• Article  

      Adaptive aggregation-based domain decomposition multigrid for twisted mass fermions 

      Alexandrou, Constantia; Bacchio, S.; Finkenrath, J.; Frommer, A.; Kahl, K.; Rottmann, M. (2016)
      The adaptive aggregation-base domain decomposition multigrid method [A. Frommer, SIAM J. Sci. Comput. 36, A1581 (2014)] is extended for two degenerate flavors of twisted mass fermions. By fine-tuning the parameters we ...
    • Article  

      Axial charges of hyperons and charmed baryons using Nf=2+1+1 twisted mass fermions 

      Alexandrou, Constantia; Hadjiyiannakou, Kyriakos; Kallidonis, Christos (2016)
      The axial couplings of the low lying baryons are evaluated using a total of five ensembles of dynamical twisted mass fermion gauge configurations. The simulations are performed using the Iwasaki gauge action and two ...
    • Article  

      Axial nucleon and nucleon to Δ form factors and the Goldberger-Treiman relations from lattice QCD 

      Alexandrou, Constantia; Koutsou, Giannis; Leontiou, Theodoros; Negele, J. W.; Tsapalis, Antonios (2007)
      We evaluate the nucleon axial form factor, GA(q2), and induced pseudoscalar form factor, Gp(q2), as well as the pion-nucleon form factor, GπNN(q2), in lattice QCD. We also evaluate the corresponding nucleon to Δ transition ...
    • Article  

      Axial nucleon form factors from lattice QCD 

      Alexandrou, Constantia; Brinet, M.; Carbonell, J.; Constantinou, Martha; Harraud, P. A.; Guichon, P.; Jansen, K.; Korzec, T.; Papinutto, M. (2011)
      We present results on the nucleon axial form factors within lattice QCD using two flavors of degenerate twisted mass fermions. Volume effects are examined using simulations at two volumes of spatial length L=2.1fm and ...
    • Article  

      B-meson properties from lattice QCD 

      Alexandrou, Constantia; Jegerlehner, F.; Güsken, S.; Schilling, K.; Sommer, R. (1991)
      A high statistics computation of the decay constant f{hook}B is presented to study scaling and finite size effects. Smooth wave functions for the B-meson allow to suppress excited state contributions effectively. We observe ...
    • Article  

      Baryon spectrum with Nf=2+1+1 twisted mass fermions 

      Alexandrou, Constantia; Drach, V.; Jansen, K.; Kallidonis, Christos; Koutsou, Giannis (2014)
      The masses of the low-lying baryons are evaluated using a total of ten ensembles of dynamical twisted mass fermion gauge configurations. The simulations are performed using two degenerate flavors of light quarks, and a ...
    • Article  

      Baryon structure from Lattice QCD 

      Alexandrou, Constantia (2009)
      We present recent lattice results on the baryon spectrum, nucleon electromagnetic and axial form factors, nucleon to Δ transition form factors as well as the Δ electromagnetic form factors. The masses of the low lying ...
    • Article  

      Beautiful baryons from lattice QCD 

      Alexandrou, Constantia; Borrelli, A.; Güsken, S.; Jegerlehner, F.; Schilling, K.; Siegert, G.; Sommer, R. (1994)
      We perform a lattice study of heavy baryons, containing one (Λb) or two b-quarks Ξb. Using the quenched approximation we obtain for the mass of Λb, MΛb = 5.728 ± 0.144 ± 0.018 GeV. The mass splitting between the λb and the ...
    • Article  

      Bounds on |B from lattice QCD 

      Alexandrou, Constantia; Güsken, S.; Jegerlehner, F.; Schiling, K.; Sommer, R. (1992)
      We present a study of finite-a effects in the leptonic decay constant |P of heavy pseudoscalar mesons. Exploiting results on three lattices - with inverse lattice spacing a-1 = 3.35, 2.3 and 1.53 GeV - to extrapolate |P ...
    • Conference Object  

      Calculation of the decay width of decuplet baryons 

      Petschlies, Marcus; Alexandrou, Constantia; Negele, J. W.; Pochinsky, A. V.; Syritsyn, S. S. (Proceedings of Science (PoS), 2015)
      We calculate the coupling constant and decay width of the decuplet to octet baryon transitions in lattice QCD using the transfer matrix method. The transition amplitude is related to the coupling constant and via the Fermi's ...
    • Article  

      Calculation of the N to Δ electromagnetic transition matrix element 

      Alexandrou, Constantia; de Forcrand, Ph; Lippert, Th; Neff, H.; Negele, J. W.; Schilling, K.; Schroers, W.; Tsapalis, Antonios (2003)
      We present results on the ratio of electric quadrupole to magnetic dipole amplitudes, REM = GE2/GM1, for the transition γN → Δ from lattice QCD. We consider both the quenched and the 2-flavor theory.
    • Article  

      Colloquium: The shape of hadrons 

      Alexandrou, Constantia; Papanicolas, Costas N.; Vanderhaeghen, M. (2012)
      This Colloquium addresses the issue of the shape of hadrons and, in particular, that of the proton. The concept of shape in the microcosm is critically examined. Special attention is devoted to properly define the meaning ...
    • Article  

      Comparison of mean-field and exact Monte Carlo solutions of a one-dimensional nuclear model 

      Alexandrou, Constantia; Myczkowski, J.; Negele, J. W. (1989)
      The ground states of nuclear matter and finite nuclei are calculated for a one-dimensional model having a two-body potential with strong short-range repulsion and long-range attraction. Mean-field theory with a phenomenological ...
    • Article  

      A complete non-perturbative renormalization prescription for quasi-PDFs 

      Alexandrou, Constantia; Cichy, K.; Constantinou, Martha; Hadjiyiannakou, Kyriakos; Jansen, K.; Panagopoulos, Haralambos G.; Steffens, F. (2017)
      In this work we present, for the first time, the non-perturbative renormalization for the unpolarized, helicity and transversity quasi-PDFs, in an RI′ scheme. The proposed prescription addresses simultaneously all aspects ...
    • Conference Object  

      Computation of correlation matrices for tetraquark candidates with Jp = 0+ and flavor structure q1q2q3q3 

      Berlin, J.; Abdel-Rehim, A.; Alexandrou, Constantia; Dalla Brida, M.; Gravina, M.; Wagner, M. (Proceedings of Science (PoS), 2015)
      The conjecture that several recently observed mesons have a structure, which is not dominated by an ordinary quark-Antiquark pair, but by a four-quark structure, is being actively investigated both theoretical and ...
    • Conference Object  

      Computation of disconnected contributions to nucleon observables 

      Alexandrou, Constantia; Drach, V.; Jansen, K.; Koutsou, Giannis; Avilés-Casco, A. V. (Proceedings of Science (PoS), 2013)
      We compare several methods for computing disconnected fermion loops contributing to nucleon three-point functions. The comparison is carried out using one ensemble of Nf =2+1+1 twisted mass fermions with pion mass of 373 ...
    • Conference Object  

      DDalphaAMG for twisted mass fermions 

      Bacchio, S.; Alexandrou, Constantia; Finkenrath, J.; Frommer, A.; Kahl, K.; Rottmann, M. (Proceedings of Science (PoS), 2016)
      We present the Adaptive Aggregation-based Domain Decomposition Multigrid method extended to the twisted mass fermion discretization action. We show comparisons of results as a function of tuning the parameters that enter ...
    • Article  

      Deconfinement phase transition in one-flavor QCD 

      Alexandrou, Constantia; Boriçi, A.; Feo, A.; De Forcrand, P.; Galli, A.; Jegerlehner, F.; Takaishi, T. (1999)
      We present a study of the deconfinement phase transition of one-flavor QCD using the multiboson algorithm. The mass of the Wilson fermions relevant for this study is moderately large and the non-Hermitian multiboson method ...
    • Conference Object  

      Determination of the Δ resonance width from lattice QCD 

      Petschlies, Marcus; Alexandrou, Constantia; Negele, J. W. (Proceedings of Science (PoS), 2013)
      A method suitable for extracting resonance parameters of unstable baryons in lattice QCD is examined. The method is applied to the strong decay of the Δ to a pion-nucleon state, extracting the pND coupling constant and Δ ...
    • Article  

      Determination of the Δ(1232) axial and pseudoscalar form factors from lattice QCD 

      Alexandrou, Constantia; Gregory, E. B.; Korzec, T.; Koutsou, Giannis; Negele, J. W.; Sato, T.; Tsapalis, Antonios (2013)
      We present a lattice QCD calculation of the Δ(1232) matrix elements of the axial-vector and pseudoscalar currents. The decomposition of these matrix elements into the appropriate Lorentz invariant form factors is carried ...