117478307
Chiral restoration and deconfinement in two-color QCD with two flavors of staggered quarks
In preparation of lattice studies of the two-color QCD phase diagram we studychiral restoration and deconfinement at finite temperature with two flavors ofstaggered quarks using an RHMC algorithm on GPUs. We first study unquenchingeffects in local Polyakov loop distributions, and the Polyakov loop potentialobtained via Legendre transformation, in a fixed-scale approach for heavierquarks. We also present the chiral condensate and the correspondingsusceptibility over the lattice coupling across the chiral transition forlighter quarks. Using Ferrenberg-Swendsen reweighting we extract the maxima ofthe chiral susceptibility in order to determine pseudo-critical couplings onvarious lattices suitable for chiral extrapolations. These are then used to fixthe relation between coupling and temperature in the chiral limit.
17537588
Lattice simulations with chemical potential
After giving an overview of recently invented methods for simulating lattice QCD at small mu/T, we discuss some results for bulk thermodynamic quantities of QCD matter coming from those methods. We focus on the transition line and the critical endpoint in the QCD phase diagram.
16115905
Flavor and quark mass dependence of QCD thermodynamics
We calculate the transition temperature in 2 and 3-flavor QCD using improved gauge and staggered fermion actions on lattices with temporal extent Nτ = 4. We find Tc = 173 (8) MeV and 154 (8) MeV for nf = 2 and 3, respectively. In the case of 3-flavor QCD we present evidence that the chiral critical point, i.e. the second order endpoint of the line of first order chiral phase transitions, belongs to the universality class of the 3d Ising model.
119188644
QCD bulk thermodynamics and conserved charge fluctuations with HISQ fermions
After briefly reviewing recent progress by the HotQCD collaboration in studying the 2+1 flavor QCD equation of state, we will focus on results on fluctuations of conserved charges by the BNL-Bielefeld and HotQCD collaborations. Higher order cumulants of the net-charge distributions are increasingly dominated by a universal scaling behavior, which arises due to a critical point of QCD in the chiral limit. Considering cumulants up to the 6^{th} order, we observe that they generically behave as expected from universal scaling laws, which is quite different from cumulants calculated within the hadron resonance gas model. Taking ratios of these cumulants, we obtain volume independent results that can be compared to the experimental measurements. We will argue that the freeze-out chemical potentials and the freeze-out temperature, usually obtained by a HRG model fit to the measured hadronic yields, can also be obtained in a model independent way from ab-initio lattice QCD calculations by utilizing observables related to conserved charge fluctuations. Further, we will show that the freeze-out strangeness and electric charge chemical potentials can be fixed by imposing strangeness neutrality and isospin asymmetry constraints in the lattice QCD calculations, in order to accommodate conditions met in heavy ion collisions. All results have been obtained with the highly improved staggered quark action (HISQ) and almost physical quark masses on lattices with temporal extent of N_\tau=6,8,10,12. 
After briefly reviewing recent progress by the HotQCD collaboration in studying the 2+1 flavor QCD equation of state, we will focus on results on fluctuations of conserved charges by the BNL-Bielefeld and HotQCD collaborations. Higher order cumulants of the net-charge distributions are increasingly dominated by a universal scaling behavior, which arises due to a critical point of QCD in the chiral limit. Considering cumulants up to the 6(th) order, we observe that they generically behave as expected from universal scaling laws, which is quite different from cumulants calculated within the hadron resonance gas model. Taking ratios of these cumulants, we obtain volume independent results that can be compared to the experimental measurements. We will argue that the freeze-out chemical potentials and the freeze-out temperature, usually obtained by a HRG model fit to the measured hadronic yields, can also be obtained in a model independent way from ab-initio lattice QCD calculations by utilizing observables related to conserved charge fluctuations. Further, we will show that the freeze-out strangeness and electric charge chemical potentials can be fixed by imposing strangeness neutrality and isospin asymmetry constraints in the lattice QCD calculations, in order to accommodate conditions met in heavy ion collisions. All results have been obtained with the highly improved staggered quark action (HISQ) and almost physical quark masses on lattices with temporal extent of N(τ) = 6, 8, 10, 12.
15858058
Non-zero density QCD by the Taylor expansion method: The isentropic equation of state, hadronic fluctuations and more
We discuss the Taylor expansion approach to non-zero baryon chemical potential ($\mu_B$) and present results on expanion coefficients of the pressure and energy density up to the 6-th order in $\mu_B$. Calculations have been performed with (2+1)-flavor of improved staggerd fermions (p4fat3) and almost physical masses on lattices with temporal extent of four and six time slices. We use the expansion coefficients to construct the isentropic equation of state on lines of constant entropy per baryon number and various different hadronic fluctuations. Furthermore, we estimate the radius of convegence of our expansion, which can be seen as a method to analyze the structure of the QCD phase diagram.
16120128
Bulk thermodynamics and charge fluctuations at non-vanishing baryon density
We present results on bulk thermodynamic quantities as well as net baryon number, strangeness and electric charge fluctuations in QCD at non-zero density and temperature obtained from lattice calculations with almost physical quark masses for two values of the lattice cut-off aT = 1/4 and 1/6. We show that with our improved p4fa3-action the cut-off effects are under control when using lattices with a temporal extent of 6 or larger and that the contribution to the equation of state, which is due to a finite chemical potential is small for {mu}{sub q}/T < 1. Moreover, at vanishing chemical potential, i.e. under conditions almost realized at RHIC and the LHC, quartic fluctuations of net baryon number and strangeness are large in a narrow temperature interval characterizing the transition region from the low to high temperature phase. At non-zero baryon number density, strangeness fluctuations are enhanced and correlated to fluctuations of the net baryon number. If strangeness is furthermore forced to vanish, as it may be the case in systems created in heavy ion collisions, strangeness fluctuations are significantly smaller than baryon number fluctuations.
123673071
Cryogenic search for fractionally charged particles
An experiment was performed to test the hypothesis of cryogenic trapping of fractionally charged particles, suggested as a possible explanation for the results of LaRue, Fairbank, Hebard, and Phillips at Stanford. A Nb-filament source was built, which could be cooled to 4.2 /sup 0/K and rapidly heated to several hundred /sup 0/K. The source was operated in the terminal of a 700-kV Cockcroft-Walton accelerator and energy spectra of positively charged particles emerging from the filament were measured under a variety of operating conditions. No events above a background of 10/sup -2/ counts/sec were found in the energy regions where one might have expected several hundred particles of charge +(1/3)e or +(2/3)e as the source was heated. A mass range from 10 MeV/c/sup 2/ to 100 GeV/c/sup 2/ was covered in the experiment. Although negative results are rarely unambiguous, our findings exclude one class of hypotheses which might have explained the apparent fractional charges of the Stanford experiments.
119331939
Chiral perturbation theory for lattice QCD with a twisted mass term
Quantum chromodynamics on a lattice with Wilson fermions and a chirally twisted mass term for two degenerate quark flavours is considered in the framework of chiral perturbation theory. The pion mass and decay constant are calculated in next-to-leading order including terms linear in the lattice spacing a.
119495100
QCD phenomenology of charm production at HERA
We compare different schemes for the treatment of heavy quark production in Deep-Inelastic Scattering (DIS). For fully-integrated quantities such as F{sub 2}(x,Q{sup 2}), we advocate the use of the General-Massive Variable-Flavor-Number (GM-VFN) scheme; we present some results showing the progress of a Next-to-Leading Order calculation in this scheme. For differential quantities, the Fixed-Flavor-Number (FFN) scheme provides a more appropriate starting point. We present a new calculation of the azimuthal distribution of charm quark production in DIS. All results have been obtained using a Monte Carlo program under development.
1697339
Virtual next-to-leading corrections to the impact factors in the high-energy limit
We compute the virtual next-to-leading corrections to the impact factors or offshell coefficient functions in the high-energy limit. When combined with the known real corrections, these results will provide the complete NLO corrections to the impact factors, which are necessary to use the BFKL resummation at NLL for jet production at both lepton-hadron and hadron-hadron colliders.
17272111
Effects of fermion localization in Higgsless theories and electroweak constraints
Abstract Extra-dimensional Higgsless models with electroweak symmetry breaking through boundary conditions generically have difficulties with electroweak precision constraints, when the fermions are localized to the “branes” in the fifth dimension. In this Letter we show that these constraints can be relaxed by allowing the light fermions to have a finite extent into the bulk of the fifth dimension. The T and U electroweak parameters can be naturally suppressed by a custodial symmetry, while the S parameter can be made to vanish through a cancellation, if the leakage into the bulk of the light gauge fields and the light left-handed fermion fields are of the same size. This cancellation is possible while allowing realistic values for the first two generations of fermion masses, although special treatment is probably required for the top quark. We present this idea here in the context of a specific continuum theory-space model; however, it can be applied to any five-dimensional Higgsless model, either with a flat or a warped background.