821 research outputs found
Gauging Newton's Law
We derive both Lagrangian and Hamiltonian mechanics as gauge theories of
Newtonian mechanics. Systematic development of the distinct symmetries of
dynamics and measurement suggest that gauge theory may be motivated as a
reconciliation of dynamics with measurement. Applying this principle to
Newton's law with the simplest measurement theory leads to Lagrangian
mechanics, while use of conformal measurement theory leads to Hamilton's
equations.Comment: 44 pages, no figures, LaTe
Dilatation of saphenous vein grafts by nitric oxide
Objectives:To investigate firstly whether flow-dependent vasodilation is maintained in vein grafts, and secondly whether nitric oxide donors dilate vein grafts to improve the flow through graft stenoses.Design, materials and methods:The vasodilatation of mature patent vein grafts, in response to reactive hyperaemia and glyceryl trinitrate (GTN), was assessed by the change in external diameter using duplex ultrasonography. The severity (ratio of proximal systolic velocity, V1, to peak systolic velocity at the stenosis, V2, of vein graft stenoses was determined by duplex ultrasonography before and after 24 h of local application of GTN patches.Results:In post-occlusion hyperaemia the diameter of patent distal vein grafts (n = 7) increased to a maximum of 112±1.9% of resting diameter after 2 min, p = 0.026. The diameter increased further to 117±2.5% of the resting value 5 min after oral GTN (n = 5), p = 0.007. The velocity ratio, V2/V1, through graft stenoses (n = 6) decreased by 20 ± 5% after application of GTN patches, principally as a result of reduction in V2, mean difference 0.8, p = 0.15. The changes in response to GTN were more evident for proximal than distal vein graft stenoses.Conclusion:Flow-induced vasodilatation responses, which have been attributed to the endothelial release of nitric oxide, are maintained in patent vein grafts: the grafts dilate even further in response to GTN. The application of GTN patches close to a vein graft stenosis appears to reduce the velocity ratio through vein graft stenoses. GTN patches might be used to reduce the risk of graft occlusion when there is a delay between the detection and the treatment of haemodynamically significant graft stenoses
Light Unstable Sterile Neutrino
The three massless active (doublet) neutrinos may mix with two heavy and one
\underline {light} sterile (singlet) neutrinos so that the induced masses and
mixings among the former are able to explain the present data on atmospheric
and solar neutrino oscillations. If the LSND result is also to be explained,
one active neutrino mass eigenstate must mix with the light sterile neutrino. A
specific model is proposed with the spontaneous and soft explicit breaking of a
new global symmetry so that a sterile neutrino will decay into an
active antineutrino and a nearly massless pseudo-Majoron.Comment: Discussion and references adde
A two-mass expanding exact space-time solution
In order to understand how locally static configurations around
gravitationally bound bodies can be embedded in an expanding universe, we
investigate the solutions of general relativity describing a space-time whose
spatial sections have the topology of a 3-sphere with two identical masses at
the poles. We show that Israel junction conditions imply that two spherically
symmetric static regions around the masses cannot be glued together. If one is
interested in an exterior solution, this prevents the geometry around the
masses to be of the Schwarzschild type and leads to the introduction of a
cosmological constant. The study of the extension of the Kottler space-time
shows that there exists a non-static solution consisting of two static regions
surrounding the masses that match a Kantowski-Sachs expanding region on the
cosmological horizon. The comparison with a Swiss-Cheese construction is also
discussed.Comment: 15 pages, 5 figures. Replaced to match the published versio
Axions and their Relatives
A review of the status of axions and axion-like particles is given. Special
attention is devoted to the recent results of the PVLAS collaboration, which
are in conflict with the CAST data and with the astrophysical constraints.
Solutions to the puzzle and the implications for new physics are discussed. The
question of axion-like particles being dark matter is also addressed.Comment: Updated version of an invited talk at the Axion Training (CERN,
December 2005). To appear as a Lecture Notes in Physics (Springer-Verlag),
edited by B. Beltran, M. Kuster and G. Raffel
Validity of Flavor Symmetry and Charge Symmetry for Parton Distributions
Recent experimental measurements of the Gottfried Sum Rule, and pp and pD
Drell-Yan processes, suggest significant violation of flavor symmetry in the
proton sea. This interpretation rests on the assumption of parton charge
symmetry. Our model calculations suggest charge symmetry violation [CSV] for
parton valence distributions of a few percent. Precision measurements of
structure functions in muon and neutrino experiments allow us to set rather
stringent experimental limits on CSV in certain kinematic regions. In another
region, these experiments suggest substantial CSV effects. We suggest
experiments which could test parton CSV.Comment: 8 pages, 4 figures, talk at Workshop on Future Directions in
Quark-Nuclear Physics, Center for the Subatomic Structure of Matter,
Adelaide, Australia, Mar 9-20, 1998, to appear in conference proceeding
The reaction in ion-ion collisions
We study the threshold -meson production in the process , which appears as a possible important mechanism in high energy
nuclei-nuclei collisions. The isotopic invariance of the strong interaction and
the selection rules due to P-parity and total angular momentum result in a
general and model independent parametrization of the spin structure of the
matrix element in terms of three partial amplitudes. In the framework of
one-pion exchange model these amplitudes can be derived in terms of the two
threshold partial amplitudes for the process . We predict the
ratio of cross sections for meson production in - and -collisions and the polarization properties of the -meson, in
, as a function of a single parameter, which
characterizes the relative role of transversal and longitudinal -meson
polarizations in the process .Comment: 10 pages 3 figure
Indirect search for dark matter: prospects for GLAST
Possible indirect detection of neutralino, through its gamma-ray annihilation
product, by the forthcoming GLAST satellite from our galactic halo, M31, M87
and the dwarf galaxies Draco and Sagittarius is studied. Gamma-ray fluxes are
evaluated for the two representative energy thresholds, 0.1 GeV and 1.0 GeV, at
which the spatial resolution of GLAST varies considerably. Apart from dwarfs
which are described either by a modified Plummer profile or by a
tidally-truncated King profiles, fluxes are compared for halos with central
cusps and cores. It is demonstrated that substructures, irrespective of their
profiles, enhance the gamma-ray emission only marginally. The expected
gamma-ray intensity above 1 GeV at high galactic latitudes is consistent with
the residual emission derived from EGRET data if the density profile has a
central core and the neutralino mass is less than 50 GeV, whereas for a central
cusp only a substantial enhancement would explain the observations. From M31,
the flux can be detected above 0.1 GeV and 1.0 GeV by GLAST only if the
neutralino mass is below 300 GeV and if the density profile has a central cusp,
case in which a significant boost in the gamma-ray emission is produced by the
central black hole. For Sagittarius, the flux above 0.1 GeV is detectable by
GLAST provided the neutralino mass is below 50 GeV. From M87 and Draco the
fluxes are always below the sensitivity limit of GLAST.Comment: 14 Pages, 7 Figures, 3 Tables, version to appear on Physical Review
Partial Deconfinement in Color Superconductivity
We analyze the fate of the unbroken SU(2) color gauge interactions for 2
light flavors color superconductivity at non zero temperature. Using a simple
model we compute the deconfining/confining critical temperature and show that
is smaller than the critical temperature for the onset of the superconductive
state itself. The breaking of Lorentz invariance, induced already at zero
temperature by the quark chemical potential, is shown to heavily affect the
value of the critical temperature and all of the relevant features related to
the deconfining transition. Modifying the Polyakov loop model to describe the
SU(2) immersed in the diquark medium we argue that the deconfinement transition
is second order. Having constructed part of the equation of state for the 2
color superconducting phase at low temperatures our results are relevant for
the physics of compact objects featuring a two flavor color superconductive
state.Comment: 9 pp, 4 eps-figs, version to appear in PR
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