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18 pages, 1462 KiB

Open AccessArticle

From Gamma Rays to Cosmic Rays: Lepto-Hadronic Modeling of Blazar Sources as Candidates for Ultra-High-Energy Cosmic Rays

by Luiz Augusto Stuani Pereira and Samuel Victor Bernardo da Silva

Universe 2025, 11(8), 266; https://doi.org/10.3390/universe11080266 - 14 Aug 2025

Abstract

Ultra-high-energy cosmic rays (UHECRs) with energies exceeding

10^{19}

eV are believed to originate from extragalactic environments, potentially associated with relativistic jets in active galactic nuclei (AGN). Among AGNs, blazars, particularly those detected in very-high-energy (VHE) gamma rays, are promising candidates for UHECR [...] Read more.

Ultra-high-energy cosmic rays (UHECRs) with energies exceeding

10^{19}

eV are believed to originate from extragalactic environments, potentially associated with relativistic jets in active galactic nuclei (AGN). Among AGNs, blazars, particularly those detected in very-high-energy (VHE) gamma rays, are promising candidates for UHECR acceleration and high-energy neutrino production. In this work, we investigate three blazar sources, AP Librae, 1H 1914–194, and PKS 0735+178, using multiwavelength spectral energy distribution (SED) modeling. These sources span a range of synchrotron peak classes and redshifts, providing a diverse context to explore the physical conditions in relativistic jets. We employ both leptonic and lepto-hadronic models to describe their broadband emission from radio to TeV energies, aiming to constrain key jet parameters such as magnetic field strength, emission region size, and particle energy distributions. Particular attention is given to evaluating their potential as sources of UHECRs and high-energy neutrinos. Our results shed light on the complex interplay between particle acceleration mechanisms, radiative processes, and multi-messenger signatures in extreme astrophysical environments. Full article

(This article belongs to the Special Issue Ultra-High Energy Cosmic Rays: Past, Present and Future)

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11 pages, 2887 KiB

Open AccessArticle

INTEGRAL/ISGRI Post 2024-Periastron View of PSR B1259-63

by Aleksei Kuzin, Denys Malyshev, Maria Chernyakova, Brian van Soelen and Andrea Santangelo

Universe 2025, 11(8), 254; https://doi.org/10.3390/universe11080254 - 31 Jul 2025

Viewed by 158

Abstract

PSR B1259-63/LS 2883 is a well-studied gamma-ray binary hosting a pulsar in a 3.4-year eccentric orbit around a Be-type star. Its non-thermal emission spans from radio to TeV energies, exhibiting a significant increase near the periastron passage. This paper is dedicated to the [...] Read more.

PSR B1259-63/LS 2883 is a well-studied gamma-ray binary hosting a pulsar in a 3.4-year eccentric orbit around a Be-type star. Its non-thermal emission spans from radio to TeV energies, exhibiting a significant increase near the periastron passage. This paper is dedicated to the analysis of INTEGRAL observations of the system following its last periastron passage in June 2024. We aim to study the spectral evolution of this gamma-ray binary in the soft (0.3–10 keV) and hard (30–300 keV) X-ray energy bands. We performed a joint analysis of the data taken by INTEGRAL/ISGRI in July–August 2024 and quasi-simultaneous Swift/XRT observations. The spectrum of the system in the 0.3–300 keV band is well described by an absorbed power law with a photon index of

Γ = 1.42 \pm 0.03

. We place constraints on potential spectral curvature, limiting the break energy

E_{b} > 30

keV for

Δ Γ > 0.3

and cutoff energy

E_{cutoff} > 150

keV at a 95% confidence level. For one-zone leptonic emission models, these values correspond to electron distribution spectral parameters of

E_{b, e} > 0.8

TeV and

E_{cutoff, e} > 1.7

TeV, consistent with previous constraints derived by H.E.S.S. Full article

(This article belongs to the Section Compact Objects)

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12 pages, 690 KiB

Open AccessArticle

An Overview of the MUSES Calculation Engine and How It Can Be Used to Describe Neutron Stars

by Mateus Reinke Pelicer, Veronica Dexheimer and Joaquin Grefa

Universe 2025, 11(7), 200; https://doi.org/10.3390/universe11070200 - 20 Jun 2025

Cited by 1 | Viewed by 247

Abstract

For densities beyond nuclear saturation, there is still a large uncertainty in the equations of state (EoSs) of dense matter that translate into uncertainties in the internal structure of neutron stars. The MUSES Calculation Engine provides a free and open-source composable workflow management [...] Read more.

For densities beyond nuclear saturation, there is still a large uncertainty in the equations of state (EoSs) of dense matter that translate into uncertainties in the internal structure of neutron stars. The MUSES Calculation Engine provides a free and open-source composable workflow management system, which allows users to calculate the EoSs of dense and hot matter that can be used, e.g., to describe neutron stars. For this work, we make use of two MUSES EoS modules, i.e., Crust Density Functional Theory and Chiral Mean Field model, with beta-equilibrium with leptons enforced in the Lepton module, then connected by the Synthesis module using different functions: hyperbolic tangent, generalized Gaussian, bump, and smoothstep. We then calculate stellar structure using the QLIMR module and discuss how the different interpolating functions affect our results. Full article

(This article belongs to the Special Issue Compact Stars in the QCD Phase Diagram 2024)

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11 pages, 432 KiB

Open AccessArticle

Inclusive Neutrino and Antineutrino Scattering on the ¹²C Nucleus Within the Coherent Density Fluctuation Model

by Martin V. Ivanov and Anton N. Antonov

Universe 2025, 11(4), 119; https://doi.org/10.3390/universe11040119 - 4 Apr 2025

Viewed by 388

Abstract

We investigate quasielastic (anti)neutrino scattering on the ¹²C nucleus utilizing a novel scaling variable,

ψ^{*}

. This variable is derived from the interacting relativistic Fermi gas model, which incorporates both scalar and vector interactions, leading to a relativistic effective mass for [...] Read more.

We investigate quasielastic (anti)neutrino scattering on the ¹²C nucleus utilizing a novel scaling variable,

ψ^{*}

. This variable is derived from the interacting relativistic Fermi gas model, which incorporates both scalar and vector interactions, leading to a relativistic effective mass for the interacting nucleons. For inclusive lepton scattering from nuclei, we develop a new scaling function, denoted as

f^{QE} (ψ^{*})

, based on the coherent density fluctuation model (CDFM). This model serves as a natural extension of the relativistic Fermi gas (RFG) model applicable to finite nuclei. In this study, we compute theoretical predictions and compare them with experimental data from Miner

ν

a and T2K for inclusive (anti)neutrino cross-sections. The scaling function is derived within the CDFM framework, employing a relativistic effective mass of

m_{N}^{*} = 0.8 m_{N}

. The findings demonstrate a high degree of consistency with experimental data across all (anti)neutrino energy ranges. Full article

(This article belongs to the Special Issue Neutrino Insights: Peering into the Subatomic Universe)

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9 pages, 1080 KiB

Open AccessReview

Lepton Flavour Universality Tests Using Semileptonic b-Hadron Decays at the LHCb Detector

by Bogdan Kutsenko

Particles 2025, 8(1), 5; https://doi.org/10.3390/particles8010005 - 14 Jan 2025

Viewed by 825

Abstract

This review highlights advancements in testing Lepton Flavour Universality (LFU) through semileptonic b-hadron decays at the LHCb detector. Measurements of the LFU

R (D)

and

R (D^{*})

provide evidence of deviations from Standard Model (SM) predictions, suggesting [...] Read more.

This review highlights advancements in testing Lepton Flavour Universality (LFU) through semileptonic b-hadron decays at the LHCb detector. Measurements of the LFU

R (D)

and

R (D^{*})

provide evidence of deviations from Standard Model (SM) predictions, suggesting the presence of possible New Physics (NP). However, the

D^{★}

longitudinal polarisation results are in good agreement with SM expectations, placing constraints on potential NP theories, such as the leptoquarks or charged Higgs models. Further improvements in the measurements’ precision are expected with the new data from LHCb Run 3, collected with higher instantaneous luminosity and improved trigger. Full article

(This article belongs to the Special Issue Selected Papers from the 13th International Conference on New Frontiers in Physics (ICNFP 2024))

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10 pages, 333 KiB

Open AccessReview

Hunting for Bileptons at Hadron Colliders

by Gennaro Corcella

Entropy 2024, 26(10), 850; https://doi.org/10.3390/e26100850 - 8 Oct 2024

Cited by 1 | Viewed by 728

Abstract

I review possible signals at hadron colliders of bileptons, namely doubly charged vectors or scalars with lepton number

L = \pm 2

, as predicted by a 331 model, based on a [...] Read more.

I review possible signals at hadron colliders of bileptons, namely doubly charged vectors or scalars with lepton number

L = \pm 2

, as predicted by a 331 model, based on a

S U {(3)}_{c} \times S U {(3)}_{L} \times U {(1)}_{X}

symmetry. In particular, I account for a version of the 331 model wherein the embedding of the hypercharge is obtained with the addition of three exotic quarks and vector bileptons. Furthermore, a sextet of

S U {(3)}_{L}

, necessary to provide masses to leptons, yields an extra scalar sector, including a doubly charged Higgs, i.e., scalar bileptons. As bileptons are mostly produced in pairs at hadron colliders, their main signal is provided by two same-sign lepton pairs at high invariant mass. Nevertheless, they can also decay according to non-leptonic modes, such as a TeV-scale heavy quark, charged 4/3 or 5/3, plus a Standard Model quark. I explore both leptonic and non-leptonic decays and the sensitivity to the processes of the present and future hadron colliders. Full article

(This article belongs to the Special Issue Particle Theory and Theoretical Cosmology—Dedicated to Professor Paul Howard Frampton on the Occasion of His 80th Birthday)

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16 pages, 11726 KiB

Open AccessArticle

Future Circular Lepton Collider Vibrational Crosstalk

by Purinut Lersnimitthum, Audrey Piccini, Federico Carra, Tirawat Boonyatee, Niphon Wansophark and Nopdanai Ajavakom

Vibration 2024, 7(4), 912-927; https://doi.org/10.3390/vibration7040048 - 4 Oct 2024

Cited by 1 | Viewed by 2093

Abstract

CERN, the European Organisation for Nuclear Research is studying the feasibility of the Future Circular Collider, considering both financial and technical aspects. One of the challenges is that the performance of particle accelerators relies on the dynamic stability of structures, affected by multiple [...] Read more.

CERN, the European Organisation for Nuclear Research is studying the feasibility of the Future Circular Collider, considering both financial and technical aspects. One of the challenges is that the performance of particle accelerators relies on the dynamic stability of structures, affected by multiple sources of vibrations, including crosstalk vibration between two particle accelerators, the Booster and Collider, in the Future Circular Lepton Collider. This research aims to find a methodology for determining transfer functions, specifically crosstalk transfer functions, between the Collider and Booster within an underground tunnel. Also, it aims to determine how significant crosstalk is compared to the vibration from other sources, such as ground vibrations. The transfer functions of the tunnel were independently determined from internal structures using the Finite Element Method, employing 2D plane strain and the standard absorbing boundary to model the underground tunnel. It was found that the overall gain of crosstalk was less than 10% of that of ground-to-magnetic axis of either the Collider or Booster. This method may be used to optimize the tunnel layout from a vibration point of view. It appears that vibrations from crosstalk are far lower compared to vibrations from ground vibrations. Full article

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18 pages, 1023 KiB

Open AccessEditor’s ChoiceReview

Nuclear Symmetry Energy in Strongly Interacting Matter: Past, Present and Future

by Jirina R. Stone

Symmetry 2024, 16(8), 1038; https://doi.org/10.3390/sym16081038 - 13 Aug 2024

Cited by 2 | Viewed by 2071

Abstract

The concept of symmetry under various transformations of quantities describing basic natural phenomena is one of the fundamental principles in the mathematical formulation of physical laws. Starting with Noether’s theorems, we highlight some well–known examples of global symmetries and symmetry breaking on the [...] Read more.

The concept of symmetry under various transformations of quantities describing basic natural phenomena is one of the fundamental principles in the mathematical formulation of physical laws. Starting with Noether’s theorems, we highlight some well–known examples of global symmetries and symmetry breaking on the particle level, such as the separation of strong and electroweak interactions and the Higgs mechanism, which gives mass to leptons and quarks. The relation between symmetry energy and charge symmetry breaking at both the nuclear level (under the interchange of protons and neutrons) and the particle level (under the interchange of u and d quarks) forms the main subject of this work. We trace the concept of symmetry energy from its introduction in the simple semi-empirical mass formula and liquid drop models to the most sophisticated non-relativistic, relativistic, and ab initio models. Methods used to extract symmetry energy attributes, utilizing the most significant combined terrestrial and astrophysical data and theoretical predictions, are reviewed. This includes properties of finite nuclei, heavy-ion collisions, neutron stars, gravitational waves, and parity–violating electron scattering experiments such as CREX and PREX, for which selected examples are provided. Finally, future approaches to investigation of the symmetry energy and its properties are discussed. Full article

(This article belongs to the Special Issue Strongly Interacting Matter at Extreme Conditions—the Role of Symmetry Energy in Nuclear Physics and Astrophysics)

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23 pages, 940 KiB

Open AccessEditor’s ChoiceReview

Overview of B→K^(∗)ℓℓ Theoretical Calculations and Uncertainties

by Farvah Mahmoudi and Yann Monceaux

Symmetry 2024, 16(8), 1006; https://doi.org/10.3390/sym16081006 - 7 Aug 2024

Cited by 6 | Viewed by 1240

Abstract

The search for New Physics (NP) beyond the Standard Model (SM) has been a central focus of particle physics, including in the context of B-meson decays involving

b \to s ℓ ℓ

transitions. These transitions, mediated by flavour-changing neutral currents, are highly [...] Read more.

The search for New Physics (NP) beyond the Standard Model (SM) has been a central focus of particle physics, including in the context of B-meson decays involving

b \to s ℓ ℓ

transitions. These transitions, mediated by flavour-changing neutral currents, are highly sensitive to small NP effects due to their suppression in the SM. While direct searches at colliders have not yet led to NP discoveries, indirect probes through semi-leptonic decays have revealed anomalies in observables such as the branching fraction

B (B \to K μ μ)

and the angular observable

P_{5}^{'} (B \to K^{*} μ μ)

. In order to assess the observed tensions, it is essential to ensure an accurate SM prediction. In this review, we examine the theoretical basis of the

B \to K^{(*)} ℓ ℓ

decays, addressing in particular key uncertainties arising from local and non-local form factors. We also discuss the impact of QED corrections to the Wilson coefficients, as well as the effect of CKM matrix elements on the predictions and the tension with the experimental measurements. We discuss the most recent results, highlighting ongoing efforts to refine predictions and to constrain potential signs of NP in these critical decay processes. Full article

(This article belongs to the Special Issue Symmetries and Anomalies in Flavour Physics)

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26 pages, 1071 KiB

Open AccessReview

Lepton Flavor Universality Tests in Semileptonic b→c Decays

by Suzanne Klaver and Marcello Rotondo

Symmetry 2024, 16(8), 964; https://doi.org/10.3390/sym16080964 - 29 Jul 2024

Viewed by 1491

Abstract

Semileptonic decays of b- to c-hadrons provide an exciting environment to probe new physics and currently present some of the most compelling anomalies in the field of flavor physics. Measurements of the lepton flavor universality ratios

R (D^{*})

, comparing [...] Read more.

Semileptonic decays of b- to c-hadrons provide an exciting environment to probe new physics and currently present some of the most compelling anomalies in the field of flavor physics. Measurements of the lepton flavor universality ratios

R (D^{*})

, comparing branching fractions with

τ

and

μ

leptons, show a discrepancy of over 3σ with respect to the Standard Model, and suggest that the coupling to

τ

leptons is stronger than predicted. Measurements of angular distributions as well as polarization in b- to c-hadron decays provide additional sensitivity to new physics. This review article offers an overview of the theory of semileptonic b- to c-hadron decays, presents the experiments and experimental techniques used to perform measurements of these decays, and summarizes the latest experimental results with their implications. Full article

(This article belongs to the Special Issue Symmetries and Anomalies in Flavour Physics)

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13 pages, 1812 KiB

Open AccessReview

Short-Distance Physics with Rare Kaon Decays

by Siavash Neshatpour

Symmetry 2024, 16(8), 946; https://doi.org/10.3390/sym16080946 - 24 Jul 2024

Cited by 1 | Viewed by 1708

Abstract

In this write-up, we provide an overview of the existing theoretical framework concerning rare kaon decays, with a particular emphasis on flavour-changing neutral current processes. These decays offer crucial indirect pathways for investigating short-distance new physics. Our discussion will encompass standard model predictions [...] Read more.

In this write-up, we provide an overview of the existing theoretical framework concerning rare kaon decays, with a particular emphasis on flavour-changing neutral current processes. These decays offer crucial indirect pathways for investigating short-distance new physics. Our discussion will encompass standard model predictions for relevant observables, alongside an assessment of their capacity to probe new physics through a comparison with experimental data. Full article

(This article belongs to the Special Issue Symmetries and Anomalies in Flavour Physics)

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15 pages, 3695 KiB

Open AccessArticle

Lepton Flavour Universality in Rare B Decays

by Paula Álvarez Cartelle and Richard Morgan Williams

Symmetry 2024, 16(7), 822; https://doi.org/10.3390/sym16070822 - 30 Jun 2024

Viewed by 1806

Abstract

Tests of lepton flavour universality in rare decays of b hadrons mediated by flavour-changing neutral-current transitions constitute sensitive probes for physics beyond the standard model. In recent years, such tests have become increasingly precise and have attracted significant theoretical and experimental attention. In [...] Read more.

Tests of lepton flavour universality in rare decays of b hadrons mediated by flavour-changing neutral-current transitions constitute sensitive probes for physics beyond the standard model. In recent years, such tests have become increasingly precise and have attracted significant theoretical and experimental attention. In this article, we review the status of searches for lepton flavour universality violations in these processes and discuss prospects for future measurements at various facilities. Full article

(This article belongs to the Special Issue Symmetries and Anomalies in Flavour Physics)

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9 pages, 243 KiB

Open AccessArticle

Flipped Quartification: Product Group Unification with Leptoquarks

by James B. Dent, Thomas W. Kephart, Heinrich Päs and Thomas J. Weiler

Entropy 2024, 26(7), 533; https://doi.org/10.3390/e26070533 - 21 Jun 2024

Viewed by 968

Abstract

The quartification model is an

S U {(3)}^{4}

extension with a bi-fundamental fermion sector of the well-known

S U {(3)}^{3}

bi-fundamentalfication model. An alternative “flipped” version of the quartification model is obtained by rearrangement of the particle [...] Read more.

The quartification model is an

S U {(3)}^{4}

extension with a bi-fundamental fermion sector of the well-known

S U {(3)}^{3}

bi-fundamentalfication model. An alternative “flipped” version of the quartification model is obtained by rearrangement of the particle assignments. The flipped model has two standard (bi-fundamentalfication) families and one flipped quartification family. In contrast to traditional product group unification models, flipped quartification stands out by featuring leptoquarks and thus allows for new mechanisms to explain the generation of neutrino masses and possible hints of lepton-flavor non-universality. Full article

(This article belongs to the Special Issue Particle Theory and Theoretical Cosmology—Dedicated to Professor Paul Howard Frampton on the Occasion of His 80th Birthday)

12 pages, 577 KiB

Open AccessCommunication

Search for R-Parity-Violation-Induced Charged Lepton Flavor Violation at Future Lepton Colliders

by Xunye Cai, Jingshu Li, Ran Ding, Meng Lu, Zhengyun You and Qiang Li

Universe 2024, 10(6), 243; https://doi.org/10.3390/universe10060243 - 31 May 2024

Cited by 3 | Viewed by 1177

Abstract

Interest in searches for Charged Lepton Flavor Violation (CLFV) has continued in the past few decades since the observation of CLFV would indicate a new physics Beyond the Standard Model (BSM). As several future lepton colliders with high luminosity have been proposed, the [...] Read more.

Interest in searches for Charged Lepton Flavor Violation (CLFV) has continued in the past few decades since the observation of CLFV would indicate a new physics Beyond the Standard Model (BSM). As several future lepton colliders with high luminosity have been proposed, the search for CLFV will reach an unprecedented level of precision. Many BSM models allow CLFV processes at the tree level, such as the R-parity-violating (RPV) Minimal Supersymmetric Standard Model (MSSM), which is a good choice for benchmarking. In this paper, we perform a detailed fast Monte Carlo simulation study on RPV-induced CLFV processes at future lepton colliders, including a 240

GeV

circular electron positron collider (CEPC) and a 6 or 14

TeV

Muon Collider. As a result, we found that the upper limits on the

τ

-related RPV couplings will be significantly improved, while several new limits on RPV couplings can be set, which are inaccessible by low-energy experiments. Full article

(This article belongs to the Special Issue Search for New Physics at the LHC and Future Colliders)

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14 pages, 2601 KiB

Open AccessArticle

Sedenion Algebra Model as an Extension of the Standard Model and Its Link to SU(5)

by Qiang Tang and Jau Tang

Symmetry 2024, 16(5), 626; https://doi.org/10.3390/sym16050626 - 17 May 2024

Viewed by 1629

Abstract

In the Standard Model, ad hoc hypotheses assume the existence of three generations of point-like leptons and quarks, which possess a point-like structure and follow the Dirac equation involving four anti-commutative matrices. In this work, we consider the sedenion hypercomplex algebra as an [...] Read more.

In the Standard Model, ad hoc hypotheses assume the existence of three generations of point-like leptons and quarks, which possess a point-like structure and follow the Dirac equation involving four anti-commutative matrices. In this work, we consider the sedenion hypercomplex algebra as an extension of the Standard Model and show its close link to SU(5), which is the underlying symmetry group for the grand unification theory (GUT). We first consider the direct-product quaternion model and the eight-element octonion algebra model. We show that neither the associative quaternion model nor the non-associative octonion model could generate three fermion generations. Instead, we show that the sedenion model, which contains three octonion sub-algebras, leads naturally to precisely three fermion generations. Moreover, we demonstrate the use of basis sedenion operators to construct twenty-four 5 × 5 generalized lambda matrices representing SU(5) generators, in analogy to the use of octonion basis operators to generate Gell-Mann’s eight 3 × 3 lambda-matrix generators for SU(3). Thus, we provide a link between the sedenion algebra and Georgi and Glashow’s SU(5) GUT model that unifies the electroweak and strong interactions for the Standard Model’s elementary particles, which obey SU(3)

\otimes

SU(2)

\otimes

U(1) symmetry. Full article

(This article belongs to the Special Issue Symmetry in Geometric Mechanics and Mathematical Physics)

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