257 Matching Results

Search Results

Advanced search parameters have been applied.

The axial anomaly and the dynamical breaking of chiral symmetry

Description: Using the quark triangle diagram for the Adler-Bell-Jackiw axial anomaly, we calculate the form factor for the {gamma}{sup *}{pi}{sup 0}{yields}{gamma} transition. This form factor depends on the quark mass, and we predict the right behavior with m{sub q}{approx_equal}250 MeV, the same quark mass generated by the dynamical breaking of chiral symmetry through a Nambu-Jona-Lasinio mechanism.
Date: October 1, 1991
Creator: Gross, Franz; Ito, Hiroshi & Buck, Warren
Partner: UNT Libraries Government Documents Department

WHY ROOTING FAILS.

Description: I explore the origins of the unphysical predictions from rooted staggered fermion algorithms. Before rooting, the exact chiral symmetry of staggered fermions is a flavored symmetry among the four 'tastes.' The rooting procedure averages over tastes of different chiralities. This averaging forbids the appearance of the correct 't Hooft vertex for the target theory.
Date: July 30, 2007
Creator: Creutz, M.
Partner: UNT Libraries Government Documents Department

Hunting the Scalar Glueball: Prospects for BES III

Description: The search for the ground state scalar glueball $G_0$ isreviewed. Spin zero glueballs will have unique dynamical properties ifthe $<G_0|\overline qq>$ amplitude is suppressed by chiralsymmetry, as it is to all orders in perturbation theory: for instance,mixing of $G_0$ with $\overline qq$ mesons would be suppressed, radiative$\jp$ decay would be a filter for new physics in the spin zero channel,and the decay $G_0 \rightarrow \overline KK$ could be enhanced relativeto $G_0 \rightarrow \pi \pi$. These properties are consistent with theidentification of $f_0(1710)$ as the largely unmixed ground state scalarglueball, while recent BES data implies that $f_0(1500)$ does not containthe dominant glueball admixture. Three hypotheses are discussed: that$G_0$ is 1) predominantly $f_0(1500)$ or 2) predominantly $f_0(1710)$ or3) is strongly mixed between $f_0(1500)$ and $f_0(1710)$.
Date: September 18, 2006
Creator: Chanowitz, Michael S.
Partner: UNT Libraries Government Documents Department

On Yang--Mills Theories with Chiral Matter at Strong Coupling

Description: Strong coupling dynamics of Yang-Mills theories with chiral fermion content remained largely elusive despite much effort over the years. In this work, we propose a dynamical framework in which we can address non-perturbative properties of chiral, non-supersymmetric gauge theories, in particular, chiral quiver theories on S{sub 1} x R{sub 3}. Double-trace deformations are used to stabilize the center-symmetric vacuum. This allows one to smoothly connect smaller(S{sub 1}) to larger(S{sub 1}) physics (R{sub 4} is the limiting case) where the double-trace deformations are switched off. In particular, occurrence of the mass gap in the gauge sector and linear confinement due to bions are analytically demonstrated. We find the pattern of the chiral symmetry realization which depends on the structure of the ring operators, a novel class of topological excitations. The deformed chiral theory, unlike the undeformed one, satisfies volume independence down to arbitrarily small volumes (a working Eguchi-Kawai reduction) in the large N limit. This equivalence, may open new perspectives on strong coupling chiral gauge theories on R{sub 4}.
Date: August 20, 2008
Creator: Shifman, M.; /Minnesota U., Theor. Phys. Inst. /Saclay, SPhT; Unsal, Mithat & /SLAC /Stanford U., Phys. Dept.
Partner: UNT Libraries Government Documents Department

Weak matrix elements for CP violation.

Description: We present preliminary results of matrix elements of four fermion operators relevant to the determination of e and E ' / E using staggered fermions. To calculate the matrix elements relevant to CP violation in Kaon decays it is important to use a lattice formulation which preserves (some) chiral symmetry.
Date: January 1, 2001
Creator: Lee, W. (Weonjong); Gupta, R. (Rajan); Christ, N.; Fleming, G. T.; Kilcup, G. (Gregory); Liu, G. et al.
Partner: UNT Libraries Government Documents Department

A lattice formulation of chiral gauge theories

Description: We present a method for implementing gauge theories of chiral fermions on the lattice. Discussed topics include: the lattice as a UV regulator, a chiral QED model, modification of the fermion determinant, large gauge-field momenta, and a non-perturbative problem.
Date: August 1, 1996
Creator: Bodwin, G.T.
Partner: UNT Libraries Government Documents Department

QCD with chiral 4-fermion interactions ({chi}QCD)

Description: Lattice QCD with staggered quarks is augmented by the addition of a chiral 4-fermion interaction. The Dirac operator is now non-singular at m{sub q}=0, decreasing the computing requirements for light quark simulations by at least an order of magnitude. We present preliminary results from simulations at finite and zero temperatures for m{sub q}=0, with and without gauge fields. Chiral QCD enables simulations at physical u and d quark masses with at least an order of magnitude saving in CPU time. It also enables simulations with zero quark masses which is important for determining the equation of state. A renormalization group analysis will be needed to continue to the continuum limit. 7 refs., 2 figs.
Date: October 1, 1996
Creator: Kogut, J.B. & Sinclair, D.K.
Partner: UNT Libraries Government Documents Department

Strong WW scattering chiral lagrangians, unitarity and resonances

Description: Chiral lagrangians provide a model independent description of the strongly interacting symmetry breaking sector. In this work, first we review the LHC sensitivity to the chiral parameters (in the hardest case of non-resonant low-energy WW scattering). Later we show how to reproduce or predict the resonance spectrum by means of dispersion theory and the inverse amplitude method. We present a parameter space scan that covers many different strong WW scattering scenarios.
Date: August 1, 1996
Creator: Pelaez, J.R.
Partner: UNT Libraries Government Documents Department

A search for disoriented chiral condensate at Fermilab

Description: A small test/experiment at the Fermilab Collider which measures charged particle and photon multiplicities in the forward direction, {eta} {approx} 4.1, has been carried out, with the primary goal being the search for disoriented chiral condensate (DCC). The author describes the experiment and analysis methods, together with preliminary results.
Date: October 1, 1996
Creator: Bjorken, J.D.
Partner: UNT Libraries Government Documents Department

Thermal rho`s in the quark-gluon plasma

Description: I discuss different models which predict changes in the mass of the thermal {rho} field. I emphasize that while the predictions are strongly model dependent, nevertheless substantial shifts in the thermal {rho} mass are expected to occur at the point of phase transition. As long as the thermal {rho} peak does not become too broad, this should provide a striking signature of the existence of a phase transition.
Date: March 1, 1995
Creator: Pisarski, R.D.
Partner: UNT Libraries Government Documents Department

Introduction to lattice QCD

Description: The goal of the lectures on lattice QCD (LQCD) is to provide an overview of both the technical issues and the progress made so far in obtaining phenomenologically useful numbers. The lectures consist of three parts. The author`s charter is to provide an introduction to LQCD and outline the scope of LQCD calculations. In the second set of lectures, Guido Martinelli will discuss the progress they have made so far in obtaining results, and their impact on Standard Model phenomenology. Finally, Martin Luescher will discuss the topical subjects of chiral symmetry, improved formulation of lattice QCD, and the impact these improvements will have on the quality of results expected from the next generation of simulations.
Date: December 1998
Creator: Gupta, R.
Partner: UNT Libraries Government Documents Department

Applications of chiral symmetry

Description: The author discusses several topics in the applications of chiral symmetry at nonzero temperature. First, where does the rho go? The answer: up. The restoration of chiral symmetry at a temperature T{sub {chi}} implies that the {rho} and a{sub 1} vector mesons are degenerate in mass. In a gauged linear sigma model the {rho} mass increases with temperature, m{sub {rho}}(T{sub {chi}}) > m{sub {rho}}(0). The author conjectures that at T{sub {chi}} the thermal {rho} - a{sub 1}, peak is relatively high, at about {approximately}1 GeV, with a width approximately that at zero temperature (up to standard kinematic factors). The {omega} meson also increases in mass, nearly degenerate with the {rho}, but its width grows dramatically with temperature, increasing to at least {approximately}100 MeV by T{sub {chi}}. The author also stresses how utterly remarkable the principle of vector meson dominance is, when viewed from the modern perspective of the renormalization group. Secondly, he discusses the possible appearance of disoriented chiral condensates from {open_quotes}quenched{close_quotes} heavy ion collisions. It appears difficult to obtain large domains of disoriented chiral condensates in the standard two flavor model. This leads to the last topic, which is the phase diagram for QCD with three flavors, and its proximity to the chiral critical point. QCD may be very near this chiral critical point, and one might thereby generated large domains of disoriented chiral condensates.
Date: March 1, 1995
Creator: Pisarski, R.D.
Partner: UNT Libraries Government Documents Department

QCD scales and chiral symmetry in finite nuclei

Description: The authors report on this progress in the calculation of nuclear ground-state properties using effective Lagrangians whose construction is constrained by QCD scales and chiral symmetry. Good evidence is found that QCD and chiral symmetry apply to finite nuclei.
Date: October 1, 1997
Creator: Madland, D.G.
Partner: UNT Libraries Government Documents Department

A lattice formulation of chiral gauge theories

Description: The authors present a method for formulating gauge theories of chiral fermions in lattice field theory. The method makes use of a Wilson mass to remove doublers. Gauge invariance is then restored by modifying the theory in two ways: the magnitude of the fermion determinant is replaced with the square root of the determinant for a fermion with vector-like couplings to the gauge field; a double limit is taken in which the lattice spacing associated with the fermion field is taken to zero before the lattice spacing associated with the gauge field. The method applies only to theories whose fermions are in an anomaly-free representation of the gauge group. They also present a related technique for computing matrix elements of operators involving fermion fields. Although the analyses of these methods are couched in weak-coupling perturbation theory, it is argued that computational prescriptions are gauge invariant in the presence of a nonperturbative gauge-field configuration.
Date: December 1, 1995
Creator: Bodwin, G.T.
Partner: UNT Libraries Government Documents Department

Quark-antiquark bound states in the relativistic spectator formalism

Description: The quark-antiquark bound states are discussed using the relativistic spectator (Gross) equations. A relativistic covariant framework for analyzing confined bound states is developed. The relativistic linear potential developed in an earlier work is proven to give vanishing meson {r_arrow} q + {anti q} decay amplitudes, as required by confinement. The regularization of the singularities in the linear potential that are associated with nonzero energy transfers (i.e. q{sup 2} = 0, q{sup {mu}} {ne} 0) is improved. Quark mass functions that build chiral symmetry into the theory and explain the connection between the current quark and constituent quark masses are introduced. The formalism is applied to the description of pions and kaons with reasonable results.
Date: November 1, 1999
Creator: Savkli, Cetin & Gross, Franz
Partner: UNT Libraries Government Documents Department

First experiences with HMC for dynamical overlap fermions

Description: The authors describe an HMC algorithm for dynamical overlap fermions which makes use of their good chiral properties. They test the algorithm in the Schwinger model. Topological sectors are readily changed even in the massless case.
Date: December 1, 1999
Creator: Bode, Achim; Heller, Urs M.; Edwards, Robert G. & Narayanan, Rajamani
Partner: UNT Libraries Government Documents Department

Isospin violation and the proton's neutral weak magnetic form factor

Description: The effects of isospin violation on the neutral weak magnetic form factor of the proton are studied using two-flavour chiral perturbation theory. The first nonzero contributions appear at O(p{sup 4}) in the small-momentum expansion, and the O(p{sup 5}) corrections are also calculated. The leading contributions from an explicit Delta(1232) isomultiplet are included as well. At such a high order in the chiral expansion, one might have expected a large number of unknown parameters to contribute. However, it is found that no unknown parameters can appear within loop diagrams, and a single tree-level counterterm at O(p{sup 4}) is sufficient to absorb all divergences. The momentum dependence of the neutral weak magnetic form factor is not affected by this counterterm.
Date: October 1, 1998
Creator: Lewis, Randy & Mobed, Nader
Partner: UNT Libraries Government Documents Department

Residual Chiral Symmetry Breaking in Domain-Wall Fermions

Description: The authors study the effective quark mass induced by the finite separation of the domain walls in the domain-wall formulation of chiral fermion as the function of the size of the fifth dimension ($L-s$), the gauge coupling $beta$ and the physical volume $V$. They measure the mass by calculating the small eigenvalues of the hermitian domain-wall Dirac operator ($H-[rm DWF](m-0))$ in the topologically-nontrivial quenched SU(3) gauge configurations. The authors find that the induced quark mass is nearly independent of the physical volume, decays exponentially as a function of $L-s$, and has a strong dependence on the size of quantum fluctuations controlled by $beta$. The effect of the choice of the lattice gluon action is also studied.
Date: September 1, 2000
Creator: Jung, Chulwoo; Gadiyak, Valeriya; Ji, Xiangdong & Edwards, Robert G.
Partner: UNT Libraries Government Documents Department

Exact Chiral Symmetry for Domain Wall Fermions with Finite L{sub s}*

Description: We show how the standard domain wall action can be simply modified to allow arbitrarily exact chiral symmetry at finite fifth dimensional extent. We note that the method can be used for both quenched and dynamical calculations. We test the method using smooth and thermalized gauge field configurations. We also make comparisons of the performance (cost) of the domain wall operator for spectroscopy compared to other methods such as the overlap-Dirac operator and find both methods are comparable in cost.
Date: October 1, 2000
Creator: Edwards, Robert G. & Heller, Urs M.
Partner: UNT Libraries Government Documents Department

Goldstone pion and other mesons

Description: A covariant wave equation for q{anti q} interactions with an interaction kernel composed of the sum of constant vector and linear scalar confining interactions is solved for states with two quarks with identical mass. The model includes an NJL-like mechanism which links the dynamical breaking of chiral symmetry to the spontaneous generation of quark mass and the appearance of a low mass Goldstone pion. A novel feature of this approach is that it automatically explains the small mass of the pion even though the linear potential is a scalar interaction in Dirac space, and hence breaks chiral symmetry. Solutions for mesons composed of light quarks ({pi},{rho}, and low lying excited states) and heavy quarks ({rho}{sub c}, J/{Psi}, and low lying excited states) are presented and discussed.
Date: January 1, 1994
Creator: Gross, F. & Milana, J.
Partner: UNT Libraries Government Documents Department

Dyson-Schwinger equations: connecting small and large length-scales.

Description: The phenomenological application of Dyson-Schwinger equations to the calculation of meson properties observable at TJNAF is illustrated. Particular emphasis is given to the ability of this framework to unify long-range effects constrained by chiral symmetry with short-range effects prescribed by perturbation theory, and interpolate between them.
Date: February 8, 1999
Creator: Roberts, C.
Partner: UNT Libraries Government Documents Department

Nuclear forces and chiral theories

Description: Recent successes in ab initio calculations of light nuclei (A=2-6) will be reviewed and correlated with the dynamical consequences of chiral symmetry. The tractability of nuclear physics evinced by these results is evidence for that symmetry. The relative importance of three-nucleon forces, four-nucleon forces, multi-pion exchanges, and relativistic corrections will be discussed in the context of effective field theories and dimensional power counting. Isospin violation in the nuclear force will also be discussed in this context.
Date: September 1, 1995
Creator: Friar, J.L.
Partner: UNT Libraries Government Documents Department

FUN WITH DIRAC EIGENVALUES.

Description: It is popular to discuss low energy physics in lattice gauge theory ill terms of the small eigenvalues of the lattice Dirac operator. I play with some ensuing pitfalls in the interpretation of these eigenvalue spectra. In short, thinking about the eigenvalues of the Dirac operator in the presence of gauge fields can give some insight, for example the elegant Banks-Casher picture for chiral symmetry breaking. Nevertheless, care is necessary because the problem is highly non-linear. This manifests itself in the non-intuitive example of how adding flavors enhances rather than suppresses low eigenvalues. Issues involving zero mode suppression represent one facet of a set of connected unresolved issues. Are there non-perturbative ambiguities in quantities such as the topological susceptibility? How essential are rough gauge fields, i.e. gauge fields on which the winding number is ambiguous? How do these issues interplay with the quark masses? I hope the puzzles presented here will stimulate more thought along these lines.
Date: January 26, 2006
Creator: CREUTZ, M.
Partner: UNT Libraries Government Documents Department