Browsing by Author "Viollier, Raoul D"

Now showing 1 - 14 of 14
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    The anomalous magnetic moment of baryons in cavity QCD
    (1992) Lindebaum, R J; Viollier, Raoul D
    Using a generalised form of the Gell-Mann and Low theorem, all the diagrams in cavity QCD to order as that contribute to the magnetic moment are calculated. The calculations are performed for massive quarks so a mass renormalisation scheme has been developed to cope with the new divergences this brings into the self-energy insert diagrams. The results of this work show that no improvement on the simple SU(3) model is made by including these corrections. These calculations point to a smaller value of αs than that which is usually used.
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    Bound states of heavy and light quarks in the framework of quantum chromodynamics
    (1985) Gavin, Elizabeth Jane Ogle; Viollier, Raoul D
    The spectra of the D, F, B and E mesons have been calculated using the MIT bag model together with a static potential related to the Fourier transform of the "dressed" gluon propagator. The heavy quark has been assumed to coincide with the centre of the bag, while the Light antiquark was treated relativistically using the Dirac equation. The spectra obtained are compared with experimental data as well as with the results of other models of these Qq mesons. The ratio mb/mc obtained in the fit to experimentally known states is compared with the result expected from the hyperfine splitting of the D and B mesons. It appears that tris ratio is model dependent. More experimental data are required to further evaluate the validity of this model.
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    Canonical quantization and quantum chromodynamics in a cavity
    (1986) Zimak, Petr; Viollier, Raoul D
    The canonical quantization formalism is applied to the Lagrange density of chromodynamics in a general covariant gauge. The physical states are characterized by their BRS-invariance. We develop the quantum theory of the interacting fields in the Dirac picture, based on the Gell-Mann and Low Theorem and the Dyson expansion of the time evolution operator. Subsequently, confinement is introduced phenomenologically by imposing, on the quark, gluon and ghost field operators, the linear boundary conditions of the M.I.T. bag model at the surface of a spherically symmetric and static cavity. Based on this formalism, we calculate, in the Feynman gauge, all non-divergent Feynman diagrams of second order in the strong coupling constant g. Explicit values of the matrix elements are given for low-lying quark and gluon cavity modes.
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    The gluon self-energy in cavity quantum chromodynamics
    (1991) Schreiber, Gunhild Ursula; Viollier, Raoul D
    A numerical technique to regularize divergent loop diagrams in cavity quantum chromodynamics is discussed, which is closely related to free space dimensional regularization. In this cavity regularization method, the energy shift is expressed as the integral of a divergent spectral function, from which the divergence may be extracted by analogy to the free space expression. It is shown for the case of the self-energy of a gluon in a cavity that no new divergences arise due to the presence of the boundary, provided that the regularization can be achieved in such a way that no subtractions are necessary. In order to avoid such subtractions, the so-called method of separation is developed, in which the spectral forms in the cavity are separated in such a way that the divergences of the various terms cancel exactly. This method is in close analogy to the free space regularization method of separation where tadpole contributions are separated off from the rest of the momentum integrals. The technique is used to evaluate the self-energy of a gluon in a cavity, which turns out to be positive for both the quark loop and the gauge loops. The positive value obtained offers a possible explanation for the absence of gluonic exotic states.
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    Heavy neutrino balls and the supermassive dark object at the Galactic center
    (1999) Munyaneza, Faustin; Viollier, Raoul D
    Massive neutrinos were the first proposed, and still remain the most natural, particle candidate for the dark matter. We investigate here the properties and astrophysical implications of self-gravitating degenerate heavy neutrino matter. Neutrinos of 10 to 25 keV/c² might cluster around the sun forming a halo of a few solar masses and a few light years radius. We calculate the perihelion shifts of planetary and asteroidal orbits that are expected due to the presence of a conjectured degenerate heavy neutrino halo around the sun. While the General Relativistic perihelion shifts are positive, those due to a possible dark matter halo are in general negative. A neutrino mass around ~16 keV is consistent with the observed mass excesses within the orbits of various outer planets, as obtailled from astrometrical data and Voyager 1 and 2 and Pioneer 10 and 11 ranging data. We then study the general relativistic effects on degenerate neutrino balls using the Tolman-Oppenheimer-Yolkoff (TOV ) equations of hydrostatic equilibrium. An extension of the TOV equations is made to describe the detailed properties of supermassive neutrino balls around compact objects such as white dwarfs and neutron stars. We further show that the supermassive compact dark object near Sgr A* at the Galactic center could be an extended object rather than a black hole. In fact these two scenarios can be distinguished by tracking the orbit of one of the fast moving stars near the Galactic center. VVe finally calculate the emission spectrum of the supermassive compact dark object using the standard accretion theory and show that the calculated radio wave to infrared emission spectrum between λ = 0.3 cm and λ = 10-³ cm is consistent with the observations.
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    Introduction to supersymmetry
    (1987) Schreiber, Gunhild Ursula; Viollier, Raoul D
    The tendency in theoretical physics, particularly in the past few decades, has been towards unification: over the years it has emerged that increasingly many physical phenomena can be explained by a common underlying theory. Symmetry principles, both global and local, play an important role in this unification programme. Global symmetries often account for approximate regularities we observe in nature - local or gauge symmetries are understood as basic symmetries which lie at the heart of the interactions of the constituents of matter.
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    Massive quark self-energy in cavity QCD
    (1991) Cuthbert, J A; Viollier, Raoul D
    The greatest obstacle in calculating the self-energy Feynman diagram is that it is, in principle, linearly divergent. So far the self-energy of a massive quark in cavity quantum chromodynamics has only been calculated for the lowest cavity mode ls1/2. The methods used so far, have been based on the multiple reflection formalism, in which the zero reflection term is extracted out analytically and evaluated separately using Pauli-Villars regularization. This thesis is based on the dimensional regularization scheme, adapted for use in the cavity, by Stoddart et al., who calculated the self-energy for a massless quark. This involves analytically isolating the divergences using dimensional regularization and then removing the divergences using the minimal subtraction (ms) scheme or some similar subtraction scheme. In this thesis, the self-energies of massive quarks have been calculated using the ms scheme for a number of low-lying cavity modes. The ls1/2 results have also been compared with the Pauli-Villars regularization scheme used by Goldhaber, Jaffe and Hansson.
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    Muon regeneration in muon catalyzed dt-fusion
    (1988) Rafelski, Helga E; Viollier, Raoul D
    The origin of the experimentally observed density dependence of the effective muon alpha sticking fraction will in muon catalyzed deuterium- tritium fusion has been comprehensively reanalyzed with the particular emphasis put on the density dependence of the stopping power in dense hydrogen. The main technical details and improvements in this work are: The (aμ)+ 2s and 2p states are treated independently and are assigned individual reaction rates. The essential muonic excitation rates have been recalculated taking into account finite nuclear mass effects. The stopping power for a charged projectile in liquid heavy hydrogen is modified to account for dynamic screening effects and a density dependent effective ionization potential. It is shown that the medium dependent stopping power for the (aμ)+ ion is the crucial entity controlling the density dependance of the effective sticking fraction. It is also pointed out that the muonic helium Ka X-ray yield and the sticking fraction at high density can not be simultaneously brought into agreement with the experimental results without invoking novel mechanisms suppressing Stark mixing in the (Heμ) L-shell.
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    Pion electromagnetic form factor in the Kroll-Lee-Zumino model at zero and finite temperature
    (2008) Willers, Bernard; Dominguez, Cesareo A; Viollier, Raoul D
    The renormalizable Abelian quantum field theory model of Kroll, Lee and Zumino is used to calculate next-to-leading order corrections to the pion electromagnetic form factor in vector meson dominance. At zero temperature the predictions for both the form factor and electromagnetic radius are found to improve greatly over the tree level result, and are in good agreement with the experimental data. A calculation of the vertex and self energy functions in the Matsubara formalism at finite temperature do not agree with the results of the Gale & Kapusta calculations. The resulting prediction for the radius is found to increase with temperature, consistent vith ideas about haclronic deconfinernent.
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    The ratio gA/gV in cavity QCD
    (1991) Page, Philip R; Viollier, Raoul D
    BRS invariant quantum chromodynamics in a spherical cavity is developed using canonical quantization. The weak vector and axial form factors are defined, employing a classical external W- field. The Gell-Mann and Low theorem is extended to include non-diagonal matrix elements and degenerate perturbation theory. The Sucher form of the Gell-Mann and Low theorem is employed to calculate corrections of order GFg² in the weak and strong coupling constants to gA and gv for neutron beta decay. Up and down quarks are assumed massless. The gauge-independent divergences from the loop diagrams cancel each other and can be regularized dimensionally, making renormalization unnecessary. We find that the weak vector and axial current coupling constants are respectively: 9v = 1.0000 gA = 1.0883 + 0.2425 αs', where the preferred value of αs = 2.2 in the M.I.T. bag model gives gA = 1.62.
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    Renormalization of cavity field theories
    (1990) Stoddart, A J; Viollier, Raoul D
    A major obstacle to calculating Feynman diagrams in field theories, confined to a cavity, has always been the divergent loop diagrams. So far, only the quantum chromodynamic and electrodynamic self-energies of a ls1/2 quark, confined to a static spherical cavity, have been accurately calculated. These quantities are of immediate interest in the M.I.T. bag model. The existing methods to calculate loop diagrams are based on the multiple reflection scheme, in which the zero reflection term is separated out analytically, and evaluated separately. Thus far, there are some indications that this method is unsuitable for the quadratically divergent one loop vacuum polarization. In this thesis we firstly develop a set of Fourier transforms, appropriate to a discussion of renormalization in a cavity. Using these, we renormalize the cavity propagators to one loop for scalar, Dirac, and gauge fields. We then introduce a new computational method to subtract out the divergences, based on dimensional regularization. Using this method, we present results for various loop diagrams. The scalar φ⁴ theory is used as a pedagogical example. We then present the quark self-energy for several low lying cavity modes. Finally we tackle the long standing and hitherto unresolved question of the vacuum polarization. For this we give a detailed discussion of surface divergences, and present results for scalar quantum electrodynamics. We make a suggestion for the implementation of the running coupling constant in the cavity.
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    Spherically symmetric dark energy structures in the context of Chaplygin gas model
    (2006) Tekola, Abiy G; Tupper, Gary B; Viollier, Raoul D
    This paper investigates the existence of spherically symmetrical dark energy structures under the context of Chaplygin gas. A scaling solution of the form r -2/3 is found for the density and then we calculated the corresponding rotational curve and it turns out to be unrealistic implying that such objects don't exist. Finally we modified the equation of state of the Chaplygin gas to an equation of state of the form P = (j 2 P - A and compared p with observational data to see to what physical extent this equation works and it isdetermined that it works as far as a couple of hundred Mpc while the physical length of galaxies is in Kpc. implying the modified Chaplygin equation fits the observed rotational curves.
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    A study in spherical accretion of self-gravitating fluids in a general relativistic framework
    (2010) Richter, M C; Viollier, Raoul D; Tupper, Gary B
    A new general framework for studying relativistic spherical accretion of a self-gravitating fluid onto a central black hole is introduced in stationary coordinates for an observer at infinity. The important feature of gravitational backreaction due to a self-gravitating fluid on the metric is included in the model. The model is solved numerically for the most simple case of a polytropic fluid and compared to analytical solutions, which the model approximates in the "test-fluid" limit. The model is then focused on the accretion of a relativistic Fermi gas and the implications this might have on the rapid growth of supermassive black holes from clouds of sterile neutrino dark matter in the early universe. The results give good agreement with a Newtonian model of supermassive black hole growth called the symbiotic scenario.
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    Two-gluon exchange graphs in cavity QCD to order αs2
    (1998) Schumann, Marc; Viollier, Raoul D
    The purpose of this thesis is to go beyond the usual first order calculations and to evaluate the two-gluon exchange diagrams, which are second order in as. Two distinct Feynman diagrams exist, of which each consists of twenty-four timeordered diagrams. All the possible time-ordered diagrams are calculated here. A similar calculation of only the first six time-ordered diagrams has been performed by Stoddart et al.The purpose of this thesis is to go beyond the usual first order calculations and to evaluate the two-gluon exchange diagrams, which are second order in αs. Two distinct Feynman diagrams exist, of which each consists of twenty-four timeordered diagrams. All the possible time-ordered diagrams are calculated here. A similar calculation of only the first six time-ordered diagrams has been performed by Stoddart et al.