Search

We report on the determination of the improvement coefficient $c_{\rm A}$ for the non-singlet axial-vector current $A^{a}_{\mu}(x)$ in the framework of stabilised Wilson-Clover fermions within three flavour lattice QCD. This is done by requiring the PCAC relation to hold for two different pseudo-scalar states. To generate these states, wavefunctions altering spatial structures on the boundaries of a Schr\"odinger functional lattice are employed and some variations of the (previously applied) wavefunction method are explored. The improvement coefficient is determined on a few ensembles for a range of gauge couplings that is potentially useful for future applications. Preliminary results on the renormalisation constants $Z_{\rm V}$ for the vector current and $Z_{\rm A}$ for the axial-vector current are also presented., Comment: 9 pages, 5 figures, contribution to the 39th International Symposium on Lattice Field Theory, Lattice 2022, Bonn, Germany

Our exploratory study looks for direct access to the resonant hadronic transition amplitude without resorting to the L\"uscher formalism. We study the decay $\Psi(3770)\to\bar{D}D$ by applying partially twisted boundary conditions to the quenched charm quark, circumventing possible problems with final state interactions. If successful, we could compute the dependence of the transition amplitude on the charm-quark mass and test the predictions made by phenomenological quark-pair-creation models. Finally, we study if and to what extent an extraction of the excited state $\Psi(3770)$ is necessary for this analysis.

We report on a two-flavor lattice QCD study of the Bs→Ds and Bs→Ds* transitions parametrized, in the heavy quark limit, by the form factors G, and hA1, hA2, and hA3, respectively. In the search for New Physics through tests of lepton flavor universality, Bs decay channels are complementary to the B decays widely studied at B factories and LHCb, while on the theory side they can be better controlled than the Bc and Λb decays. The purpose of this exploratory two-flavor study is, in preparation for future analyses of lattice QCD simulations with Nf>2 and physical quark masses, to gain experience on a suitable method for a lattice extraction of form factors associated with b→c currents that may yield tighter control over systematic effects like contamination from excited states and cutoff effects. We obtain the zero-recoil values GBs→Ds(1)=1.03(14) and hBs→Ds*(1)=0.85(16).

We report on a two-flavour lattice QCD study of the $B_s \to D_s$ and $B_s \to D^*_s$ transitions parameterized, in the heavy quark limit, by the form factors ${\cal G}$, and $h_{A_1}$, $h_{A_2}$ and $h_{A_3}$, respectively. In the search for New Physics through tests of lepton flavour universality, $B_s$ decay channels are complementary to the $B$ decays widely studied at $B$ factories and LHCb, while on the theory side they can be better controlled than the $B_c$ and $\Lambda_b$ decays. The purpose of this exploratory two-flavour study is, in preparation for future analyses of lattice QCD simulations with ${N_f>2}$ and physical quark-masses, to gain experience on a suitable method for a lattice extraction of form factors associated with $b \to c$ currents that may yield tighter control over systematic effects like contamination from excited states and cut-off effects. We obtain the zero-recoil values ${\cal G}^{B_s \to D_s}(1)=1.03(14)$ and $h^{B_s \to D^*_s}(1)=0.85(16)$.

We consider three-flavor QCD and perform a determination of the low-energy coupling $\hat{g}_\chi$ of SU(2) Heavy Meson Chiral Perturbation Theory. It is the $B^*B\pi$ coupling in the limit of static heavy and chiral light quarks and has not been determined with precision thus far. The calculation is performed on a large set of the $2+1$ flavor CLS ensembles with pion masses from 420 MeV down to 130 MeV. This allows us to significantly reduce the systematic uncertainty from the chiral extrapolation compared to previous works. Only a weak dependence on the lattice spacing is visible in our results., Comment: 9 pages, 4 figures, The 38th International Symposium on Lattice Field Theory, LATTICE2021 26th-30th July, 2021, Zoom/Gather@Massachusetts Institute of Technology

We report on a two-flavour lattice QCD study of the $B_s \to D_s$ and $B_s \to D^*_s$ transitions parameterized, in the heavy quark limit, by the form factors ${\cal G}$, and $h_{A_1}$, $h_{A_2}$ and $h_{A_3}$, respectively. In the search for New Physics through tests of lepton flavour universality, $B_s$ decay channels are complementary to the $B$ decays widely studied at $B$ factories and LHCb, while on the theory side they can be better controlled than the $B_c$ and $\Lambda_b$ decays. The purpose of this exploratory two-flavour study is, in preparation for future analyses of lattice QCD simulations with ${N_f>2}$ and physical quark-masses, to gain experience on a suitable method for a lattice extraction of form factors associated with $b \to c$ currents that may yield tighter control over systematic effects like contamination from excited states and cut-off effects. We obtain the zero-recoil values ${\cal G}^{B_s \to D_s}(1)=1.03(14)$ and $h^{B_s \to D^*_s}(1)=0.85(16)$.

We determine non-perturbatively the normalisation factor $$r_{\mathrm{m}}\equiv Z_{\mathrm{S}}/Z_{\mathrm{S}}^{0}$$ r m ≡ Z S / Z S 0 , where $$Z_{\mathrm{S}}$$ Z S and $$Z_{\mathrm{S}}^{0}$$ Z S 0 are the renormalisation parameters of the flavour non-singlet and singlet scalar densities, respectively. This quantity is required in the computation of quark masses with Wilson fermions and for instance the renormalisation of nucleon matrix elements of scalar densities. Our calculation involves simulations of finite-volume lattice QCD with the tree-level Symanzik-improved gauge action, $$N_{\mathrm{f}}= 3$$ N f = 3 mass-degenerate $${\mathrm{O}}(a)$$ O ( a ) improved Wilson fermions and Schrödinger functional boundary conditions. The slope of the current quark mass, as a function of the subtracted Wilson quark mass is extracted both in a unitary setup (where nearly chiral valence and sea quark masses are degenerate) and in a non-unitary setup (where all valence flavours are chiral and the sea quark masses are small). These slopes are then combined with $$Z \equiv Z_{\mathrm{P}}/(Z_{\mathrm{S}}Z_{\mathrm{A}})$$ Z ≡ Z P / ( Z S Z A ) in order to obtain $$r_{\mathrm{m}}$$ r m . A novel chiral Ward identity is employed for the calculation of the normalisation factor Z. Our results cover the range of gauge couplings corresponding to lattice spacings below $$0.1\,$$ 0.1 fm, for which $$N_{\mathrm{f}}= 2+1$$ N f = 2 + 1 QCD simulations in large volumes with the same lattice action are typically performed.

We derive chiral Ward identities for lattice QCD with Wilson quarks and $$N_{\mathrm{f}}\ge 3$$ Nf≥3 flavours, on small lattices with Schrödinger functional boundary conditions and vanishingly small quark masses. These identities relate the axial variation of the non-singlet pseudoscalar density to the scalar one, thus enabling the non-perturbative determination of the scale-independent ratio $$Z_{\mathrm {S}}/Z_{\mathrm {P}}$$ ZS/ZP of the renormalisation parameters of these operators. We obtain results for $$N_{\mathrm{f}}=3$$ Nf=3 QCD with tree-level Symanzik-improved gluons and Wilson-Clover quarks, for bare gauge couplings which cover the typical range of large-volume $$N_{\mathrm{f}}= 2+1$$ Nf=2+1 simulations with Wilson fermions at lattice spacings below $$0.1\,$$ 0.1 fm. The precision of our results varies from 0.3 to 1%, except for the coarsest lattice, where it is 2%. We discuss how the $$Z_{\mathrm {S}}/Z_{\mathrm {P}}$$ ZS/ZP ratio can be used in the non-perturbative calculations of $${\mathrm {O}}(a)$$ O(a) improved renormalised quark masses.

37th International Symposium on Lattice Field Theory, Lattice 2019, Wuhan, China, 16 Jun 2019 - 22 Jun 2019; Proceedings of Science / International School for Advanced Studies (LATTICE2019), 212 (2020). doi:10.22323/1.363.0212, We present our progress in the non-perturbative $O(a)$ improvement and renormalization of tensor currents in three-flavor lattice QCD with Wilson-clover fermions and tree-level Symanzik improved gauge action. The mass-independent $O(a)$ improvement factor of tensor currents isdetermined via a Ward identity approach, and their renormalization group running is calculated via recursive finite-size scaling techniques, both implemented within the Schrödinger functional framework. We also address the matching factor between bare and renormalization group invariant currents for a range of lattice spacings < 0.1 fm, relevant for phenomenological large-volume lattice QCD applications., Published by SISSA, Trieste

We determine non-perturbatively the normalisation parameter $$Z_\mathrm{m}Z_\mathrm{P}/Z_\mathrm{A}$$ ZmZP/ZA as well as the Symanzik coefficients $$b_\mathrm{m}$$ bm and $$b_\mathrm{A}-b_\mathrm{P}$$ bA-bP , required in $$\mathrm{O}(a)$$ O(a) improved quark mass renormalisation with Wilson fermions. The strategy underlying their computation involves simulations in $$N_\mathrm{f}=3$$ Nf=3 QCD with $$\mathrm{O}(a)$$ O(a) improved massless sea and non-degenerate valence quarks in the finite-volume Schrödinger functional scheme. Our results, which cover the typical gauge coupling range of large-volume $$N_\mathrm{f}=2+1$$ Nf=2+1 QCD simulations with Wilson fermions at lattice spacings below $$0.1\,\mathrm{fm}$$ 0.1fm , are of particular use for the non-perturbative calculation of $$\mathrm{O}(a)$$ O(a) improved renormalised quark masses.

We report on advances in the non-perturbative determination of the ratio $Z_S/Z_P$ of the pseudoscalar to the scalar renormalization constants in three-flavour lattice QCD with Wilson-clover quarks and tree-level Symanzik improved gluons. The computations are based on the Ward identity approach, using Schr\"odinger functional boundary conditions. Our results for $Z_S/Z_P$ cover a range of couplings along a line of constant physics with lattice spacings of about 0.09 fm and below, relevant for phenomenological applications such as the calculation of renormalized quark masses., Comment: 7 pages including figures and tables, latex2e; Proceedings of the 36th International Symposium on Lattice Field Theory (Lattice 2018), 22-28 July 2018, Michigan State University, East Lansing, Michigan, USA

We report on a two-flavour lattice QCD study of the D_s and D_s^* leptonic decays parameterized by the decay constants f_{D_s} and f_{D_s^*}. As the phenomenology in the D_s sector seems very promising in the next years with the experiments LHCb and Belle II, it is worth putting a big effort in lattice computations regarding its non-perturbative QCD contributions. Before examining more challenging processes such as hadron-hadron transitions, a natural first step is to address some basic aspects in the context of leptonic decays, where systematic uncertainties from excited state contaminations and cut-off effects in the computation of charmed meson decay matrix elements can be investigated in a more straightforward setting., 11 pages including figures and tables, latex2e; version published in Phys. Rev. D; expanded discussion of systematics, small additions to the text and references added; results unchanged

We nonperturbatively determine the renormalization factor of the axial vector current in lattice QCD with Nf=3 flavors of Wilson-clover fermions and the tree-level Symanzik-improved gauge action. The (by now standard) renormalization condition is derived from the massive axial Ward identity, and it is imposed among Schrödinger functional states with large overlap on the lowest lying hadronic state in the pseudoscalar channel, in order to reduce kinematically enhanced cutoff effects. We explore a range of couplings relevant for simulations at lattice spacings of ≈0.09 fm and below. An interpolation formula for ZA(g02), smoothly connecting the nonperturbative values to the 1-loop expression, is provided together with our final results.

We present a study of the B spectrum performed in the framework of Heavy Quark Effective Theory expanded to next-to-leading order in 1/m and non-perturbative in the strong coupling. Our analyses have been performed on Nf=2 lattice gauge field ensembles corresponding to three different lattice spacings and a wide range of pion masses. We obtain the Bs-meson mass and hyperfine splittings of the B- and Bs-mesons that are in good agreement with the experimental values and examine the mass difference m_{Bs}-m_B as a further cross-check of our previous estimate of the b-quark mass. We also report on the mass splitting between the first excited state and the ground state in the B and Bs systems.