3,932 research outputs found
Effect of charged partons on black hole production at the Large Hadron Collider
The cross section for black hole production in hadron colliders is calculated
using a factorization hypothesis in which the parton-level process is
integrated over the parton density functions of the protons. The mass, spin,
charge, colour, and finite size of the partons are usually ignored. We examine
the effects of parton electric charge on black hole production using the
trapped-surface approach of general relativity. Accounting for electric charge
of the partons could reduce the black hole cross section by one to four orders
of magnitude at the Large Hadron Collider. The cross section results are
sensitive to the Standard Model brane thickness. Lower limits on the amount of
energy trapped behind the event horizon in the collision of charged particles
are also calculated.Comment: corrected typo in figure 1b; added some clarification in 3 places; 21
pages, 9 figures, JHEP3 forma
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 two high-frequency peaked BL Lac objects 1ES 1218+304 and H 1426+428
We present results of very-high-energy gamma-ray observations (E > 160 GeV)
of two high-frequency-peaked BL Lac (HBL) objects, 1ES 1218+304 and H 1426+428,
with the Solar Tower Atmospheric Cherenkov Effect Experiment (STACEE). Both
sources are very-high-energy gamma-ray emitters above 100 GeV, detected using
ground-based Cherenkov telescopes. STACEE observations of 1ES 1218+304 and H
1426+428 did not produce detections; we present 99% CL flux upper limits for
both sources, assuming spectral indices measured mostly at higher energies
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
Properties of Entanglement Monotones for Three-Qubit Pure States
Various parameterizations for the orbits under local unitary transformations
of three-qubit pure states are analyzed. The interconvertibility, symmetry
properties, parameter ranges, calculability and behavior under measurement are
looked at. It is shown that the entanglement monotones of any multipartite pure
state uniquely determine the orbit of that state under local unitary
transformations. It follows that there must be an entanglement monotone for
three-qubit pure states which depends on the Kempe invariant defined in [Phys.
Rev. A 60, 910 (1999)]. A form for such an entanglement monotone is proposed. A
theorem is proved that significantly reduces the number of entanglement
monotones that must be looked at to find the maximal probability of
transforming one multipartite state to another.Comment: 14 pages, REVTe
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