1,693 research outputs found
Conformal invariance and QCD Pomeron vertices in the limit
Using the dipole framework for QCD at small x in the 1/N_c limit, we derive
the expression of the 1 -> p dipole multiplicity density in momentum space.
This gives an analytical expression for the 1 -> p QCD Pomeron amplitudes in
terms of one-loop integration of effective vertices in transverse momentum.
Conformal invariance and a Hilbert space construction for dipole correlation
functions are the main tools of the derivation. Relations with conformal field
theories in the classical limit are discussed.Comment: 16 pages, LATEX file, 1 .eps figur
Optical properties of TiBe2 in the range from 0.5 to 3.3 eV
The optical properties of polycrystalline TiBe2 have been determined by ellipsometry in the visible and infrared region. The most predominant features of the spectra are in excellent agreement with a calculation of the optical conductivity
OSETI with STACEE: A Search for Nanosecond Optical Transients from Nearby Stars
We have used the STACEE high-energy gamma-ray detector to look for fast
blue-green laser pulses from the vicinity of 187 stars. The STACEE detector
offers unprecedented light-collecting capability for the detection of
nanosecond pulses from such lasers. We estimate STACEE's sensitivity to be
approximately 10 photons per square meter at a wavelength of 420 nm. The stars
have been chosen because their characteristics are such that they may harbor
habitable planets and they are relatively close to Earth. Each star was
observed for 10 minutes and we found no evidence for laser pulses in any of the
data sets.Comment: 38 pages, 12 figures. Accepted for publication in Astrobiolog
Very high energy observations of the BL Lac objects 3C 66A and OJ 287
Using the Solar Tower Atmospheric Cherenkov Effect Experiment (STACEE), we
have observed the BL Lac objects 3C 66A and OJ 287. These are members of the
class of low-frequency-peaked BL Lac objects (LBLs) and are two of the three
LBLs predicted by Costamante and Ghisellini to be potential sources of very
high energy (>100 GeV) gamma-ray emission. The third candidate, BL Lacertae,
has recently been detected by the MAGIC collaboration. Our observations have
not produced detections; we calculate a 99% CL upper limit of flux from 3C 66A
of 0.15 Crab flux units and from OJ 287 our limit is 0.52 Crab. These limits
assume a Crab-like energy spectrum with an effective energy threshold of 185
GeV.Comment: 24 pages, 15 figures, Accepted for publication in Astroparticle
Physic
Traveling wave fronts and the transition to saturation
We propose a general method to study the solutions to nonlinear QCD evolution
equations, based on a deep analogy with the physics of traveling waves. In
particular, we show that the transition to the saturation regime of high energy
QCD is identical to the formation of the front of a traveling wave. Within this
physical picture, we provide the expressions for the saturation scale and the
gluon density profile as a function of the total rapidity and the transverse
momentum. The application to the Balitsky-Kovchegov equation for both fixed and
running coupling constants confirms the effectiveness of this method.Comment: 9 pages, 3 figures, references adde
Time-variability in the Interstellar Boundary Conditions of the Heliosphere: Effect of the Solar Journey on the Galactic Cosmic Ray Flux at Earth
During the solar journey through galactic space, variations in the physical
properties of the surrounding interstellar medium (ISM) modify the heliosphere
and modulate the flux of galactic cosmic rays (GCR) at the surface of the
Earth, with consequences for the terrestrial record of cosmogenic
radionuclides. One phenomenon that needs studying is the effect on cosmogenic
isotope production of changing anomalous cosmic ray fluxes at Earth due to
variable interstellar ionizations. The possible range of interstellar ram
pressures and ionization levels in the low density solar environment generate
dramatically different possible heliosphere configurations, with a wide range
of particle fluxes of interstellar neutrals, their secondary products, and GCRs
arriving at Earth. Simple models of the distribution and densities of ISM in
the downwind direction give cloud transition timescales that can be directly
compared with cosmogenic radionuclide geologic records. Both the interstellar
data and cosmogenic radionuclide data are consistent with cloud transitions
during the Holocene, with large and assumption-dependent uncertainties. The
geomagnetic timeline derived from cosmic ray fluxes at Earth may require
adjustment to account for the disappearance of anomalous cosmic rays when the
Sun is immersed in ionized gas.Comment: Submitted to Space Sciences Review
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