448 research outputs found
A Groenewold-Van Hove Theorem for S^2
We prove that there does not exist a nontrivial quantization of the Poisson
algebra of the symplectic manifold S^2 which is irreducible on the subalgebra
generated by the components {S_1,S_2,S_3} of the spin vector. We also show that
there does not exist such a quantization of the Poisson subalgebra P consisting
of polynomials in {S_1,S_2,S_3}. Furthermore, we show that the maximal Poisson
subalgebra of P containing {1,S_1,S_2,S_3} that can be so quantized is just
that generated by {1,S_1,S_2,S_3}.Comment: 20 pages, AMSLaTe
Constraint algorithm for k-presymplectic Hamiltonian systems. Application to singular field theories
The k-symplectic formulation of field theories is especially simple, since
only tangent and cotangent bundles are needed in its description. Its defining
elements show a close relationship with those in the symplectic formulation of
mechanics. It will be shown that this relationship also stands in the
presymplectic case. In a natural way, one can mimick the presymplectic
constraint algorithm to obtain a constraint algorithm that can be applied to
-presymplectic field theory, and more particularly to the Lagrangian and
Hamiltonian formulations of field theories defined by a singular Lagrangian, as
well as to the unified Lagrangian-Hamiltonian formalism (Skinner--Rusk
formalism) for k-presymplectic field theory. Two examples of application of the
algorithm are also analyzed.Comment: 22 p
Ethnic differential item functioning in the assessment of quality of life in cancer patients
BACKGROUND: Past research has shown that Filipino cancer patients report lower levels of quality of life (QoL) than other ethnic groups. One possible explanation for this is that Filipinos do not define QoL in the same manner as others, resulting in bias in their assessments. Hence, Filipinos would not necessarily have lower QoL. METHODS: Item response theory methods were used to assess differential item functioning (DIF) in the quality of life (measured by the EORTC QLQ-C30) of cancer patients across four ethnic groups (Caucasian, Filipino, Hawaiian, and Japanese). The sample consisted of 359 cancer patients. RESULTS: Results showed the presence of DIF on several items, indicating ethnic differences in the assessment of quality of life. Relative to the Caucasian and Japanese groups, items related to physical functioning, cognitive functioning, social functioning, nausea and vomiting, and financial difficulties exhibited DIF for Filipinos. On these items Filipinos exhibited either higher or lower QoL scores, even though their overall QoL was the same. CONCLUSION: This evidence may explain why Filipinos have previously been found to have lower overall QoL. Although Filipinos score lower on QoL than other groups, this may not reflect lower QoL, but rather differences in how QoL is defined. The presence of DIF did not appear, however, to alter the psychometric properties of the QLQ-C30
Covariant Symplectic Structure and Conserved Charges of New Massive Gravity
We show that the symplectic current obtained from the boundary term, which
arises in the first variation of a local diffeomorphism invariant action, is
covariantly conserved for any gravity theory described by that action.
Therefore, a Poincare invariant 2-form can be constructed on the phase space,
which is shown to be closed without reference to a specific theory. Finally, we
show that one can obtain a charge expression for gravity theories in various
dimensions, which plays the role of the Abbott-Deser-Tekin (ADT) charge for
spacetimes with non-constant curvature backgrounds, by using the diffeomorphism
invariance of the symplectic 2-form. As an example, we calculate the conserved
charges of some solutions of New Massive Gravity (NMG) and compare the results
with the previous works.Comment: 18 pages, No figures, RevTEX4.1; ver 2: minor corrections, version
accepted for publication in Physical Review
Pre-multisymplectic constraint algorithm for field theories
We present a geometric algorithm for obtaining consistent solutions to
systems of partial differential equations, mainly arising from singular
covariant first-order classical field theories. This algorithm gives an
intrinsic description of all the constraint submanifolds.
The field equations are stated geometrically, either representing their
solutions by integrable connections or, what is equivalent, by certain kinds of
integrable m-vector fields. First, we consider the problem of finding
connections or multivector fields solutions to the field equations in a general
framework: a pre-multisymplectic fibre bundle (which will be identified with
the first-order jet bundle and the multimomentum bundle when Lagrangian and
Hamiltonian field theories are considered). Then, the problem is stated and
solved in a linear context, and a pointwise application of the results leads to
the algorithm for the general case. In a second step, the integrability of the
solutions is also studied.
Finally, the method is applied to Lagrangian and Hamiltonian field theories
and, for the former, the problem of finding holonomic solutions is also
analized.Comment: 30 pp. Presented in the International Workshop on Geometric Methods
in Modern Physics (Firenze, April 2005
Semiclassical states for quantum cosmology
In a metric variable based Hamiltonian quantization, we give a prescription
for constructing semiclassical matter-geometry states for homogeneous and
isotropic cosmological models. These "collective" states arise as infinite
linear combinations of fundamental excitations in an unconventional "polymer"
quantization. They satisfy a number of properties characteristic of
semiclassicality, such as peaking on classical phase space configurations. We
describe how these states can be used to determine quantum corrections to the
classical evolution equations, and to compute the initial state of the universe
by a backward time evolution.Comment: 13 page
On the Hamilton-Jacobi Theory for Singular Lagrangian Systems
We develop a Hamilton-Jacobi theory for singular lagrangian systems using the
Gotay-Nester-Hinds constraint algorithm. The procedure works even if the system
has secondary constraints.Comment: 36 page
Symmetries in Classical Field Theory
The multisymplectic description of Classical Field Theories is revisited,
including its relation with the presymplectic formalism on the space of Cauchy
data. Both descriptions allow us to give a complete scheme of classification of
infinitesimal symmetries, and to obtain the corresponding conservation laws.Comment: 70S05; 70H33; 55R10; 58A2
Parametrization and Stress-Energy-Momentum Tensors in Metric Field Theories
We give an exposition of the parametrization method of Kuchar [1973] in the
context of the multisymplectic approach to field theory, as presented in Gotay
and Marsden [2008a]. The purpose of the formalism developed herein is to make
any classical field theory, containing a metric as a sole background field,
generally covariant (that is, "parametrized," with the spacetime diffeomorphism
group as a symmetry group) as well as fully dynamic. This is accomplished by
introducing certain "covariance fields" as genuine dynamic fields. As we shall
see, the multimomenta conjugate to these new fields form the Piola-Kirchhoff
version of the stress-energy-momentum tensor field, and their Euler-Lagrange
equations are vacuously satisfied. Thus, these fields have no additional
physical content; they serve only to provide an efficient means of
parametrizing the theory. Our results are illustrated with two examples, namely
an electromagnetic field and a Klein-Gordon vector field, both on a background
spacetime.Comment: 13 pages, 1 figur
Use of complementary and alternative medicine in Hawaii cancer patients.
This research investigated complementary and alternative medicine (CAM) use by Hawaii cancer patients. Thirty-six percent of patients used CAM, most commonly religious/spiritual therapy and herbal treatments. CAM use was linked with younger age, female gender, Catholic religion, and more education. More research is needed to inform decision-making.R01 CA 61711/CA/NCI NIH HHS/United StatesR01 CA 64045/CA/NCI NIH HHS/United State
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