Fri·Oct 14, 2022Friday·October 14, 2022

1. 01*

   $B\pi$-state contamination in $B$-meson observables

   Oliver Bar🇩🇪 · Alexander Broll🇩🇪 · Rainer Sommer🇩🇪

   Multi-particle states with additional pions are expected to result in a non-negligible excited-state contamination in lattice simulations. We show that heavy meson chiral perturbation theory can be employed to calculate the contamination due to two-particle $B\pi$ states in various $B$-meson observables like the $B$-meson decay constant and the $B{B}^{\ast }\pi$ coupling. We work in the static limit and to next-to-leading order in the chiral expansion. The $B\pi$ states are found to typically overestimate the observables at the few percent level depending on the size of two currently unknown NLO low-energy coefficients. A strategy to independently measure one of them with the 3-point function of the light axial vector current will be discussed.

   hep-latPoS(2023)·3 citations
2. 02*

   ${\mathbf{c}}_{\text{SW}}$ at One-Loop Order for Brillouin Fermions

   Maximilian Ammer🇩🇪 · Stephan Durr🇩🇪

   Wilson-like Dirac operators can be written in the form $D={\gamma }_{\mu }{\nabla }_{\mu }-\frac{ar}{2}\Delta$. For Wilson fermions the standard two-point derivative ${\nabla }_{\mu }^{(\mathrm{std})}$ and 9-point Laplacian ${\Delta }^{(\mathrm{std})}$ are used. For Brillouin fermions these are replaced by improved discretizations ${\nabla }_{\mu }^{(\mathrm{iso})}$ and ${\Delta }^{(\mathrm{bri})}$ which have 54- and 81-point stencils respectively. We derive the Feynman rules in lattice perturbation theory for the Brillouin action and apply them to the calculation of the improvement coefficient $c_{\mathrm{SW}}$, which, similar to the Wilson case, has a perturbative expansion of the form $c_{\mathrm{SW}}=1+{c_{\mathrm{SW}}}^{(1)}{g}_0^2+\mathcal{O}(g_0^4)$. For $N_c=3$ we find ${c_{\mathrm{SW}}}_{\mathrm{Brillouin}}^{(1)}=0.12362580(1)$, compared to ${c_{\mathrm{SW}}}_{\mathrm{Wilson}}^{(1)}=0.26858825(1)$, both for $r=1$.

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

   Estimating excited states contamination of $B\to \pi$ form factors using heavy meson chiral perturbation theory

   Oliver Bär🇩🇪 · Alexander Broll🇩🇪 · Rainer Sommer🇩🇪

   Using Heavy Meson Chiral Perturbation Theory (HMChPT), the $B^{\ast }\pi$ excited states contamination of the $B\to \pi$ vector form factors is computed to NLO in the chiral expansion and in the static limit. The results suggest that the excited states for $h_{\parallel }$ are of the order of a few percent whereas $h_{\perp }$ receives large negative contributions and thus might be significantly underestimated in lattice simulations.

   hep-latPoS(2023)·3 citations
4. 04*

   Lattice QCD at finite temperature: some aspects related to chiral symmetry

   Gert Aarts🇬🇧

   Out of the many exciting results obtained with the lattice approach to QCD under extreme conditions, I discuss a few selected items related to chiral symmetry: the chiral condensate as an approximate order parameter, meson screening masses, and masses of baryons and mesons, including D(s) mesons, when approaching the crossover from the hadronic side.

   hep-latnucl-thActa Phys.Polon.Supp.(2023)·1 citation
5. 05*

   Noether supercurrent operator mixing from lattice perturbation theory

   Georg Bergner🇩🇪 · Marios Costa🇨🇾 · Haralambos Panagopoulos🇨🇾 · Ivan Soler🇩🇪 · Gregoris Spanoudes🇨🇾

   In this work we present perturbative results for the renormalization of the supercurrent operator, $S_{\mu }$, in $\mathcal{N}=1$ Supersymmetric Yang-Mills theory. At the quantum level, this operator mixes with both gauge invariant and noninvariant operators, which have the same global transformation properties. In total, there are 13 linearly independent mixing operators of the same and lower dimensionality. We determine, via lattice perturbation theory, the first two rows of the mixing matrix, which refer to the renormalization of $S_{\mu }$, and of the gauge invariant mixing operator, $T_{\mu }$. To extract these mixing coefficients in the $\overline{\mathrm{MS}}$ renormalization scheme and at one-loop order, we compute the relevant two-point and three-point Green's functions of $S_{\mu }$ and $T_{\mu }$ in two regularizations: dimensional and lattice. On the lattice, we employ the plaquette gluonic action and for the gluinos we use the fermionic Wilson action with clover improvement.

   hep-latPoS(2023)·0 citations
6. 06*

   Hartree-Fock with Nambu spinors, and d-wave condensation in the 2D Hubbard model

   Kazue Matsuyama🇺🇸 · Jeff Greensite🇺🇸

   The usual Hartree-Fock approximation to the Hubbard model is based on eigenstates of the electron number operator. But this formulation is not unique. A different (and inequivalent) version, formulated in terms of Nambu two-component spinors, is based on eigenstates of the difference between the numbers of spin up and spin down electrons, with electron density dependent on parameters $U,t,t^{\prime }$ and chemical potential $\mu$. The advantage of this formulation is that electron pairing condensates can be directly computed. We show that in the ground states away from half-filling, obtained in this "Nambu" Hartree-Fock approximation, a discrete rotation symmetry is spontaneously broken, and the condensates exhibit the expected d-wave form in momentum space. We also show that the Mott insulator electron configuration is obtained in this formulation at large $U/t$ and half-filling, and roughly locate the boundary, in the hole doping$-$$U/t$ plane, between a region of local antiferromagnetism and stripe/domain formation, and the region of d-wave condensation.

   ↳ cond-mat.str-elcond-mat.supr-conhep-latAnnals Phys.(2023)·0 citations
7. 07*

   Stochastic and Tensor Network simulations of the Hubbard Model

   Johann Ostmeyer🇬🇧

   The Hubbard model is an important tool to understand the electrical properties of various materials. More specifically, on the honeycomb lattice it is used to describe graphene predicting a quantum phase transition from a semimetal to a Mott insulating state. In this work two different numerical techniques are presented that have been employed for simulations of the Hubbard model: The Hybrid Monte Carlo algorithm on the one hand allowed us to simulate unprecedentedly large lattices, whereas Tensor Networks can be used to completely avoid the sign problem. Respective strengths and weaknesses of the methods are discussed.

   ↳ cond-mat.str-elhep-latphysics.comp-phPoS(2023)·1 citation

* 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.