9,941 research outputs found
Further search for a neutral boson with a mass around 9 MeV/c2
Two dedicated experiments on internal pair conversion (IPC) of isoscalar M1
transitions were carried out in order to test a 9 MeV/c2 X-boson scenario. In
the 7Li(p,e+e-)8Be reaction at 1.1 MeV proton energy to the predominantly T=0
level at 18.15 MeV, a significant deviation from IPC was observed at large pair
correlation angles. In the 11B(d,n e+e-)12C reaction at 1.6 MeV, leading to the
12.71 MeV 1+ level with pure T=0 character, an anomaly was observed at 9
MeV/c2. The compatibility of the results with the scenario is discussed.Comment: 12 pages, 5 figures, 2 table
A multi-detector array for high energy nuclear e+e- pair spectrosocopy
A multi-detector array has been constructed for the simultaneous measurement
of energy- and angular correlation of electron-positron pairs produced in
internal pair conversion (IPC) of nuclear transitions up to 18 MeV. The
response functions of the individual detectors have been measured with
mono-energetic beams of electrons. Experimental results obtained with 1.6 MeV
protons on targets containing B and F show clear IPC over a wide
angular range. A comparison with GEANT simulations demonstrates that angular
correlations of pairs of transitions in the energy range between 6 and
18 MeV can be determined with sufficient resolution and efficiency to search
for deviations from IPC due to the creation and subsequent decay into
of a hypothetical short-lived neutral boson.Comment: 20 pages, 8 figure
model as effective Hamiltonian for generalized Hubbard models with broken -symmetry
We consider the limit of strong Coulomb attraction for generalized Hubbard
models with -symmetry. In this limit these models are equivalent to the
ferromagnetic spin-1/2 Heisenberg quantum spin chain. In order to study the
behaviour of the superconducting phase in the electronic model under
perturbations which break the -symmetry we investigate the ground state
of the ferromagnetic non-critical -chain in the sector with fixed
magnetization. It turns out to be a large bound state of magnons. We find
that the perturbations considered here lead to the disappearance of the
off-diagonal longe-range order.Comment: Results of previous version are generalized, new title, references
added. 10 pages, Latex, no figure
Bosonization in d=2 from finite chiral determinants with a Gauss decomposition
We show how to bosonize two-dimensional non-abelian models using finite
chiral determinants calculated from a Gauss decomposition. The calculation is
quite straightforward and hardly more involved than for the abelian case. In
particular, the counterterm , which is normally motivated from gauge
invariance and then added by hand, appears naturally in this approach.Comment: 4 pages, Revte
A Re-evaluation of Evidence for Light Neutral Bosons in Nuclear Emulsions
Electron-positron pair-production data obtained by bombardment of emulsion
detectors with either cosmic rays or projectiles with mass between one and 207
and kinetic energies between 18 GeV and 32 TeV have been re-analysed using a
consistent and conservative model of the background from electromagnetic pair
conversion. The combined data yield a spectrum of putative neutral bosons
decaying to e+e- pairs, with masses between 3 and 20 MeV/c^2 and femtosecond
lifetimes. The statistical significance against background for these "X-bosons"
varies between 2 and 8 sigma. The cross-section for direct production of
X-bosons increases slowly with projectile energy, remaining over 1,000 times
smaller the the pion production cross-section.Comment: major revision with improved figures; accepted by Int J Mod Phys
Note on Gauge Theory on Fuzzy Supersphere
We construct a supermatrix model whose classical background gives
two-dimensional noncommutative supersphere. Quantum fluctuations around it give
the supersymmetric gauge theories on the fuzzy supersphere constructed by
Klimcik. This model has a parameter which can tune masses of the
particles in the model and interpolate various supersymmetric gauge theories on
sphere.Comment: 13 pages, LaTe
Domain Walls in MQCD and Monge-Ampere Equation
We study Witten's proposal that a domain wall exists in M-theory fivebrane
version of QCD (MQCD) and that it can be represented as a supersymmetric
three-cycle in G_2 holonomy manifold. It is shown that equations defining the
U(1) invariant domain wall for SU(2) group can be reduced to the Monge-Ampere
equation. A proof of an algebraic formula of Kaplunovsky, Sonnenschein and
Yankielowicz is presented. The formal solution of equations for domain wall is
constructed.Comment: Latex, 18 pages, section 4.2 modified, typos correcte
AdS Duals of Matrix Strings
We review recent work on the holographic duals of type II and heterotic
matrix string theories described by warped AdS_3 supergravities. In particular,
we compute the spectra of Kaluza-Klein primaries for type I, II supergravities
on warped AdS_3xS^7 and match them with the primary operators in the dual
two-dimensional gauge theories. The presence of non-trivial warp factors and
dilaton profiles requires a modification of the familiar dictionary between
masses and ``scaling'' dimensions of fields and operators. We present these
modifications for the general case of domain wall/QFT correspondences between
supergravities on warped AdS_{d+1}xS^q geometries and super Yang-Mills theories
with 16 supercharges.Comment: 7 pages, Proceedings of the RTN workshop ``The quantum structure of
spacetime and the geometric nature of fundamental interactions'', Leuven,
September 200
GHRS and ORFEUS-II Observations of the Highly Ionized Interstellar Medium Toward ESO141-055
We present Goddard High Resolution Spectrograph and ORFEUS-II measurements of
Si IV, CIV, N V, and O VI absorption in the interstellar medium of the Galactic
disk and halo toward the nucleus of the Seyfert galaxy ESO141-055. The high
ionization absorption is strong, with line strengths consistent with the
spectral signature expected for hot (log T = 5-6) collisionally ionized gas in
either a ``Galactic fountain'' or an inhomogeneous medium containing a mixture
of conductive interfaces and turbulent mixing layers. The total O VI column
density of log N ~ 15 suggests that the scale height of O VI is large (>3 kpc)
in this direction. Comparison of the high ion column densities with
measurements for other sight lines indicates that the highly ionized gas
distribution is patchy. The amount of O VI perpendicular to the Galactic plane
varies by at least a factor of ~4 among the complete halo sight lines thus far
studied. In addition to the high ion absorption, lines of low ionization
species are also present in the spectra. With the possible exception of Ar I,
which may have a lower than expected abundance resulting from partial
photoionization of gas along the sight line, the absorption strengths are
typical of those expected for the warm, neutral interstellar medium. The sight
line intercepts a cold molecular cloud with log N(H2) ~ 19. The cloud has an
identifiable counterpart in IRAS 100-micron emission maps of this region of the
sky. We detect a Ly-alpha absorber associated with ESO141-055 at z = 0.03492.
This study presents an enticing glimpse into the interstellar and intergalactic
absorption patterns that will be observed at high spectral resolution by the
Far Ultraviolet Spectroscopic Explorer.Comment: 24 pages + 8 figures, uses aaspp4.sty. Accepted for publication in
Ap
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