13,939 research outputs found
Abelian Landau-Pomeranchuk-Migdal effects
It is shown that the high-energy expansion of the scattering amplitude
calculated from Feynman diagrams factorizes in such a way that it can be
reduced to the eikonalized form up to the terms of inverse power in energy in
accordance with results obtained by solving the Klein-Gordon equation.
Therefore the two approaches when applied to the suppression of the emission of
soft photons by fast charged particles in dense matter should give rise to the
same results. A particular limit of thin targets is briefly discussed.Comment: 14 pages, LATEX, 1 Fig. ps, submitted to Mod. Phys. Lett.
Multiple Reggeon Exchange from Summing QCD Feynman Diagrams
Multiple reggeon exchange supplies subleading logs that may be used to
restore unitarity to the Low-Nussinov Pomeron, provided it can be proven that
the sum of Feynman diagrams to all orders gives rise to such multiple regge
exchanges. This question cannot be easily tackled in the usual way except for
very low-order diagrams, on account of delicate cancellations present in the
sum which necessitate individual Feynman diagrams to be computed to subleading
orders. Moreover, it is not clear that sums of high-order Feynman diagrams with
complicated criss-crossing of lines can lead to factorization implied by the
multi-regge scenario. Both of these difficulties can be overcome by using the
recently developed nonabelian cut diagrams. We are then able to show that the
sum of -channel-ladder diagrams to all orders does lead to such multiple
reggeon exchanges.Comment: uu-encoded latex file with 11 postscript figures (20 pages
Combinatorial Hopf algebras and Towers of Algebras
Bergeron and Li have introduced a set of axioms which guarantee that the
Grothendieck groups of a tower of algebras can be
endowed with the structure of graded dual Hopf algebras. Hivert and Nzeutzhap,
and independently Lam and Shimozono constructed dual graded graphs from
primitive elements in Hopf algebras. In this paper we apply the composition of
these constructions to towers of algebras. We show that if a tower
gives rise to graded dual Hopf algebras then we must
have where .Comment: 7 page
The Absorptive Extra Dimensions
It is well known that gravity and neutrino oscillation can be used to probe
large extra dimensions in a braneworld scenario. We argue that neutrino
oscillation remains a useful probe even when the extra dimensions are small,
because the brane-bulk coupling is likely to be large. Neutrino oscillation in
the presence of a strong brane-bulk coupling is vastly different from the usual
case of a weak coupling. In particular, some active neutrinos could be absorbed
by the bulk when they oscillate from one kind to another, a signature which can
be taken as the presence of an extra dimension. In a very large class of models
which we shall discuss, the amount of absorption for all neutrino oscillations
is controlled by a single parameter, a property which distinguishes extra
dimensions from other mechanisms for losing neutrino fluxes.Comment: Introduction enlarged; conclusions added. To appear in Phys. Rev.
Computation of saddle type slow manifolds using iterative methods
This paper presents an alternative approach for the computation of trajectory
segments on slow manifolds of saddle type. This approach is based on iterative
methods rather than collocation-type methods. Compared to collocation methods,
that require mesh refinements to ensure uniform convergence with respect to
, appropriate estimates are directly attainable using the method of
this paper. The method is applied to several examples including: A model for a
pair of neurons coupled by reciprocal inhibition with two slow and two fast
variables and to the computation of homoclinic connections in the
FitzHugh-Nagumo system.Comment: To appear in SIAM Journal of Applied Dynamical System
Once again on the equivalence theorem
We present the proof of the equivalence theorem in quantum field theory which
is based on a formulation of this problem in the field-antifield formalism. As
an example, we consider a model in which a different choices of natural finite
counterterms is possible, leading to physically non-equivalent quantum theories
while the equivalent theorem remains valid.Comment: 12 pages, LATEX, report number was correcte
Obstructing extensions of the functor Spec to noncommutative rings
In this paper we study contravariant functors from the category of rings to
the category of sets whose restriction to the full subcategory of commutative
rings is isomorphic to the prime spectrum functor Spec. The main result reveals
a common characteristic of these functors: every such functor assigns the empty
set to M_n(C) for n >= 3. The proof relies, in part, on the Kochen-Specker
Theorem of quantum mechanics. The analogous result for noncommutative
extensions of the Gelfand spectrum functor for C*-algebras is also proved.Comment: 23 pages. To appear in Israel J. Math. Title was changed;
introduction was rewritten; old Section 2 was removed to streamline the
exposition; final section was rewritten to omit an error in the earlier proof
of Theorem 1.
A phase III wait-listed randomised controlled trial of novel targeted inter-professional clinical education intervention to improve cancer patients' reported pain outcomes (The Cancer Pain Assessment (CPAS) Trial): Study protocol
© 2019 The Author(s). Background: Variations in care models contribute to cancer pain being under-recognised and under-treated in half of all patients with cancer. International and national cancer pain management guidelines are achievable with minimal investment but require practice changes. While much of the cancer pain research over the preceding decades has focused on management interventions, little attention has been given to achieving better adherence to recommended cancer pain guideline screening and assessment practices. This trial aims to reduce unrelieved cancer pain by improving cancer and palliative doctors' and nurses' ('clinicians') pain assessment capabilities through a targeted inter-professional clinical education intervention delivered to participants' mobile devices ('mHealth'). Methods: A wait-listed, randomised control trial design. Cancer and/or palliative care physicians and nurses employed at one of the six participating sites across Australia will be eligible to participate in this trial and, on enrolment, will be allocated to the active or wait-listed arm. Participants allocated to the active arm will be invited to complete the mHealth cancer pain assessment intervention. In this trial, mHealth is defined as medical or public health practice supported by mobile devices (i.e. phones, patient monitoring devices, personal digital assistants and other wireless devices). This mHealth intervention integrates three evidence-based elements, namely: the COM-B theoretical framework; spaced learning pedagogy; and audit and feedback. This intervention will be delivered via the QStream online platform to participants' mobile devices over four weeks. The trial will determine if a tailored mHealth intervention, targeting clinicians' cancer pain assessment capabilities, is effective in reducing self-reported cancer pain scores, as measured by a Numerical Rating Scale (NRS). Discussion: If this mHealth intervention is found to be effective, in addition to improving cancer pain assessment practices, it will provide a readily transferable evidence-based framework that could readily be applied to other evidence practice gaps and a scalable intervention that could be administered simultaneously to multiple clinicians across diverse geographical locations. Moreover, if found to be cost-effective, it will help transform clinical continuing professional development. In summary, this mHealth intervention will provide health services with an opportunity to offer an evidence-based, pedagogically robust, cost-effective, scalable training alternative. Trial registration: Australian New Zealand Clinical Trials Registry (ANZCTR), ACTRN12618001103257. Registered on 3 July 2018
Two-soliton solution for the derivative nonlinear Schr\"odinger equation with nonvanishing boundary conditions
An explicit two-soliton solution for the derivative nonlinear Schr\"odinger
equation with nonvanishing boundary conditions is derived, demonstrating
details of interactions between two bright solitons, two dark solitons, as well
as one bright soliton and one dark soliton. Shifts of soliton positions due to
collisions are analytically obtained, which are irrespective of the bright or
dark characters of the participating solitons.Comment: 11 pages, 4 figures. Phys. Lett. A 2006 (in press
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