192 research outputs found
Quark Mass Dependence of Nucleon Properties and Extrapolation from Lattice QCD
We summarize developments concerning the quark mass dependence of nucleon
magnetic moments and the axial-vector coupling constant g_A. The aim is to
explore the feasibility of chiral effective field theory methods for the
extrapolation of lattice QCD results, from the relatively large quark masses
that can be handled in such computations down to the physically relevant range.Comment: 9 pages, Latex, 4ps figures, uses World Scientific style file;
presented at International School ``Quarks in Hadrons and Nuclei'', Erice,
Sicily, September 200
Quark mass dependence of nucleon mass and axial-vector coupling constant
We present an updated analysis of the quark mass dependence of the nucleon
mass and nucleon axial-vector coupling g_A, comparing different formulations of
SU(2) Baryon Chiral Effective Field Theory, with and without explicit delta
(1232) degrees of freedom. We discuss the outcome of the corresponding
interpolations between lattice QCD data and the physical values for these two
nucleon observables. It turns out that in order to obtain successful
interpolating functions at one-loop order, the inclusion of explicit delta
(1232) degrees of freedom is not decisive for the nucleon mass but crucial for
g_A. A chiral extrapolation of recent lattice results by the LHP collaborations
is also shown.Comment: 5 pages, 7 figures, Talk given at the Workshop on Computational
Hadron Physics, Nicosia, Cyprus, 14-17 September 200
On the Early History of Current Algebra
The history of Current Algebra is reviewed up to the appearance of the
Adler-Weisberger sum rule. Particular emphasis is given to the role current
algebra played for the historical struggle in strong interaction physics of
elementary particles between the S-matrix approach based on dispersion
relations and field theory. The question whether there are fundamental
particles or all hadrons are bound or resonant states of one another played an
important role in this struggle and is thus also regarded.Comment: 17 page
Quark Description of Hadronic Phases
We extend our proposal that major universality classes of hadronic matter can
be understood, and in favorable cases calculated, directly in the microscopic
quark variables, to allow for splitting between strange and light quark masses.
A surprisingly simple but apparently viable picture emerges, featuring
essentially three phases, distinguished by whether strangeness is conserved
(standard nuclear matter), conserved modulo two (hypernuclear matter), or
locked to color (color flavor locking). These are separated by sharp phase
transitions. There is also, potentially, a quark phase matching hadronic
K-condensation. The smallness of the secondary gap in two-flavor color
superconductivity corresponds to the disparity between the primary dynamical
energy scales of QCD and the much smaller energy scales of nuclear physics.Comment: 21 pages, 2 figure
Robin conditions on the Euclidean ball
Techniques are presented for calculating directly the scalar functional
determinant on the Euclidean d-ball. General formulae are given for Dirichlet
and Robin boundary conditions. The method involves a large mass asymptotic
limit which is carried out in detail for d=2 and d=4 incidentally producing
some specific summations and identities. Extensive use is made of the
Watson-Kober summation formula.Comment: 36p,JyTex, misprints corrected and a section on the massive case
adde
Quark mass dependence of the nucleon axial-vector coupling constant
We study the quark mass expansion of the axial-vector coupling constant g_A
of the nucleon. The aim is to explore the feasibility of chiral effective field
theory methods for extrapolation of lattice QCD results - so far determined at
relatively large quark masses corresponding to pion masses larger than 0.6 GeV
- down to the physical value of the pion mass. We compare two versions of
non-relativistic chiral effective field theory: One scheme restricted to pion
and nucleon degrees of freedom only, and an alternative approach which
incorporates explicit Delta(1230) resonance degrees of freedom. It turns out
that, in order to approach the physical value of g_A in a leading-one-loop
calculation, the inclusion of the explicit Delta(1230) degrees of freedom is
crucial. With information on important higher order couplings constrained from
analyses of inelastic pion production processes, a chiral extrapolation
function for g_A is obtained, which works well from the chiral limit across the
physical point into the region of present lattice data. The resulting
enhancement of our extrapolation function near the physical pion mass is found
to arise from an interplay between long- and short- distance physics.Comment: 21 pages, LaTeX, 7 figure
Right Handed Weak Currents in Sum Rules for Axialvector Constant Renormalization
The recent experimental results on deep inelastic polarized lepton scattering
off proton, deuteron and He together with polari% zed neutron
-decay data are analyzed. It is shown that the problem of Ellis-Jaffe
and Bjorken sum rules deficiency and the neutron paradox could be solved
simultaneously by assuming the small right handed current (RHC) admixture in
the weak interaction Lagrangian. The possible RHC impact on pion-nucleon
-term and Gamow-Teller sum rule for nuclear reactions is
pointed out.Comment: to be published in Phys. Rev. Lett. LaTeX, 8 pages, 21 k
Further functional determinants
Functional determinants for the scalar Laplacian on spherical caps and
slices, flat balls, shells and generalised cylinders are evaluated in two,
three and four dimensions using conformal techniques. Both Dirichlet and Robin
boundary conditions are allowed for. Some effects of non-smooth boundaries are
discussed; in particular the 3-hemiball and the 3-hemishell are considered. The
edge and vertex contributions to the coefficient are examined.Comment: 25 p,JyTex,5 figs. on request
Chiral Multiplets of Large-N Ground State Baryons
I show that in the large-N limit the ground state baryons with helicity h
fall into an ((N-2h)/4,(N+2h)/4) irreducible representation of SU(2)XSU(2).
This representation determines the absolute normalization of the ground state
baryon axial vector couplings at large-N. Results map precisely to
(spin-flavor) SU(4) results. For instance, I find g_A =(N+2)/3. As a
consequence of this multiplet structure, chiral symmetry forbids pion
transitions between the ground state baryons and other baryon towers in the
large-N limit.Comment: 6 pages TeX and mtexsis.te
Energy States of Colored Particle in a Chromomagnetic Field
The unitary transformation, which diagonalizes squared Dirac equation in a
constant chromomagnetic field is found. Applying this transformation, we find
the eigenfunctions of diagonalized Hamiltonian, that describe the states with
definite value of energy and call them energy states. It is pointed out that,
the energy states are determined by the color interaction term of the particle
with the background chromofield and this term is responsible for the splitting
of the energy spectrum.
We construct supercharge operators for the diagonal Hamiltonian, that ensure
the superpartner property of the energy states.Comment: 25 pages, some calculation details have been removed, typos correcte
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