Publications (92)319.4 Total impact
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ABSTRACT: Electromagnetic effects are increasingly being accounted for in lattice quantum chromodynamics computations. Because of their longrange nature, they lead to large finitesize effects over which it is important to gain analytical control. Nonrelativistic effective field theories provide an efficient tool to describe these effects. Here we argue that some care has to be taken when applying these methods to quantum electrodynamics in a finite volume.  [Show abstract] [Hide abstract]
ABSTRACT: We present preliminary results of a 2+1flavor study of finitevolume effects in the lattice QCD computation of the leadingorder hadronic contribution to the muon anomalous magnetic moment. We also present methods for obtaining directly the invariant hadronic polarization function, $\Pi(Q^2)$, and the Adler function at all discrete lattice values of $Q^2$, including $Q^2=0$. Results are obtained with HEXsmeared clover fermions.  [Show abstract] [Hide abstract]
ABSTRACT: We study the correlators of Polyakov loops, and the corresponding gauge invariant free energy of a static quarkantiquark pair in 2+1 flavor QCD at finite temperature. Our simulations were carried out on $N_t$ = 6, 8, 10, 12, 16 lattices using Symanzik improved gauge action and a stout improved staggered action with physical quark masses. The free energies calculated from the Polyakov loop correlators are extrapolated to the continuum limit. For the free energies we use a two step renormalization procedure that only uses data at finite temperature. We also measure correlators with definite Euclidean time reversal and charge conjugation symmetry to extract two different screening masses, one in the magnetic, and one in the electric sector, to distinguish two different correlation lengths in the full Polyakov loop correlator.Journal of High Energy Physics 01/2015; 2015(4). DOI:10.1007/JHEP04(2015)138 · 6.22 Impact Factor  [Show abstract] [Hide abstract]
ABSTRACT: We perform a detailed, fullycorrelated study of the chiral behavior of the pion mass and decay constant, based on 2+1 flavor lattice QCD simulations. These calculations are implemented using treelevel, O(a)improved Wilson fermions, at four values of the lattice spacing down to 0.054 fm and all the way down to below the physical value of the pion mass. They allow a sharp comparison with the predictions of SU(2) chiral perturbation theory (\chi PT) and a determination of some of its low energy constants. In particular, we systematically explore the range of applicability of NLO SU(2) \chi PT in two different expansions: the first in quark mass (xexpansion), and the second in pion mass (\xiexpansion). We find that these expansions begin showing signs of failure around M_\pi=300 MeV for the typical percentlevel precision of our N_f=2+1 lattice results. We further determine the LO low energy constants (LECs), F=88.0 \pm 1.3\pm 0.3 and B^\msbar(2 GeV)=2.58 \pm 0.07 \pm 0.02 GeV, and the related quark condensate, \Sigma^\msbar(2 GeV)=(271\pm 4\pm 1 MeV)^3, as well as the NLO ones, l_3=2.5 \pm 0.5 \pm 0.4 and l_4=3.8 \pm 0.4 \pm 0.2, with fully controlled uncertainties. We also explore the NNLO expansions and the values of NNLO LECs. In addition, we show that the lattice results favor the presence of chiral logarithms. We further demonstrate how the absence of lattice results with pion masses below 200 MeV can lead to misleading results and conclusions. Our calculations allow a fully controlled, ab initio determination of the pion decay constant with a total 1% error, which is in excellent agreement with experiment.Physical Review D 12/2014; DOI:10.1103/PhysRevD.90.114504 · 4.86 Impact Factor  [Show abstract] [Hide abstract]
ABSTRACT: We report on a continuum extrapolated result (arXiv:1309.5258) for the equation of state (EoS) of QCD with $N_f=2+1$ dynamical quark flavors and discuss preliminary results obtained with an additional dynamical charm quark ($N_f=2+1+1$). For all our final results, the systematics are controlled, quark masses are set to their physical values, and the continuum limit is taken using at least three lattice spacings corresponding to temporal extents up to $N_t=16$.  [Show abstract] [Hide abstract]
ABSTRACT: Finite temperature charmonium spectral functions in the pseudoscalar(PS) and vector(V) channels are studied in lattice QCD with 2+1 flavours of dynamical Wilson quarks, on fine isotropic lattices (with a lattice spacing of 0.057fm), with a nonphysical pion mass of 545MeV. The highest temperature studied is approximately 1.4Tc. Up to this temperature no significant variation of the spectral function is seen in the PS channel. The V channel shows some temperature dependence, which seems to be consistent with a temperature dependent low frequency peak related to heavy quark transport, plus a temperature independent term at omega > 0. These results are in accord with previous calculations using the quenched approximation.  [Show abstract] [Hide abstract]
ABSTRACT: We present our latest results for fluctuations of electric charge and baryon number, simulated on the lattice in a system of 2+1 dynamical quark flavors at the physical quark masses and continuum extrapolated. In order to extract the chemical freezeout temperature and chemical potential, we compare our results to the moments of multiplicity distribution of the corresponding conserved charges, measured in heavy ion collision experiments by the STAR collaboration. Consistency between the freezeout parameters obtained through different conserved charges is discussed.Journal of Physics Conference Series 09/2014; 535(1):012030. DOI:10.1088/17426596/535/1/012030  [Show abstract] [Hide abstract]
ABSTRACT: The latest results on fluctuations of electric charge and baryon number, simulated on the lattice by the Wuppertal–Budapest collaboration, are compared to the moments of multiplicity distribution of the corresponding conserved charges, measured in heavy ion collision experiments by the STAR collaboration. The purpose of this study is to extract the chemical freezeout parameters (temperature and chemical potential) as a function of the collision energy, from first principles. Consistency between the freezeout parameters obtained through the two different conserved charges used in the analysis is discussed.Nuclear Physics A 08/2014; 931. DOI:10.1016/j.nuclphysa.2014.08.014 · 2.50 Impact Factor  [Show abstract] [Hide abstract]
ABSTRACT: The existence and stability of atoms rely on the fact that neutrons are more massive than protons. The measured mass difference is only 0.14% of the average of the two masses. A slightly smaller or larger value would have led to a dramatically different universe. Here, we show that this difference results from the competition between electromagnetic and mass isospin breaking effects. We performed lattice quantumchromodynamics and quantumelectrodynamics computations with four nondegenerate Wilson fermion flavors and computed the neutronproton masssplitting with an accuracy of 300 kiloelectron volts, which is greater than 0 by 5 standard deviations. We also determine the splittings in the Σ, Ξ, D, and Ξcc isospin multiplets, exceeding in some cases the precision of experimental measurements. Copyright © 2015, American Association for the Advancement of Science.Science 06/2014; 347(6229). DOI:10.1126/science.1257050 · 31.48 Impact Factor 
Article: FreezeOut Parameters from Electric Charge and Baryon Number Fluctuations: Is There Consistency?
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ABSTRACT: Recent results for moments of multiplicity distributions of netprotons and netelectric charge from the STAR collaboration are compared to lattice QCD results for higher order fluctuations of baryon number and electric charge by the WuppertalBudapest collaboration, with the purpose of extracting the freezeout temperature and chemical potential. All lattice simulations are performed at the physical mass for light and strange quarks; all results are continuum extrapolated. We show that it is possible to extract an upper value for the freezeout temperature, as well as precise baryochemical potential values corresponding to the four highest collision energies of the experimental beam energy scan. Consistency between the freezeout parameters obtained from baryon number and electric charge fluctuations is found. The freezeout chemical potentials are now in agreement with the statistical hadronization model.Physical Review Letters 03/2014; 113(5). DOI:10.1103/PhysRevLett.113.052301 · 7.73 Impact Factor  [Show abstract] [Hide abstract]
ABSTRACT: Finite temperature charmonium spectral functions in the pseudoscalar and vector channels are studied in lattice QCD with 2+1 flavours of dynamical Wilson quarks, on fine isotropic lattices (with a lattice spacing of 0.057 fm), with a nonphysical pion mass of $m_{\pi} \approx$ 545 MeV. The highest temperature studied is approximately $1.4 T_c$. Up to this temperature no significant variation of the spectral function is seen in the pseudoscalar channel. The vector channel shows some temperature dependence, which seems to be consistent with a temperature dependent low frequency peak related to heavy quark transport, plus a temperature independent term at \omega>0. These results are in accord with previous calculations using the quenched approximation.Journal of High Energy Physics 01/2014; 2014(4). DOI:10.1007/JHEP04(2014)132 · 6.22 Impact Factor  [Show abstract] [Hide abstract]
ABSTRACT: A status of lattice QCD thermodynamics, as of 2013, is summarized. Only bulk thermodynamics is considered. There is a separate section on magnetic fields.  [Show abstract] [Hide abstract]
ABSTRACT: We report on a continuum extrapolated result [arXiv:1309.5258] for the equation of state (EoS) of QCD with $N_f=2+1$ dynamical quark flavors. In this study, all systematics are controlled, quark masses are set to their physical values, and the continuum limit is taken using at least three lattice spacings corresponding to temporal extents up to $N_t=16$. A Symanzik improved gauge and stoutlink improved staggered fermion action is used. Our results are available online [ancillary file to arXiv:1309.5258].  [Show abstract] [Hide abstract]
ABSTRACT: We present continuum extrapolated lattice results for the higher order fluctuations of conserved charges in high temperature Quantum Chromodynamics. Through the matching of the grand canonical ensemble on the lattice to the net charge and net baryon distribution realized in heavy ion experiments the temperature and the chemical potential may be estimated at the time of chemical freezeout  [Show abstract] [Hide abstract]
ABSTRACT: We present preliminary lattice results for the leadingorder hadronic contribution to the muon anomalous magnetic moment, calculated with HEXsmeared clover fermions. In our calculation we include 2+1flavor ensembles with pions at the physical mass.  [Show abstract] [Hide abstract]
ABSTRACT: We present a full result for the 2+1 flavor QCD equation of state. All the systematics are controlled, the quark masses are set to their physical values, and the continuum extrapolation is carried out. This extends our previous studies [JHEP 0601:089 (2006); 1011:077 (2010)] to even finer lattices and now includes ensembles with Nt = 6,8,10,12 up to Nt = 16. We use a Symanzik improved gauge and a stoutlink improved staggered fermion action. Our findings confirm our earlier results. In order to facilitate the direct use of our equation of state we make our tabulated results available for download.Physics Letters B 09/2013; 730. DOI:10.1016/j.physletb.2014.01.007 · 6.02 Impact Factor  [Show abstract] [Hide abstract]
ABSTRACT: We present our results for ratios of higher order fluctuations of electric charge as functions of the temperature. These results are obtained in a system of 2+1 quark flavors at physical quark masses and continuum extrapolated. We compare them to preliminary data on higher order moments of the net electric charge distribution from the STAR collaboration. This allows us to determine the freezeout temperature and chemical potential from first principles. We also show continuumextrapolated results for ratios of higher order fluctuations of baryon number. These will allow us to test the consistency of the approach, by comparing them to the corresponding experimental data (once they become available) and thus, extracting the freezeout parameters in an independent way.Physical Review Letters 08/2013; 111(6):062005. DOI:10.1103/PhysRevLett.111.062005 · 7.73 Impact Factor  [Show abstract] [Hide abstract]
ABSTRACT: While electromagnetic and updown quark mass difference effects on octet baryon masses are very small, they have important consequences. The stability of the hydrogen atom against beta decay is a prominent example. Here we include these effects by adding them to valence quarks in a lattice QCD calculation based on N_f=2+1 simulations with 5 lattice spacings down to 0.054 fm, lattice sizes up to 6 fm and average updown quark masses all the way down to their physical value. This allows us to gain control over all systematic errors, except for the one associated with neglecting electromagnetism in the sea. We compute the octet baryon isomultiplet mass splittings, as well as the individual contributions from electromagnetism and the updown quark mass difference. Our results for the total splittings are in good agreement with experiment.Physical Review Letters 06/2013; 111(25). DOI:10.1103/PhysRevLett.111.252001 · 7.73 Impact Factor  [Show abstract] [Hide abstract]
ABSTRACT: We present an update on the 2+1 flavor QCD equation of state of the WuppertalBudapest Collaboration, extending our previous studies to finer lattice spacings and providing a continuum extrapolation of the trace anomaly. A Symanzik improved gauge and a stoutlink improved staggered fermion action is utilized. We also present preliminary results for the fully dynamical charmed equation of state.Nuclear Physics A 05/2013; 904:869872. DOI:10.1016/j.nuclphysa.2013.02.153 · 2.50 Impact Factor  [Show abstract] [Hide abstract]
ABSTRACT: By fitting pion masses and decay constants from 2+1 flavor staggered lattice simulations to the predictions of NLO and NNLO SU(2) chiral perturbation theory we determine the lowenergy constants l_3 and l_4. The lattice ensembles were generated by the WuppertalBudapest collaboration and cover pion masses in the range of 135 to 435 MeV and lattice scales between 0.7 and 2.0 GeV. By choosing a suitable scaling trajectory, we were able to demonstrate that precise and stable results for the LECs can be obtained from continuum ChPT to NLO. The pion masses available in this work also allow us to study the applicability of using ChPT to extrapolate from higher masses to the physical pion mass.
Publication Stats
3k  Citations  
319.40  Total Impact Points  
Top Journals
Institutions

2015

Forschungszentrum Jülich
 Jülich Supercomputing Centre (JSC)
Jülich, North RhineWestphalia, Germany


2004–2015

Bergische Universität Wuppertal
 Physical and Theoretical Chemistry
Wuppertal, North RhineWestphalia, Germany


2013

Universität Regensburg
Ratisbon, Bavaria, Germany


2002–2004

Eötvös Loránd University
 Department of Theoretical Physics
Budapeŝto, Budapest, Hungary
