24,485 research outputs found
Entanglement is not very useful for estimating multiple phases
The problem of the estimation of multiple phases (or of commuting unitaries)
is considered. This is a sub-model of the estimation of a completely unknown
unitary operation where it has been shown in recent works that there are
considerable improvements by using entangled input states and entangled
measurements. Here it is shown that when estimating commuting unitaries, there
is practically no advantage in using entangled input states or entangled
measurements.Comment: v2. New title, improved Fig.3, other minor changes, Accepted in PR
Exact predictions from Edwards ensemble vs. realistic simulations of tapped narrow two-dimensional granular columns
We simulate via a Discrete Element Method the tapping of a narrow column of
disk under gravity. For frictionless disks, this system has a simple analytic
expression for the density of states in the Edwards volume ensemble. We compare
the predictions of the ensemble at constant compactivity against the results
for the steady states obtained in the simulations. We show that the steady
states cannot be properly described since the microstates sampled are not in
correspondence with the predicted distributions, suggesting that the postulates
of flat measure and ergodicity are, either or both, invalid for this simple
realization of a static granular system. However, we show that certain
qualitative features of the volume fluctuations difficult to predict from
simple arguments are captured by the theory.Comment: 11 pages, 6 figure
Solar Abundance of Elements from Neutron-Capture Cross Sections
Excess lightweight products of slow neutron capture in the photosphere, over
the mass range of 25 to 207 amu, confirm the solar mass separation recorded by
excess lightweight isotopes in the solar wind, over the mass range of 3 to 136
amu [Solar Abundance of the Elements, Meteoritics, volume 18, 1983, pages 209
to 222]. Both measurements show that major elements inside the Sun are Fe, O,
Ni, Si and S, like those in rocky planets.Comment: 2 pages with 4 figures, submitted for oral presentation in the
Genesis Mission Special Session, 36th Lunar and Planetary Science Conference,
Houston, TX, 14-18 March 200
Mitigation of the LHC Inverse Problem
The LHC inverse problem refers to the difficulties in determining the
parameters of an underlying theory from data (to be) taken by the LHC
experiments: if they find signals of new physics, and an underlying theory is
assumed, could its parameters be determined uniquely, or do different parameter
choices give indistinguishable experimental signatures? This inverse problem
was studied before for a supersymmetric Standard Model with 15 free parameters.
This earlier study found 283 indistinguishable pairs of parameter choices,
called degenerate pairs, even if backgrounds are ignored. We can resolve all
but 23 of those pairs by constructing a true \chi^2 distribution using mostly
counting observables. The elimination of systematic errors would even allow
separating the residual degeneracies. Taking the Standard Model background into
account we still can resolve 237 of the 283 "degenerate" pairs. This indicates
that (some of) our observables should also be useful for the purpose of
determining the values of SUSY parameters.Comment: 32 pages, 13 figures, typo in (3.6) corrected, version to appear in
Phys. Rev.
CP-violating Supersymmetric Higgs at the Tevatron and LHC
We analyze the prospect for observing the intermediate neutral Higgs boson
() in its decay to two lighter Higgs bosons () at the presently
operating hadron colliders in the framework of the CP violating MSSM using the
PYTHIA event generator. We consider the lepton+ 4-jets+ \met channel from
associate production, with W h_2 \ra W h_1 h_1 \ra \ell \nu_\ell b
\bar b b\bar b. We require two, three or four tagged -jets. We explicitly
consider all relevant Standard Model backgrounds, treating -jets separately
from light flavor and gluon jets and allowing for mistagging. We find that it
is very hard to observe this signature at the Tevatron, even with 20 fb
of data, in the LEP--allowed region of parameter space due to the small signal
efficiency, even though the background is manageable. At the LHC, a priori huge
SM backgrounds can be suppressed by applying judiciously chosen kinematical
selections. After all cuts, we are left with a signal cross section of around
0.5 fb, and a signal to background ratio between 1.2 and 2.9. According to our
analysis this Higgs signal should be viable at the LHC in the vicinity of
present LEP exclusion once 20 to 50 fb of data have been accumulated at
TeV.Comment: 27 pages, 12 figure
RVB signatures in the spin dynamics of the square-lattice Heisenberg antiferromagnet
We investigate the spin dynamics of the square-lattice spin-1/2 Heisenberg
antiferromagnet by means of an improved mean field Schwinger boson calculation.
By identifying both, the long range N\'eel and the RVB-like components of the
ground state, we propose an educated guess for the mean field triplet
excitation consisting on a linear combination of local and bond spin flips to
compute the dynamical structure factor. Our main result is that when this
triplet excitation is optimized in such a way that the corresponding sum rule
is fulfilled, we recover the low and high energy spectral weight features of
the experimental spectrum. In particular, the anomalous spectral weight
depletion at found in recent inelastic neutron scattering experiments
can be attributed to the interference of the triplet bond excitations of the
RVB component of the ground state. We conclude that the Schwinger boson theory
seems to be a good candidate to adequately interpret the dynamic properties of
the square-lattice Heisenberg antiferromagnet.Comment: 6 pages with 3 figure
The Buenos Aires water concession
The signing of a concession contract for the Buenos Aires water and sanitation system in December 1992, attracted worldwide attention, and caused considerable controversy in Argentina. It was one of the world's largest concessions, but the case was also interesting for other reasons. The concession was implemented rapidly, in contrast with slow implementation of privatization in Santiago, for example. And reform generated major improvements in the sector, including wider coverage, better service, more efficient company operations, and reduced waste. Moreover, the winning bid brought an immediate 26.9 percent reduction in water system tariffs. Consumers benefited from the system's expansion and from the immediate drop in real prices, which was only partly reversed by subsequent changes in tariffs, and access charges. And these improvements would probably not have occurred under public administration of the system. Still, the authors show information asymmetries, perverse incentives, and weak regulatory institutions could threaten the concession's sustainability. Opportunities for the company to act opportunistically - and the regulator, arbitrarily - exist, because of politicized regulation, a poor information base, serious flaws in the concession contract, a lumpy and ad hoc tariff system, and a general lack of transparency in the regulatory process. Because of these circumstances, public confidence in the process has eroded. The Buenos Aires concession shows how important transparent, rule-based decision-making is to maintain public trust in regulated infrastructure.Health Economics&Finance,Environmental Economics&Policies,Water Conservation,Water and Industry,Decentralization,Town Water Supply and Sanitation,Environmental Economics&Policies,Water and Industry,Water Supply and Sanitation Governance and Institutions,Water Conservation
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