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  • 1.
    Alexandrou, Constantia
    et al.
    Department of Physics, University of Cyprus.
    Constantinou, Martha
    Department of Physics, University of Cyprus.
    Korzec, Tomasz
    Institut fur Physik, Humboldt Universitat zu Berlin.
    Panagopoulos, Haralambos G.
    Department of Physics, University of Cyprus.
    Stylianou, Fotos
    Department of Physics, University of Cyprus.
    Renormalization constants for 2-twist operators in twisted mass QCD2011In: Physical Review D. Particles and fields, ISSN 0556-2821, E-ISSN 1089-4918, Vol. 83, no 1, article id 014503Article in journal (Refereed)
    Abstract [en]

    Perturbative and nonperturbative results on the renormalization constants of the fermion field and the twist-2 fermion bilinears are presented with emphasis on the nonperturbative evaluation of the one-derivative twist-2 vector and axial-vector operators. Nonperturbative results are obtained using the twisted mass Wilson fermion formulation employing two degenerate dynamical quarks and the tree-level Symanzik improved gluon action. The simulations have been performed for pion masses in the range of about 450-260 MeV and at three values of the lattice spacing a corresponding to β=3.9, 4.05, 4.20. Subtraction of O(a2) terms is carried out by performing the perturbative evaluation of these operators at 1-loop and up to O(a2). The renormalization conditions are defined in the RI⊃′-MOM scheme, for both perturbative and nonperturbative results. The renormalization factors, obtained for different values of the renormalization scale, are evolved perturbatively to a reference scale set by the inverse of the lattice spacing. In addition, they are translated to MS̄ at 2 GeV using 3-loop perturbative results for the conversion factors

  • 2.
    Alexandrou, Constantia
    et al.
    Department of Physics, University of Cyprus.
    Constantinou, Martha
    Department of Physics, University of Cyprus.
    Korzec, Tomasz
    Institut fur Physik, Humboldt Universitat zu Berlin.
    Panagopoulos, Haralambos G.
    Department of Physics, University of Cyprus.
    Stylianou, Fotos
    Department of Physics, University of Cyprus.
    Renormalization constants of local operators for Wilson type improved fermions2012In: Physical Review D. Particles and fields, ISSN 0556-2821, E-ISSN 1089-4918, Vol. 86, no 1, article id 014505Article in journal (Refereed)
    Abstract [en]

    Perturbative and nonperturbative results are presented on the renormalization constants of the quark field and the vector, axial-vector, pseudoscalar, scalar, and tensor currents. The perturbative computation, carried out at one-loop level and up to second order in the lattice spacing, is performed for a fermion action, which includes the clover term and the twisted mass parameter yielding results that are applicable for unimproved Wilson fermions, as well as for improved clover and twisted mass fermions. We consider ten variants of the Symanzik improved gauge action corresponding to ten different values of the plaquette coefficients. Nonperturbative results are obtained using the twisted mass Wilson fermion formulation employing two degenerate dynamical quarks and the tree-level Symanzik improved gluon action. The simulations are performed for pion masses in the range of 480-260 MeV and at three values of the lattice spacing, a, corresponding to β=3.9, 4.05, 4.20. For each renormalization factor computed nonperturbatively we subtract its perturbative O(a2) terms so that we eliminate part of the cutoff artifacts. The renormalization constants are converted to MS̄ at a scale of μ=2GeV. The perturbative results depend on a large number of parameters and are made easily accessible to the reader by including them in the distribution package of this paper, as a Mathematica input file.

  • 3.
    Anselmino, Mauro
    et al.
    Dipartimento di Fisica Teorica, Università di Torino and Istituto Nazionale di Fisica Nucleare, Sezione di Torino.
    Boglione, Maria
    Dipartimento di Fisica Teorica, Università di Torino and Istituto Nazionale di Fisica Nucleare, Sezione di Torino.
    Hansson, Johan
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Murgia, Francesco
    Istituto Nazionale di Fisica Nucleare, Sezione di Cagliari.
    Polarized inclusive leptoproduction, lN→hX, and the hadron helicity density matrix ρ(h): Possible measurements and predictions1996In: Physical Review D. Particles and fields, ISSN 0556-2821, E-ISSN 1089-4918, Vol. 54, no 1, p. 828-837Article in journal (Refereed)
    Abstract [en]

    We discuss the production of hadrons in polarized lepton-nucleon interactions and in the current jet fragmentation region; using the QCD hard scattering formalism we compute the helicity density matrix of the hadron and show how its elements, when measurable, can give information on the spin structure of the nucleon and the spin dependence of the quark fragmentation process. The cases of ρ vector mesons and Λ baryons are considered in more detail and, within simplifying assumptions, some estimates are given

  • 4. Bergström, Lars
    et al.
    Fredriksson, Sverker
    Backward production on nuclei and the tube model1980In: Physical Review D. Particles and fields, ISSN 0556-2821, E-ISSN 1089-4918, Vol. 21, no 1, p. 305-307Article in journal (Refereed)
    Abstract [en]

    It is shown that the recent data from Burke et al. on backward production in 200-GeV/c nA collisions are in good agreement with expectations from the collective tube model with tube fragmentation taken into account.

  • 5.
    Blaschke, D.
    et al.
    Gesellschaft für Schwerionenforschung mbH (GSI).
    Fredriksson, Sverker
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Grigorian, H.
    Institut für Physik, Universität Rostock.
    Öztas, A.M.
    Department of Physics, Hacettepe University.
    Sandin, Fredrik
    The Phase diagram of three-flavor quark matter under compact star constraints2005In: Physical Review D. Particles and fields, ISSN 0556-2821, E-ISSN 1089-4918, Vol. 72, no 6Article in journal (Refereed)
    Abstract [en]

    The phase diagram of three-flavor quark matter under compact star constraints is investigated within a Nambu-Jona-Lasinio model. Global color and electric charge neutrality is imposed for beta-equilibrated superconducting quark matter. The constituent quark masses and the diquark condensates are determined self-consistently in the plane of temperature and quark chemical potential. Both strong and intermediate diquark coupling strengths are considered. We show that in both cases, gapless superconducting phases do not occur at temperatures relevant for compact star evolution, i.e., below T~50 MeV. The stability and structure of isothermal quark star configurations are evaluated. For intermediate coupling, quark stars are composed of a mixed phase of normal (NQ) and two-flavor superconducting (2SC) quark matter up to a maximum mass of 1.21 M[sun]. At higher central densities, a phase transition to the three-flavor color flavor locked (CFL) phase occurs and the configurations become unstable. For the strong diquark coupling we find stable stars in the 2SC phase, with masses up to 1.33 M[sun]. A second family of more compact configurations (twins) with a CFL quark matter core and a 2SC shell is also found to be stable. The twins have masses in the range 1.30...1.33 M[sun]. We consider also hot isothermal configurations at temperature T=40 MeV. When the hot maximum mass configuration cools down, due to emission of photons and neutrinos, a mass defect of 0.1 M[sun] occurs and two final state configurations are possible

  • 6.
    Constantinou, Martha
    et al.
    Department of Physics, University of Cyprus.
    Dimopoulos, Petros
    Dipartimento di Fisica, Sapienza, Università di Roma.
    Frezzotti, Roberto
    Dipartimento di Fisica, Università di Roma.
    Jensen, Karl
    DESY.
    Gimenez, Vicent Castillo
    Departament de Fisica Teòrica and IFIC, Univ. de València-CSIC.
    Lubicz, Vittorio
    Dipartimento di Fisica, Università Roma.
    Mescia, Frederico
    Departament d'Estructura i Constituents de la Matéria, Universitat de Barcelona.
    Panagopoulos, Haralambos G.
    Department of Physics, University of Cyprus.
    Papinutto, Mauro
    Laboratoire de Physique Subatomique et de Cosmologie, UJF/CNRS-IN2P3/INPG.
    Rossi, Giancarlo
    Dipartimento di Fisica, Università di Roma.
    Simula, Silvano
    INFN, Sezione di Roma Tre.
    Skouroupathis, Apostolos
    Department of Physics, University of Cyprus.
    Stylianou, Fotos
    Department of Physics, University of Cyprus.
    Vladikas, Anastassios
    INFN, Sezione di Tor Vergata.
    BK-parameter from Nf=2 twisted mass lattice QCD2011In: Physical Review D. Particles and fields, ISSN 0556-2821, E-ISSN 1089-4918, Vol. 83, no 1, article id 014505Article in journal (Refereed)
    Abstract [en]

    We present an unquenched Nf=2 lattice computation of the B K parameter which controls K0-K̄0 oscillations. A partially quenched setup is employed with two maximally twisted dynamical (sea) light Wilson quarks, and valence quarks of both the maximally twisted and the Osterwalder-Seiler variety. Suitable combinations of these two kinds of valence quarks lead to a lattice definition of the BK parameter which is both multiplicatively renormalizable and O(a) improved. Employing the nonperturbative RI-MOM scheme, in the continuum limit and at the physical value of the pion mass we get BKRGI=0.729±0.030, a number well in line with the existing quenched and unquenched determinations.

  • 7.
    Constantinou, Martha
    et al.
    Department of Physics, University of Cyprus.
    Dimopoulos, Petros
    Dipartimento di Fisica, Sapienza, Università di Roma.
    Frezzotti, Roberto
    Dipartimento di Fisica, Università di Roma.
    Lubicz, Vittorio
    Dipartimento di Fisica, Università Roma.
    Panagopoulos, Haralambos G.
    Department of Physics, University of Cyprus.
    Skouroupathis, Apostolos
    Department of Physics, University of Cyprus.
    Stylianou, Fotos
    Department of Physics, University of Cyprus.
    Perturbative renormalization factors and Oða2Þ corrections for latticefour-fermion operators with improved fermion/gluon actions2011In: Physical Review D. Particles and fields, ISSN 0556-2821, E-ISSN 1089-4918, Vol. 83, no 7, article id 074503Article in journal (Refereed)
    Abstract [en]

    In this work we calculate the corrections to the amputated Green's functions of four-fermion operators, in 1-loop lattice perturbation theory. One of the novel aspects of our calculations is that they are carried out to second order in the lattice spacing, O(a2). We employ the Wilson/clover action for massless fermions (also applicable for the twisted mass action in the chiral limit) and a family of Symanzik improved actions for gluons. Our calculations have been carried out in a general covariant gauge. Results have been obtained for several popular choices of values for the Symanzik coefficients (Plaquette, Tree-level Symanzik, Iwasaki, TILW and DBW2 action). While our Green's function calculations regard any pointlike four-fermion operators which do not mix with lower dimension ones, we pay particular attention to ΔF=2 operators, both parity conserving and parity violating (F stands for flavor: S, C, B). By appropriately projecting those bare Green's functions we compute the perturbative renormalization constants for a complete basis of four-fermion operators and we study their mixing pattern. For some of the actions considered here, even O(a0) results did not exist in the literature to date. The correction terms which we calculate (along with our previous O(a2) calculation of Z Ψ) are essential ingredients for minimizing the lattice artifacts which are present in nonperturbative evaluations of renormalization constants with the RI-MOM method. Our perturbative results, for the matrix elements of ΔF=2 operators and for the corresponding renormalization matrices, depend on a large number of parameters: coupling constant, number of colors, lattice spacing, external momentum, clover parameter, Symanzik coefficients, gauge parameter. To make these results most easily accessible to the reader, we have included them in the distribution package of this paper, as an ASCII file named: 4-fermi.m; the file is best perused as Mathematica input. The main results of this work have been applied to improve nonperturbative estimates of the BK-parameter in N F=2 twisted mass lattice QCD

  • 8. Ekelin, Svante
    et al.
    Fredriksson, Sverker
    Jändel, Magnus
    Larsson, Tomas
    Baryons from diquarks in e+e- annihilation1983In: Physical Review D. Particles and fields, ISSN 0556-2821, E-ISSN 1089-4918, Vol. 28, no 1, p. 257-259Article in journal (Other academic)
    Abstract [en]

    We find experimental support for the view that diquarks appear only as spin-0 objects. When their production rate in the color field of a quark from e+e- annihilation is described by the appropriate Schwinger formula for scalars, it turns out that they must be substantially lighter than earlier believed in order to explain the baryon yield.

  • 9. Fredriksson, Sverker
    Phenomenological relations between large-pT meson spectra1978In: Physical Review D. Particles and fields, ISSN 0556-2821, E-ISSN 1089-4918, Vol. 18, no 11, p. 4144-4151Article in journal (Refereed)
    Abstract [en]

    Recent data on the hadron ratios π+π-, K+π+, K-π-, and ηπ0 at large transverse momenta are shown to be consistent with predictions from a simple phenomenological two-component picture for large-pT production. The very-large-pT part of meson spectra is assumed to be dominated by particles that contain one of the incoming valence quarks, while small-and medium-pT mesons are built up mostly of quarks created in quark-antiquark pairs. Exceptions are K- and φ spectra, where for obvious reasons the very-large-pT component is missing. Simple relations between π, K, and η spectra are found. Predictions for the large-pT spectrum of φ mesons are presented.

  • 10. Fredriksson, Sverker
    et al.
    Larsson, Tomas
    A comment on diquark fragmentation1983In: Physical Review D. Particles and fields, ISSN 0556-2821, E-ISSN 1089-4918, Vol. 28, no 1, p. 255-256Article in journal (Other academic)
    Abstract [en]

    We discuss diquark fragmentation and suggest that a spectator uu system in deep-inelastic lepton-nucleon scattering has a larger breakup probability than a ud system. The reason for this is argued to be that half of the leftover ud systems are in bound (ud)0 diquark configurations, while no such bound uu diquarks exist.

  • 11.
    Hansson, Johan
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Olevik, David
    Türk, Christian
    Luleå tekniska universitet.
    Wiklund, Hanna
    Luleå tekniska universitet.
    Comment on "Measurement of quantum states of neutrons in the Earth's gravitational field"2003In: Physical Review D. Particles and fields, ISSN 0556-2821, E-ISSN 1089-4918, Vol. 68, no 10, p. 1087011-13Article in journal (Refereed)
    Abstract [en]

    In the paper by Nesvizhevsky et al. [Phys. Rev. D 67, 102002 (2003)], it is argued that the lowest quantum state of neutrons in the Earth's gravitational field has been experimentally identified. While this is most likely correct, it is imperative to investigate all alternative explanations of the result in order to close all loopholes, as it is the first experiment ever claimed to have observed gravitational quantum states. Here we show that geometrical effects in the experimental setup can mimic the results attributed to gravity. Modifications of the experimental setup to close these possible loopholes are suggested.

  • 12.
    Sandin, Fredrik
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Blaschke, D.
    Universität Rostock.
    Quark core of protoneutron stars in the phase diagram of quark matter2007In: Physical Review D. Particles and fields, ISSN 0556-2821, E-ISSN 1089-4918, Vol. 75, no 12Article in journal (Refereed)
    Abstract [en]

    We study the effect of neutrino trapping in new-born quark stars within a three-flavor Nambu-Jona-Lasinio (NJL) model with self-consistently calculated quark masses. The phase diagrams and equations of state for charge neutral quark matter in beta-equilibrium are presented, with and without trapped neutrinos. The compact star sequences for different neutrino untrapping scenarios are investigated and the energy release due to neutrino untrapping is found to be of the order of 1053 erg. We find that hot quark stars characterized, e.g., by an entropy per baryon of 1-2 and a lepton fraction of 0.4, as models for the cores of newborn protoneutron stars are in the two-flavor color superconducting (2SC) state. High temperatures and/or neutrino chemical potentials disfavor configurations with a color-flavor-locked (CFL) phase. Stable quark star solutions with CFL cores exist only at low temperatures and neutrino chemical potentials.

  • 13. Sandin, Fredrik
    et al.
    Hansson, Johan
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Observational legacy of preon stars: probing new physics beyond the CERN LHC2007In: Physical Review D. Particles and fields, ISSN 0556-2821, E-ISSN 1089-4918, Vol. 76, no 12Article in journal (Refereed)
    Abstract [en]

    We discuss possible ways to observationally detect the superdense cosmic objects composed of hypothetical subconstituent fermions beneath the quark/lepton level, recently proposed by us. The characteristic mass and size of such objects depend on the compositeness scale, and their huge density cannot arise within a context of quarks and leptons alone. Their eventual observation would therefore be a direct vindication of physics beyond the standard model of particle physics, possibly far beyond the reach of the Large Hadron Collider (LHC), in a relatively simple and inexpensive manner. If relic objects of this type exist, they can possibly be detected by present and future x-ray observatories, high-frequency gravitational wave detectors, and seismological detectors. To have a realistic detection rate, i.e., to be observable, they must necessarily constitute a significant fraction of cold dark matter.

  • 14.
    Uggla, Claes
    et al.
    Luleå tekniska universitet.
    Jantzen, Robert T.
    Villanova University.
    Rosquist, Kjell
    Stockholms Universitet.
    Exact hypersurface-homogeneous solutions in cosmology and astrophysics1995In: Physical Review D. Particles and fields, ISSN 0556-2821, E-ISSN 1089-4918, Vol. 51, no 10, p. 5522-5557Article in journal (Refereed)
    Abstract [en]

    A framework is introduced which explains the existence and similarities of most exact solutions of the Einstein equations with a wide range of sources for the class of hypersurface-homogeneous spacetimes which admit a Hamiltonian formulation. This class includes the spatially homogeneous cosmological models and the astrophysically interesting static spherically symmetric models as well as the stationary cylindrically symmetric models. The framework involves methods for finding and exploiting hidden symmetries and invariant submanifolds of the Hamiltonian formulation of the field equations. It unifies, simplifies, and extends most known work on hypersurface-homogenous exact solutions. It is shown that the same framework is also relevant to gravitational theories with a similar structure, such as Brans-Dicke or higher-dimensional theories.

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