2,078 research outputs found
Off shell -symmetry of the superparticle and the spinning superparticle
The spinorial local world-line -symmetry of the covariant
Brink-Schwarz formulation of the 4- superparticle is abelian in an off-shell
phase-space formulation. The result is shown to generalize to the extended
spinorial transformations of the spinning superparticle.Comment: 9 pages, no fig
Nucleon Structure from Lattice QCD Using a Nearly Physical Pion Mass
We report the first Lattice QCD calculation using the almost physical pion
mass mpi=149 MeV that agrees with experiment for four fundamental isovector
observables characterizing the gross structure of the nucleon: the Dirac and
Pauli radii, the magnetic moment, and the quark momentum fraction. The key to
this success is the combination of using a nearly physical pion mass and
excluding the contributions of excited states. An analogous calculation of the
nucleon axial charge governing beta decay has inconsistencies indicating a
source of bias at low pion masses not present for the other observables and
yields a result that disagrees with experiment.Comment: journal version; 15 pages, 6 figure
The Structure of D2-Branes in the Presence of an RR field
A Born--Infeld theory describing a --brane coupled to a 3--form RR
potential is reconsidered and a new type of static solution is obtained which
is even stable.Comment: 11 pages, 2 postscript figures, v2 a significantly revised including
title, v3 expression of energy for D2 brane is improved, version to appear in
JHE
Oxygen mapping of melanoma spheroids using small molecule platinum probe and phosphorescence lifetime imaging microscopy
Solid tumours display varied oxygen levels and this characteristic can be exploited to develop new diagnostic tools to determine and exploit these variations. Oxygen is an efficient quencher of emission of many phosphorescent compounds, thus oxygen concentration could in many cases be derived directly from relative emission intensity and lifetime. In this study, we extend our previous work on phosphorescent, low molecular weight platinum(II) complex as an oxygen sensing probe to study the variation in oxygen concentration in a viable multicellular 3D human tumour model. The data shows one of the first examples of non-invasive, real-time oxygen mapping across a melanoma tumour spheroid using one-photon phosphorescence lifetime imaging microscopy (PLIM) and a small molecule oxygen sensitive probe. These measurements were quantitative and enabled real time oxygen mapping with high spatial resolution. This combination presents as a valuable tool for optical detection of both physiological and pathological oxygen levels in a live tissue mass and we suggest has the potential for broader clinical application
Charge Conjugation Invariance of the Vacuum and the Cosmological Constant Problem
We propose a method of field quantization which uses an indefinite metric in
a Hilbert space of state vectors. The action for gravity and the standard model
includes, as well as the positive energy fermion and boson fields, negative
energy fields. The Hamiltonian for the action leads through charge conjugation
invariance symmetry of the vacuum to a cancellation of the zero-point vacuum
energy and a vanishing cosmological constant in the presence of a gravitational
field. To guarantee the stability of the vacuum, we introduce a Dirac sea
`hole' theory of quantization for gravity as well as the standard model. The
vacuum is defined to be fully occupied by negative energy particles with a hole
in the Dirac sea, corresponding to an anti-particle. We postulate that the
negative energy bosons in the vacuum satisfy a para-statistics that leads to a
para-Pauli exclusion principle for the negative energy bosons in the vacuum,
while the positive energy bosons in the Hilbert space obey the usual
Bose-Einstein statistics. This assures that the vacuum is stable for both
fermions and bosons. Restrictions on the para-operator Hamiltonian density lead
to selection rules that prohibit positive energy para-bosons from being
observable. The problem of deriving a positive energy spectrum and a consistent
unitary field theory from a pseudo-Hermitian Hamiltonian is investigated.Comment: 15 pages, Latex file, no figures. Typos corrected. To be published in
Physics Letters
The Matter and the Pseudoscalar Densities in Lattice QCD
The matter and the pseudoscalar densities inside a hadron are calculated via
gauge-invariant equal-time correlation functions. A comparison is made between
the charge charge and the matter density distributions for the pion, the rho,
the nucleon and the within the quenched theory, and with two
flavours of dynamical quarks.Comment: Typos corrected; 13 pages, 16 figure
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