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Jon A. Bailey; A. Bazavov; C. Bernard; C. M. Bouchard; C. DeTar; A. X. ElKhadra; E. D. Freeland; E. Gamiz; Steven Gottlieb; U. M. Heller; J. E. Hetrick; A. S. Kronfeld; J. Laiho; L. Levkova; P. B. Mackenzie; M. B. Oktay; J. N. Simone; R. Sugar; D. Toussaint; R. S. Van de Water
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The experimentally measured rates of the semileptonic decays K > pi l nu and D > K(pi) l nu can be combined with lattice calculations of the associated form factors to precisely extract the CKM matrix elements V_{us} and V_{cs(d)}. We report on the status of form factor calculations with Fermilab charm quarks and staggered light quarks on the 2+1 flavor asqtad staggered MILC ensembles. Analysis of data for the D > pi l nu form factor provides a nontrivial test of our methods via...
Source: http://arxiv.org/abs/1011.2423v1
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MILC collaboration; A. Bazavov; C. Bernard; C. DeTar; W. Freeman; Steven Gottlieb; U. M. Heller; J. E. Hetrick; J. Laiho; L. Levkova; M. Oktay; J. Osborn; R. L. Sugar; D. Toussaint; R. S. Van de Water
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We study the lattice spacing dependence, or scaling, of physical quantities using the highly improved staggered quark (HISQ) action introduced by the HPQCD/UKQCD collaboration, comparing our results to similar simulations with the asqtad fermion action. Results are based on calculations with lattice spacings approximately 0.15, 0.12 and 0.09 fm, using four flavors of dynamical HISQ quarks. The strange and charm quark masses are near their physical values, and the lightquark mass is set to 0.2...
Source: http://arxiv.org/abs/1004.0342v2
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MILC Collaboration; S. Basak; A. Bazavov; C. Bernard; C. DeTar; E. Freeland; J. Foley; Steven Gottlieb; U. M. Heller; J. Komijani; J. Laiho; L. Levkova; J. Osborn; R. L. Sugar; A. Torok; D. Toussaint; R. S. Van de Water; R. Zhou
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The MILC Collaboration has completed production running of electromagnetic effects on light mesons using asqtad improved staggered quarks. In these calculations, we use quenched photons in the noncompact formalism. We study four lattice spacings from $\approx\!0.12\:$fm to $\approx\!0.045\:$fm. To study finitevolume effects, we used six spatial lattice sizes $L/a=12$, 16, 20, 28, 40, and 48, at $a\!\approx\!0.12\:$fm. We update our preliminary values for the correction to Dashen's theorem...
Topics: High Energy Physics  Phenomenology, High Energy Physics  Lattice
Source: http://arxiv.org/abs/1606.01228
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A. Bazavov; Tanmoy Bhattacharya; C. DeTar; H. T. Ding; Steven Gottlieb; Rajan Gupta; P. Hegde; U. M. Heller; F. Karsch; E. Laermann; L. Levkova; Swagato Mukherjee; P. Petreczky; C. Schmidt; C. Schroeder; R. A. Soltz; W. Soeldner; R. Sugar; M. Wagner; P. Vranas
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We present results for the equation of state in (2+1)flavor QCD using the highly improved staggered quark action and lattices with temporal extent $N_{\tau}=6,~8,~10$, and $12$. We show that these data can be reliably extrapolated to the continuum limit and obtain a number of thermodynamic quantities and the speed of sound in the temperature range $(130400)$ MeV. We compare our results with previous calculations, and provide an analytic parameterization of the pressure, from which other...
Topics: High Energy Physics  Phenomenology, High Energy Physics  Lattice, Nuclear Theory
Source: http://arxiv.org/abs/1407.6387
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A. Bazavov; C. Bernard; C. Bouchard; C. DeTar; D. Du; A. X. ElKhadra; J. Foley; E. D. Freeland; E. Gámiz; Steven Gottlieb; U. M. Heller; J. Kim; J. Komijani; A. S. Kronfeld; J. Laiho; L. Levkova; P. B. Mackenzie; D. Mohler; E. T. Neil; M. B. Oktay; S. Qiu; J. N. Simone; R. L. Sugar; D. Toussaint; R. S. Van de Water; R. Zhou
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We present a study of the $D$ and $B$ leptonic decay constants on the MILC $N_f=2+1$ asqtad gauge ensembles using asqtadimproved staggered light quarks and clover heavy quarks in the Fermilab interpretation. Our previous analysis \cite{Bazavov:2011aa} computed the decay constants at lattice spacings $a \approx 0.14, 0.11$ and $0.083$ fm. We have extended the simulations to finer $a \approx 0.058$ and $0.043$ fm lattice spacings, and have also increased statistics; this allows us to address...
Topic: High Energy Physics  Lattice
Source: http://arxiv.org/abs/1403.6796
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Fermilab Lattice; MILC Collaborations; :; Jon A. Bailey; A. Bazavov; C. Bernard; C. M. Bouchard; C. DeTar; Daping Du; A. X. ElKhadra; J. Foley; E. D. Freeland; E. Gámiz; Steven Gottlieb; U. M. Heller; J. Komijani; A. S. Kronfeld; J. Laiho; L. Levkova; Yuzhi Liu; P. B. Mackenzie; Y. Meurice; E. T. Neil; SiWei Qiu; J. Simone; R. Sugar; D. Toussaint; R. S. Van de Water; Ran Zhou
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We present a latticeQCD calculation of the $B\to\pi\ell\nu$ semileptonic form factors and a new determination of the CKM matrix element $V_{ub}$. We use the MILC asqtad 2+1flavor lattice configurations at four lattice spacings and lightquark masses down to 1/20 of the physical strangequark mass. We extrapolate the lattice form factors to the continuum using staggered chiral perturbation theory in the hardpion and SU(2) limits. We employ a modelindependent $z$ parameterization to...
Topics: High Energy Physics  Experiment, High Energy Physics  Phenomenology, High Energy Physics  Lattice
Source: http://arxiv.org/abs/1503.07839
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C. Bernard; C. DeTar; M. Di Pierro; A. X. ElKhadra; R. T. Evans; E. D. Freeland; E. Gamiz; Steven Gottlieb; U. M. Heller; J. E. Hetrick; A. S. Kronfeld; J. Laiho; L. Levkova; P. B. Mackenzie; J. Simone; R. Sugar; D. Toussaint; R. S. Van de Water
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We present an update of our calculations of the decay constants of the D, D_s, B, and B_s mesons in unquenched 2+1 flavor QCD. We use the MILC library of improved staggered gauge ensembles at lattice spacings 0.09, 0.12, and 0.15 fm, clover heavy quarks with the Fermilab normalizations, and improved staggered light valence quarks.
Source: http://arxiv.org/abs/0904.1895v1
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S. Basak; A. Bazavov; C. Bernard; C. DeTar; W. Freeman; Steven Gottlieb; U. M. Heller; J. E. Hetrick; J. Laiho; L. Levkova; J. Osborn; R. Sugar; D. Toussaint
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We present our initial study of the electromagnetic splittings of charged and neutral mesons, and the violation of Dashen's theorem. Hadron masses are calculated on MILC N_f=2+1 QCD ensembles at lattice spacing \approx 0.15fm, together with quenched noncompact U(1) configurations. The O(a^2) tadpole improved staggered quark (asqtad) action is used both for the sea quarks and for six different valence quark masses. Chiral extrapolations are performed using partially quenched chiral perturbation...
Source: http://arxiv.org/abs/0812.4486v1
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C. Bernard; C. DeTar; M. Di Pierro; A. X. ElKhadra; R. T. Evans; E. D. Freeland; E. Gamiz; Steven Gottlieb; U. M. Heller; J. E. Hetrick; A. S. Kronfeld; J. Laiho; L. Levkova; P. B. Mackenzie; M. Okamoto; M. B. Oktay; J. N. Simone; R. Sugar; D. Toussaint; R. S. Van de Water
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Comparisons of latticeQCD calculations of semileptonic form factors with experimental measurements often display two sets of points, one each for lattice QCD and experiment. Here we propose to display the output of a latticeQCD analysis as a curve and error band. This is justified, because latticeQCD results rely in part on fitting, both for the chiral extrapolation and to extend latticeQCD data over the full physically allowed kinematic domain. To display an error band, correlations in the...
Source: http://arxiv.org/abs/0906.2498v2
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H. Neuberger; U. M. Heller; M. Klomfass; P. Vranas
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Older lattice work exploring the Higgs mass triviality bound is briefly reviewed. It indicates that a strongly interacting scalar sector in the minimal standard model cannot exist; on the other hand low energy QCD phenomenology might be interpreted as an indication that it could. We attack this puzzle using the $1/N$ expansion and discover a simple criterion for selecting a lattice action that is more likely to produce a heavy Higgs particle. Depending on the precise form of the limitation put...
Source: http://arxiv.org/abs/heplat/9208017v1
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U. M. Heller; Khalil M. Bitar; R. G. Edwards; A. D. Kennedy
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We compute the heavy quark potential on configurations generated by the HEMCGC collaboration with dynamical staggered fermions at $6/g^2 = 5.6$ and with dynamical Wilson fermions at $6/g^2 = 5.3$. The computations are done on $16^3 \times 32$ lattices, corresponding to physical sizes of about 1.6 and 2.3 fm, respectively. Up to the distances probed no sign of string breaking is detectable. We also compute the recently proposed scale $r_0$ defined by $r_0^2 F(r_0) = 1.65$.
Source: http://arxiv.org/abs/heplat/9401025v1
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G. Cella; U. M. Heller; V. K. Mitrjushkin; A. Vicere
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We study the heavy charge potential in the Coulomb phase of pure gauge compact U(1) theory on the lattice. We calculate the static potential $V_W(T,{\vec R})$ from Wilson loops on a $16^3 \times 32$ lattice and compare with the predictions of lattice perturbation theory. We investigate finite size effects and, in particular, the importance of nonCoulomb contributions to the potential. We also comment on the existence of a maximal coupling in the Coulomb phase of pure gauge U(1) theory.
Source: http://arxiv.org/abs/heplat/9704012v1
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Jon A. Bailey; A. Bazavov; C. Bernard; C. M. Bouchard; C. DeTar; Daping Du; A. X. ElKhadra; J. Foley; E. D. Freeland; E. Gamiz; Steven Gottlieb; U. M. Heller; Jongjeong Kim; A. S. Kronfeld; J. Laiho; L. Levkova; P. B. Mackenzie; Y. Meurice; E. Neil; M. B. Oktay; SiWei Qiu; J. N. Simone; R. Sugar; D. Toussaint; R. S. Van de Water; Ran Zhou
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We calculate formfactor ratios between the semileptonic decays \bar{B}>D^+\ell^\bar{\nu} and \bar{B}_s>D_s^+\ell^\bar{\nu} with lattice QCD. These ratios are a key theoretical input in a new strategy to determine the fragmentation fractions of the neutral B decays, which are needed for measurements of BR(B^0_s> \mu^+\mu^). We use the MILC ensembles of gauge configurations with 2+1 flavors of sea quarks at two lattice spacings of approximately 0.12 fm and 0.09 fm. We use the...
Source: http://arxiv.org/abs/1202.6346v2
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A. Bazavov; C. Bernard; C. DeTar; J. Foley; W. Freeman; Steven Gottlieb; U. M. Heller; J. E. Hetrick; J. Kim; J. Laiho; L. Levkova; M. Lightman; J. Osborn; S. Qiu; R. L. Sugar; D. Toussaint; R. S. Van de Water; R. Zhou
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A calculation of the ratio of leptonic decay constants f_{K^+}/f_{\pi^+} makes possible a precise determination of the ratio of CKM matrix elements V_{us}/V_{ud} in the Standard Model, and places a stringent constraint on the scale of new physics that would lead to deviations from unitarity in the first row of the CKM matrix. We compute f_{K^+}/f_{\pi^+} numerically in unquenched lattice QCD using gaugefield ensembles recently generated that include four flavors of dynamical quarks: up,...
Source: http://arxiv.org/abs/1301.5855v3
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S. Basak; A. Bazavov; C. Bernard; C. DeTar; E. Freeland; W. Freeman; J. Foley; Steven Gottlieb; U. M. Heller; J. E. Hetrick; J. Laiho; L. Levkova; M. Oktay; J. Osborn; R. L. Sugar; A. Torok; D. Toussaint; R. S. Van de Water; R. Zhou
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We calculate pseudoscalar masses on gauge configurations containing the effects of 2+1 flavors of dynamical asqtad quarks and quenched electromagnetism. The lattice spacings vary from 0.12 to 0.06 fm. The masses are fit with staggered chiral perturbation theory including NLO electromagnetic terms. We attempt to extract the fit parameters for the electromagnetic contributions, while taking into account the finite volume effects, and extrapolate them to the physical limit.
Source: http://arxiv.org/abs/1210.8157v2
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The MILC Collaboration; C. Bernard; T. Burch; C. DeTar; Steven Gottlieb; E. B. Gregory; U. M. Heller; J. Osborn; R. L. Sugar; D. Toussaint
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We have continued our study of the phase diagram of high temperature QCD with three flavors of improved staggered quarks. We are performing simulations with three degenerate quarks with masses less than or equal to the strange quark mass m_s and with degenerate up and down quarks with masses m_{u,d} less than the strange quark mass. For the quark masses studied to date, we find a crossover that strengthens as m_{u,d} decreases, rather than a bona fide phase transition. We present new results...
Source: http://arxiv.org/abs/heplat/0409097v1
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P. H. Damgaard; U. M. Heller; K. Splittorff; B. Svetitsky; D. Toublan
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We consider the chiral limit of QCD subjected to an imaginary isospin chemical potential. In the epsilonregime of the theory we can perform precise analytical calculations based on the zeromomentum Goldstone modes in the lowenergy effective theory. We present results for the spectral correlation functions of the associated Dirac operators.
Source: http://arxiv.org/abs/hepth/0604054v2
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The MILC Collaboration; A. Bazavov; C. Bernard; C. DeTar; W. Freeman; Steven Gottlieb; U. M. Heller; J. E. Hetrick; J. Komijani; J. Laiho; L. Levkova; J. Osborn; R. L. Sugar; D. Toussaint; R. S. Van de Water; Ran Zhou
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We present results from our simulations of quantum chromodynamics (QCD) with four flavors of quarks: u, d, s, and c. These simulations are performed with a oneloop Symanzik improved gauge action, and the highly improved staggered quark (HISQ) action. We are generating gauge configurations with four values of the lattice spacing ranging from 0.06 fm to 0.15 fm, and three values of the light quark mass, including the value for which the Goldstone pion mass is equal to the physical pion mass. We...
Source: http://arxiv.org/abs/1212.4768v3
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C. Bernard; C. DeTar; Steven Gottlieb; U. M. Heller; J. E. Hetrick; L. Levkova; J. Osborn; D. Renner; R. Sugar; D. Toussaint
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We discuss the current status of our calculation of the physics of pi and K mesons using three dynamical flavors of improved staggered quarks. This year, we have a new ensemble with a lattice spacing of 0.06 fm and a light sea mass of 0.2 m_s, as well as significant increases in statistics at several coarser lattice spacings and/or heavier sea masses. Results for decay constants, quark masses, low energy constants, condensates, and V_{us} are presented.
Source: http://arxiv.org/abs/0710.1118v2
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C. Bernard; T. Burch; S. Datta; T. A. DeGrand; C. E. DeTar; Steven Gottlieb; U. M. Heller; K. Orginos; R. L. Sugar; D. Toussaint
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We present preliminary results from exploring the phase diagram of finite temperature QCD with three degenerate flavors and with two light flavors and the mass of the third held approximately at the strange quark mass. We use an order $\alpha_s^2 a^2, a^4$ Symanzik improved gauge action and an order $\alpha_s a^2, a^4$ improved staggered quark action. The improved staggered action leads to a dispersion relation with diminished lattice artifacts, and hence better thermodynamic properties. It...
Source: http://arxiv.org/abs/heplat/0110067v1
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P. H. Damgaard; U. M. Heller; R. Niclasen; K. Rummukainen
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We compute by Monte Carlo methods the individual distributions of the $k$th smallest Dirac operator eigenvalues in QCD, and compare them with recent analytical predictions. We do this for both massless and massive quarks in an SU(3) gauge theory with staggered fermions. Very precise agreement is found in all cases. As a simple byproduct we also extract the microscopic spectral density of the Dirac operator in SU(3) gauge theory with dynamical massive fermions for $N_f=1$ and 2, and obtain...
Source: http://arxiv.org/abs/heplat/0007041v2
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A. Bazavov; C. Bernard; N. Brown; C. DeTar; J. Foley; Steven Gottlieb; U. M. Heller; J. E. Hetrick; J. Komijani; J. Laiho; L. Levkova; M. Oktay; R. L. Sugar; D. Toussaint; R. S. Van de Water; R. Zhou
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We report on a preliminary scale determination with gradientflow techniques on the $N_f = 2 + 1 + 1$ HISQ ensembles generated by the MILC collaboration. The ensembles include four lattice spacings, ranging from 0.15 to 0.06 fm, and both physical and unphysical values of the quark masses. The scales $\sqrt{t_0}/a$ and $w_0/a$ are computed using Symanzik flow and the cloverleaf definition of $\langle E \rangle$ on each ensemble. Then both scales and the meson masses $aM_\pi$ and $aM_K$ are...
Topic: High Energy Physics  Lattice
Source: http://arxiv.org/abs/1411.0068
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A. Bazavov; C. Bernard; C. Bouchard; C. DeTar; D. Du; A. X. ElKhadra; J. Foley; E. D. Freeland; E. Gámiz; Steven Gottlieb; U. M. Heller; J. Kim; J. Komijani; A. S. Kronfeld; J. Laiho; L. Levkova; P. B. Mackenzie; E. T. Neil; J. N. Simone; R. L. Sugar; D. Toussaint; R. S. Van de Water; R. Zhou
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We compute the leptonic decay constants $f_{D^+}$, $f_{D_s}$, and $f_{K^+}$, and the quarkmass ratios $m_c/m_s$ and $m_s/m_l$ in unquenched lattice QCD. We use the MILC highly improved staggered quark (HISQ) ensembles with four dynamical quark flavors. Our primary results are $f_{D^+} = 212.6(0.4)({}^{+1.0}_{1.2})\ \mathrm{MeV}$, $f_{D_s} = 249.0(0.3)({}^{+1.1}_{1.5})\ \mathrm{MeV}$, and $f_{D_s}/f_{D^+} = 1.1712(10)({}^{+29}_{32})$, where the errors are statistical and total systematic,...
Topic: High Energy Physics  Lattice
Source: http://arxiv.org/abs/1411.2667
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E. Gamiz; A. Bazavov; C. Bernard; C. DeTar; D. Du; A. X. ElKhadra; E. D. Freeland; Steven Gottlieb; U. M. Heller; J. Komijani; A. S. Kronfeld; J. Laiho; P. B. Mackenzie; E. T. Neil; T. Primer; J. N. Simone; R. Sugar; D. Toussaint; R. S. Van de Water; Ran Zhou
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We discuss the reduction of errors in the calculation of the form factor $f_+^{K \pi}(0)$ with HISQ fermions on the $N_f=2+1+1$ MILC configurations from increased statistics on some key ensembles, new data on ensembles with lattice spacings down to 0.042 fm and the study of finitevolume effects within staggered ChPT. We also study the implications for the unitarity of the CKM matrix in the first row and for current tensions with leptonic determinations of $\vert V_{us}\vert$.
Topics: High Energy Physics  Phenomenology, High Energy Physics  Lattice, High Energy Physics  Experiment
Source: http://arxiv.org/abs/1611.04118
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J. Fingberg; U. M. Heller; F. Karsch
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We determine the critical couplings for the deconfinement phase transition in $SU(2)$ gauge theory on $N_\tau \times N_\sigma^3$ lattices with $N_\tau = 8$ and 16 and $N_\sigma$ varying between 16 and 48. A comparison with string tension data shows scaling of the ratio $T_c / \sqrt{\sigma}$ in the entire coupling regime $\beta =2.302.75$, while the individual quantities still exhibit large scaling violations. We find $T_c / \sqrt{\sigma}=0.69(2)$. We also discuss in detail the extrapolation of...
Source: http://arxiv.org/abs/heplat/9208012v2
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Jon A. Bailey; A. Bazavov; C. Bernard; C. M. Bouchard; C. DeTar; Daping Du; A. X. ElKhadra; J. Foley; E. D. Freeland; E. Gamiz; Steven Gottlieb; U. M. Heller; A. S. Kronfeld; J. Laiho; L. Levkova; P. B. Mackenzie; E. T. Neil; SiWei Qiu; J. Simone; R. Sugar; D. Toussaint; R. S. Van de Water; Ran Zhou
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We compute the zerorecoil form factor for the semileptonic decay $\bar{B}^0\to D^{*+}\ell^\bar{\nu}$ (and modes related by isospin and charge conjugation) using lattice QCD with three flavors of sea quarks. We use an improved staggered action for the light valence and sea quarks (the MILC \asqtad\ configurations), and the Fermilab action for the heavy quarks. Our calculations incorporate higher statistics, finer lattice spacings, and lighter quark masses than our 2008 work. As a byproduct of...
Topics: High Energy Physics  Phenomenology, High Energy Physics  Lattice
Source: http://arxiv.org/abs/1403.0635
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J. Komijani; A. Bazavov; C. Bernard; N. Brambilla; N. Brown; C. DeTar; D. Du; A. X. ElKhadra; E. D. Freeland; E. Gámiz; Steven Gottlieb; U. M. Heller; A. S. Kronfeld; J. Laiho; P. B. Mackenzie; C. Monahan; Heechang Na; E. T. Neil; J. N. Simone; R. L. Sugar; D. Toussaint; A. Vairo; R. S. Van de Water
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We present a progress report on our calculation of the decay constants $f_B$ and $f_{B_s}$ from latticeQCD simulations with highlyimproved staggered quarks. Simulations are carried out with several heavy valencequark masses on $(2+1+1)$flavor ensembles that include charm sea quarks. We include data at six lattice spacings and several light seaquark masses, including an approximately physicalmass ensemble at all but the smallest lattice spacing, 0.03 fm. This range of parameters provides...
Topics: High Energy Physics  Phenomenology, High Energy Physics  Lattice
Source: http://arxiv.org/abs/1611.07411
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Fermilab Lattice; MILC Collaborations; :; A. Bazavov; C. Bernard; C. Bouchard; N. Brown; C. DeTar; D. Du; A. X. ElKhadra; E. D. Freeland; E. Gámiz; Steven Gottlieb; U. M. Heller; J. Komijani; A. S. Kronfeld; J. Laiho; L. Levkova; P. B. Mackenzie; C. Monahan; T. Primer; Heechang Na; E. T. Neil; J. N. Simone; R. L. Sugar; D. Toussaint; R. S. Van de Water; R. Zhou
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We give a progress report on a project aimed at a highprecision calculation of the decay constants $f_B$ and $f_{B_s}$ from simulations with HISQ heavy and light valence and sea quarks. Calculations are carried out with several heavy valencequark masses on ensembles with 2+1+1 flavors of HISQ sea quarks at five lattice spacings and several light seaquark mass ratios $m_{ud}/m_s$, including approximately physical seaquark masses. This range of parameters provides excellent control of the...
Topic: High Energy Physics  Lattice
Source: http://arxiv.org/abs/1511.02294
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C. Bernard; T. Burch; C. DeTar; Steven Gottlieb; E. B. Gregory; U. M. Heller; J. Osborn; R. Sugar; D. Toussaint
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We report on a lattice determination of the mass of the exotic $1^{+}$ hybrid meson using an improved KogutSusskind action. Results from both quenched and dynamical quark simulations are presented. We also compare with earlier results using Wilson quarks at heavier quark masses. The results on lattices with three flavors of dynamical quarks show effects of sea quarks on the hybrid propagators which probably result from coupling to two meson states. We extrapolate the quenched results to the...
Source: http://arxiv.org/abs/heplat/0301024v2
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G. S. Bali; J. Fingberg; U. M. Heller; F. Karsch; K. Schilling
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A detailed investigation of the temperature dependence of the spatial string tension $\sigma_s$ in $SU(2)$ gauge theory is presented. A sustained performance of 3~GFLOPS on a 64K Connection Machine CM2 equivalent has been achieved. Scaling of $\sigma_s$ between $\beta=2.5115$ and $\beta=2.74$, on large lattices, is demonstrated. Below the critical temperature, $T_c$, $\sigma_s$ remains constant. For temperatures larger than $2T_c$ the temperature dependence can be parametrized by $\sigma_s(T)...
Source: http://arxiv.org/abs/heplat/9308003v2
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R. V. Gavai; U. M. Heller; F. Karsch; B. Plache; T. Neuhaus
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Results of investigations of the O(4) spin model at finite temperature using anisotropic lattices are presented. In both the large $N$ approximation and the numerical simulations using the Wolff cluster algorithm we find that the ratio of the symmetry restoration temperature $T_{\rm SR}$ to the Higgs mass $m_{\rm H}$ is independent of the anisotropy. We obtain a lower bound of $0.59 \pm 0.04$ for the ratio, $T_{\rm SR}/m_{\rm H}$, at $m_{\rm H}a \simeq 0.5$, which is lowered further by about...
Source: http://arxiv.org/abs/heplat/9201002v1
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The MILC Collaboration; C. Bernard; T. Burch; C. E. DeTar; Steven Gottlieb; Eric Gregory; U. M. Heller; J. Osborn; R. L. Sugar; D. Toussaint
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We present an update of our study of high temperature QCD with three flavors of quarks, using a Symanzik improved gauge action and the Asqtad staggered quark action. Simulations are being carried out on lattices with Nt=4, 6 and 8 for the case of three degenerate quarks with masses less than or equal to the strange quark mass, $m_s$, and on lattices with Nt=6 and 8 for degenerate up and down quarks with masses in the range 0.2 m_s \leq m_{u,d} \leq 0.6 m_s, and the strange quark fixed near its...
Source: http://arxiv.org/abs/heplat/0209079v1
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LHP Collaboration; R. Edwards; R. Fiebig; G. Fleming; U. M. Heller; C. Morningstar; D. Richards; I. Sato; S. Wallace
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The construction of baryonic operators for determining the N* excitation spectrum is discussed. The operators are designed with one eye towards maximizing overlaps with the lowlying states of interest, and the other eye towards minimizing the number of sources needed in computing the required quark propagators. Issues related to spin identification are outlined. Although we focus on triquark baryon operators, the construction method is applicable to both mesons and pentaquark operators.
Source: http://arxiv.org/abs/heplat/0309079v1
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C. Aubin; C. Bernard; C. DeTar; M. Di Pierro; E. D. Freeland; Steven Gottlieb; U. M. Heller; J. E. Hetrick; A. X. ElKhadra; A. S. Kronfeld; L. Levkova; P. B. Mackenzie; D. Menscher; F. Maresca; M. Nobes; M. Okamoto; D. Renner; J. Simone; R. Sugar; D. Toussaint; H. D. Trottier
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We present the first lattice QCD calculation with realistic sea quark content of the D^+ meson decay constant f_{D^+}. We use the MILC Collaboration's publicly available ensembles of lattice gauge fields, which have a quark sea with two flavors (up and down) much lighter than a third (strange). We obtain f_{D^+} = 201 +/ 3 +/ 17 MeV, where the errors are statistical and a combination of systematic errors. We also obtain f_{D_s} = 249 +/ 3 +/ 16 MeV for the D_s meson.
Source: http://arxiv.org/abs/heplat/0506030v2
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Jon A. Bailey; A. Bazavov; C. Bernard; C. M. Bouchard; C. DeTar; Daping Du; A. X. ElKhadra; J. Foley; E. D. Freeland; E. Gámiz; Steven Gottlieb; U. M. Heller; R. D. Jain; J. Komijani; A. S. Kronfeld; J. Laiho; L. Levkova; Yuzhi Liu; P. B. Mackenzie; Y. Meurice; E. T. Neil; SiWei Qiu; J. N. Simone; R. Sugar; D. Toussaint; R. S. Van de Water; Ran Zhou
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We compute the form factors for the $B \to Kl^+l^$ semileptonic decay process in lattice QCD using gaugefield ensembles with 2+1 flavors of sea quark, generated by the MILC Collaboration. The ensembles span lattice spacings from 0.12 to 0.045 fm and have multiple seaquark masses to help control the chiral extrapolation. The asqtad improved staggered action is used for the light valence and sea quarks, and the clover action with the Fermilab interpretation is used for the heavy $b$ quark. We...
Topics: High Energy Physics  Phenomenology, High Energy Physics  Lattice
Source: http://arxiv.org/abs/1509.06235
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P. H. Damgaard; U. M. Heller; K. Splittorff; B. Svetitsky; D. Toublan
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We calculate the response of the microscopic Dirac spectrum to an imaginary isospin chemical potential for QCD with two dynamical flavors in the chiral limit. This extends our previous calculation from the quenched to the unquenched theory. The resulting spectral correlation function in the $\epsilon$regime provides here, too, a new and efficient way to measure $F_\pi$ on the lattice. We test the method in a hybrid Monte Carlo simulation of the theory with two staggered quarks.
Source: http://arxiv.org/abs/heplat/0602030v1
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LHPC Collaboration; SESAM Collaboration; D. Dolgov; R. Brower; S. Capitani; P. Dreher; J. W. Negele; A. Pochinsky; D. B. Renner; N. Eicker; Th. Lippert; K. Schilling; R. G. Edwards; U. M. Heller
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Moments of the quark density, helicity, and transversity distributions are calculated in unquenched lattice QCD. Calculations of proton matrix elements of operators corresponding to these moments through the operator product expansion have been performed on $16^3 \times 32$ lattices for Wilson fermions at $\beta = 5.6$ using configurations from the SESAM collaboration and at $\beta = 5.5$ using configurations from SCRI. Oneloop perturbative renormalization corrections are included. At quark...
Source: http://arxiv.org/abs/heplat/0201021v3
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A. Bazavov; T. Bhattacharya; M. Cheng; C. DeTar; H. T. Ding; Steven Gottlieb; R. Gupta; P. Hegde; U. M. Heller; F. Karsch; E. Laermann; L. Levkova; S. Mukherjee; P. Petreczky; C. Schmidt; R. A. Soltz; W. Soeldner; R. Sugar; D. Toussaint; W. Unger; P. Vranas
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We present results on the chiral and deconfinement properties of the QCD transition at finite temperature. Calculations are performed with 2+1 flavors of quarks using the p4, asqtad and HISQ/tree actions. Lattices with temporal extent N_tau=6, 8 and 12 are used to understand and control discretization errors and to reliably extrapolate estimates obtained at finite lattice spacings to the continuum limit. The chiral transition temperature is defined in terms of the phase transition in a theory...
Source: http://arxiv.org/abs/1111.1710v2
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Jon A. Bailey; A. Bazavov; C. Bernard; C. M. Bouchard; C. DeTar; Daping Du; A. X. ElKhadra; E. D. Freeland; E. Gamiz; Steven Gottlieb; U. M. Heller; A. S. Kronfeld; J. Laiho; L. Levkova; Yuzhi Liu; E. Lunghi; P. B. Mackenzie; Y. Meurice; E. Neil; SiWei Qiu; J. N. Simone; R. Sugar; D. Toussaint; R. S. Van de Water; Ran Zhou
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The rare decay $B\to\pi\ell^+\ell^$ arises from $b\to d$ flavorchanging neutral currents and could be sensitive to physics beyond the Standard Model. Here, we present the first $ab$$initio$ QCD calculation of the $B\to\pi$ tensor form factor $f_T$. Together with the vector and scalar form factors $f_+$ and $f_0$ from our companion work [J. A. Bailey $et~al.$, Phys. Rev. D 92, 014024 (2015)], these parameterize the hadronic contribution to $B\to\pi$ semileptonic decays in any extension of the...
Topics: High Energy Physics  Phenomenology, High Energy Physics  Lattice
Source: http://arxiv.org/abs/1507.01618
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P. H. Damgaard; U. M. Heller; R. Niclasen; K. Rummukainen
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We classify SU(3) gauge field configurations in different topological sectors by the smearing technique. In each sector we compute the distribution of low lying eigenvalues of the staggered Dirac operator. In all sectors we find perfect agreement with the predictions for the sector of topological charge zero. The smallest Dirac operator eigenvalues of staggered fermions at presently realistic lattice couplings are thus insensitive to gauge field topology. On the smeared configurations, $4\nu$...
Source: http://arxiv.org/abs/heplat/9909017v1
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MILC Collaboration; S. Basak; A. Bazavov; C. Bernard; C. DeTar; E. Freeland; J. Foley; Steven Gottlieb; U. M. Heller; J. Komijani; J. Laiho; L. Levkova; R. Li; J. Osborn; R. L. Sugar; A. Torok; D. Toussaint; R. S. Van de Water; R. Zhou
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For some time, the MILC Collaboration has been studying electromagnetic effects on light mesons. These calculations use fully dynamical QCD, but only quenched photons, which suffices to NLO in XPT. That is, the sea quarks are electrically neutral, while the valence quarks carry charge. For the photons we use the noncompact formalism. We have new results with lattice spacing as small as 0.045 fm and a large range of volumes. We consider how well chiral perturbation theory describes these...
Topics: High Energy Physics  Lattice, High Energy Physics  Phenomenology
Source: http://arxiv.org/abs/1510.04997
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A. Bazavov; C. Bernard; C. M. Bouchard; C. DeTar; M. Di Pierro; A. X. ElKhadra; R. T. Evans; E. D. Freeland; E. Gamiz; Steven Gottlieb; U. M. Heller; J. E. Hetrick; R. Jain; A. S. Kronfeld; J. Laiho; L. Levkova; P. B. Mackenzie; E. T. Neil; M. B. Oktay; J. N. Simone; R. Sugar; D. Toussaint; R. S. Van de Water
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We calculate the leptonic decay constants of B_{(s)} and D_{(s)} mesons in lattice QCD using staggered light quarks and Fermilab bottom and charm quarks. We compute the heavylight meson correlation functions on the MILC asqtadimproved staggered gauge configurations which include the effects of three light dynamical sea quarks. We simulate with several values of the light valence and seaquark masses (down to ~m_s/10) and at three lattice spacings (a ~ 0.15, 0.12, and 0.09 fm) and extrapolate...
Source: http://arxiv.org/abs/1112.3051v1
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R. Höllwieser; M. Faber; U. M. Heller
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We analyze topological charge contributions from classical SU(2) center vortices with shapes of planes and spheres using different topological charge definitions, namely the center vortex picture of topological charge, a discrete version of F\~{F} in the plaquette and hypercube definitions and the lattice index theorem. For the latter the zeromodes of the Dirac operator in the fundamental and adjoint representations using both the overlap and asqtad staggered fermion formulations are...
Source: http://arxiv.org/abs/1202.0929v3
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A. Bazavov; C. Bernard; C. Bouchard; C. DeTar; D. Du; A. X. ElKhadra; J. Foley; E. D. Freeland; E. Gamiz; Steven Gottlieb; U. M. Heller; J. E. Hetrick; J. Kim; A. S. Kronfeld; J. Laiho; L. Levkova; M. Lightman; P. B. Mackenzie; E. T. Neil; M. Oktay; J. N. Simone; R. L. Sugar; D. Toussaint; R. S. Van de Water; R. Zhou; for the Fermilab Lattice Collaboration; for the MILC Collaboration
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We present our methods to fit the two point correlators for light, strange, and charmed pseudoscalar meson physics with the highly improved staggered quark (HISQ) action. We make use of the leastsquares fit including the full covariance matrix of the correlators and including Gaussian constraints on some parameters. We fit the correlators on a variety of the HISQ ensembles. The lattice spacing ranges from 0.15 fm down to 0.06 fm. The light sea quark mass ranges from 0.2 times the strange quark...
Source: http://arxiv.org/abs/1212.0613v1
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P. H. Damgaard; U. M. Heller; K. Splittorff
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The microscopic spectral density of the Hermitian WilsonDirac operator is computed numerically in quenched lattice QCD. We demonstrate that the results given for fixed index of the WilsonDirac operator can be matched by the predictions from Wilson chiral perturbation theory. We test successfully the finite volume and the mass scaling predicted by Wilson chiral perturbation theory at fixed lattice spacing.
Source: http://arxiv.org/abs/1110.2851v2
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C. Bernard; T. DeGrand; C. DeTar; Steven Gottlieb; U. M. Heller; J. Hetrick; C. McNeile; K. Rummukainen; R. Sugar; D. Toussaint; M. Wingate
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MILC collaboration results for \fB, \fBs, \fD, \fDs and their ratios are presented. These results are still preliminary, but the analysis is close to being completed. Sources of systematic error, both within the quenched approximation and from quenching itself, are estimated. We find, for example, $f_B=153\pm 10 {}^{+36}_{13} {}^{+13}_{0} MeV$, and $f_{B_s}/f_B = 1.10 \pm 0.02 {}^{+0.05}_{0.03} {}^{+0.03}_{0.02}$, where the errors are statistical, systematic (within the quenched...
Source: http://arxiv.org/abs/heplat/9709142v1
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The MILC Collaboration; C. Bernard; T. Blum; T. A. DeGrand; C. DeTar; S. Gottlieb; U. M. Heller; J. Hetrick; C. McNeile; K. Rummukainen; R. Sugar; D. Toussaint
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We present an update on the MILC Collaboration's light hadron spectrum calculation with two flavors of dynamical, staggered quarks. We present extrapolations of the nucleon to rho mass ratio to the continuum limit for fixed values of the pi to rho mass ratio including the physical one.
Source: http://arxiv.org/abs/heplat/9710063v1
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C. Bernard; T. Blum; C. E. DeTar; U. M. Heller; S. Gottlieb; J. E. Hetrick; Beat Jegerlehner; K. Rummukainen; R. L. Sugar; D. Toussaint; M. Wingate
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Quantum chromodynamics with two zero mass flavors is expected to exhibit a phase transition with O(4) critical behavior. Fixing the universality class is important for phenomenology and for facilitating the extrapolation of simulation data to physical quark mass values. At Lattice '96 the Tsukuba and Bielefeld groups reported results from new simulations with dynamical staggered quarks at $N_t = 4$, which suggested a departure from the expected critical behavior. We report observations of...
Source: http://arxiv.org/abs/heplat/9710038v1
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P. H. Damgaard; U. M. Heller; R. Niclasen; B. Svetitsky
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It has been conjectured that spontaneous chiral symmetry breaking in strongly coupled vectorlike gauge theories falls into only three different classes, depending on the gauge group and the representations carried by the fermions. We test this proposal by studying SU(2), SU(3) and SU(4) lattice gauge theories with staggered fermions in different irreducible representations. Staggered fermions away from the continuum limit should, for all complex representations, still belong to the continuum...
Source: http://arxiv.org/abs/heplat/0110028v2
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J. W. Negele; R. C. Brower; P. Dreher; R. Edwards; G. Fleming; Ph. Hagler; U. M. Heller; Th. Lippert; A. V. Pochinsky; D. B. Renner; D. Richards; K. Schilling; W. Schroers
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This talk presents recent calculations in full QCD of the lowest three moments of generalized parton distributions and the insight they provide into the behavior of nucleon electromagnetic form factors, the origin of the nucleon spin, and the transverse structure of the nucleon. In addition, new exploratory calculations in the chiral regime of full QCD are discussed.
Source: http://arxiv.org/abs/heplat/0404005v1