Fri·Sep 24, 2021Friday·September 24, 2021

1. 01*

   Spectral reconstruction details of a gradient-flowed color-electric correlator

   Luis Altenkort🇩🇪 · Alexander M. Eller🇩🇪 · Olaf Kaczmarek🇩🇪 · Lukas Mazur🇩🇪 · Guy D. Moore🇩🇪 · Hai-Tao Shu🇩🇪

   In a recently published work we provide a proof-of-concept of a novel method to extract the heavy quark momentum diffusion coefficient from color-electric correlators on the lattice using gradient flow. The transport coefficient can be found in the infrared limit of the corresponding spectral function which is reconstructed through perturbative model fits of the correlator data. In this proceedings report we want to give more detailed insights into the systematic uncertainties of this procedure and compare our results with other studies.

   hep-latEPJ Web Conf.(2022)·4 citations
2. 02*

   Tensor network simulation of the (1+1)-dimensional $O(3)$ nonlinear $\sigma$-model with $\theta =\pi$ term

   Wei Tang🇨🇳 · X. C. Xie🇨🇳 · Lei Wang🇨🇳 · Hong-Hao Tu🇩🇪

   We perform a tensor network simulation of the (1+1)-dimensional $O(3)$ nonlinear $\sigma$-model with $\theta =\pi$ term. Within the Hamiltonian formulation, this field theory emerges as the finite-temperature partition function of a modified quantum rotor model decorated with magnetic monopoles. Using the monopole harmonics basis, we derive the matrix representation for this modified quantum rotor model, which enables tensor network simulations. We employ our recently developed continuous matrix product operator method [Tang et al., Phys. Rev. Lett. 125, 170604 (2020)] to study the finite-temperature properties of this model and reveal its massless nature. The central charge as a function of the coupling constant is directly extracted in our calculations and compared with field theory predictions.

   hep-latcond-mat.str-elquant-phPRD(2021)·11 citations
3. 03*

   Non-perturbative BRST symmetry and the spectral structure of the ghost propagator

   Shirley Weishi Li🇺🇸 · Peter Lowdon🇩🇪 · Orlando Oliveira🇵🇹 · Paulo J. Silva🇵🇹

   In BRST-quantised Yang-Mills theory the existence of BRST symmetry imposes significant constraints on the analytic structure of the continuum theory. In particular, the presence of this symmetry in the non-perturbative regime implies that any on-shell state with vanishing norm must have an associated partner state with identical mass, but negative inner product. In this work we demonstrate that for quantum chromodynamics (QCD) this constraint gives rise to an interconnection between the ghost and gluon spectra, and in doing so provides a non-trivial test of whether BRST symmetry is realised non-perturbatively. By analysing infrared lattice data for the minimal Landau gauge ghost propagator in pure $\mathrm{SU}(3)$ Yang-Mills theory, and comparing this with previous results for the gluon propagator, we show that this interconnection is violated, and hence conclude that continuum and current lattice formulations of Yang-Mills theory in Landau gauge represent two distinct realisations of the theory.

   ↳ hep-thhep-lathep-phPLB(2021)·13 citations
4. 04*

   Quantitative analysis of phase transitions in two-dimensional XY models using persistent homology

   Nicholas Sale🇬🇧 · Jeffrey Giansiracusa🇬🇧 · Biagio Lucini🇬🇧

   We use persistent homology and persistence images as an observable of three different variants of the two-dimensional XY model in order to identify and study their phase transitions. We examine models with the classical XY action, a topological lattice action, and an action with an additional nematic term. In particular, we introduce a new way of computing the persistent homology of lattice spin model configurations and, by considering the fluctuations in the output of logistic regression and k-nearest neighbours models trained on persistence images, we develop a methodology to extract estimates of the critical temperature and the critical exponent of the correlation length. We put particular emphasis on finite-size scaling behaviour and producing estimates with quantifiable error. For each model we successfully identify its phase transition(s) and are able to get an accurate determination of the critical temperatures and critical exponents of the correlation length.

   ↳ cond-mat.stat-mechcs.LGhep-lathep-th+1PRE(2022)·28 citations
5. 05*

   Searching for New Physics in Rare $K$ and $B$ Decays without $|V_{cb}|$ and $|V_{ub}|$ Uncertainties

   Andrzej J. Buras🇩🇪 · Elena Venturini🇩🇪

   We reemphasize the strong dependence of the branching ratios $B(K^{+}\to {\pi }^{+}\nu \bar{\nu })$ and $B(K_L\to {\pi }^0\nu \bar{\nu })$ on $|V_{cb}|$ that is stronger than in rare $B$ decays, in particular for $K_L\to {\pi }^0\nu \bar{\nu }$. Thereby the persistent tension between inclusive and exclusive determinations of $|V_{cb}|$ weakens the power of these theoretically clean decays in the search for new physics (NP). We demonstrate how this uncertainty can be practically removed by considering within the SM suitable ratios of the two branching ratios between each other and with other observables like the branching ratios for $K_S\to {\mu }^{+}{\mu }^{-}$, $B_{s,d}\to {\mu }^{+}{\mu }^{-}$ and $B\to K(K^{\ast })\nu \bar{\nu }$. We use as basic CKM parameters $V_{us}$, $|V_{cb}|$ and the angles $\beta$ and $\gamma$ in the unitarity triangle (UT). This avoids the use of the problematic $|V_{ub}|$. A ratio involving $B(K^{+}\to {\pi }^{+}\nu \bar{\nu })$ and $B(B_s\to {\mu }^{+}{\mu }^{-})$ while being $|V_{cb}|$-independent exhibits sizable dependence on the angle $\gamma$. It should be of interest for several experimental groups in the coming years. We point out that the $|V_{cb}|$-independent ratio of $B(B^{+}\to K^{+}\nu \bar{\nu })$ and $B(B_s\to {\mu }^{+}{\mu }^{-})$ from Belle II and LHCb signals a $1.8\sigma$ tension with its SM value. As a complementary test of the Standard Model, we propose to extract $|V_{cb}|$ from different observables as a function of $\beta$ and $\gamma$. We illustrate this with ${ϵ}_K$, $\Delta M_d$ and $\Delta M_s$ finding tensions between these three determinations of $|V_{cb}|$ within the SM. From $\Delta M_s$ and $S_{\psi K_S}$ alone we find $|V_{cb}|=41.8(6)\times 10^{-3}$ and $|V_{ub}|=3.65(12)\times 10^{-3}$. We stress the importance of a precise measurement of $\gamma$. We obtain most precise SM predictions for considered branching ratios of rare K and B decays to date.

   ↳ hep-phhep-exhep-latActa Phys.Polon.B·88 citations
6. 06*

   Effects of the quark anomalous magnetic moment in the chiral symmetry restoration: magnetic catalysis and inverse magnetic catalysis

   Ricardo L. S. Farias🇧🇷 · William R. Tavares🇧🇷 · Rodrigo M. Nunes🇺🇸 · Sidney S. Avancini🇧🇷

   In this work, we consider the effect of a constant anomalous magnetic moment (AMM) of quarks in the SU(2) Nambu--Jona-Lasinio model in the mean field approximation. To this end, we use the Schwinger {\it ansatz}, which represents a linear magnetic field term in the Lagrangian. A regularization method inspired in the vacuum magnetic regularization (VMR) is adopted to avoid ultraviolet divergences. Our results indicate a smooth decrease of the pseudocritical temperature and quark condensates for magnetic fields $B\le 0.1$ GeV${}^2$ when a sizable AMM is considered. We found only a small window for Inverse Magnetic Catalysis (IMC), in contradiction with NJL predictions made in the literature. For a low value of AMM, we observe for all ranges of magnetic fields considered that the pseudocritical temperature increases with the magnetic field, indicating only Magnetic Catalysis (MC). In our approach, for nonvanishing quark AMM, the chiral symmetry restoration happens always as a smooth crossover and never turns into a first order phase transition.

   ↳ hep-phhep-lathep-thnucl-thEPJC(2022)·33 citations
7. 07*

   Understanding the index theorems with massive fermions

   Hidenori Fukaya🇯🇵

   The index theorems relate the gauge field and metric on a manifold to the solution of the Dirac equation on it. In the standard approach, the Dirac operator must be massless in order to make the chirality operator well-defined. In physics, however, the index theorem appears as a consequence of chiral anomaly, which is an explicit breaking of the symmetry. It is then natural to ask if we can understand the index theorems in a massive fermion system which does not have chiral symmetry. In this review, we discuss how to reformulate the chiral anomaly and index theorems with massive Dirac operators, where we find nontrivial mathematical relations between massless and massive fermions. A special focus is placed on the Atiyah-Patodi-Singer index, whose original formulation requires a physicist-unfriendly boundary condition, while the corresponding massive domain-wall fermion reformulation does not. The massive formulation provides a natural understanding of the anomaly inflow between the bulk and edge in particle and condensed matter physics.

   ↳ hep-thhep-latmath.DGInt.J.Mod.Phys.A(2021)·10 citations
8. 08*

   Dark Confinement and Chiral Phase Transitions: Gravitational Waves vs Matter Representations

   Manuel Reichert🇬🇧 · Francesco Sannino🇩🇰 · Zhi-Wei Wang🇩🇰 · Chen Zhang🇮🇹

   We study the gravitational-wave signal stemming from strongly coupled models featuring both, dark chiral and confinement phase transitions. We therefore identify strongly coupled theories that can feature a first-order phase transition. Employing the Polyakov-Nambu-Jona-Lasinio model, we focus our attention on SU(3) Yang-Mills theories featuring fermions in fundamental, adjoint, and two-index symmetric representations. We discover that for the gravitational-wave signals analysis, there are significant differences between the various representations. Interestingly we also observe that the two-index symmetric representation leads to the strongest first-order phase transition and therefore to a higher chance of being detected by the Big Bang Observer experiment. Our study of the confinement and chiral phase transitions is further applicable to extensions of the Standard Model featuring composite dynamics.

   ↳ hep-phastro-ph.HEgr-qchep-lat+1JHEP(2022)·71 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.