11,908 research outputs found
Fully differential NLO predictions for rare and radiative lepton decays
We present a general purpose, parton-level Monte Carlo program for the
calculation of the radiative () and rare
() muon and tau decays at NLO in the effective Fermi
theory. In the case of muon, these processes are irreducible Standard Model
backgrounds to searches for lepton flavour violation at the PSI experiments MEG
and Mu3e as they become indistinguishable from the corresponding signals when
the neutrinos carry little energy.
Furthermore, we argue that fully differential NLO corrections are very
important for the analysis of measurements aiming at the percent level or
better. This is especally true if very stringent phase-space cuts are applied.
To illustrate this, we use a tension between BaBar's recent measurement of the
radiative tau decay and the Standard Model prediction as an example of such an
analysis. Finally, we present the branching ratios of the rare tau decay
at NLO.
We generally find that QED corrections of are very well
possible.Comment: Proceedings of the 19th International Workshop on Neutrinos from
Accelerators (NUFACT 2017
Fully differential NLO predictions for the radiative decay of muons and taus
We present a general purpose Monte Carlo program for the calculation of the
radiative muon decay and the radiative decays
and at
next-to-leading order in the Fermi theory. The full dependence on the lepton
masses and polarization of the initial-sate lepton are kept. We study the
branching ratios for these processes and show that fully-differential
next-to-leading order corrections are important for addressing a tension
between BaBar's recent measurement of the branching ratio and the Standard Model prediction. In addition, we
study various distributions of the process and
obtain precise predictions for the irreducible background to
searches, tailored to the geometry of the MEG detector.Comment: 14 pages, 5 figures, published versio
Small-mass effects in heavy-to-light form factors
We present the heavy-to-light form factors with two different non-vanishing
masses at next-to-next-to-leading order and study its expansion in the small
mass. The leading term of this small-mass expansion leads to a factorized
expression for the form factor. The presence of a second mass results in a new
feature, in that the soft contribution develops a factorization anomaly. This
cancels with the corresponding anomaly in the collinear contribution. With the
generalized factorization presented here, it is possible to obtain the leading
small-mass terms for processes with large masses, such as muon-electron
scattering, from the corresponding massless amplitude and the soft
contribution.Comment: 20 pages, 4 figures, 1 ancillary file, published versio
Is there a universality of the helix-coil transition in protein models?
The similarity in the thermodynamic properties of two completely different
theoretical models for the helix-coil transition is examined critically. The
first model is an all-atomic representation for a poly-alanine chain, while the
second model is a minimal helix-forming model that contains no system
specifics. Key characteristics of the helix-coil transition, in particular, the
effective critical exponents of these two models agree with each other, within
a finite-size scaling analysis.Comment: Latex, to appear in Eur. Phys. J.
Nitrogen fluorescence in air for observing extensive air showers
Extensive air showers initiate the fluorescence emissions from nitrogen
molecules in air. The UV-light is emitted isotropically and can be used for
observing the longitudinal development of extensive air showers in the
atmosphere over tenth of kilometers. This measurement technique is
well-established since it is exploited for many decades by several cosmic ray
experiments. However, a fundamental aspect of the air shower analyses is the
description of the fluorescence emission in dependence on varying atmospheric
conditions. Different fluorescence yields affect directly the energy scaling of
air shower reconstruction. In order to explore the various details of the
nitrogen fluorescence emission in air, a few experimental groups have been
performing dedicated measurements over the last decade. Most of the
measurements are now finished. These experimental groups have been discussing
their techniques and results in a series of Air Fluorescence Workshops
commenced in 2002. At the 8 Air Fluorescence Workshop 2011, it was
suggested to develop a common way of describing the nitrogen fluorescence for
application to air shower observations. Here, first analyses for a common
treatment of the major dependences of the emission procedure are presented.
Aspects like the contributions at different wavelengths, the dependence on
pressure as it is decreasing with increasing altitude in the atmosphere, the
temperature dependence, in particular that of the collisional cross sections
between molecules involved, and the collisional de-excitation by water vapor
are discussed.Comment: 12 pages, 17 figures, 2 tables, International Symposium on Future
Directions in UHECR Physics, 13-16 February 2012, CERN, Geneva (Switzerland);
the updated version corrects for a typo in Eq. (1
The classification of non-local chiral CFT with c<1
All non-local but relatively local irreducible extensions of Virasoro chiral
CFTs with c<1 are classified. The classification, which is a prerequisite for
the classification of local c<1 boundary CFTs on a two-dimensional half-space,
turns out to be 1 to 1 with certain pairs of A-D-E graphs with distinguished
vertices.Comment: 13 pages. v3: additional material (concerning the Hilbert spaces)
adde
Binary black-hole evolutions of excision and puncture data
We present a new numerical code developed for the evolution of binary
black-hole spacetimes using different initial data and evolution techniques.
The code is demonstrated to produce state-of-the-art simulations of orbiting
and inspiralling black-hole binaries with convergent waveforms. We also present
the first detailed study of the dependence of gravitational waveforms resulting
from three-dimensional evolutions of different types of initial data. For this
purpose we compare the waveforms generated by head-on collisions of superposed
Kerr-Schild, Misner and Brill-Lindquist data over a wide range of initial
separations.Comment: 21 pages, 13 figures, final version accepted for publication in PR
Magnetic Resonant excitations in High-{} superconductors
The observation of an unusual spin resonant excitation in the superconducting
state of various High-Tc ~copper oxides by inelastic neutron scattering
measurements is reviewed. This magnetic mode % (that does not exist in
conventional superconductors) is discussed in light of a few theoretical models
and likely corresponds to a spin-1 collective mode.Comment: 4 figures, Proceedings conference MSM'03 (september 2003) in Monastir
(Tunisia) to be published in Phys. Stat. Solid
Current-Driven Domain-Wall Dynamics in Curved Ferromagnetic Nanowires
The current-induced motion of a domain wall in a semicircle nanowire with
applied Zeeman field is investigated. Starting from a micromagnetic model we
derive an analytical solution which characterizes the domain-wall motion as a
harmonic oscillation. This solution relates the micromagnetic material
parameters with the dynamical characteristics of a harmonic oscillator, i.e.,
domain-wall mass, resonance frequency, damping constant, and force acting on
the wall. For wires with strong curvature the dipole moment of the wall as well
as its geometry influence the eigenmodes of the oscillator. Based on these
results we suggest experiments for the determination of material parameters
which otherwise are difficult to access. Numerical calculations confirm our
analytical solution and show its limitations
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