156 research outputs found
Quantum Stability of Accelerated Black Holes
We study quantum aspects of the accelerated black holes in some detail.
Explicitly shown is the fact that a uniform acceleration stabilizes certain
charged black holes against the well-known thermal evaporation. Furthermore, a
close inspection of the geometry reveals that this is possible only for
near-extremal black holes and that most nonextremal varieties continue to
evaporate with a modified spectrum under the acceleration. We also introduce a
two-dimensional toy model where the energy-momentum flow is easily obtained for
general accelerations, and find the behavior to be in accordance with the
four-dimensional results. After a brief comparison to the classical system of a
uniformly accelerated charge, we close by pointing out the importance of this
result in the WKB expansion of the black hole pair-creation rate.Comment: LaTeX, 22 pages, 5 uuencoded figures (minor errors corrected, more
discussions on the case with black holes formed by gravitational collapse.
Virtual Black Holes
One would expect spacetime to have a foam-like structure on the Planck scale
with a very high topology. If spacetime is simply connected (which is assumed
in this paper), the non-trivial homology occurs in dimension two, and spacetime
can be regarded as being essentially the topological sum of and
bubbles. Comparison with the instantons for pair creation of black holes
shows that the bubbles can be interpreted as closed loops of
virtual black holes. It is shown that scattering in such topological
fluctuations leads to loss of quantum coherence, or in other words, to a
superscattering matrix that does not factorise into an matrix and its
adjoint. This loss of quantum coherence is very small at low energies for
everything except scalar fields, leading to the prediction that we may never
observe the Higgs particle. Another possible observational consequence may be
that the angle of QCD is zero without having to invoke the
problematical existence of a light axion. The picture of virtual black holes
given here also suggests that macroscopic black holes will evaporate down to
the Planck size and then disappear in the sea of virtual black holes.Comment: 24p, LaTeX, 3 postscript figures included with epsf sent in a
seperate uuencoded fil
Persistent currents in mesoscopic rings with a quantum dot
Using the Anderson model in the Kondo regime, we calculate the persistent
current j in a ring with an embedded quantum dot (QD) as a function of the
Aharonov-Bohm flux Phi for different ring length L, temperature T and
broadening of the conduction states delta . For T=delta =0 and L >> xi, where
xi is the Kondo screening length, Lj tends to the value for a non interacting
ideal ring, while it is suppressed for a side coupled QD. For any L/xi, Lj is
also suppressed when either T or delta increase above a fraction of the level
spacing which depends on Phi.Comment: 5 pages, 6 figures, submitted to Phys. Rev. B, (Refs. added
Single gluino production in the R-parity lepton number violating MSSM at the LHC
We examine the -violating signal of single gluino production
associated with a charged lepton or neutrino at the large hadron collider
(LHC), in the model of R-parity relaxed supersymmetric model. If the parameters
in the supersymmetric interactions are not too small, and the
mass of gluino is considered in the range from several GeV (as the Lightest
Supersymmetric Particle) to 800 GeV, the cross section of the single gluino
production via Drell-Yan processes can be in the order of
femto barn, and that via gluon fusion in the order of femto
barn. If the gluino decay can be well detected in the CERN LHC, this process
provides a prospective way to probe supersymmetry and violation.Comment: LaTex, 22 pages, 5 EPS file
Electroweak Corrections to the Charged Higgs Boson Decay into Chargino and Neutralino
The electroweak corrections to the partial widths of the decays including one-loop
diagrams of the third generation quarks and squarks, are investigated within
the Supersymmetric Standard Model. The relative corrections can reach the
values about 10%, therefore they should be taken into account for the precise
experimental measurement at future colliders.Comment: 21 pages, 6 eps figures, 1 Latex fil
Measurements of J/psi Decays into 2(pi+pi-)eta and 3(pi+pi-)eta
Based on a sample of 5.8X 10^7 J/psi events taken with the BESII detector,
the branching fractions of J/psi--> 2(pi+pi-)eta and J/psi-->3(pi+pi-)eta are
measured for the first time to be (2.26+-0.08+-0.27)X10^{-3} and
(7.24+-0.96+-1.11)X10^{-4}, respectively.Comment: 11 pages, 6 figure
BESII Detector Simulation
A Monte Carlo program based on Geant3 has been developed for BESII detector
simulation. The organization of the program is outlined, and the digitization
procedure for simulating the response of various sub-detectors is described.
Comparisons with data show that the performance of the program is generally
satisfactory.Comment: 17 pages, 14 figures, uses elsart.cls, to be submitted to NIM
Measurement of branching fractions for the inclusive Cabibbo-favored ~K*0(892) and Cabibbo-suppressed K*0(892) decays of neutral and charged D mesons
The branching fractions for the inclusive Cabibbo-favored ~K*0 and
Cabibbo-suppressed K*0 decays of D mesons are measured based on a data sample
of 33 pb-1 collected at and around the center-of-mass energy of 3.773 GeV with
the BES-II detector at the BEPC collider. The branching fractions for the
decays D+(0) -> ~K*0(892)X and D0 -> K*0(892)X are determined to be BF(D0 ->
\~K*0X) = (8.7 +/- 4.0 +/- 1.2)%, BF(D+ -> ~K*0X) = (23.2 +/- 4.5 +/- 3.0)% and
BF(D0 -> K*0X) = (2.8 +/- 1.2 +/- 0.4)%. An upper limit on the branching
fraction at 90% C.L. for the decay D+ -> K*0(892)X is set to be BF(D+ -> K*0X)
< 6.6%
Study of
New data are presented on from a sample of 58M
events in the upgraded BES II detector at the BEPC. There is a
conspicuous signal for and a peak at higher mass which
may be fitted with . From a combined analysis with
data, the branching ratio
is at the 95%
confidence level.Comment: 11 pages, 5 figures. Submitted to Phys. Lett.
Search for the Rare Decays J/Psi --> Ds- e+ nu_e, J/Psi --> D- e+ nu_e, and J/Psi --> D0bar e+ e-
We report on a search for the decays J/Psi --> Ds- e+ nu_e + c.c., J/Psi -->
D- e+ nu_e + c.c., and J/Psi --> D0bar e+ e- + c.c. in a sample of 5.8 * 10^7
J/Psi events collected with the BESII detector at the BEPC. No excess of signal
above background is observed, and 90% confidence level upper limits on the
branching fractions are set: B(J/Psi --> Ds- e+ nu_e + c.c.)<4.8*10^-5, B(J/Psi
--> D- e+ nu_e + c.c.) D0bar e+ e- + c.c.)<1.1*10^-5Comment: 10 pages, 4 figure
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