1,767 research outputs found
Beyond Rainbow-Ladder in bound state equations
In this work we devise a new method to study quark anti-quark interactions
beyond simple ladder-exchange that yield massless pions in the chiral limit.
The method is based on the requirement to have a representation of the
quark-gluon vertex that is explicitly given in terms of quark dressings
functions. We outline a general procedure to generate the Bethe-Salpeter kernel
for a given vertex representation. Our method allows not only the
identification of the mesons' masses but also the extraction of their
Bethe-Salpeter wave functions exposing their internal structure. We exemplify
our method with vertex models that are of phenomenological interest.Comment: 13 pages, 6 figures; v2: typos corrected, colors improve
The role of momentum dependent dressing functions and vector meson dominance in hadronic light-by-light contributions to the muon g-2
We present a refined calculation of the quark-loop contribution to hadronic
light-by-light scatter- ing that focuses upon the impact of the transverse
components of the quark-photon vertex. These structures are compared and
contrasted with those found within the extended NJL-models. We discuss
similarities and differences between the two approaches and further clarify the
important role of momentum dependent dressing functions. As expected we find
that the transverse structures of the quark-photon vertex lead to a suppression
of the quark-loop contribution to the anomalous magnetic moment of the muon.
However, we find evidence that this suppression is overestimated within models
with simple approximations for the quark-photon interaction.Comment: 13 pages, 5 figures, v2: typos corrected, references added, version
submitted to PR
A fresh look at hadronic light-by-light scattering in the muon g-2 with the Dyson-Schwinger approach
We present first results for the hadronic light-by-light scattering
contribution to the anomalous magnetic moment of the muon a_{\mu} in the
framework of Dyson-Schwinger and Bethe-Salpeter equations. We determine the
quark loop and pseudoscalar ({\pi}^0, {\eta}, {\eta}') meson exchange diagram
using a phenomenological model for the combined strength of the gluon
propagator and the quark-gluon interaction as the only input. Our result for
meson exchange, a_{\mu}^{LBL;PS}=(84 \pm 13) x 10^{-11}, is commensurate with
previous calculations. However, our number for the quark loop contribution,
a_{\mu}^{LBL;quarkloop} = (107 \pm 2 \pm 46) x 10^{-11}, is significantly
larger due to dressing effects in the quark propagator and the quark-photon
vertex. Taken at face value, this then leads to a revised estimate of the total
a_{\mu}=116 591 865.0(96.6) x 10^{-11}, which reduces the difference between
theory and experiment to about 1.9 {\sigma}.Comment: 5 pages, 7 figures, v2: title slightly changed, minor corrections,
version accepted by EP
No collective neutrino flavor conversions during the supernova accretion phase
The large neutrino fluxes emitted with a distinct flavor hierarchy from
core-collapse supernovae (SNe) during the post-bounce accretion phase, offer
the best opportunity to detect effects from neutrino flavor oscillations. We
perform a dedicated study of the SN neutrino flavor evolution during the
accretion phase, using results from recent neutrino radiation hydrodynamics
simulations. In contrast to what expected in the presence of only
neutrino-neutrino interactions, we find that the multi-angle effects associated
with the dense ordinary matter suppress collective oscillations. This is
related to the high matter densities during the accretion phase in
core-collapse SNe of massive iron-core progenitors. The matter suppression
implies that neutrino oscillations will start outside the neutrino transport
region and therefore will have a negligible impact on the neutrino heating and
the explosion dynamics. Furthermore, the possible detection of the next
galactic SN neutrino signal from the accretion phase, based on the usual
Mikheyev- Smirnov-Wolfenstein effect in the SN mantle and Earth matter effects,
can reveal the neutrino mass hierarchy in the case that the mixing angle
is not very small.Comment: (4 pages, 4 eps figures, v2 revised version. Discussion clarified.
Matches the version published on PRL
Stability analysis of collective neutrino oscillations in the supernova accretion phase with realistic energy and angle distributions
We revisit our previous results on the matter suppression of self-induced
neutrino flavor conversions during a supernova (SN) accretion phase, performing
a linearized stability analysis of the neutrino equations of motion, in the
presence of realistic SN density profiles. In our previous numerical study, we
used a simplified model based on an isotropic neutrino emission with a single
typical energy. Here, we take into account realistic neutrino energy and angle
distributions. We find that multi-energy effects have a sub-leading impact in
the flavor stability of the SN neutrino fluxes with respect to our previous
single-energy results. Conversely, realistic forward-peaked neutrino angular
distributions would enhance the matter suppression of the self-induced
oscillations with respect to an isotropic neutrino emission. As a result, in
our models for iron-core SNe, collective flavor conversions have a negligible
impact on the characterization of the observable neutrino signal during the
accretion phase. Instead, for a low-mass O-Ne-Mg core SN model, with lower
matter density profile and less forward-peaked angular distributions,
collective conversions are possible also at early times.Comment: v2: 8 pages, 3 eps figures. Revised version. Minor changes.
References updated. Matches the version published on PR
Analysis of matter suppression in collective neutrino oscillations during the supernova accretion phase
The usual description of self-induced neutrino flavor conversions in core
collapse supernovae (SNe) is based on the dominance of the neutrino density
n_nu over the net electron density n_e. However, this condition is not met
during the post-bounce accretion phase, when the dense matter in a SN is piled
up above the neutrinosphere. As recently pointed-out, a dominant matter term in
the anisotropic SN environment would dephase the flavor evolution for neutrinos
traveling on different trajectories, challenging the occurrence of the
collective behavior in the dense neutrino gas. Using the results from recent
long term simulations of core-collapse SN explosions, based on three flavor
Boltzmann neutrino transport in spherical symmetry, we find that both the
situations of complete matter suppression (when n_e >> n_nu) and matter-induced
decoherence (when n_e \gtrsim n_nu) of flavor conversions are realized during
the accretion phase. The matter suppression at high densities prevents any
possible impact of the neutrino oscillations on the neutrino heating and hence
on the dynamics of the explosion. Furthermore, it changes the interpretation of
the Earth matter effect on the SN neutrino signal during the accretion phase,
allowing the possibility of the neutrino mass hierarchy discrimination at not
too small values of the leptonic mixing angle \theta_{13} (i.e.
\sin^2{\theta}_{13} \gtrsim 10^{-3}).Comment: Revised version (15 pages, 13 eps figures) published on Physical
Review D. Discussion enlarged, references update
Leading-order calculation of hadronic contributions to the muon using the Dyson-Schwinger approach
We present a calculation of the hadronic vacuum polarization (HVP) tensor
within the framework of Dyson--Schwinger equations. To this end we use a
well-established phenomenological model for the quark-gluon interaction with
parameters fixed to reproduce hadronic observables. From the HVP tensor we
compute both the Adler function and the HVP contribution to the anomalous
magnetic moment of the muon, . We find which deviates about two percent from the value extracted from
experiment. Additionally, we make comparison with a recent lattice
determination of and find good agreement within our approach. We
also discuss the implications of our result for a corresponding calculation of
the hadronic light-by-light scattering contribution to .Comment: 9 pages, 8 figure
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