Search

We present the first lattice investigation of coupled-channel D D ¯ $$ D\overline{D} $$ and D s D ¯ s $$ {D}_s{\overline{D}}_s $$ scattering in the J PC = 0++ and 2++ channels. The scattering matrix for partial waves l = 0, 2 and isospin zero is determined using multiple volumes and inertial frames via Lüscher’s formalism. Lattice QCD ensembles from the CLS consortium with m π ≃ 280 MeV, a ≃ 0.09 fm and L/a = 24, 32 are utilized. The resulting scattering matrix suggests the existence of three charmonium-like states with J PC = 0++ in the energy region ranging from slightly below 2 mD up to 4.13 GeV. We find a so far unobserved D D ¯ $$ D\overline{D} $$ bound state just below threshold and a D D ¯ $$ D\overline{D} $$ resonance likely related to χ c0(3860), which is believed to be χ c0(2P). In addition, there is an indication for a narrow 0++ resonance just below the D s D ¯ s $$ {D}_s{\overline{D}}_s $$ threshold with a large coupling to D s D ¯ s $$ {D}_s{\overline{D}}_s $$ and a very small coupling to D D ¯ $$ D\overline{D} $$ . This resonance is possibly related to the narrow X(3915)/χ c0(3930) observed in experiment also just below D s D ¯ s $$ {D}_s{\overline{D}}_s $$ . The partial wave l = 2 features a resonance likely related to χ c2(3930). We work with several assumptions, such as the omission of J/ψω, η c η and three-particle channels. Only statistical uncertainties are quantified, while the extrapolations to the physical quark-masses and the continuum limit are challenges for the future.

We present a lattice QCD study of charmonium resonances and bound states with JPC=1−− and 3−− near the open-charm threshold, taking into account their strong transitions to D¯D. Vector charmonia are the most abundant in the experimentally established charmonium spectrum, while recently LHCb reported also the first discovery of a charmonium with likely spin three. The D¯D scattering amplitudes for partial waves l=1 and l=3 are extracted on the lattice by means of the Lüscher formalism, using multiple volumes and inertial frames. Parametrizations of the scattering amplitudes provide masses and widths of the resonances, as well as the masses of bound states. CLS ensembles with 2+1 dynamical flavors of nonperturbatively O(a) improved Wilson quarks are employed with mπ≃280 MeV, a single lattice spacing of a=0.09 fm and two lattice spatial extents of L=24 and 32. Two values of the charm quark mass are considered to examine the influence of the position of the D¯D threshold on the hadron masses. For the lighter charm quark mass we find the vector resonance ψ(3770) with mass m=3780(7) MeV and coupling g=16.0(−0.2+2.1) (related to the width by Γ=g2p3/6πm2). Both quantities are consistent with their experimental values, mexp=3773.13(35) MeV and gexp=18.7(9). The vector ψ(2S) appears as a bound state with m=3666(10) MeV. The charmonium resonance with JPC=3−− is found at m=3831(−16+10) MeV, consistent with the X(3842) recently discovered by LHCb. At our heavier charm-quark mass the ψ(2S) as well as the ψ(3770) are bound states and the X(3842) remains a resonance. We stress that all quoted uncertainties are only statistical, while lattice spacing effects and the approach to the physical point (for the light and strange quarks) still need to be explored. This study of conventional charmonia sets the stage for more challenging future studies of unconventional charmoniumlike states.

The realization of center and chiral symmetries in N=1 super Yang-Mills theory (SYM) is investigated on a four-dimensional Euclidean lattice by means of Monte Carlo methods. At zero temperature this theory is expected to confine external fundamental charges and to have a nonvanishing gaugino condensate, which breaks the nonanomalous Z2Nc chiral symmetry. In this work we find, for the first time, a nonvanishing condensate at zero temperature and zero gaugino mass with Wilson fermions. This is achieved by means of the renormalization properties of the Yang-Mills and fermion gradient flows, which are independent of the lattice regularization. At finite temperatures, we find that the phase transitions corresponding to deconfinement and chiral restoration occur at roughly the same critical temperature for SU(2) gauge group, implying the saturation of the bound Tchiralc≤Tdecc, recently obtained through anomaly matching. We furthermore discuss the agreement of our findings with conjectures from superstring theory.

We present a lattice QCD study of charmonium resonances and bound states with JPC = 1(--) and 3(--) near the open-charm threshold, taking into account their strong transitions to (D) over barD. Vector charmonia are the most abundant in the experimentally established charmonium spectrum, while recently LHCb reported also the first discovery of a charmonium with likely spin three. The (D) over barD scattering amplitudes for partial waves l = 1 and l = 3 are extracted on the lattice by means of the Luscher formalism, using multiple volumes and inertial frames. Parametrizations of the scattering amplitudes provide masses and widths of the resonances, as well as the masses of bound states. CLS ensembles with 2 + 1 dynamical flavors of nonperturbatively O(a) improved Wilson quarks are employed with m(pi) similar or equal to 280 MeV, a single lattice spacing of a = 0.09 fm and two lattice spatial extents of L = 24 and 32. Two values of the charm quark mass are considered to examine the influence of the position of the (D) over barD threshold on the hadron masses. For the lighter charm quark mass we find the vector resonance psi(3770) with mass m = 3780(7) MeV and coupling g = 16.0((+2.1)(-0.2)) (related to the width by Gamma = g(2)p(3)/6 pi m(2)). Both quantities are consistent with their experimental values, m(exp) = 3773.13(35) MeV and g(exp) = 18.7(9). The vector psi(2S) appears as a bound state with m = 3666(10) MeV. The charmonium resonance with J(PC) = 3(--) is found at m = 3831((+10)(-16)) MeV, consistent with the Xo3842+ recently discovered by LHCb. At our heavier charm-quark mass the psi(2S) as well as the psi(3770) are bound states and the Xo3842+ remains a resonance. We stress that all quoted uncertainties are only statistical, while lattice spacing effects and the approach to the physical point (for the light and strange quarks) still need to be explored. This study of conventional charmonia sets the stage for more challenging future studies of unconventional charmoniumlike states.

In this article we summarise our results from numerical simulations of N=1 $$ \mathcal{N}=1 $$ supersymmetric Yang-Mills theory with gauge group SU(3). We use the formulation of Curci and Veneziano with clover-improved Wilson fermions. The masses of various bound states have been obtained at different values of the gluino mass and gauge coupling. Extrapolations to the limit of vanishing gluino mass indicate that the bound states form mass-degenerate supermultiplets.

Journal of high energy physics 1801(91), 119 (2018). doi:10.1007/JHEP01(2018)119, In this work we present the results of a numerical investigation of SU(2) gauge theory with N_f = 3/2 flavours of fermions, corresponding to 3 Majorana fermions, which transform in the adjoint representation of the gauge group. At two values of the gauge coupling, the masses of bound states are considered as a function of the fundamental fermion mass, represented by the PCAC quark mass. The scaling of bound states masses indicates an infrared conformal behaviour of the theory. We obtain estimates for the fixed-point value of the mass anomalous dimension $\gamma^{\ast}$ from the scaling of masses and from the scaling of the mode number of the Wilson-Dirac operator. The difference of the estimates at the two gauge couplings should be due to scaling violations and lattice spacing effects. The more reliable estimate at the smaller gauge coupling is $\gamma^{\ast} \approx 0.38(2)$., Published by Springer, Berlin

In this work we present the results of a numerical investigation of SU(2) gauge theory with N_f = 3/2 flavours of fermions, corresponding to 3 Majorana fermions, which transform in the adjoint representation of the gauge group. At two values of the gauge coupling, the masses of bound states are considered as a function of the fundamental fermion mass, represented by the PCAC quark mass. The scaling of bound states masses indicates an infrared conformal behaviour of the theory. We obtain estimates for the fixed-point value of the mass anomalous dimension $\gamma^{\ast}$ from the scaling of masses and from the scaling of the mode number of the Wilson-Dirac operator. The difference of the estimates at the two gauge couplings should be due to scaling violations and lattice spacing effects. The more reliable estimate at the smaller gauge coupling is $\gamma^{\ast} \approx 0.38(2)$.

The spectrum of the lightest bound states in N=1 supersymmetric Yang-Mills theory with SU(2) gauge group, calculated on the lattice, is presented. The masses have first been extrapolated towards vanishing gluino mass and then to the continuum limit. The final picture is consistent with the formation of degenerate supermultiplets., Comment: 6 pages; 3 figures; proceedings of the EPS-HEP Conference 2015, 22-29 July 2015, Vienna, Austria