153 research outputs found
Charge independence breaking and charge symmetry breaking in the nucleon-nucleon interaction from effective field theory
We discuss charge symmetry and charge independence breaking in an effective
field theory approach for few-nucleon systems. We systematically introduce
strong isospin-violating and electromagnetic operators in the theory. The
charge dependence observed in the nucleon-nucleon scattering lengths is due to
one-pion exchange and one electromagnetic four-nucleon contact term. This gives
a parameter free expression for the charge dependence of the corresponding
effective ranges, which is in agreement with the rather small and uncertain
empirical determinations. We also compare the low energy phase shifts of the
and the system.Comment: 11 pp, LaTeX, 2 figures (uses epsfig), dedicated to Walter Gloeckle
on the occasion of his 60th birthda
Delta-excitations and the three-nucleon force
We study the three-nucleon force in chiral effective field theory with
explicit Delta-resonance degrees of freedom. We show that up to
next-to-next-to-leading order, the only contribution to the isospin symmetric
three-nucleon force involving the spin-3/2 degrees of freedom is given by the
two-pion-exchange diagram with an intermediate delta, frequently called the
Fujita-Miyazawa force. We also analyze the leading isospin-breaking corrections
due to the delta. For that, we give the first analysis of the delta quartet
mass splittings in chiral effective field theory. The charge-symmetry breaking
three-nucleon force due to an intermediate delta excitation is small, of the
order of a few keV.Comment: 12 pages, 2 figures; minor changes, reference adde
Sequential vector and axial-vector meson exchange and chiral loops in radiative phi decay
We study the radiative decay into and taking into account mechanisms in which there are two sequential
vector-vector-pseudoscalar or axial-vector--vector--pseudoscalar steps followed
by the coupling of a vector meson to the photon, considering the final state
interaction of the two mesons. There are other mechanisms in which two kaons
are produced through the same sequential mechanisms or from decay into
two kaons and then undergo final state interaction leading to the final pair of
pions or , this latter mechanism being the leading one. The results
of the parameter free theory, together with the theoretical uncertainties, are
compared with the latest experimental results of KLOE at Frascati.Comment: 28 pages, 20 figure
Hadronic light-by-light scattering contribution to the muon g-2: an effective field theory approach
The hadronic light-by-light contribution to a_{mu}, the anomalous magnetic
moment of the muon, is discussed from the point of view of an effective
low-energy theory. As an application, the coefficient of the leading logarithm
arising from the two-loop graphs involving two anomalous vertices is computed,
and found to be positive. This corresponds to a positive sign for the pion-pole
contribution to the hadronic light-by-light correction to a_{mu}, and to a
sizeable reduction of the discrepancy between the present experimental value of
a_{mu} and its theoretical counterpart in the standard model.Comment: 4 pages, 1 figure. v2: published versio
Electromagnetic Corrections to Pi Pi Scattering: Some Lessons for the Implementation of Meson Exchange Models
The leading non-Coulombic electromagnetic contributions to pi pi s-wave
scattering lengths are computed in Chiral Perturbation Theory. It is shown that
these corrections are zeroth order in the chiral expansion and associated with
electromagnetic contact terms in the effective Lagrangian, i.e. that they do
not involve explicit photon fields in the low-energy effective theory. It is
pointed out that, if one followed the standard meson-exchange-model ansatz for
removing electromagnetic effects, i.e. of subtracting contributions associated
with explicit photon exchange and radiative corrections, as determined by the
photon coupling vertices of the effective hadronic theory, one would completely
miss these contributions and arrive at the erroneous conclusion that the strong
interactions exhibited very large isospin breaking in pi pi scattering.
Implications for electromagnetic "subtraction" procedures in other hadronic
systems and the utility of the effective Lagrangian method for avoiding such
errors are obvious.Comment: 16 pages, REVTE
Pion and Kaon Vector Form Factors
We develop a unitarity approach to consider the final state interaction
corrections to the tree level graphs calculated from Chiral Perturbation Theory
() allowing the inclusion of explicit resonance fields. The method is
discussed considering the coupled channel pion and kaon vector form factors.
These form factors are then matched with the one loop results. A very
good description of experimental data is accomplished for the vector form
factors and for the P-wave phase shifts up to
GeV, beyond which multiparticle states play a non negligible role. In
particular the low and resonance energy regions are discussed in detail and for
the former a comparison with one and two loop is made showing a
remarkable coincidence with the two loop results.Comment: 20 pages, 7 figs, to appear in Phys. Rev.
The electroweak chiral Lagrangian reanalyzed
In this paper we reanalyze the electroweak chiral Lagrangian with particular
focus on two issues related to gauge invariance. Our analysis is based on a
manifestly gauge-invariant approach that we introduced recently. It deals with
gauge-invariant Green's functions and provides a method to evaluate the
corresponding generating functional without fixing the gauge. First we show,
for the case where no fermions are included in the effective Lagrangian, that
the set of low-energy constants currently used in the literature is redundant.
In particular, by employing the equations of motion for the gauge fields one
can choose to remove two low-energy constants which contribute to the
self-energies of the gauge bosons. If fermions are included in the effective
field theory analysis the situation is more involved. Even in this case,
however, these contributions to the self-energies of the gauge bosons can be
removed. The relation of this result to the experimentally determined values
for the oblique parameters S, T, and U is discussed. In the second part of the
paper we consider the matching relation between a full and an effective theory.
We show how the low-energy constants of the effective Lagrangian can be
determined by matching gauge-invariant Green's functions in both theories. As
an application we explicitly evaluate the low-energy constants for the standard
model with a heavy Higgs boson. The matching at the one-loop level and at
next-to-leading order in the low-energy expansion is performed employing
functional methods.Comment: 44 pages, Revtex. v2: Sections II and III interchanged. New section
II now self-contained. Discussions improved in sections I, II, V.C and VI.
Conclusions unchanged. Published versio
Gauge-invariant Green's functions for the bosonic sector of the standard model
There are many applications in gauge theories where the usually employed
framework involving gauge-dependent Green's functions leads to considerable
problems. In order to overcome the difficulties invariably tied to gauge
dependence, we present a manifestly gauge-invariant approach. We propose a
generating functional of appropriately chosen gauge-invariant Green's functions
for the bosonic sector of the standard model. Since the corresponding external
sources emit one-particle states, these functions yield the same S-matrix
elements as those obtained in the usual framework. We evaluate the generating
functional for the bosonic sector of the standard model up to the one-loop
level and carry out its renormalization in the on-shell scheme. Explicit
results for some two-point functions are given. Gauge invariance is manifest at
any step of our calculation.Comment: 29 pages, Revtex. v2: Discussions improved, conclusions unchanged.
Some references added. v3: Published versio
Shape modeling technique KOALA validated by ESA Rosetta at (21) Lutetia
We present a comparison of our results from ground-based observations of
asteroid (21) Lutetia with imaging data acquired during the flyby of the
asteroid by the ESA Rosetta mission. This flyby provided a unique opportunity
to evaluate and calibrate our method of determination of size, 3-D shape, and
spin of an asteroid from ground-based observations. We present our 3-D
shape-modeling technique KOALA which is based on multi-dataset inversion. We
compare the results we obtained with KOALA, prior to the flyby, on asteroid
(21) Lutetia with the high-spatial resolution images of the asteroid taken with
the OSIRIS camera on-board the ESA Rosetta spacecraft, during its encounter
with Lutetia. The spin axis determined with KOALA was found to be accurate to
within two degrees, while the KOALA diameter determinations were within 2% of
the Rosetta-derived values. The 3-D shape of the KOALA model is also confirmed
by the spectacular visual agreement between both 3-D shape models (KOALA pre-
and OSIRIS post-flyby). We found a typical deviation of only 2 km at local
scales between the profiles from KOALA predictions and OSIRIS images, resulting
in a volume uncertainty provided by KOALA better than 10%. Radiometric
techniques for the interpretation of thermal infrared data also benefit greatly
from the KOALA shape model: the absolute size and geometric albedo can be
derived with high accuracy, and thermal properties, for example the thermal
inertia, can be determined unambiguously. We consider this to be a validation
of the KOALA method. Because space exploration will remain limited to only a
few objects, KOALA stands as a powerful technique to study a much larger set of
small bodies using Earth-based observations.Comment: 15 pages, 8 figures, 2 tables, accepted for publication in P&S
Attitudes towards digital treatment for depression: A European stakeholder survey
The integration of digital treatments into national mental health services is on the agenda in the European Union. The E-COMPARED consortium conducted a survey aimed at exploring stakeholders' knowledge, acceptance and expectations of digital treatments for depression, and at identifying factors that might influence their opinions when considering the implementation of these approaches. An online survey was conducted in eight European countries: France, Germany, Netherlands, Poland, Spain, Sweden, Switzerland and The United Kingdom. Organisations representing government bodies, care providers, service-users, funding/insurance bodies, technical developers and researchers were invited to participate in the survey. The participating countries and organisations reflect the diversity in health care infrastructures and e-health implementation across Europe. A total of 764 organisations were invited to the survey during the period March–June 2014, with 175 of these organisations participating in our survey. The participating stakeholders reported moderate knowledge of digital treatments and considered cost-effectiveness to be the primary incentive for integration into care services. Low feasibility of delivery within existing care services was considered to be a primary barrier. Digital treatments were regarded more suitable for milder forms of depression. Stakeholders showed greater acceptability towards blended treatment (the integration of face-to-face and internet sessions within the same treatment protocol) compared to standalone internet treatments. Organisations in countries with developed e-health solutions reported greater knowledge and acceptability of digital treatments. Mental health stakeholders in Europe are aware of the potential benefits of digital interventions. However, there are variations between countries and stakeholders in terms of level of knowledge about such interventions and their feasibility within routine care services. The high acceptance of blended treatments is an interesting finding that indicates a gradual integration of technology into clinical practice may fit the attitudes and needs of stakeholders. The potential of the blended treatment approach, in terms of enhancing acceptance of digital treatment while retaining the benefit of cost-effectiveness in delivery, should be further explored. The E-COMPARED project has received funding from the European Union Seventh Framework Programme (FP7/2007–2013) under grant agreement no. 603098
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