4,388 research outputs found
Reliability Equivalence in Public Transport Contexts
This work provides initial investigation into whether equivalence between the mean-variance and scheduling approaches to transport reliability can be applied in the context high frequency public transport services. Each of these approaches is briefly outlined and the current work is framed by previous research attempting to demonstrate equivalence: both theoretically and empirically. The basic assumptions underpinning the theoretical approach to equivalence are explored and then re-formulated based upon which variables are likely to be known. The concept of headway is introduced to the theoretical approach using notation from previous research in order to represent public transport services. An empirical illustration of the method is undertaken using smart card data obtained from the London Underground metro system. The data are combined with timetable data and a previously developed method for estimating passenger preferred arrival times, which in turn allows the theoretical equivalence between mean-variance and scheduling approaches to be tested empirically. This is initially performed for a single origin-destination (OD) pair and then for 23 other ODs of varying headways. The example using a single OD demonstrates that even for a high frequency metro service, application of the theoretical equivalence is problematic, with variable parameters substantially affected. In the case of many ODs, a linear relationship is observed between the ratio of public transport to standard scheduling parameters and headway, suggesting the theoretical equivalence becomes less viable as headway increases. At the lowest values of headway, it is concluded that the equivalence remains problematic and further work is required before equivalence between the mean variance and scheduling approaches can be implemented in the public transport context
On the low energy end of the QCD spectrum
The energy gap of QCD is now understood very well. There is no doubt that the
expansion in powers of the two lightest quark masses does represent a very
useful tool for the analysis of the low energy structure. Concerning the
expansion in powers of m_s, however, the current situation leaves much to be
desired. While some of the lattice results indicate, for instance, that the
violations of the Okubo-Iizuka-Zweig rule in the quark condensate and in the
decay constants are rather modest, others point in the opposite direction. I am
confident that the dust will settle soon, so that the effective coupling
constants that govern the dependence of the various quantities of physical
interest on m_s can be determined, to next-to-next-to-leading order of the
chiral expansion.
The range of validity of ChPT can be extended by means of dispersive methods.
The properties of the physical states occurring in the spectrum of QCD below
KKbar threshold can reliably be investigated on this basis. In particular, as
shown only rather recently, general principles of quantum field theory lead to
an exact formula that expresses the mass and width of resonances in terms of
observable quantities. The formula removes the ambiguities inherent in the
analytic continuation from the real axis into the complex plane, which plagued
previous determinations of the pole positions of broad resonances.Comment: Talks given at QCD08 and Confinement
Multiscale Technicolor and the Zbb-bar Vertex
We estimate the correction to the Zbb-bar vertex arising from the exchanges
of the sideways extended technicolor (ETC) boson and the flavor-diagonal ETC
boson in the multiscale walking technicolor model. The obtained result is too
large to explain the present data. However, if we introduce a new self-
interaction for the top quark to induce the top quark condensate serving as the
origin of the large top quark mass, the corrected R_b=Gamma_b/Gamma_h can be
consistent with the recent LEP data. The corresponding correction to
R_c=Gamma_c/Gamma_h is shown to be negligibly small.Comment: 9-page LaTex fil
The isospin symmetry breaking effects in decays
The Fermi-Watson theorem is generalized to the case of two coupled channels
with different masses and applied to final state interaction in
decays. The impact of considered effect on the phase of the scattering
is estimated and shown that it can be crucial for scattering lengths extraction
from experimental data on decays
Two-loop representations of low-energy pion form factors and pi-pi scattering phases in the presence of isospin breaking
Dispersive representations of the pi-pi scattering amplitudes and pion form
factors, valid at two-loop accuracy in the low-energy expansion, are
constructed in the presence of isospin-breaking effects induced by the
difference between the charged and neutral pion masses. Analytical expressions
for the corresponding phases of the scalar and vector pion form factors are
computed. It is shown that each of these phases consists of the sum of a
"universal" part and a form-factor dependent contribution. The first one is
entirely determined in terms of the pi-pi scattering amplitudes alone, and
reduces to the phase satisfying Watson's theorem in the isospin limit. The
second one can be sizeable, although it vanishes in the same limit. The
dependence of these isospin corrections with respect to the parameters of the
subthreshold expansion of the pi-pi amplitude is studied, and an equivalent
representation in terms of the S-wave scattering lengths is also briefly
presented and discussed. In addition, partially analytical expressions for the
two-loop form factors and pi-pi scattering amplitudes in the presence of
isospin breaking are provided.Comment: 57 pages, 12 figure
Empirical parameterization of the K+- -> pi+- pi0 pi0 decay Dalitz plot
As first observed by the NA48/2 experiment at the CERN SPS, the \p0p0
invariant mass (M00) distribution from \kcnn decay shows a cusp-like anomaly
at M00=2m+, where m+ is the charged pion mass. An analysis to extract the pi pi
scattering lengths in the isospin I=0 and I=2 states, a0 and a2, respectively,
has been recently reported. In the present work the Dalitz plot of this decay
is fitted to a new empirical parameterization suitable for practical purposes,
such as Monte Carlo simulations of K+- -> pi+- pi0 pi0 decays.Comment: 9 pages, 3 figures
K^+ -> pi^+pi^0e^+e^-: a novel short-distance probe
We study the decay K^+ -> pi^+ pi^0 e^+ e^-, currently under analysis by the
NA62 Collaboration at CERN. In particular, we provide a detailed analysis of
the Dalitz plot for the long-distance, gamma^*-mediated, contributions
(Bremsstrahlung, direct emission and its interference). We also examine a set
of asymmetries to isolate genuine short-distance effects. While we show that
charge asymmetries are not required to test short distances, they provide the
best environment for its detection. This constitutes by itself a strong
motivation for NA62 to study K^- decays in the future. We therefore provide a
detailed study of different charge asymmetries and the corresponding estimated
signals. Whenever possible, we make contact with the related processes K^+ ->
pi^+ pi^0 gamma and K_L -> pi^+ pi^- e^+ e^- and discuss the advantages of K^+
-> pi^+ pi^0 e^+ e^- over them.Comment: 25 pages, 6 figure
The electromagnetic effects in decay
The final state interaction of pions in decay allows one to obtain
the value of the isospin and angular momentum zero scattering length
.We take into account the electromagnetic interaction of pions and
isospin symmetry breaking effects caused by different masses of neutral and
charged pions and estimate the impact of these effects on the procedure of
scattering length extraction from decay.Comment: 8 pages,1 figur
Bremsstrahlung simulation in K to pi l^pm nu_l (gamma) decays
In physics simulation chains, the PHOTOS Monte Carlo program is often used to
simulate QED effects in decays of intermediate particles and resonances. The
program is based on an exact multiphoton phase space. In general, the matrix
element is obtained from iterations of a universal kernel and approximations
are involved. To evaluate the program precision, it is necessary to formulate
and implement within the generator the exact matrix element, which depends on
the decay channel. Then, all terms necessary for non-leading logarithms are
taken into account.
In the present letter we focus on the decay K to pi l^pm nu_l and tests of
the PHOTOS Monte Carlo program. We conclude a 0.2% relative precision in the
implementation of the hard photon matrix element into the emission kernel,
including the case where approximations are used.Comment: 1+20 pages, 8 figure
On ordinal utility, cardinal utility, and random utility
Though the Random Utility Model (RUM) was conceived
entirely in terms of ordinal utility, the apparatus throughwhich it is widely practised exhibits properties of
cardinal utility. The adoption of cardinal utility as a
working operation of ordinal is perfectly valid, provided
interpretations drawn from that operation remain faithful
to ordinal utility. The paper considers whether the latterrequirement holds true for several measurements commonly
derived from RUM. In particular it is found that
measurements of consumer surplus change may depart from
ordinal utility, and exploit the cardinality inherent in
the practical apparatus.
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