arXiv subjects

J. Osborn

Publications and source records attributed to J. Osborn.

At least 55 records · Page 3Linked to original sources

arXiv2009

MILC results for light pseudoscalars

We present the latest preliminary results of the MILC collaboration's analysis of the light pseudoscalar meson sector. The analysis includes data from new ensembles with smaller lattice spacings, smaller light quark masses and lighter-than-physical strange quark masses. Both SU(2) and SU(3) chiral fits, including NNLO chiral logarithms, are shown. We give results for decay constants, quark masses, Gasser-Leutwyler low energy constants, and condensates in the two- and three-flavor chiral limits.

hep-ph↗

arXiv2009

QCD equation of state at non-zero chemical potential

We present our new results for the QCD equation of state at nonzero chemical potential at N_t=6 and compare them with N_t=4. We use the Taylor expansion method with terms up to sixth order in simulations with 2+1 flavors of improved asqtad quarks along a line of constant physics with m_l=0.1 m_s and approximately physical strange quark mass m_s.

hep-lat↗

arXiv2009

Chebyshev type lattice path weight polynomials by a constant term method

We prove a constant term theorem which is useful for finding weight polynomials for Ballot/Motzkin paths in a strip with a fixed number of arbitrary `decorated' weights as well as an arbitrary `background' weight. Our CT theorem, like Viennot's lattice path theorem from which it is derived primarily by a change of variable lemma, is expressed in terms of orthogonal polynomials which in our applications of interest often turn out to be non-classical. Hence we also present an efficient method for finding explicit closed form polynomial expressions for these non-classical orthogonal polynomials. Our method for finding the closed form polynomial expressions relies on simple combinatorial manipulations of Viennot's diagrammatic representation for orthogonal polynomials. In the course of the paper we also provide a new proof of Viennot's original orthogonal polynomial lattice path theorem. The new proof is of interest because it uses diagonalization of the transfer matrix, but gets around difficulties that have arisen in past attempts to use this approach. In particular we show how to sum over a set of implicitly defined zeros of a given orthogonal polynomial, either by using properties of residues or by using partial fractions. We conclude by applying the method to two lattice path problems important in the study of polymer physics as models of steric stabilization and sensitized flocculation.

math.CO↗

arXiv2009

HISQ action in dynamical simulations

We report on recent progress in employing the Highly Improved Staggered Quark (HISQ) action introduced by the HPQCD/UKQCD collaboration in simulations with dynamical fermions. The HISQ action is an order $a^2$ Symanzik-improved action with further suppressed taste symmetry violations. The improvement in taste symmetry is achieved by introducing Fat7 smearing of the original gauge links and reunitarization (projection to an element of U(3) or SU(3)) followed by Asq-type smearing. Major challenges for calculating the fermion force are related to the reunitarization step. We present a preliminary study of the HISQ action on two 2+1+1 flavor ensembles with the lattice spacing roughly equivalent to the MILC asqtad a=0.125 and 0.09 fm ensembles.

hep-lat↗

arXiv2008

Electromagnetic splittings of hadrons from improved staggered quarks in full QCD

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 non-compact 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 theory incorporating electromagnetic corrections.

hep-lat↗

arXiv2007

Baryon masses with improved staggered quarks

The MILC collaboration's simulations with improved staggered quarks are being extended with runs at a lattice spacing of 0.06 fm with quark masses down to one tenth the strange quark mass. We give a brief introduction to these new simulations and the determination of the lattice spacing. Then we combine these new runs with older results to study the masses of the nucleon and the Omega minus in the continuum and chiral limits.

hep-lat↗

arXiv2007

The 2+1 flavor topological susceptibility from the asqtad action at 0.06 fm

We report new data for the topological susceptibility computed on 2+1 flavor dynamical configurations with lattice spacing 0.06 fm, generated with the asqtad action. The topological susceptibility is computed by HYP smearing and compared with rooted staggered chiral perturbation theory as the pion mass goes to zero. At 0.06 fm, the raw data is already quite close to the continuum extrapolated values obtained from coarser lattices. These results provide a further test of the asqtad action with rooted staggered flavors.

hep-lat↗

arXiv2007

Status of the MILC light pseudoscalar meson project

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.

hep-lat↗

arXiv2006

Update on the physics of light pseudoscalar mesons

We present an update of the MILC investigation of the properties of light pseudoscalar mesons using three flavors of improved staggered quarks. Results are presented for the $π$ and $K$ leptonic decay constants, the CKM matrix element $V_{us}$, the up, down and strange quark masses, and the coefficients of the $O(p^4)$ chiral lagrangian. We have new data for lattice spacing $a \approx 0.15$ fm with several values of the light quark mass down to one-tenth the strange quark mass, higher statistics for $a \approx 0.09$ fm with the light quark mass equal to one-tenth the strange quark mass, and initial results for our smallest lattice spacing, $a \approx 0.06$ fm with light quark mass two-fifths of the strange quark mass.

hep-lat↗

arXiv2005

Predictions from Lattice QCD

In the past year, we calculated with lattice QCD three quantities that were unknown or poorly known. They are the $q^2$ dependence of the form factor in semileptonic $D\to Klν$ decay, the decay constant of the $D$ meson, and the mass of the $B_c$ meson. In this talk, we summarize these calculations, with emphasis on their (subsequent) confirmation by experiments.

hep-lat↗

arXiv2005

Update on pi and K Physics

We present an update of the MILC studies of the physics of light pseudoscalars using improved staggered fermions. New runs at lighter quark mass, as well as increased statistics for older sets, are enabling us to improve the results for decay constants in full QCD. In addition, we have analyzed quenched runs at two different lattice spacings. This makes possible a test of the applicability of staggered chiral perturbation theory in a different context.

hep-lat↗

arXiv2004

QCD Thermodynamics with Three Flavors of Improved Staggered Quarks

We report on a study of QCD thermodynamics with three flavors of quarks, using a Symanzik improved gauge action and the Asqtad O(a^2) improved staggered quark action. Simulations were carried out with lattice spacings 1/4T, 1/6T and 1/8T both for three degenerate quarks with masses less than or equal to the strange quark mass, m_s, and for degenerate up and down quarks with masses in the range 0.1 m_s \leq m_{u,d} \leq 0.6 m_s, and the strange quark mass fixed near its physical value. We present results for standard thermodynamics quantities, such as the Polyakov loop, the chiral order parameter and its susceptibility. For the quark masses studied to date we find a rapid crossover rather than a bona fide phase transition. We have carried out the first calculations of quark number susceptibilities with three flavors of sea quarks. These quantities are of physical interest because they are related to event-by-event fluctuations in heavy ion collision experiments. Comparison of susceptibilities at different lattice spacings show that our results are close to the continuum values.

hep-lat↗

arXiv2004

Light pseudoscalar decay constants, quark masses, and low energy constants from three-flavor lattice QCD

As part of our program of lattice simulations of three flavor QCD with improved staggered quarks, we have calculated pseudoscalar meson masses and decay constants for a range of valence quark masses and sea quark masses on lattices with lattice spacings of about 0.125 fm and 0.09 fm. We fit the lattice data to forms computed with staggered chiral perturbation theory. Our results provide a sensitive test of the lattice simulations, and especially of the chiral behavior, including the effects of chiral logarithms. We find: f_π=129.5(0.9)(3.5)MeV, f_K=156.6(1.0)(3.6)MeV, and f_K/f_π=1.210(4)(13), where the errors are statistical and systematic. Following a recent paper by Marciano, our value of f_K/f_πimplies |V_{us}|=0.2219(26). Further, we obtain m_u/m_d= 0.43(0)(1)(8), where the errors are from statistics, simulation systematics, and electromagnetic effects, respectively. The data can also be used to determine several of the constants of the low energy effective Lagrangian: in particular we find 2L_8-L_5=-0.2(1)(2) 10^{-3} at chiral scale m_η. This provides an alternative (though not independent) way of estimating m_u; 2L_8-L_5 is far outside the range that would allow m_u=0. Results for m_s^\msbar, \hat m^\msbar, and m_s/\hat m can be obtained from the same lattice data and chiral fits, and have been presented previously in joint work with the HPQCD and UKQCD collaborations. Using the perturbative mass renormalization reported in that work, we obtain m_u^\msbar=1.7(0)(1)(2)(2)MeV and m_d^\msbar=3.9(0)(1)(4)(2)MeV at scale 2 GeV, with errors from statistics, simulation, perturbation theory, and electromagnetic effects, respectively.

hep-lat↗

arXiv2004

Leptonic decay constants f_Ds and f_D in three flavor lattice QCD

We determine the leptonic decay constants in three flavor unquenched lattice QCD. We use O(a^2)-improved staggered light quarks and O(a)-improved charm quarks in the Fermilab heavy quark formalism. Our preliminary results, based upon an analysis at a single lattice spacing, are f_Ds = 263(+5-9)(+/-24) MeV and f_D = 225(+11-13)(+/-21) MeV. In each case, the first reported error is statistical while the is the combined systematic uncertainty.

hep-lat↗

arXiv2004

The scaling dimension of low lying Dirac eigenmodes and of the topological charge density

As a quantitative measure of localization, the inverse participation ratio of low lying Dirac eigenmodes and topological charge density is calculated on quenched lattices over a wide range of lattice spacings and volumes. Since different topological objects (instantons, vortices, monopoles, and artifacts) have different co-dimension, scaling analysis provides information on the amount of each present and their correlation with the localization of low lying eigenmodes.

hep-lat↗

arXiv2004

Heavy-light decay constants using clover valence quarks and three flavors of dynamical improved staggered quarks

Starting in 2001, the MILC Collaboration began a large scale calculation of heavy-light meson decay constants using clover valence quarks on ensembles of three flavor configurations. For the coarse configurations, with a=0.12 fm, eight combinations of dynamical light and strange quarks have been analyzed. For the fine configurations, with a=0.09 fm, three combinations of quark masses are studied. Since we last reported on this calculation, statistics have been increased on the fine ensembles, and, more importantly, a preliminary value for the perturbative renormalization of the axial-vector current has become available. Thus, results for f_B, f_{B_s}, f_D and f_{D_s} can, in principle, be calculated in MeV, in addition to decay-constant ratios that were calculated previously.

hep-lat↗

arXiv2004

First determination of the strange and light quark masses from full lattice QCD

We compute the strange quark mass $m_s$ and the average of the $u$ and $d$ quark masses $\hat m$ using full lattice QCD with three dynamical quarks combined with experimental values for the pion and kaon masses. The simulations have degenerate $u$ and $d$ quarks with masses $m_u=m_d\equiv \hat m$ as low as $m_s/8$, and two different values of the lattice spacing. The bare lattice quark masses obtained are converted to the $\msbar$ scheme using perturbation theory at $O(alpha_s)$. Our results are: $m_s^\msbar$(2 GeV) = 76(0)(3)(7)(0) MeV, $\hat m^\msbar$(2 GeV) = 2.8(0)(1)(3)(0) MeV and $m_s/\hat m$ = 27.4(1)(4)(0)(1), where the errors are from statistics, simulation, perturbation theory, and electromagnetic effects, respectively.

hep-lat↗

arXiv2004

Semileptonic D->pi/K and B->pi/D decays in 2+1 flavor lattice QCD

We present results for form factors of semileptonic decays of $D$ and $B$ mesons in 2+1 flavor lattice QCD using the MILC gauge configurations. With an improved staggered action for light quarks, we successfully reduce the systematic error from the chiral extrapolation. The results for $D$ decays are in agreement with experimental ones. The results for B decays are preliminary. Combining our results with experimental branching ratios, we then obtain the CKM matrix elements $|V_{cd}|$, $|V_{cs}|$, $|V_{cb}|$ and $|V_{ub}|$. We also check CKM unitarity, for the first time, using only lattice QCD as the theoretical input.

hep-lat↗