Mon·Dec 20, 2021Monday·December 20, 2021

1. 01*

   Composition of the inclusive semi-leptonic decay of B meson

   Gabriela Bailas🇯🇵 · Shoji Hashimoto🇯🇵

   Utilizing the approach recently proposed for the inclusive semi-leptonic decay rate on the lattice, we compute the differential decay rate of a $B_s$ meson for various kinematical channels. The results are compared with the contributions from the ground states (D and D^*) as well as from the orbitally excited states (D^**'s). The computation so far is carried out with an unphysically light bottom quark and strange spectator quark.

   hep-lathep-phPoS(2022)·3 citations
2. 02*

   Towards a lattice determination of the form factors of the rare Hyperon decay ${\Sigma }^{+}\to p{\ell }^{+}{\ell }^{-}$

   Felix Erben🇬🇧 · Vera Gülpers🇬🇧 · Raoul Hodgson🇬🇧 · Antonin Portelli🇬🇧

   The rare Hyperon decay ${\Sigma }^{+}\to p{\ell }^{+}{\ell }^{-}$ is an $s\to d$ flavour changing neutral current, and is therefore suppressed in within the Standard Model, making it an excellent probe for new physics. The process is dominated by long distance processes and therefore lattice QCD is the only existing technique to obtain a first principles Standard Model theoretical prediction. We present our work on an unphysical exploratory study of the rare Hyperon decay on the lattice, including an investigation into the applicability of source-sink sampling for this decay, and we show a generalisation of the summed method for arbitrary 3-point functions and 4-point functions. In addition we show preliminary results for a computation of the $s\to u$ semileptonic Hyperon decays.

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

   Results for ${\alpha }_s$ from the decoupling strategy

   Mattia Dalla Brida🇨🇭 · Roman Höllwieser🇩🇪 · Francesco Knechtli🇩🇪 · Tomasz Korzec🇩🇪 · Alessandro Nada🇩🇪 · Alberto Ramos🇪🇸 · Stefan Sint🇮🇪 · Rainer Sommer🇩🇪

   We present analysis details and new results for the strong coupling ${\alpha }_s(m_Z)$, determined by the decoupling strategy. We measure a massive gradient flow (GF) coupling defined in finite volume with Schrödinger functional (SF) boundary conditions in a theory with $N_{\text{f}}=3$ degenerate heavy quarks of mass $M$. The massive couplings are matched to effective couplings in pure gauge. Using the running in the pure gauge theory and the perturbative relation of the Lambda parameters, the Lambda parameter of the three flavor theory is obtained by an extrapolation to infinite M. Our final result is compatible both with the FLAG average and with the previous ALPHA result, albeit with a slightly smaller, yet still statistics dominated, error. This constitutes a non-trivial check, as the decoupling strategy is conceptually very different from the 3-flavor QCD step-scaling method, and so are most of its systematic errors. These include the uncertainties of the decoupling and continuum limits, which we discuss in some detail. Furthermore, by relying on decoupling once again, we could estimate the small $O(a)$ and $O(1/M)$ contaminations to the massive GF coupling stemming from the SF boundaries by means of pure gauge simulations.

   hep-latPoS(2022)·4 citations
4. 04*

   Chiral Ising Gross-Neveu criticality of a single Dirac cone: A quantum Monte Carlo study

   S. Mojtaba Tabatabaei🇮🇷 · Amir-Reza Negari🇮🇷 · Joseph Maciejko🇨🇦 · Abolhassan Vaezi🇮🇷

   We perform large-scale quantum Monte Carlo simulations of SLAC fermions on a two-dimensional square lattice at half filling with a single Dirac cone with $N=2$ spinor components and repulsive on-site interactions. Despite the presence of a sign problem, we accurately identify the critical interaction strength $U_c=7.28\pm 0.02$ in units of the hopping amplitude, for a continuous quantum phase transition between a paramagnetic Dirac semimetal and a ferromagnetic insulator. Using finite-size scaling, we extract the critical exponents for the corresponding $N=2$ chiral Ising Gross-Neveu universality class: the inverse correlation length exponent ${\nu }^{-1}=1.19\pm 0.03$, the order parameter anomalous dimension ${\eta }_{\varphi }=0.31\pm 0.01$, and the fermion anomalous dimension ${\eta }_{\psi }=0.136\pm 0.005$.

   ↳ cond-mat.str-elcond-mat.stat-mechhep-latPRL(2022)·30 citations
5. 05*

   Concerning pion parton distributions

   Z.-F. Cui🇨🇳 · M. Ding🇩🇪 · J. M. Morgado🇪🇸 · K. Raya🇪🇸 · D. Binosi🇮🇹 · L. Chang🇨🇳 · J. Papavassiliou🇪🇸 · C. D. Roberts🇨🇳 · J. Rodríguez-Quintero🇪🇸 · S. M. Schmidt🇩🇪

   Analyses of the pion valence-quark distribution function (DF), $u^{\pi }(x;\zeta )$, which explicitly incorporate the behaviour of the pion wave function prescribed by quantum chromodynamics (QCD), predict $u^{\pi }(x\simeq 1;\zeta )\sim (1-x{)}^{\beta (\zeta )}$, $\beta (\zeta \gtrsim m_p)>2$, where $m_p$ is the proton mass. Nevertheless, more than forty years after the first experiment to collect data suitable for extracting the $x\simeq 1$ behaviour of $u^{\pi }$, the empirical status remains uncertain because some methods used to fit existing data return a result for $u^{\pi }$ that violates this constraint. Such disagreement entails one of the following conclusions: the analysis concerned is incomplete; not all data being considered are a true expression of qualities intrinsic to the pion; or QCD, as it is currently understood, is not the theory of strong interactions. New, precise data are necessary before a final conclusion is possible. In developing these positions, we exploit a single proposition, viz. there is an effective charge which defines an evolution scheme for parton DFs that is all-orders exact. This proposition has numerous corollaries, which can be used to test the character of any DF, whether fitted or calculated.

   ↳ hep-phhep-exhep-latnucl-ex+1EPJA(2022)·57 citations
6. 06*

   Alpha-alpha scattering in the Multiverse

   Serdar Elhatisari🇹🇷 · Timo A. Lähde🇩🇪 · Dean Lee🇺🇸 · Ulf-G. Meißner🇩🇪 · Thomas Vonk🇩🇪

   We investigate the phase shifts of low-energy alpha-alpha scattering under variations of the fundamental parameters of the Standard Model, namely the light quark mass, the electromagnetic fine-structure constant as well as the QCD theta-angle. As a first step, we recalculate alpha-alpha scattering in our Universe utilizing various improvements in the adiabatic projection method, which leads to an improved, parameter-free prediction of the S- and D-wave phase shifts for laboratory energies below 10 MeV. We find that positive shifts in the pion mass have a small effect on the S-wave phase shift, whereas lowering the pion mass adds some repulsion in the two-alpha system. The effect on the D-wave phase shift turns out to be more pronounced as signaled by the D-wave resonance parameters. Variations of the fine-structure constant have almost no effect on the low-energy alpha-alpha phase shifts. We further show that up-to-and-including next-to-leading order in the chiral expansion, variations of these phase shifts with respect to the QCD theta-angle can be expressed in terms of the theta-dependent pion mass.

   ↳ hep-thastro-ph.COhep-lathep-ph+1JHEP(2022)·17 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.