Wed·Aug 25, 2021Wednesday·August 25, 2021

1. 01*

   Spectrum of SU(2) gauge theory at large number of flavors

   Jarno Rantaharju🇫🇮 · Tobias Rindlisbacher🇫🇮 · Kari Rummukainen🇫🇮 · Ahmed Salami🇫🇮 · Kimmo Tuominen🇫🇮

   We present a numerical study of the spectrum of an asymptotically non-free $SU(2)$ gauge theory with $N_f=24$ massive fermion flavors. For such large number of flavors, asymptotic freedom is lost and the massless theory is governed by a gaussian fixed point at long distances. If fermions are massive they decouple at low energy scales and the theory is confining. We present a scaling law for the masses of the hadrons, glueballs and string tension as functions of fermion mass. The hadrons become effectively heavy quark systems, with masses approximately twice the fermion mass, whereas the energy scale of the confinement, probed by e.g. the string tension, is much smaller and vanishes asymptotically as $m_{\text{fermion}}^{2.18}$. Our results from lattice simulations are compatible with this behaviour.

   hep-latPRD(2021)·8 citations
2. 02*

   Existence and Non-Existence of Doubly Heavy Tetraquark Bound States

   Martin Pflaumer🇩🇪 · Luka Leskovec🇺🇸 · Stefan Meinel🇺🇸 · Marc Wagner🇩🇪

   In this work we investigate the existence of bound states for doubly heavy tetraquark systems $\bar{Q}{\bar{Q}}^{\prime }q{q}^{\prime }$ in a full lattice-QCD computation, where heavy bottom quarks are treated in the framework of non-relativistic QCD. We focus on three systems with quark content $\bar{b}\bar{b}ud$, $\bar{b}\bar{b}us$ and $\bar{b}\bar{c}ud$. We show evidence for the existence of $\bar{b}\bar{b}ud$ and $\bar{b}\bar{b}us$ bound states, while no binding appears to be present for $\bar{b}\bar{c}ud$. For the bound four-quark states we also discuss the importance of various creation operators and give an estimate of the meson-meson and diquark-antidiquark percentages.

   hep-latPoS(2022)·16 citations
3. 03*

   Transversity GPDs of the proton from lattice QCD

   Constantia Alexandrou🇨🇾 · Krzysztof Cichy🇵🇱 · Martha Constantinou🇺🇸 · Kyriakos Hadjiyiannakou🇨🇾 · Karl Jansen🇩🇪 · Aurora Scapellato🇺🇸 · Fernanda Steffens🇩🇪

   We present the first calculation of the $x$-dependence of the isovector transversity generalized parton distributions (GPDs) for the proton within lattice QCD. We compute the matrix elements with non-local operators containing a Wilson line. The calculation implements the Breit symmetric frame. The proton momenta are chosen as $0.83,1.25,1.67$ GeV, and the values of the momentum transfer squared are $0.69,1.02$ GeV${}^2$. These combinations include cases with zero and nonzero skewness. The calculation is performed using one ensemble of two degenerate-mass light, a strange and a charm quark of maximally twisted mass fermions with a clover term. The lattice results are renormalized non-perturbatively and finally matched to the light-cone GPDs using one-loop perturbation theory within the framework of large momentum effective theory. The final GPDs are given in the $\overline{\mathrm{MS}}$ scheme at a scale of 2 GeV. In addition to the individual GPDs, we form the combination of the transversity GPDs that is related to the transverse spin structure of the proton. Finally, we extract the lowest two moments of GPDs and draw a number of important qualitative conclusions.

   hep-lathep-exhep-phhep-th+1PRD(2022)·82 citations
4. 04*

   A variational study of two-nucleon systems with lattice QCD

   Saman Amarasinghe🇺🇸 · Riyadh Baghdadi🇺🇸 · Zohreh Davoudi🇺🇸 · William Detmold🇺🇸 · Marc Illa🇪🇸 · Assumpta Parreno🇪🇸 · Andrew V. Pochinsky🇺🇸 · Phiala E. Shanahan🇺🇸 · Michael L. Wagman🇺🇸

   The low-energy spectrum and scattering of two-nucleon systems are studied with lattice quantum chromodynamics using a variational approach. A wide range of interpolating operators are used: dibaryon operators built from products of plane-wave nucleons, hexaquark operators built from six localized quarks, and quasi-local operators inspired by two-nucleon bound-state wavefunctions in low-energy effective theories. Sparsening techniques are used to compute the timeslice-to-all quark propagators required to form correlation-function matrices using products of these operators. Projection of these matrices onto irreducible representations of the cubic group, including spin-orbit coupling, is detailed. Variational methods are applied to constrain the low-energy spectra of two-nucleon systems in a single finite volume with quark masses corresponding to a pion mass of 806 MeV. Results for S- and D-wave phase shifts in the isospin singlet and triplet channels are obtained under the assumption that partial-wave mixing is negligible. Tests of interpolating-operator dependence are used to investigate the reliability of the energy spectra obtained and highlight both the strengths and weaknesses of variational methods. These studies and comparisons to previous studies using the same gauge-field ensemble demonstrate that interpolating-operator dependence can lead to significant effects on the two-nucleon energy spectra obtained using both variational and non-variational methods, including missing energy levels and other discrepancies. While this study is inconclusive regarding the presence of two-nucleon bound states at this quark mass, it provides robust upper bounds on two-nucleon energy levels that can be improved in future calculations using additional interpolating operators and is therefore a step toward reliable nuclear spectroscopy from the underlying Standard Model of particle physics.

   hep-lathep-phnucl-thPRD(2023)·93 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.