241 research outputs found
Conservation laws for the classical Toda field theories
We have performed some explicit calculations of the conservation laws for
classical (affine) Toda field theories, and some generalizations of these
models. We show that there is a huge class of generalized models which have an
infinite set of conservation laws, with their integrated charges being in
involution. Amongst these models we find that only the and
() Toda field theories admit such conservation laws for spin-3. We
report on our explicit calculations of spin-4 and spin-5 conservation laws in
the (affine) Toda models. Our perhaps most interesting finding is that there
exist conservation laws in the models ( which have a different
origin than the exponents of the corresponding affine theory or the
energy-momentum tensor of a conformal theory.Comment: 9 pages, Late
Using Conservation Laws to Solve Toda Field Theories
We investigate the question of how the knowledge of sufficiently many local
conservation laws for a model can be utilized to solve the model. We show that
for models where the conservation laws can be written in one-sided forms, like
\barpartial Q_s = 0, the problem can always be reduced to solving a closed
system of ordinary differential equations. We investigate the , , and
Toda field theories in considerable detail from this viewpoint. One of
our findings is that there is in each case a transformation group intrinsic to
the model. This group is built on a specific real form of the Lie algebra used
to label the Toda field theory. It is the group of field transformations which
leaves the conserved densities invariant.Comment: Latex, 24 page
On the form of local conservation laws for some relativistic field theories in 1+1 dimensions
We investigate the possible form of local translation invariant conservation
laws associated with the relativistic field equations
\partial\bar\partial\phi_i=-v_i(\bphi) for a multicomponent field \bphi.
Under the assumptions that (i)~the 's can be expressed as linear
combinations of partial derivatives of a set of
functions w_j(\bphi), (ii)~the space of functions spanned by the 's is
closed under partial derivations, and (iii)~the fields \bphi take values in a
simply connected space, the local conservation laws can either be transformed
to the form (where
and are homogeneous polynomials in the variables
, ,\ldots), or to the parity
transformed version of this expression .Comment: 12 pages, Late
Realizing vector meson dominance with transverse charge densities
The transverse charge density in a fast-moving nucleon is represented as a
dispersion integral of the imaginary part of the Dirac form factor in the
timelike region (spectral function). At a given transverse distance b the
integration effectively extends over energies in a range sqrt{t} ~< 1/b, with
exponential suppression of larger values. The transverse charge density at
peripheral distances thus acts as a low-pass filter for the spectral function
and allows one to select energy regions dominated by specific t-channel states,
corresponding to definite exchange mechanisms in the spacelike form factor. We
show that distances b ~ 0.5 - 1.5 fm in the isovector density are maximally
sensitive to the rho meson region, with only a ~10% contribution from
higher-mass states. Soft-pion exchange governed by chiral dynamics becomes
relevant only at larger distances. In the isoscalar density higher-mass states
beyond the omega are comparatively more important. The dispersion approach
suggests that the positive transverse charge density in the neutron at b ~ 1
fm, found previously in a Fourier analysis of spacelike form factor data, could
serve as a sensitive test of the the isoscalar strength in the ~1 GeV mass
region. In terms of partonic structure, the transverse densities in the vector
meson region b ~ 1 fm support an approximate mean-field picture of the motion
of valence quarks in the nucleon.Comment: 14 pages, 12 figure
The role of the resonance in the reaction
We investigate the photo-production in the reaction within the effective Lagrangian method near
threshold. In addition to the "background" contributions from the contact,
channel exchange, and channel nucleon pole terms, which were
already considered in previous works, the contribution from the nucleon
resonance (spin-parity ) is also considered. We show
that the inclusion of the nucleon resonance leads to a fairly good
description of the new LEPS differential cross section data, and that these
measurements can be used to determine some of the properties of this latter
resonance. However, serious discrepancies appear when the predictions of the
model are compared to the photon-beam asymmetry also measured by the LEPS
Collaboration.Comment: 9 pages,6 figures, 1 tabl
Herschel-Bulkley rheology from lattice kinetic theory of soft-glassy materials
We provide a clear evidence that a two species mesoscopic Lattice Boltzmann
(LB) model with competing short-range attractive and mid-range repulsive
interactions supports emergent Herschel-Bulkley (HB) rheology, i.e. a power-law
dependence of the shear-stress as a function of the strain rate, beyond a given
yield-stress threshold. This kinetic formulation supports a seamless transition
from flowing to non-flowing behaviour, through a smooth tuning of the
parameters governing the mesoscopic interactions between the two species. The
present model may become a valuable computational tool for the investigation of
the rheology of soft-glassy materials on scales of experimental interest.Comment: 5 figure
Teaching in groups in grade III.
Thesis (Ed.M.)--Boston University
N.B.:Pages 28, 144 and 145 are missing from original thesis
Strangeness and Chiral Symmetry Breaking
The implications of chiral symmetry breaking and SU(3) symmetry breaking have
been studied in the chiral constituent quark model (CQM). The role of
hidden strangeness component has been investigated for the scalar matrix
elements of the nucleon with an emphasis on the meson-nucleon sigma terms. The
CQM is able to give a qualitative and quantitative description of the
"quark sea" generation through chiral symmetry breaking. The significant
contribution of the strangeness is consistent with the recent available
experimental observations.Comment: 10 pages, 1 table. To appear in Mod. Phys. Lett.
Bulk spectral function sum rule in QCD-like theories with a holographic dual
We derive the sum rule for the spectral function of the stress-energy tensor
in the bulk (uniform dilatation) channel in a general class of strongly coupled
field theories. This class includes theories holographically dual to a theory
of gravity coupled to a single scalar field, representing the operator of the
scale anomaly. In the limit when the operator becomes marginal, the sum rule
coincides with that in QCD. Using the holographic model, we verify explicitly
the cancellation between large and small frequency contributions to the
spectral integral required to satisfy the sum rule in such QCD-like theories.Comment: 16 pages, 2 figure
The barrel DIRC of PANDA
Cooled antiproton beams of unprecedented intensities in the momentum range of 1.5-15 GeV/c will be used for the PANDA experiment at FAIR to perform high precision experiments in the charmed quark sector. The PANDA detector will investigate antiproton annihilations with beams in the momentum range of 1.5 GeV/c to 15 GeV/c on a fixed target. An almost 4π acceptance double spectrometer is divided in a forward spectrometer and a target spectrometer. The charged particle identification in the latter is performed by ring imaging Cherenkov counters employing the DIRC principle
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