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Child Exploitation and the FIFA World Cup: A review of risks and protective interventions
This review was commissioned by the Child Abuse Programme (CAP) of Oak Foundation, a large international philanthropic organisation. It forms part of CAP’s effort to win societal rejection of practices such as the sexual exploitation of children and adolescents around major sporting events (MSEs), and to embed prevention and protection from exploitation as a permanent concern for global sports-related bodies. This review is intended to inform action in countries that host MSEs and to provide some suggestions on how hosting countries can avoid past pitfalls and mistakes in relation to child exploitation, especially economic and sexual exploitation. Importantly, it also acts as a call to action by those responsible for commissioning and staging MSEs, such as FIFA and the IOC, to anticipate, prepare for and adopt risk mitigation strategies and interventions. Positive leadership from these culturally powerful bodies could prove decisive in shifting hearts, minds and actions in the direction of improved safety for children
Generating quantum states through spin chain dynamics
Spin chains can realise perfect quantum state transfer between the two ends
via judicious choice of coupling strengths. In this paper, we study what other
states can be created by engineering a spin chain. We conclude that, up to
local phases, all single excitation quantum states with support on every site
of the chain can be created. We pay particular attention to the generation of
W-states that are superposed over every site of the chain.Comment: 9 pages, 1 figur
Quantum field theory and time machines
We analyze the "F-locality condition" (proposed by Kay to be a mathematical
implementation of a philosophical bias related to the equivalence principle, we
call it the "GH-equivalence principle"), which is often used to build a
generalization of quantum field theory to non-globally hyperbolic spacetimes.
In particular we argue that the theorem proved by Kay, Radzikowski, and Wald to
the effect that time machines with compactly generated Cauchy horizons are
incompatible with the F-locality condition actually does not support the
"chronology protection conjecture", but rather testifies that the F-locality
condition must be modified or abandoned. We also show that this condition
imposes a severe restriction on the geometry of the world (it is just this
restriction that comes into conflict with the existence of a time machine),
which does not follow from the above mentioned philosophical bias. So, one need
not sacrifice the GH-equivalence principle to "emend" the F-locality condition.
As an example we consider a particular modification, the "MF-locality
condition". The theory obtained by replacing the F-locality condition with the
MF-locality condition possesses a few attractive features. One of them is that
it is consistent with both locality and the existence of time machines.Comment: Revtex, 14 pages, 1 .ps figure. To appear in Phys. Rev. D More
detailed discussion is given on the MF-locality condition. Minor corrections
in terminolog
The economic optimisation of the main parameters of the 3-GeV electron booster synchrotron for DIAMOND
Evaluation of bistable systems versus matched filters in detecting bipolar pulse signals
This paper presents a thorough evaluation of a bistable system versus a
matched filter in detecting bipolar pulse signals. The detectability of the
bistable system can be optimized by adding noise, i.e. the stochastic resonance
(SR) phenomenon. This SR effect is also demonstrated by approximate statistical
detection theory of the bistable system and corresponding numerical
simulations. Furthermore, the performance comparison results between the
bistable system and the matched filter show that (a) the bistable system is
more robust than the matched filter in detecting signals with disturbed pulse
rates, and (b) the bistable system approaches the performance of the matched
filter in detecting unknown arrival times of received signals, with an
especially better computational efficiency. These significant results verify
the potential applicability of the bistable system in signal detection field.Comment: 15 pages, 9 figures, MikTex v2.
Brick Walls and AdS/CFT
We discuss the relationship between the bulk-boundary correspondence in
Rehren's algebraic holography (and in other 'fixed-background' approaches to
holography) and in mainstream 'Maldacena AdS/CFT'. Especially, we contrast the
understanding of black-hole entropy from the viewpoint of QFT in curved
spacetime -- in the framework of 't Hooft's 'brick wall' model -- with the
understanding based on Maldacena AdS/CFT. We show that the brick-wall
modification of a Klein Gordon field in the Hartle-Hawking-Israel state on
1+2-Schwarzschild AdS (BTZ) has a well-defined boundary limit with the same
temperature and entropy as the brick-wall-modified bulk theory. One of our main
purposes is to point out a close connection, for general AdS/CFT situations,
between the puzzle raised by Arnsdorf and Smolin regarding the relationship
between Rehren's algebraic holography and mainstream AdS/CFT and the puzzle
embodied in the 'correspondence principle' proposed by Mukohyama and Israel in
their work on the brick-wall approach to black hole entropy. Working on the
assumption that similar results will hold for bulk QFT other than the Klein
Gordon field and for Schwarzschild AdS in other dimensions, and recalling the
first author's proposed resolution to the Mukohyama-Israel puzzle based on his
'matter-gravity entanglement hypothesis', we argue that, in Maldacena AdS/CFT,
the algebra of the boundary CFT is isomorphic only to a proper subalgebra of
the bulk algebra, albeit (at non-zero temperature) the (GNS) Hilbert spaces of
bulk and boundary theories are still the 'same' -- the total bulk state being
pure, while the boundary state is mixed (thermal). We also argue from the
finiteness of its boundary (and hence, on our assumptions, also bulk) entropy
at finite temperature, that the Rehren dual of the Maldacena boundary CFT
cannot itself be a QFT and must, instead, presumably be something like a string
theory.Comment: 54 pages, 3 figures. Arguments strengthened in the light of B.S. Kay
`Instability of Enclosed Horizons' arXiv:1310.739
The thermal and two-particle stress-energy must be ill-defined on the 2-d Misner space chronology horizon
We show that an analogue of the (four dimensional) image sum method can be
used to reproduce the results, due to Krasnikov, that for the model of a real
massless scalar field on the initial globally hyperbolic region IGH of
two-dimensional Misner space there exist two-particle and thermal Hadamard
states (built on the conformal vacuum) such that the (expectation value of the
renormalised) stress-energy tensor in these states vanishes on IGH. However, we
shall prove that the conclusions of a general theorem by Kay, Radzikowski and
Wald still apply for these states. That is, in any of these states, for any
point b on the Cauchy horizon and any neighbourhood N of b, there exists at
least one pair of non-null related points (x,x'), with x and x' in the
intersection of IGH with N, such that (a suitably differentiated form of) its
two-point function is singular. (We prove this by showing that the two-point
functions of these states share the same singularities as the conformal vacuum
on which they are built.) In other words, the stress-energy tensor in any of
these states is necessarily ill-defined on the Cauchy horizon.Comment: 6 pages, LaTeX, RevTeX, no figure
Best chirplet chain: near-optimal detection of gravitational wave chirps
The list of putative sources of gravitational waves possibly detected by the
ongoing worldwide network of large scale interferometers has been continuously
growing in the last years. For some of them, the detection is made difficult by
the lack of a complete information about the expected signal. We concentrate on
the case where the expected GW is a quasi-periodic frequency modulated signal
i.e., a chirp. In this article, we address the question of detecting an a
priori unknown GW chirp. We introduce a general chirp model and claim that it
includes all physically realistic GW chirps. We produce a finite grid of
template waveforms which samples the resulting set of possible chirps. If we
follow the classical approach (used for the detection of inspiralling binary
chirps, for instance), we would build a bank of quadrature matched filters
comparing the data to each of the templates of this grid. The detection would
then be achieved by thresholding the output, the maximum giving the individual
which best fits the data. In the present case, this exhaustive search is not
tractable because of the very large number of templates in the grid. We show
that the exhaustive search can be reformulated (using approximations) as a
pattern search in the time-frequency plane. This motivates an approximate but
feasible alternative solution which is clearly linked to the optimal one.
[abridged version of the abstract]Comment: 23 pages, 9 figures. Accepted for publication in Phys. Rev D Some
typos corrected and changes made according to referee's comment
Not all adiabatic vacua are physical states
Adiabatic vacua are known to be Hadamard states. We show, however that the
energy-momentum tensor of a linear Klein-Gordon field on Robertson-Walker
spaces developes a generic singularity on the initial hypersurface if the
adiabatic vacuum is of order less than four. Therefore, adiabatic vacua are
physically reasonable only if their order is at least four.
A certain non-local large momentum expansion of the mode functions has
recently been suggested to yield the subtraction terms needed to remove the
ultraviolet divergences in the energy-momentum tensor. We find that this scheme
fails to reproduce the trace anomaly and therefore is not equivalent to
adiabatic regularisation.Comment: 13 pages, LaTex2
Massive scalar field in multiply connected flat spacetimes
The vacuum expectation value of the stress-energy tensor is calculated in several multiply
connected flat spacetimes for a massive scalar field with arbitrary curvature
coupling. We find that a nonzero field mass always decreases the magnitude of
the energy density in chronology-respecting manifolds such as ,
, , the M\"{o}bius strip, and the Klein bottle.
In Grant space, which contains nonchronal regions, whether diverges on a chronology horizon or
not depends on the field mass. For a sufficiently large mass remains finite, and the metric
backreaction caused by a massive quantized field may not be large enough to
significantly change the Grant space geometry.Comment: 19 pages, REVTeX, 5 figures in separate uuencoded compressed fil
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