We determine the strange and light quark condensates in full lattice QCD for the first time. This is done by direct calculation of the expectation value of the trace of the quark propagator followed by subtraction of the appropriate perturbative cont
ribution to convert to a value for the condensate in the MS-bar scheme at 2 GeV. We use lattice QCD configurations including u, d, s and c quarks in the sea with u/d quark masses going down to the physical value. We find the ratio of the strange to the light quark condensate to be 1.08(16).
We determine the strange quark condensate from lattice QCD for the first time and compare its value to that of the light quark and chiral condensates. The results come from a direct calculation of the expectation value of the trace of the quark propa
gator followed by subtraction of the appropriate perturbative contribution, derived here, to convert the non-normal-ordered $mbar{psi}psi$ to the $bar{MS}$ scheme at a fixed scale. This is then a well-defined physical `nonperturbative condensate that can be used in the Operator Product Expansion of current-current correlators. The perturbative subtraction is calculated through $mathcal{O}(alpha_s)$ and estimates of higher order terms are included through fitting results at multiple lattice spacing values. The gluon field configurations used are `second generation ensembles from the MILC collaboration that include 2+1+1 flavors of sea quarks implemented with the Highly Improved Staggered Quark action and including $u/d$ sea quarks down to physical masses. Our results are : $<bar{s}{s}>^{bar{MS}}(2 mathrm{GeV})= -(290(15) mathrm{MeV})^3$, $<bar{l}{l}>^{bar{MS}}(2, mathrm{GeV})= -(283(2) mathrm{MeV})^3$, where $l$ is a light quark with mass equal to the average of the $u$ and $d$ quarks. The strange to light quark condensate ratio is 1.08(16). The light quark condensate is significantly larger than the chiral condensate in line with expectations from chiral analyses. We discuss the implications of these results for other calculations.
We determine masses and decay constants of heavy-heavy and heavy-charm pseudoscalar mesons as a function of heavy quark mass using a fully relativistic formalism known as Highly Improved Staggered Quarks for the heavy quark. We are able to cover the
region from the charm quark mass to the bottom quark mass using MILC ensembles with lattice spacing values from 0.15 fm down to 0.044 fm. We obtain f_{B_c} = 0.427(6) GeV; m_{B_c} = 6.285(10) GeV and f_{eta_b} = 0.667(6) GeV. Our value for f_{eta_b} is within a few percent of f_{Upsilon} confirming that spin effects are surprisingly small for heavyonium decay constants. Our value for f_{B_c} is significantly lower than potential model values being used to estimate production rates at the LHC. We discuss the changing physical heavy-quark mass dependence of decay constants from heavy-heavy through heavy-charm to heavy-strange mesons. A comparison between the three different systems confirms that the B_c system behaves in some ways more like a heavy-light system than a heavy-heavy one. Finally we summarise current results on decay constants of gold-plated mesons.
We present a new determination of the $B_s$ leptonic decay constant from lattice QCD simulations that use gluon configurations from MILC and a highly improved discretization of the relativistic quark action for both valence quarks. Our result, $f_{B_
s} = 0.225(4)$,GeV, is almost three times more accurate than previous determinations. We analyze the dependence of the decay constant on the heavy quarks mass and obtain the first empirical evidence for the leading $1/sqrt{m_h}$ dependence predicted by Heavy Quark Effective Theory (HQET). As a check, we use our analysis technique to calculate the $m_{B_s}-m_{eta_b}/2$ mass difference. Our result agrees with experiment to within errors of $11,mathrm{MeV}$ (better than 2%). We discuss how to extend our analysis to other quantities in $B_s$ and $B$ physics, making 2%-precision possible for the first time.
We extend our earlier lattice-QCD analysis of heavy-quark correlators to smaller lattice spacings and larger masses to obtain new values for the c mass and QCD coupling, and, for the first time, values for the b mass: m_c(3GeV,n_f=4)=0.986(6)GeV, alp
ha_msb(M_Z,n_f=5)=0.1183(7), and m_b(10GeV,n_f=5)=3.617(25)GeV. These are among the most accurate determinations by any method. We check our results using a nonperturbative determination of the mass ratio m_b(mu,n_f)/m_c(mu,n_f); the two methods agree to within our 1% errors and taken together imply m_b/m_c=4.51(4). We also update our previous analysis of alpha_msb from Wilson loops to account for revised values for r_1 and r_1/a, finding a new value alpha_msb(M_Z,n_f=5)=0.1184(6); and we update our recent values for light-quark masses from the ratio m_c/m_s. Finally, in the Appendix, we derive a procedure for simplifying and accelerating complicated least-squares fits.
We discuss the status of our ongoing efforts to improve on our calculation of the $D_s$ decay constant. We show preliminary results on the ratio of the charm to the strange quark mass. We also present preliminary results for spectroscopy, decay const
ants and bottom quark mass obtained by performing calculations with highly improved staggered quarks at masses above the c mass and close to the b mass.
We present some early results from a high statistics study of the scalar and pseudoscalar singlet sectors of lattice QCD using 2+1 flavours of Asqtad improved staggered fermions. The use of the Asqtad action has allowed us to generate an unprecedente
d number of configurations at 2 lattice spacings which on completion we hope will give us a significantly improved view of both the scalar and pseudoscalar singlet sectors.
The effect of Stout smearing is investigated in numerical simulations with twisted mass Wilson quarks. The phase transition near zero quark mass is studied on 12^3x24, 16^3x32 and 24^3x48 lattices at lattice spacings a = 0.1 - 0.125 fm.
