14,472 research outputs found
A non-rational CFT with c=1 as a limit of minimal models
We investigate the limit of minimal model conformal field theories where the
central charge approaches one. We conjecture that this limit is described by a
non-rational CFT of central charge one. The limiting theory is different from
the free boson but bears some resemblance to Liouville theory. Explicit
expressions for the three point functions of bulk fields are presented, as well
as a set of conformal boundary states. We provide analytic and numerical
arguments in support of the claim that this data forms a consistent CFT.Comment: latex2e, 37 pages, 4 figure
Spatial clusters of gonorrhoea in England with particular reference to the outcome of partner notification: 2012 and 2013
Background: This study explored spatial-temporal variation in diagnoses of gonorrhoea to identify and quantify endemic areas and clusters in relation to patient characteristics and outcomes of partner notification (PN) across England, UK. Methods: Endemic areas and clusters were identified using a two-stage analysis with Kulldorffâs scan statistics (SaTScan). Results Of 2,571,838 tests, 53,547 diagnoses were gonorrhoea positive (positivity = 2.08%). The proportion of diagnoses in heterosexual males was 1.5 times that in heterosexual females. Among index cases, men who have sex with men (MSM) were 8 times more likely to be diagnosed with gonorrhoea than heterosexual males (p<0.0001). After controlling for age, gender, ethnicity and deprivation rank, 4 endemic areas were identified including 11,047 diagnoses, 86% of which occurred in London. 33 clusters included 17,629 diagnoses (34% of total diagnoses in 2012 and 2013) and spanned 21 locations, some of which were dominated by heterosexually acquired infection, whilst others were MSM focused. Of the 53,547 diagnoses, 14.5% (7,775) were the result of PN. The proportion of patients who attended services as a result of PN varied from 0% to 61% within different age, gender and sexual orientation cohorts. A third of tests resulting from PN were positive for gonorrhoea. 25% of Local Authorities (n = 81, 95% CI: 20.2, 29.5) had a higher than expected proportion for female PN diagnoses as compared to 16% for males (n = 52, 95% CI: 12.0, 19.9). Conclusions: The English gonorrhoea epidemic is characterised by spatial-temporal variation. PN success varied between endemic areas and clusters. Greater emphasis should be placed on the role of PN in the control of gonorrhoea to reduce the risk of onward transmission, re-infection, and complications of infection
Detection of K+ mesons in segmented electromagnetic calorimeters
The combination of the CrystalBall and TAPS electromagnetic calorimeters were installed in the MAMI A2 hall in 2003. Here they are able to detect the reaction products from photo-induced reactions in combination with the Glasgow photon tagger. In the last two years the MAMI facility was upgraded from 885 MeV to 1.5 GeV, the A2 photon tagger underwent a similar upgrade crossing the threshold for strangeness photoproduction. For the CrystalBall this created a new challenge, to identify K+ mesons above the large background from other charged hadrons, in a situation where the detector setup does not benefit from a magnetic field to help separate particle species. These proceedings outline a novel technique which uses the decay products of the K+ as a strangeness tag
Parameter estimation and the statistics of nonlinear cosmic fields
The large scale distribution of matter in the universe contains valuable information
about fundamental cosmological parameters, the properties of dark matter
and the formation processes of galaxies. The best hope of retrieving this information
lies in providing a statistical description of the matter distribution that
may be used for comparing models with observation. Unfortunately much of the
important information lies on scales below which nonlinear gravitational effects
have taken hold, complicating both models and statistics considerably. This thesis
deals with the distribution of matter - mass and galaxies - on such scales. The
aim is to develop new statistical tools that make use of the nonlinear evolution
for the purposes of constraining cosmological models.A new derivation for the 1 -point probability distribution function (PDF) for density
inhomogeneities is presented first. The calculation is based upon an exact
statistical treatment, using the Chapman -Kolmogorov equation and second order
Eulerian perturbation theory to propagate the initial density field into the nonlinear
regime. The analysis yields the generating function for moments, allowing
for a straightforward derivation of the skewness. A new dependance upon the
perturbation spectrum is found for the skewness at second order. The results of
the analysis are compared against other methods for deriving the 1 -point PDF
and against data from numerical N -body simulations. Good agreement is found
in both cases.The 1 -point PDF for galaxies is derived next, taking into account nonlinear biasing
of the density field and the distorting effects associated with working in
redshift space. Once again perturbation theory is used to evolve the density field
into the nonlinear regime and the Chapman -Kolmogorov equation to propagate
the initial probabilities. Transformation of the dark matter density to a biased
galaxy distribution is done through an Eulerian biasing prescription, expanding
the nonlinear bias function to second order. An advantage of the Chapman-
Kolmogorov approach is the natural way that different initial conditions and biasing
models may be incorporated. It is shown that the method is general enough
to allow a non -deterministic (hidden variable) bias. The dependance on cosmological
parameters of the evolution of the galaxy 1 -point PDF is demonstrated
and a method for differentiating between degenerate models in linear theory is
presented. A new derivation of the skewness for a biased density field in red - shift space is also given and shown to depend significantly on the density and
bias parameters. The results are compared favourably with those of numerical
simulations.Finally a new, general formalism for analysing parameter information from non - Gaussian cosmic fields is developed. The method is general enough for application
to a range of problems including the measurement of parameters from galaxy
redshift surveys, weak lensing surveys and velocity field surveys. It may also be
used to test for non -Gaussianity in the Cosmic Microwave Background. Generalising
maximum likelihood analysis to second order, the non -Gaussian Fisher
information matrix is derived and the detailed shapes of likelihood surfaces in parameter
space are explored via a parameter entropy function. Concentrating on
non -Gaussianity due to nonlinear evolution under gravity, the generalised Fisher
analysis is applied to a model of a Galaxy redshift survey, including the effects
of biasing, redshift space distortions and shot noise. Incorporating second order
moments into the parameter estimation is found to have a large effect, breaking
all of the degeneracies between parameters. The results indicate that using
nonlinear likelihood analysis may yield parameter uncertainties around the few
percent level from forthcoming large galaxy redshift surveys
Thermodynamic limit of the first-order phase transition in the Kuramoto model
In the Kuramoto model, a uniform distribution of the natural frequencies
leads to a first-order (i.e., discontinuous) phase transition from incoherence
to synchronization, at the critical coupling parameter . We obtain the
asymptotic dependence of the order parameter above criticality: . For a finite population, we demonstrate that the population
size may be included into a self-consistency equation relating and
in the synchronized state. We analyze the convergence to the thermodynamic
limit of two alternative schemes to set the natural frequencies. Other
frequency distributions different from the uniform one are also considered.Comment: 6 page
Finite size effects in perturbed boundary conformal field theories
We discuss the finite-size properties of a simple integrable quantum field
theory in 1+1 dimensions with non-trivial boundary conditions. Novel
off-critical identities between cylinder partition functions of models with
differing boundary conditions are derived.Comment: 7 pages, 11 figures, JHEP proceedings style. Uses epsfig, amssymb.
Talk given at the conference `Nonperturbative Quantum Effects 2000', Pari
Magnetar giant flare high-energy emission
High energy ( keV) emission has been detected persisting for several
tens of seconds after the initial spike of magnetar giant flares. It has been
conjectured that this emission might arise via inverse Compton scattering in a
highly extended corona generated by super-Eddington outflows high up in the
magnetosphere. In this paper we undertake a detailed examination of this model.
We investigate the properties of the required scatterers, and whether the
mechanism is consistent with the degree of pulsed emission observed in the tail
of the giant flare. We conclude that the mechanism is consistent with current
data, although the origin of the scattering population remains an open
question. We propose an alternative picture in which the emission is closer to
that star and is dominated by synchrotron radiation. The observations
of the December 2004 flare modestly favor this latter picture. We assess the
prospects for the Fermi Gamma-Ray Space Telescope to detect and characterize a
similar high energy component in a future giant flare. Such a detection should
help to resolve some of the outstanding issues.Comment: 20 pages, 14 figure
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