39 research outputs found
Investigation of a0-f0 mixing
We investigate the isospin-violating mixing of the light scalar mesons
a0(980) and f0(980) within the unitarized chiral approach. Isospin-violating
effects are considered to leading order in the quark mass differences and
electromagnetism. In this approach both mesons are generated through
meson-meson dynamics. Our results provide a description of the mixing
phenomenon within a framework consistent with chiral symmetry and unitarity,
where these resonances are not predominantly q q-bar states. Amongst the
possible experimental signals, we discuss observable consequences for the
reaction J/Psi -> phi pi0 eta in detail. In particular we demonstrate that the
effect of a0-f0 mixing is by far the most important isospin-breaking effect in
the resonance region and can indeed be extracted from experiment.Comment: 15 pages, 9 figures; discussion extended, title changed, version
published in Phys. Rev.
Ultra-High Energy Cosmic Rays and Stable H-dibaryon
It is shown that an instanton induced interaction between quarks produces a
very deeply bound H-dibaryon with mass below 2M_N, M_H=1718 MeV. Therefore the
H-dibaryon is predicted to be a stable particle. The reaction of
photodisintegration of H-dibaryon to in during of its penetration
into cosmic microwave background will result in a new possible cut-off in the
cosmic-ray spectrum. This provides an explanation of ultra-high energy cosmic
ray events observed above the GZK cut-off as a result of the strong interaction
of high energy H-dibaryons from cosmic rays with nuclei in Earth's atmosphere.Comment: 5 pages, Late
Cosmological mass limits on neutrinos, axions, and other light particles
The small-scale power spectrum of the cosmological matter distribution
together with other cosmological data provides a sensitive measure of the hot
dark matter fraction, leading to restrictive neutrino mass limits. We extend
this argument to generic cases of low-mass thermal relics. We vary the cosmic
epoch of thermal decoupling, the radiation content of the universe, and the new
particle's spin degrees of freedom. Our treatment covers various scenarios of
active plus sterile neutrinos or axion-like particles. For three degenerate
massive neutrinos, we reproduce the well-known limit of m_nu < 0.34 eV. In a
3+1 scenario of 3 massless and 1 fully thermalized sterile neutrino we find
m_nu < 1.0 eV. Thermally produced QCD axions must obey m_a < 3.0 eV,
superseding limits from a direct telescope search, but leaving room for solar
eV-mass axions to be discovered by the CAST experiment.Comment: 15 pages, 6 figures, matches version in JCA
Casimir Effects in Renormalizable Quantum Field Theories
We review the framework we and our collaborators have developed for the study
of one-loop quantum corrections to extended field configurations in
renormalizable quantum field theories. We work in the continuum, transforming
the standard Casimir sum over modes into a sum over bound states and an
integral over scattering states weighted by the density of states. We express
the density of states in terms of phase shifts, allowing us to extract
divergences by identifying Born approximations to the phase shifts with low
order Feynman diagrams. Once isolated in Feynman diagrams, the divergences are
canceled against standard counterterms. Thus regulated, the Casimir sum is
highly convergent and amenable to numerical computation. Our methods have
numerous applications to the theory of solitons, membranes, and quantum field
theories in strong external fields or subject to boundary conditions.Comment: 27 pp., 11 EPS figures, LaTeX using ijmpa1.sty; email correspondence
to R.L. Jaffe ; based on talks presented by the authors at
the 5th workshop `QFTEX', Leipzig, September 200
On impact parameter dependence of low-x structure functions
We consider impact parameter dependence of the polarized and unpolarized
structure functions. Unitarity does not allow factorization of the structure
functions over the Bjorken x and the impact parameter b variables. On the basis
of the particular geometrical model approach we conclude that spin of
constituent quark may have a significant orbital angular momentum component
which can manifest itself through the peripherality of the spin dependent
structure functions.Comment: 5 pages, 1 figur
Hyperon-Nucleon Final State Interaction in Kaon Photoproduction of the Deuteron
Final state hyperon-nucleon interaction in strangeness photoproduction of the
deuteron is investigated making use of the covariant reaction formalism and the
P-matrix approach to the YN system. Remarkably simple analytical expression for
the amplitude is obtained. Pronounced effects due to final state interaction
are predicted including the manifestation of the 2.13 GeV resonance.Comment: LaTeX, 13 page
Signatures of Relativistic Neutrinos in CMB Anisotropy and Matter Clustering
We present a detailed analytical study of ultra-relativistic neutrinos in
cosmological perturbation theory and of the observable signatures of
inhomogeneities in the cosmic neutrino background. We note that a modification
of perturbation variables that removes all the time derivatives of scalar
gravitational potentials from the dynamical equations simplifies their solution
notably. The used perturbations of particle number per coordinate, not proper,
volume are generally constant on superhorizon scales. In real space an
analytical analysis can be extended beyond fluids to neutrinos.
The faster cosmological expansion due to the neutrino background changes the
acoustic and damping angular scales of the cosmic microwave background (CMB).
But we find that equivalent changes can be produced by varying other standard
parameters, including the primordial helium abundance. The low-l integrated
Sachs-Wolfe effect is also not sensitive to neutrinos. However, the gravity of
neutrino perturbations suppresses the CMB acoustic peaks for the multipoles
with l>~200 while it enhances the amplitude of matter fluctuations on these
scales. In addition, the perturbations of relativistic neutrinos generate a
*unique phase shift* of the CMB acoustic oscillations that for adiabatic
initial conditions cannot be caused by any other standard physics. The origin
of the shift is traced to neutrino free-streaming velocity exceeding the sound
speed of the photon-baryon plasma. We find that from a high resolution, low
noise instrument such as CMBPOL the effective number of light neutrino species
can be determined with an accuracy of sigma(N_nu) = 0.05 to 0.09, depending on
the constraints on the helium abundance.Comment: 38 pages, 7 figures. Version accepted for publication in PR
Probing neutrino masses with future galaxy redshift surveys
We perform a new study of future sensitivities of galaxy redshift surveys to
the free-streaming effect caused by neutrino masses, adding the information on
cosmological parameters from measurements of primary anisotropies of the cosmic
microwave background (CMB). Our reference cosmological scenario has nine
parameters and three different neutrino masses, with a hierarchy imposed by
oscillation experiments. Within the present decade, the combination of the
Sloan Digital Sky Survey (SDSS) and CMB data from the PLANCK experiment will
have a 2-sigma detection threshold on the total neutrino mass close to 0.2 eV.
This estimate is robust against the inclusion of extra free parameters in the
reference cosmological model. On a longer term, the next generation of
experiments may reach values of order sum m_nu = 0.1 eV at 2-sigma, or better
if a galaxy redshift survey significantly larger than SDSS is completed. We
also discuss how the small changes on the free-streaming scales in the normal
and inverted hierarchy schemes are translated into the expected errors from
future cosmological data.Comment: 14 pages, 7 figures. Added results with the KAOS proposal and 1
referenc