141 research outputs found
Direct Force In High Momentum Limit of QCD For Proton Physics
An explicit construction of the proton wave function is outlined in the high
momentum limit of QCD dominated by a direct force, one generated by
hooking the ends of a vertex to 3 distinct vertices, thus
making up a -shaped diagram (see fig.1). The high degree of symmetry
thus involved ensures that the wave function is a mixture of
and components, rather than the traditional and
type. Some results of this paradigm shift are offered.Comment: 6 pages, Presented at 4th International Symposium on Symmetries in
Subatomic Physics at NTU, Taipei, 200
MarKov-Yukawa Transversality On Covariant Null Plane: Pion Form Factor, Gauge Invariance And Lorentz Completion
The Markov-Yukawa Transversality Principle (MYTP) on a 2-body Bethe-Salpeter
kernel is formulated on a covariant Null Plane (NP) to reconstruct the 4D BS
wave function for 2 fermion quarks in terms of 3D entities that satisfy a 3D
BSE. This result is the null-plane counterpart of a 3D-4D interconnection for
the 2-body BS wave functions found earlier by imposing MYTP covariantly in the
instantaneous rest frame (termed CIA) of the composite. This formulation yields
a 3D BSE which is formally identical to its Covariant Instantaneity form, thus
fully preserving its spectral results, while ensuring full covariance. More
importantly, the reconstructed 4D vertex functions in the covariant null-plane
ensure that 4D quark-loops are now free from ill-defined time-like momentum
integrations (which had plagued the earlier CIA vertex functions), while a
simple prescription of `Lorentz completion' in the new description yields a
manifestly Lorentz-invariant result.This is illustrated for the pion and kaon
form factors with full QED gauge-invariance, showing a behaviour at
large , and `correct' slopes at small . This method is compared with
the Kadychevsky-Karmanov light-front formalism.Comment: 17 pages, Late
Center of mass integral in canonical general relativity
For a two-surface B tending to an infinite--radius round sphere at spatial
infinity, we consider the Brown--York boundary integral H_B belonging to the
energy sector of the gravitational Hamiltonian. Assuming that the lapse
function behaves as N \sim 1 in the limit, we find agreement between H_B and
the total Arnowitt--Deser--Misner energy, an agreement first noted by Braden,
Brown, Whiting, and York. However, we argue that the Arnowitt--Deser--Misner
mass--aspect differs from a gauge invariant mass--aspect by a pure divergence
on the unit sphere. We also examine the boundary integral H_B corresponding to
the Hamiltonian generator of an asymptotic boost, in which case the lapse N
\sim x^k grows like one of the asymptotically Cartesian coordinate functions.
Such an integral defines the kth component of the center of mass for a Cauchy
surface \Sigma bounded by B. In the large--radius limit, we find agreement
between H_B and an integral introduced by Beig and O'Murchadha. Although both
H_B and the Beig--O'Murchadha integral are naively divergent, they are in fact
finite modulo the Hamiltonian constraint. Furthermore, we examine the
relationship between H_B and a certain two--surface integral linear in the
spacetime Riemann curvature tensor. Similar integrals featuring the curvature
appear in works by Ashtekar and Hansen, Penrose, Goldberg, and Hayward. Within
the canonical 3+1 formalism, we define gravitational energy and
center--of--mass as certain moments of Riemann curvature.Comment: 52 pages, revtex4, uses amsmath and amssym
Is the evidence for dark energy secure?
Several kinds of astronomical observations, interpreted in the framework of
the standard Friedmann-Robertson-Walker cosmology, have indicated that our
universe is dominated by a Cosmological Constant. The dimming of distant Type
Ia supernovae suggests that the expansion rate is accelerating, as if driven by
vacuum energy, and this has been indirectly substantiated through studies of
angular anisotropies in the cosmic microwave background (CMB) and of spatial
correlations in the large-scale structure (LSS) of galaxies. However there is
no compelling direct evidence yet for (the dynamical effects of) dark energy.
The precision CMB data can be equally well fitted without dark energy if the
spectrum of primordial density fluctuations is not quite scale-free and if the
Hubble constant is lower globally than its locally measured value. The LSS data
can also be satisfactorily fitted if there is a small component of hot dark
matter, as would be provided by neutrinos of mass 0.5 eV. Although such an
Einstein-de Sitter model cannot explain the SNe Ia Hubble diagram or the
position of the `baryon acoustic oscillation' peak in the autocorrelation
function of galaxies, it may be possible to do so e.g. in an inhomogeneous
Lemaitre-Tolman-Bondi cosmology where we are located in a void which is
expanding faster than the average. Such alternatives may seem contrived but
this must be weighed against our lack of any fundamental understanding of the
inferred tiny energy scale of the dark energy. It may well be an artifact of an
oversimplified cosmological model, rather than having physical reality.Comment: 12 pages, 5 figures; to appear in a special issue of General
Relativity and Gravitation, eds. G.F.R. Ellis et al; Changes: references
reformatted in journal style - text unchange
phase shifts and CP Violation in Decay
In the study of CP violation signals in {\O}\to\pi\Xi nonleptonic decays,
the strong =3/2 and phase shifts for the final-state
interactions are needed. These phases are calculated using an effective
Lagrangian model, including , (1530), and the -term,
in the intermediate states. The -term is calculated in terms of the
scalar form factor of the baryon.Comment: 6 pages, 2 figure
Coherent information analysis of quantum channels in simple quantum systems
The coherent information concept is used to analyze a variety of simple
quantum systems. Coherent information was calculated for the information decay
in a two-level atom in the presence of an external resonant field, for the
information exchange between two coupled two-level atoms, and for the
information transfer from a two-level atom to another atom and to a photon
field. The coherent information is shown to be equal to zero for all
full-measurement procedures, but it completely retains its original value for
quantum duplication. Transmission of information from one open subsystem to
another one in the entire closed system is analyzed to learn quantum
information about the forbidden atomic transition via a dipole active
transition of the same atom. It is argued that coherent information can be used
effectively to quantify the information channels in physical systems where
quantum coherence plays an important role.Comment: 24 pages, 7 figs; Final versiob after minor changes, title changed;
to be published in Phys. Rev. A, September 200
A Dynamical Principle For 3D-4D Interlinkage In Salpeter-like Equations
The half-century old Markov-Yukawa Transversality Principle () which
provides a theoretical rationale for the covariant instantaneous approximation
() that underlies all Salpeter-like equations, is generalized to a
covariant null-plane ansatz (). A common characteristic of both
formulations is an exact 3D-4D interlinkage of BS amplitudes which facilitates
a two-tier description: the 3D form for spectroscopy, and the 4D form for
transition amplitudes as 4D loop integrals. Some basic applications of
on the covariant null plane (quark mass function, vacuum condensates, and decay
constants) are given on the lines of earlier applications to these processes
under .
PACS: 03.65.-w ; 03.65.Co ; 11.10.Qr ; 11.10.St
Keywords: Markov-Yukawa Transversality Principle (); Salpeter-like eqs;
Cov Instantaneity Ansatz (); Cov Null-Plane Ansatz (); 3D-4D
interlinkage; Vertex function; 4D loopsComment: LaTeX file, 25 pages, to be published in Nuclear Phys.
Energy and decay width of the pi-K atom
The energy and decay width of the pi-K atom are evaluated in the framework of
the quasipotential-constraint theory approach. The main electromagnetic and
isospin symmetry breaking corrections to the lowest-order formulas for the
energy shift from the Coulomb binding energy and for the decay width are
calculated. They are estimated to be of the order of a few per cent. We display
formulas to extract the strong interaction S-wave pi-K scattering lengths from
future experimental data concerning the pi-K atom.Comment: 37 pages, 5 figures, uses Axodra
Effective Lagrangian Approach to the Theory of Eta Photoproduction in the Region
We investigate eta photoproduction in the resonance region
within the effective Lagrangian approach (ELA), wherein leading contributions
to the amplitude at the tree level are taken into account. These include the
nucleon Born terms and the leading -channel vector meson exchanges as the
non-resonant pieces. In addition, we consider five resonance contributions in
the - and - channel; besides the dominant , these are:
and . The amplitudes for the
and the photoproduction near threshold have significant
differences, even as they share common contributions, such as those of the
nucleon Born terms. Among these differences, the contribution to the
photoproduction of the -channel excitation of the is the most
significant. We find the off-shell properties of the spin-3/2 resonances to be
important in determining the background contributions. Fitting our effective
amplitude to the available data base allows us to extract the quantity
, characteristic of the
photoexcitation of the resonance and its decay into the
-nucleon channel, of interest to precise tests of hadron models. At the
photon point, we determine it to be from
the old data base, and from a
combination of old data base and new Bates data. We obtain the helicity
amplitude for to be from the old data base, and from the combination of the old data base and new Bates
data, compared with the results of the analysis of pion photoproduction
yielding , in the same units.Comment: 43 pages, RevTeX, 9 figures available upon request, to appear in
Phys. Rev.
Radiative Decay of a Long-Lived Particle and Big-Bang Nucleosynthesis
The effects of radiatively decaying, long-lived particles on big-bang
nucleosynthesis (BBN) are discussed. If high-energy photons are emitted after
BBN, they may change the abundances of the light elements through
photodissociation processes, which may result in a significant discrepancy
between the BBN theory and observation. We calculate the abundances of the
light elements, including the effects of photodissociation induced by a
radiatively decaying particle, but neglecting the hadronic branching ratio.
Using these calculated abundances, we derive a constraint on such particles by
comparing our theoretical results with observations. Taking into account the
recent controversies regarding the observations of the light-element
abundances, we derive constraints for various combinations of the measurements.
We also discuss several models which predict such radiatively decaying
particles, and we derive constraints on such models.Comment: Published version in Phys. Rev. D. Typos in figure captions correcte
- …