Starting from a successful model of the
π
-meson electromagnetic form factor, we calculate a similar form factor,
F
K
(
Q
2
)
, of the charged
K
meson for a wide range of the momentum transfer ...squared,
Q
2
. The only remaining free parameter is to be determined from the measurements of the
K
-meson charge radius,
r
K
. We fit this single parameter to the published data of the NA-7 experiment which measured
F
K
(
Q
2
)
at
Q
2
→
0
and determine our preferred range of
r
K
, which happens to be close to recent lattice results. Still, the accuracy in the determination of
r
K
is poor. However, future measurements of the
K
-meson electromagnetic form factor at
Q
2
≲
5.5
GeV
2
, scheduled in Jefferson Laboratory for 2017, will test our approach and will reduce the uncertainty in
r
K
significantly.
It has been shown previously that in a relativistic constituent-quark model, predictions for the electromagnetic form factor of the
π
meson match not only experimental data but also, in the limit of ...large momentum transfers, the asymptotics derived from Quantum Chromodynamics (QCD). This is remarkable since no parameters are introduced to provide for this infrared-ultraviolet link. Here, we follow this approach, going beyond QCD. We obtain numerical relations between the gauge coupling constant, the decay constant and the charge radius of the pion-like meson in general strongly-coupled theories. These relations are compared to published lattice results for
SU
(2) gauge theory with two fermion flavours, and a good agreement is demonstrated. Further applications of the approach, to be explored elsewhere, include composite Higgs and dark-matter models.
Recent astrophysical transient Swift J1913.1+1946 is possibly associated with the gamma-ray burst GRB 221009A at the redshift
. The transient was accompanied by very high-energy gamma rays up to ...18 TeV observed by LHAASO and a photon-like air shower of 251 TeV detected by Carpet-2. These energetic gamma rays cannot reach us from the claimed distance of the source because of the pair production on cosmic background radiation. If the identification and redshift measurements are correct, one would require new physics to explain the data. One possibility invokes axion-like particles (ALPs) which mix with photons but do not attenuate on the background radiation. Here we explore the ALP parameter space and find that the ALP–photon mixing in the Milky Way, and not in the intergalactic space, may help to explain the observations. However, given the low Galactic latitude of the event, misidentification with a Galactic transient remains an undiscarded explanation.
It has been previously shown that a particular nonperturbative constituent-quark model of hadrons describes experimental measurements of electromagnetic form factors of light charged mesons through a ...small number of common phenomenological parameters, matching at the same time the quantum-chromodynamics (QCD) asymptotics for the π-meson form factor at large momentum transfer. Here we start with the determination of the K0 electromagnetic form factor in this approach. Precise measurement of the K0 charge radius makes it possible to constrain model parameters with high accuracy. Then, with all parameters fixed, we revisit the K+ form factor and find that it matches experimental measurements in the infrared, lattice results at moderate momentum transfer, and the perturbative QCD asymptotics in the ultraviolet. In this way we obtain a narrow constraint on the K+ charge radius, ⟨r2K+⟩ = 0.403+0.007−0.006 fm2, and extend the successful infrared-ultraviolet connection from π to K mesons.
ABSTRACT
Evidence for bright-radio blazars being high-energy neutrino sources was found in recent years. However, specifics of how and where these particles get produced still need to be determined. ...In this paper, we add 14 new IceCube events from 2020–2022 to update our analysis of the neutrino-blazars connection. We test and refine earlier findings by utilizing the total of 71 track-like high-energy IceCube events from 2009–2022. We correlate them with the complete sample of 3412 extragalactic radio sources selected by their compact radio emission. We demonstrate that neutrinos are statistically associated with radio-bright blazars with a post-trial p-value of 3 · 10−4. In addition to this statistical study, we confirm previous individual neutrino-blazar associations, find and discuss several new ones. Notably, PKS 1741 − 038 was selected earlier and had a second neutrino detected from its direction in 2022; PKS 0735 + 168 has experienced a major flare across the whole electromagnetic spectrum coincidently with a neutrino arrival from that direction in 2021.
The Sydney University Giant Air-shower Recorder (SUGAR) measured the energy spectrum of ultra-high-energy cosmic rays reconstructed from muon-detector readings, while the Pierre Auger Observatory, ...looking at the same Southern sky, used the calorimetric fluorescence method for the same purpose. Comparison of their two spectra allows us to reconstruct the empirical dependence of the number of muons in a vertical shower on the primary energy for energies between 1017 and 1018.5 eV. We compare this dependence with the predictions of hadronic interaction models QGSJET-II-04, EPOS-LHC and SIBYLL-2.3c. The empirically determined number of muons with energies above 0.75 GeV in a vertical shower exceeds the simulated one by the factors ∼1.7 and ∼1.3 for 1017 eV proton and iron primaries, respectively. The muon excess grows moderately with the primary energy, increasing by an additional factor of ∼1.2 for 1018.5 eV primaries.
In this brief review, possible manifestations of mixing between axion-like particles (ALPs) and energetic photons propagating over astronomical distances are considered. We discuss the evidence for ...the anomalous transparency of the Universe from observations of ensembles of distant gamma-ray sources, present the general formalism for the ALP-photon mixing and explain how this mechanism may remove the anomaly. We present relevant values of ALP parameters and discuss future ways to verify the scenario and to discover the particle in question.
Abstract
Astrophysical sources of neutrinos detected by large-scale neutrino telescopes remain uncertain. While there exist statistically significant observational indications that a part of the ...neutrino flux is produced by blazars, numerous theoretical studies suggest also the presence of potential Galactic point sources. Some of them have been observed in gamma rays above 100 TeV. Moreover, cosmic-ray interactions in the Galactic disk guarantee a diffuse neutrino flux. However, these Galactic neutrinos have not been unambiguously detected so far. Here we examine whether such a Galactic component is present among the observed neutrinos of the highest energies. We analyze public track-like IceCube events with estimated neutrino energies above 200 TeV. We examine the distribution of arrival directions of these neutrinos in the Galactic latitude
b
with the help of a simple unbinned, nonparametric test statistics, the median ∣
b
∣ over the sample. This distribution deviates from that implied by the null hypothesis of the neutrino flux isotropy, and is shifted toward lower ∣
b
∣ with the
p
-value of 4 × 10
−5
, corresponding to the statistical significance of 4.1
σ
. There exists a significant component of the high-energy neutrino flux of Galactic origin, matching well the multimessenger expectations from Tibet-AS
γ
observations of diffuse Galactic gamma rays at hundreds of TeV. Together with the previously established extragalactic associations, the Galactic component we report here implies that the neutrino sky is rich and is composed of contributions from various classes of sources.
Abstract
The high-energy radiation from short period binaries containing a massive star with a compact relativistic companion was detected from radio to TeV
γ-
rays. We show here that PeV regime ...protons can be efficiently accelerated in the regions of collision of relativistic outflows of a compact object with stellar winds in these systems. The accelerated proton spectra in the presented Monte Carlo model have an upturn in the PeV regime and can provide very hard spectra of sub-PeV photons and neutrinos by photomeson processes in the stellar radiation field. The recent report of a possible sub-PeV
γ
-ray flare in coincidence with a high-energy neutrino can be understood in the frame of this model. The
γ
-ray binaries may contribute substantially to the Galactic component of the detected high-energy neutrino flux.
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