32,124 research outputs found
D-instantons, Strings and M-theory
The R^4 terms in the effective action for M-theory compactified on a
two-torus are motivated by combining one-loop results in type II superstring
theories with the Sl(2,Z) duality symmetry. The conjectured expression
reproduces precisely the tree-level and one-loop R^4 terms in the effective
action of the type II string theories compactified on a circle, together with
the expected infinite sum of instanton corrections. This conjecture implies
that the R^4 terms in ten-dimensional string type II theories receive no
perturbative corrections beyond one loop and there are also no non-perturbative
corrections in the ten-dimensional IIA theory. Furthermore, the
eleven-dimensional M-theory limit exists, in which there is an R^4 term that
originates entirely from the one-loop contribution in the type IIA theory and
is related by supersymmetry to the eleven-form C^{(3)}R^4. The generalization
to compactification on T^3 as well as implications for non-renormalization
theorems in D-string and D-particle interactions are briefly discussed.Comment: harvmac (b) 17 pages. v4: Some formulae corrected. Dimensions
corrected for eleven-dimensional expression
Atmospheric Calorimetry above 10 eV: Shooting Lasers at the Pierre Auger Cosmic-Ray Observatory
The Pierre Auger Cosmic-Ray Observatory uses the earth's atmosphere as a
calorimeter to measure extensive air-showers created by particles of
astrophysical origin. Some of these particles carry joules of energy. At these
extreme energies, test beams are not available in the conventional sense. Yet
understanding the energy response of the observatory is important. For example,
the propagation distance of the highest energy cosmic-rays through the cosmic
microwave background radiation (CMBR) is predicted to be strong function of
energy. This paper will discuss recently reported results from the observatory
and the use of calibrated pulsed UV laser "test-beams" that simulate the
optical signatures of ultra-high energy cosmic rays. The status of the much
larger 200,000 km companion detector planned for the northern hemisphere
will also be outlined.Comment: 6 pages, 11 figures XIII International Conference on Calorimetry in
High Energy Physic
Production of the X(3872) at the Tevatron and the LHC
We predict the differential cross sections for production of the X(3872) at
the Tevatron and the Large Hadron Collider from both prompt QCD mechanisms and
from decays of b hadrons. The prompt cross section is calculated using the
NRQCD factorization formula. Simplifying assumptions are used to reduce the
nonperturbative parameters to a single NRQCD matrix element that is determined
from an estimate of the prompt cross section at the Tevatron. For X(3872) with
transverse momenta greater than about 4 GeV, the predicted cross section is
insensitive to the simplifying assumptions. We also discuss critically a recent
analysis that concluded that the prompt production rate at the Tevatron is too
large by orders of magnitude for the X(3872) to be a weakly-bound charm-meson
molecule. We point out that if charm-meson rescattering is properly taken into
account, the upper bound is increased by orders of magnitude and is compatible
with the observed production rate at the Tevatron.Comment: 29 pages, 5 figure
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