Wed·Dec 22, 2021Wednesday·December 22, 2021

1. 01*

   The QCD chiral phase transition for different numbers of quark flavours

   Francesca Cuteri🇩🇪 · Owe Philipsen🇩🇪 · Alessandro Sciarra🇩🇪

   We present results from a comprehensive study of the location of the chiral critical surface, which separates regions of first-order chiral transitions from analytic crossovers, in the bare parameter space of lattice QCD with unimproved staggered fermions. We study the theories with $N_f\in [2,8]$ and trace the chiral critical surface along diminishing lattice spacing, with $N_{\tau }=\{4,6,8\}$. This allows for an extrapolation to the lattice chiral limit, where the surface has to terminate in a tricritical line, employing known tricritical scaling relations. Knowing the phase structure in the lattice bare parameter space allows to draw conclusions for the approach to the continuum and chiral limits taken in the appropriate order. Our data provide evidence for the continuum chiral limit to feature a second-order transition for all $N_f\in [2,7]$. We perform an analogous scaling analysis with already published data from $N_f=3$ $O(a)$-improved Wilson fermions, which is also consistent with a second-order transition in the continuum. A modified Columbia plot reflecting those results is suggested.

   hep-latPoS(2022)·1 citation
2. 02*

   Searching for the BCS phase at nonzero isospin asymmetry

   Bastian B. Brandt🇩🇪 · Francesca Cuteri🇩🇪 · Gergely Endrődi🇩🇪

   According to perturbation theory predictions, QCD matter in the zero-temperature, high-density limits of QCD at nonzero isospin chemical potential is expected to be in a superfluid Bardeen-Cooper-Schrieffer (BCS) phase of $u$ and $\bar{d}$ Cooper pairs. It is also expected, on symmetry grounds, that such phase connects via an analytical crossover to the phase with Bose-Einstein condensation (BEC) of charged pions at ${\mu }_{\text{I}}\ge m_{\pi }/2$. With lattice results, showing some indications that the deconfinement crossover also smoothly penetrates the BEC phase, the conjecture was made that the former connects continuously to the BEC-BCS crossover. We compute the spectrum of the Dirac operator, and use generalized Banks-Casher relations, to test this conjecture and identify signatures of the superfluid BCS phase.

   hep-lathep-phnucl-thPoS(2022)·13 citations
3. 03*

   Non-perturbative renormalisation with interpolating momentum schemes

   N Garron🇬🇧 · C Cahill🇬🇧 · M Gorbahn🇬🇧 · JA Gracey🇬🇧 · PEL Rakow🇬🇧

   Hadronic matrix elements evaluated on the lattice can be converted to a continuum scheme such as $\text{MSbar}$ using intermediate non-perturbative renormalisation schemes. Discretisation effects on the lattice and convergence of the continuum perturbation theory are both scheme dependent and we explore this dependence in the framework of the Rome-Southampton method for generalised kinematics. In particular, we implement several non-exceptional {\em interpolating} momentum schemes, where the momentum transfer is {\em not} restricted to the symmetric point defined in RI/SMOM. Using flavour non-singlet quark bilinears, we compute the renormalisation factors of the quark mass and wave function for $N_f=3$ flavours of dynamical quarks. We investigate the perturbative and non-perturbative scale-dependencies. Our numerical results are obtained from lattice simulations performed with Domain-Wall fermions, based on ensembles generated by RBC-UKQCD collaborations; we use two different lattice spacings $1/a\sim 1.79$ and $2.38$ GeV. We also give the numerical values for the relevant anomalous dimensions and matching coefficients at next-to-next-to-leading order.

   hep-lathep-phPRD(2023)·2 citations
4. 04*

   Coarse graining in effective theories of lattice QCD in 1+1d and 2+1d

   Christoph Konrad🇩🇪 · Owe Philipsen🇩🇪

   In the strong coupling and heavy quark mass regime, lattice QCD dimensionally reduces to effective theories of Polyakov loops depending on the parameters of the original Wilson action $\beta ,\kappa$ and $N_{\tau }$. We apply coarse graining techniques to such theories in 1d and 2d, corresponding to lattice QCD at finite temperature and non-zero chemical potential in 1+1d and 2+1d, respectively. In 1d the method is applied to the effective theories up to $\mathcal{O}({\kappa }^4)$. Using the transfer matrix, the recursion relations are solved analytically. The thermodynamic limit is taken for some observables. Afterwards, continuum extrapolation is performed numerically and results are discussed. In 2d the coarse graining method is applied in the pure gauge and static quark limit. Running couplings are obtained and the fixed points of the transformations are discussed. Finally, the critical coupling of the deconfinement transition is determined in both limits. Agreement to about 12% with Monte Carlo results of 2+1d Yang-Mills theory from the literature is observed.

   hep-latPoS(2022)·0 citations
5. 05*

   Inhomogeneous phases in the chirally imbalanced $2+1$-dimensional Gross-Neveu model and their absence in the continuum limit

   Laurin Pannullo🇩🇪 · Marc Wagner🇩🇪 · Marc Winstel🇩🇪

   We study the $\mu$-${\mu }_{45}$-$T$ phase diagram of the $2+1$-dimensional Gross-Neveu model, where $\mu$ denotes the ordinary chemical potential, ${\mu }_{45}$ the chiral chemical potential and $T$ the temperature. We use the mean-field approximation and two different lattice regularizations with naive chiral fermions. An inhomogeneous phase at finite lattice spacing is found for one of the two regularizations. Our results suggest that there is no inhomogeneous phase in the continuum limit. We show that a chiral chemical potential is equivalent to an isospin chemical potential. Thus, all results presented in this work can also be interpreted in the context of isospin imbalance.

   hep-lathep-phnucl-thSymmetry(2022)·24 citations
6. 06*

   The torelon spectrum and the world-sheet axion

   Andreas Athenodorou🇨🇾 · Michael Teper🇬🇧

   We present a major update on the spectrum of the closed flux-tube (torelon) in $D=3+1$ $SU(N)$ gauge theories. Namely, we calculate the excitation spectrum of a confining flux-tube which winds around a spatial torus as a function of its length $l$, for short as well as long tubes. We do so for $N=3,5,6$ and two different values of the lattice spacing. Our states are characterised by the quantum numbers of spin $J$, transverse parity $P_{\perp }$, longitudinal parity $P_{\parallel }$ as well as by the longitudinal momentum $p_{\parallel }$. Our extended basis of operators used in combination with the generalized eigenvalue method enables us to extract masses for all irreducible representations characterised by $\{|J|,P_{\perp },P_{\parallel }\}$. We confirm that most of the low-lying states are well described by the spectrum of the Goddard-Goldstone-Rebbi-Thorn string. In addition we provide strong evidence, that in addition to string like states, massive modes exist on the world-sheet. More precisely the ground state with quantum numbers ${|J|}^{P_{\perp },P_{\parallel }}=0^{--}$ exhibits a behaviour which is in agreement with the interpretation of being an axion on the world-sheet of the flux-tube. This state arises from a topological interaction term included in the effective world-sheet action. In addition we observe that the second excited state with ${|J|}^{P_{\perp },P_{\parallel }}=0^{++}$ behaves as a massive mode with mass twice that of the axion.

   hep-lathep-thPoS(2022)·14 citations
7. 07*

   Preserving gauge invariance in neural networks

   Matteo Favoni🇦🇹 · Andreas Ipp🇦🇹 · David I. Müller🇦🇹 · Daniel Schuh🇦🇹

   In these proceedings we present lattice gauge equivariant convolutional neural networks (L-CNNs) which are able to process data from lattice gauge theory simulations while exactly preserving gauge symmetry. We review aspects of the architecture and show how L-CNNs can represent a large class of gauge invariant and equivariant functions on the lattice. We compare the performance of L-CNNs and non-equivariant networks using a non-linear regression problem and demonstrate how gauge invariance is broken for non-equivariant models.

   hep-latcs.LGhep-phhep-th+1EPJ Web Conf.(2022)·1 citation
8. 08*

   Progress report on computing the disconnected QCD and the QCD plus QED hadronic contributions to the muon's anomalous magnetic moment

   Alexei Bazavov🇺🇸 · Christine Davies🇬🇧 · Carleton DeTar🇺🇸 · Aida El-Khadra🇺🇸 · Steven Gottlieb🇺🇸 · Dan Hatton🇬🇧 · Hwancheol Jeong🇺🇸 · Andreas Kronfeld🇺🇸 · Peter Lepage🇺🇸 · Craig McNeile🇬🇧 · Gaurav Ray🇬🇧 · James Simone🇺🇸 · Alejandro Vaquero🇺🇸

   We report progress on calculating the contribution to the anomalous magnetic moment of the muon from the disconnected hadronic diagrams with light and strange quarks and the valence QED contribution to the connected diagrams. The lattice QCD calculations use the highly-improved staggered quark (HISQ) formulation. The gauge configurations were generated by the MILC Collaboration with four flavors of HISQ sea quarks with physical sea-quark masses.

   hep-latPoS(2022)·9 citations
9. 09*

   Towards a discovery of BSM physics from the Cabibbo angle anomaly

   Chien-Yeah Seng🇩🇪

   New developments in both the theories and experiments related to the extraction of the top-row Cabibbo-Kobayashi-Maskawa matrix elements $V_{ud}$ and $V_{us}$ led to a series of new anomalies, for instance the apparent violation of the top-row unitarity relation. It is important to further reduce all the associated Standard Model theory uncertainties in order to better understand whether such observations point towards the possibility of physics beyond the Standard Model, or rather some unexpectedly large Standard Model effects. This requires improved studies of tree-level and higher-order Standard Model corrections that enter the beta decays of pions, neutron, nuclei and kaons. We will briefly review the recent progress along this direction and discuss possible improvements in the future.

   ↳ hep-phhep-exhep-latnucl-ex+1Mod.Phys.Lett.A(2022)·7 citations
10. 10*

    Mass spectra, wave functions and mixing effects of the $(bcq)$ baryon

    Qiang Li🇨🇳 · Chao-Hsi Chang🇨🇳 · Si-Xue Qin🇨🇳 · Guo-Li Wang🇨🇳

    Mass spectra and wave functions of the $J^P={\frac{1}{2}}^{+}$ $(bcq)$ baryons are calculated by the relativistic Bethe-Salpeter equation\,(BSE) with considering the mixing effects between the $1^{+}$ and $0^{+}$ $(bc)$-diquarks inside. Based on the diquark picture, the three-body problem of baryons is transformed into two two-body problems. The BSE and wave functions of the $0^{+}$ diquark are given, and then solved numerically to obtain the effective mass spectra and form factors. Also we present the wave functions at zero point for the $(bc)$-diquark. Considering the obtained diquark form factors, the $(bcq)$ baryons are then described by the BSE as the bound state of a diquark and a light quark, where the interaction kernel includes the inner transitions between the $0^{+}$ and $1^{+}$ diquarks. The general wave function of the ${\frac{1}{2}}^{+}$ $(bcq)$ baryons is constructed and solved to obtain the corresponding mass spectra. Especially, by using the obtained wave functions, the mixing effects between ${\Xi }_{bc}({\Omega }_{bc})$ and ${\Xi }_{bc}^{\prime }({\Omega }_{bc}^{\prime })$ in ground states are computed and determined to be small ($\sim 1\%$). The numerical results indicate that it is a good choice to take ${\Xi }_{bc}$ and ${\Xi }_{bc}^{\prime }$ as the baryon states with the inside $(bc)$-diquarks occupying the definite spin.

    ↳ hep-phhep-exhep-latEPJC(2022)·6 citations
11. 11*

    Baryonic form factors of the pion and kaon in a chiral quark model

    Wojciech Broniowski🇵🇱 · Enrique Ruiz Arriola🇪🇸 · Pablo Sanchez-Puertas🇪🇸

    The baryonic form factor of charged pions is studied in detail in the Nambu--Jona-Lasinio model with constituent quarks, where the spontaneously broken chiral symmetry is the key dynamical ingredient guaranteeing the would-be Goldstone boson nature of the pseudoscalar mesons octet. In general, this form factor arises when the isospin symmetry is broken, which is the case if the $u$ and $d$ quark masses are split, as in the real world, or if the electromagnetic effects were taken into account. We obtain estimates for this basic property of the pion resulting from the quark mass splitting for a range of model parameters, and importantly, for different pion masses, going up to the values used in lattice QCD. We find very stable model results, with the mean square radius of ${\pi }^{+}$ in the range $(0.05-0.07\mathrm{fm}{)}^2$. From charge conjugation, the baryonic form factor of ${\pi }^{+}$ and ${\pi }^{-}$ are equal and opposite. We also obtain the transverse-coordinate, relativistically invariant baryonic density of the charged pion. In ${\pi }^{+}$, the inner region carries a negative, and the outside -- a positive baryon number density, both cancelling to zero, as obviously the pion carries no net baryon charge. We also carry out an analogous analysis for the kaon, where the effect is much larger due to the sizable $s$ and $u/d$ quark mass splitting. We discuss the prospects of lattice QCD measurements of the baryonic form factors of charged pions and kaons.

    ↳ hep-phhep-latPRD(2022)·6 citations
12. 12*

    Dilaton and Massive Hadrons in a Conformal Phase

    Luigi Del Debbio🇬🇧 · Roman Zwicky🇬🇧

    As the number of fermion fields is increased, gauge theories are expected to undergo a transition from a QCD-like phase, characterised by confinement and chiral symmetry breaking, to a conformal phase, where the theory becomes scale-invariant at large distances. In this paper, we discuss some properties of a third phase, where spontaneously broken conformal symmetry is characterised by its Goldstone boson, the dilaton. In this phase, which we refer to as conformal dilaton phase, the massless pole corresponding to the Goldstone boson guarantees that the conformal Ward identities are satisfied in the infrared despite the other hadrons carrying mass. In particular, using renormalisation group arguments in Euclidean space, we show that for massless quarks the trace of the energy momentum tensor vanishes on all physical states as a result of the fixed point. This implies the vanishing of the gluon condensate and suggests that the scale breaking is driven by the quark condensate which has implications for the cosmological constant. In addition form factors obey an exact constraint for every hadron and are thus suitable probes to identify this phase in the context of lattice Monte Carlo studies. For this purpose we examine how the system behaves under explicit symmetry breaking, via quark-mass and finite-volume deformations. The dilaton mass shows hyperscaling under mass deformation, viz. $m_D=\mathcal{O}(m_q^{1/(1+{\gamma }^{\ast })})$. This provides another clean search pattern.

    ↳ hep-phhep-lathep-thJHEP(2022)·37 citations
13. 13*

    Global Symmetries and Partial Confinement

    Masanori Hanada🇬🇧 · Jack Holden🇬🇧 · Matthew Knaggs🇬🇧 · Andy O'Bannon🇬🇧

    In gauge theories, spontaneous breaking of the centre symmetry provides a precise definition of deconfinement. In large-$N$ gauge theories, evidence has emerged recently that between confined and deconfined phases a partially-deconfined phase can appear, in which only a subset of colours deconfine. In the partially-deconfined phase, the centre symmetry is spontaneously broken, raising the question of whether an order parameter exists that can distinguish completely- and partially-deconfined phases. We present two examples in gauge theories of global symmetries that are spontaneously broken in the confined phase and preserved in the deconfined phase, and we show that this symmetry is spontaneously broken in the partially-deconfined phase. As a result, in these theories the transition from complete to partial deconfinement is accompanied by the spontaneous breaking of a global symmetry. The two examples are CP symmetry in $\mathcal{N}=1$ super-Yang-Mills with a massive gluino and theta-angle $\theta =\pi$, and chiral symmetry in a strongly-coupled lattice gauge theory. For $\mathcal{N}=1$ SYM we also present numerical evidence that the same phenomenon occurs at finite $N\ge 30$. We thus conjecture that global symmetries may provide order parameters to distinguish completely and partially deconfined phases generically, including at finite $N$.

    ↳ hep-thhep-lathep-phJHEP(2022)·12 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.