same continuum limit as the $\sigma$-models associated with symmetric spaces that have the same global symmetry.

   hep-latcond-mat.stat-mechPoS(2022)·0 citations
4. 04*

   Machine learning spectral functions in lattice QCD

   S.-Y. Chen🇨🇳 · H.-T. Ding🇨🇳 · F.-Y. Liu🇨🇳 · G. Papp🇭🇺 · C.-B. Yang🇨🇳

   We study the inverse problem of reconstructing spectral functions from Euclidean correlation functions via machine learning. We propose a novel neural network, SVAE, which is based on the variational autoencoder (VAE) and can be naturally applied to the inverse problem. The prominent feature of the SVAE is that a Shannon-Jaynes entropy term having the ground truth values of spectral functions as prior information is included in the loss function to be minimized. We train the network with general spectral functions produced from a Gaussian mixture model. As a test, we use correlators generated from four different types of physically motivated spectral functions made of one resonance peak, a continuum term and perturbative spectral function obtained using non-relativistic QCD. From the mock data test we find that the SVAE in most cases is comparable to the maximum entropy method (MEM) in the quality of reconstructing spectral functions and even outperforms the MEM in the case where the spectral function has sharp peaks with insufficient number of data points in the correlator. By applying to temporal correlation functions of charmonium in the pseudoscalar channel obtained in the quenched lattice QCD at 0.75 $T_c$ on $128^3\times 96$ lattices and $1.5$ $T_c$ on $128^3\times 48$ lattices, we find that the resonance peak of ${\eta }_c$ extracted from both the SVAE and MEM has a substantial dependence on the number of points in the temporal direction ($N_{\tau }$) adopted in the lattice simulation and $N_{\tau }$ larger than 48 is needed to resolve the fate of ${\eta }_c$ at 1.5 $T_c$.

   hep-latcs.LGhep-phhep-th+134 citations
5. 05*

   Roberge-Weiss transitions at imaginary isospin chemical potential

   Amine Chabane🇩🇪 · Gergely Endrödi🇩🇪

   At finite imaginary values of the chemical potential, QCD is free of the sign problem. Moreover, at high temperatures the partition function exhibits a new symmetry (the Roberge-Weiss symmetry) connecting phases with different orientations of the Polyakov loop, and the corresponding phase transitions between these. In this contribution we investigate the perturbative one-loop effective potential for the Polyakov loop in the presence of imaginary isospin as well as baryon chemical potentials. This leads to a novel phase diagram, which reveals an interesting insight about the rich phase structure of the system and the center symmetry breaking. We check the perturbative results using direct lattice simulations.

   hep-lathep-phPoS(2022)·4 citations
6. 06*

   Non-perturbative decoupling of massive fermions

   Tobias Rindlisbacher🇨🇭 · Kari Rummukainen🇫🇮 · Ahmed Salami🇫🇮 · Kimmo Tuominen🇫🇮

   SU(2) gauge theory with Nf=24 massless fermions is non-interacting at long distances, i.e. it has an infrared fixed point at vanishing coupling. With massive fermions the fermions are expected to decouple at energy scales below the fermion mass, and the infrared behaviour is that of confining SU(2) pure gauge theory. We demonstrate this behaviour non-perturbatively with lattice Monte Carlo simulations by measuring the gradient flow running coupling.

   hep-latPRL(2022)·5 citations
7. 07*

   SU($N$) Toric Code and Nonabelian Anyons

   Manu Mathur🇮🇳 · Atul Rathor🇮🇳

   We construct SU($N$) toric code model describing the dynamics of SU($N$) electric and magnetic fluxes on a two dimensional torus. We show that the model has $N^2$ topologically distinct ground states $|{\psi }_0{⟩}_{(\mathsf{p},\mathsf{q})}$ which are loop states characterized by $Z_N\otimes Z_N$ centre charges $(\mathsf{p},\mathsf{q}=0,1,2,\cdots ,N-1)$. We explicitly construct them in terms of coherent superpositions of all possible spin network states on torus with Wigner coefficients as their amplitudes. All excited quasiparticle states with SU($N$) electric charges and magnetic fluxes are constructed. We show that the braiding statistics of these SU(N) electric, magnetic quasiparticles or nonabelian anyons is encoded in the Wigner rotation matrices.

   ↳ quant-phhep-lathep-thPRA(2022)·5 citations
8. 08*

   Complex poles of Landau-gauge QCD propagators and general properties

   Yui Hayashi🇯🇵 · Kei-Ichi Kondo🇯🇵

   We study analytic structures of the gluon, quark, and ghost propagators in the Landau-gauge QCD and general properties from the existence of unusual singularities. First, we investigate analytic structures of the QCD propagators using the massive Yang-Mills model, in which the one-loop gluon and ghost propagators are in good agreement with the numerical lattice results in the Landau gauge. We find that both gluon and quark propagators in this model have complex poles that invalidate the usual spectral representation. Second, we discuss general properties of propagators in the presence of such complex singularities, especially on the positivity and locality. Finally, we consider a possible quantum mechanical interpretation and implications on a confinement mechanism.

   ↳ hep-thhep-latPoS(2022)·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.