22 September 2026

We investigate thermal leptogenesis in an extension of the Type-I seesaw in which a real singlet scalar couples non-diagonally to the right-handed neutrinos. The interactions $-y_{ij}φN_iN_j$, with $i\neq j$, introduce new sources of CP violation in heavy-neutrino decays with a negligible enhancement of the standard leptonic washout. We derive an analytic upper bound on the scalar-induced CP asymmetry and present numerical results using fully flavoured Boltzmann equations and the density-matrix formalism. We show that the observed baryon asymmetry can be generated with a hierarchical right-handed-neutrino spectrum at the electroweak scale. In the minimal Type-I seesaw, lowering the scale of decay leptogenesis typically requires either a tuned quasi-degeneracy of the right-handed-neutrino masses or cancellations between the tree-level and one-loop contributions to the light-neutrino masses, while hierarchical leptogenesis instead requires a high scale that aggravates the Higgs hierarchy problem. This singlet-scalar extension appears to avoid these tensions, allowing successful leptogenesis with a hierarchical right-handed-neutrino spectrum down to the electroweak scale.

We present a model of freeze-in dark matter (DM) and baryogenesis in which the new particles are a TeV-scale electroweak-doublet vector-like fermion (VLF) and two gauge-singlet Majorana fermions that constitute the DM, the heavier one with a mass in the tens-to-hundreds of keV range. Feeble Yukawa couplings of the VLF to the DM and the Standard Model Higgs doublet induce freeze-in production of the DM via VLF decays in the early universe. Due to a CP-violating phase in these couplings, DM propagation and rescattering induce opposite charge asymmetries in the VLF and SM sectors. Even in the absence of $B-L$ violation, the VLF asymmetry guarantees a baryon asymmetry once in-equilibrium SM interactions are taken into account. A relatively small conversion factor from VLF asymmetry to baryon asymmetry is balanced by a more direct asymmetry generation mechanism than in other minimal models of freeze-in baryogenesis. The observed DM energy density requires the heavier DM particle to remain well out of equilibrium throughout production. This allows us to map out the VLF mass-lifetime space using a novel perturbative calculation of the baryon asymmetry. We find that the model is already significantly constrained by LHC searches and structure formation probes, which will continue to test interesting parameter space in the coming years. The addition of VLF Yukawa couplings not involving the DM breaks $B-L$ and greatly expands the viable parameter space, while inducing potential signatures from dark matter decay and lepton flavor violation.

We investigate the Higgs sector phenomenology of the minimal low scale quark-lepton unification theory. In addition to the Standard Model-like Higgs boson, the theory predicts a new CP-even neutral Higgs, a CP-odd neutral Higgs, and two charged Higgses, together with heavy right-handed neutrinos and leptoquarks. We analyze the scalar spectrum, the Yukawa structure responsible for charged-fermion masses, and the neutrino sector realized through an inverse-seesaw mechanism, emphasizing that the couplings of the new Higgs bosons are directly tied to the structure of matter unification and therefore lead to characteristic decay patterns dominated by third-generation fermions. We compute the branching ratios and production cross sections of the new Higgs states at the Large Hadron Collider (LHC) and assess their impact on present and future collider measurements. We find that current LHC data probe significant regions of parameter space for the neutral heavy Higgs bosons, with the strongest sensitivity arising from channels involving tau leptons, tops, and related final states, while the charged Higgs remains less constrained because of its electroweak production mechanism. Our results show that Higgs measurements provide a powerful and complementary probe of low-scale matter unification beyond direct leptoquark searches and open a new avenue for testing quark-lepton unification at present and future colliders, with discovery potential in high-luminosity LHC running.

We investigate the phenomenological consequences of a genuine three-body holonomy in a relativistic Dirac system in one spatial dimension. After removing the center-of-mass coordinate, the triple-coincidence point punctures the two-dimensional relative configuration space and permits a nontrivial $U(1)$ winding phase, whereas the pairwise Sakamoto--Munakata--Ino contact interactions give trivial net matching around this point. At fixed intrinsic parity, the six particle-ordering sectors reduce to a three-dimensional cyclic space. A Hermitian $C_3$-invariant effective mass operator admits a Peierls-type realization in which the gauge-invariant phase around the three links equals the three-body holonomy $θ_3$. Its eigenvalues are $$ M^{[k]}=M_0+2Δ\cos\!\left(\frac{θ_3+2πk}{3}\right), \qquad k=0,1,2. $$ The holonomy lifts the conjugate-channel degeneracy and can generate a parametrically light branch through cancellation between the common mass and the holonomy-induced shift. We further allow cyclic-symmetry breaking and consider a general Hermitian three-state mass matrix. Exact elimination of two heavy states by the Schur complement yields a low-energy correction containing the rephasing-invariant loop product $\mathrm{Re}(t_{12}t_{23}t_{31})\propto\cosθ_3$. Thus, even when only one branch is kinematically accessible, its effective mass can retain finite memory of the complete three-state loop. The complementary invariant $\mathrm{Im}(t_{12}t_{23}t_{31})\propto\sinθ_3$ is phase sensitive but does not alone imply CP violation. The construction provides a low-dimensional phenomenological proof of concept for family-like triplication, mass hierarchy, and infrared memory, rather than a microscopic theory of Standard Model fermion generations.

We study sums associated with the action of $PGL_2(\mathbb Z)$ on continuous piecewise polynomial functions with exactly two real roots, both irrational. We form weighted sums of the positive parts of their normalized transforms, using nonnegative weights compatible with translation, reflection, and inversion. Under suitable continuity, finiteness, and convergence assumptions, we prove that these sums are well defined, bounded, $1$-periodic, and continuous on $\mathbb R$, and satisfy a reciprocal functional equation. We also extend the construction to finite families of distinct function orbits. Our framework recovers Zagier's constancy result and includes the full family of quadratic sums for which Bengoechea proved convergence.

We present a method for determining whether there exists a degree $D$ rational map from $X_0(N)$ to some elliptic curve $E/\mathbb{Q}$. Moreover, we explain how to obtain a quadratic form that represents all possible degrees of such maps using the degree pairing method. This method previously required odd analytic rank and some additional technical conditions to be satisfied. In this paper, we extended the method to even rank curves as well and remove all technical conditions. We also show how to prove or disprove the existence of degree $D$ maps to elliptic curves by a lifting criterion on the lattices $H_1(-,\mathbb{Z})$ As an application of this method, we determine all $D$-elliptic curves $X_0(N)$ for all $D\leq 100$. Interestingly, in some cases we found degree $D$ rational maps that we could not explain by degeneracy maps, quotient maps, and modular parameterisation.

Adapting a construction of Kurihara in the setting of Drinfeld modular forms, we define Poincaré series on the Drinfeld half-plane $Ω$. These series are built from products of meromorphic $1$-forms that are naturally associated to geodesics on the Bruhat-Tits tree. We establish convergence under a finiteness condition on the geodesics, verify this condition in several cases, and give sufficient conditions for the resulting cusp forms to be nonzero. For the principal congruence subgroup $Γ(\mathfrak{n})$ of $GL_2(\mathbb{F}_q[T])$, we construct explicit linearly independent families of Poincaré series by lifting certain $k$-forms from the components of the analytic reduction of $Γ(\mathfrak{n})\backslashΩ$. We formulate conjectures on the vanishing orders at cusps, and we prove the first of them for an explicit family of Poincaré series by computing the corresponding expansions at the cusps; as an application, we obtain the Drinfeld modular forms $h$ and $Δ$ as Poincaré series (up to a sign). Finally, for cocompact groups attached to quaternion algebras over $\mathbb{F}_q(T)$ that split at $\infty$, we show that the Poincaré series span the whole space of modular forms of given weight and type.

The IceCube Neutrino Observatory instruments one cubic kilometer of deep-glacial ice between 1450 m and 2450 m below the surface at the geographic South Pole to detect neutrinos via Cherenkov radiation of relativistic charged particles produced in their interactions. This detector is responsible for a number of key observations in neutrino astrophysics, which include the discovery of a high-energy astrophysical neutrino flux and, more recently, the galactic plane. During the austral summer of 2025/26, five new strings equipped with new photosensor designs were deployed as a dense infill in the middle of the existing detector. The science goals of this detector are twofold: Firstly, given the higher photocathode density, an improved atmospheric neutrino event selection and reconstruction at a few GeV can be achieved for enhanced capabilities to study neutrino oscillations. Secondly, novel calibration devices will improve the knowledge of the optical properties of the glacial ice and the detector response. These new calibration results will be applied to archival IceCube data, improving angular and spatial resolution of all detected astrophysical neutrino events. The IceCube Upgrade also serves as a first step towards the next-generation neutrino telescope at the South Pole, called IceCube-Gen2.

It is an unnatural feature of the Standard Model that the difference between the baryon number $B$ and the lepton number $L$ is conserved, which implies an exact, global symmetry. We promote it to a naturally exact, local symmetry by coupling the difference $B-L$ to an Abelian gauge field. Gauge anomalies are cancelled by adding right-handed neutrinos $ν_{R}$. They are not sterile in this case, which forbids the Majorana term, but we arrange for a $ν_{R}$-mass by adding a Higgs-type 1-component complex scalar field. Thus we arrive at a well-motivated, modest extension of the Standard Model (SM). We investigate the field equations in the corresponding gauge-Higgs sector, involving both Higgs fields and the non-standard U(1) gauge field. This leads to a set of coupled, non-linear differential equations, which we solve numerically. We use cylindrical coordinates, thus focusing on the structures of cosmic strings. For a large variety of parameters, we identify the string profiles and energy densities. These profiles depend on the winding number of each of the Higgs fields. For our parameters, the characteristic string radii are below $10^{-3}~{\rm fm}$, and the string tension is not ruled out by observations of the Cosmic Microwave Background or gravitational waves. As an amazing peculiarity, we discover - for high winding numbers - ``overshooting'' and ``co-axial'' profile functions. In the latter case, the profile of the standard Higgs field changes its sign near the core of the cosmic string.

Purpose: Alpha particles from $^{214}$Po, $^{212}$Po, and $^{210}$Po are increasingly used to calibrate large liquid scintillator detectors, but Geant4 simulations of their energy deposition require detailed validation. Methods: We simulate alpha particles in a 4 m cube of LAB-based liquid scintillator with Geant4 11.4.2 and apply Birks quenching per step. We study step-size, production-threshold, Birks-constant, and electromagnetic-model dependence, and use Geant4-DNA to examine keV-scale electron track structure. Results: Delta-electron-associated fluctuations dominate the simulated response. Across the tested explicit-delta settings, the variance of the quenched-response contribution from secondary tracks is 1.01--1.12 times the total variance; a negative primary--secondary covariance reduces the total. The simulated quenching-curve shape is compatible with SNO+ data within current uncertainties, with $χ^2/\mathrm{ndf}\simeq0.14$--$0.17$ for $k_B=0.007$--$0.010$ g cm$^{-2}$ MeV$^{-1}$. Geant4-DNA gives strong electron-track curvature, with tortuosity decreasing from about 6 at 200 eV to 1.6 at 10 keV. Conclusion: Delta-electron fluctuations are the dominant contribution to the intrinsic resolution in the tested configurations. The production threshold has a larger effect than the electromagnetic model: Penelope and Livermore agree within about 3% in L/E, whereas Standard gives higher L/E, especially at low thresholds.

Axion relic pockets are phase-transition remnants consisting of regions of false vacuum stabilised from collapse by a hot axion gas. Axion relic pockets can comprise dark matter, but little is known about their phenomenology. We consider trapped axions coupled to electromagnetism and derive the axion to photon conversion rate accounting for the pocket's compactness and spherical geometry. As a case study, we show that axion-photon conversion occurs in atomic electric fields, leading to high-energy electromagnetic cascades that may be detectable by neutrino, cosmic-ray, and dark-matter experiments. The distribution of electromagnetic showers is inherently isotropic, and upward-going showers provide a smoking-gun signal for the model. Using recent data from the IceCube neutrino telescope, we derive the first limits from terrestrial experiments on axion relic pockets as dark matter. However, for the simplest realisation of the model, only a small part of the parameter space can give signals strong enough to be constrained by current data. We also comment on the prospects for discovering axion relic pockets using fluorescence and radio Cherenkov detection by atmospheric instruments and balloon-borne payloads, as well as traditional dark matter direct detection experiments. These results provide the necessary tools to initiate phenomenological studies of axion relic pockets across different environments.

We study the sensitivity of the Future Circular Collider in electron-positron mode (FCC-ee) to the axion-like particle (ALP) couplings with leptons via the process $e^{+}e^{-} \rightarrow γγjj$ at the center-of-mass energy $\sqrt{s}=91$ GeV with the integrated luminosity $\mathcal{L}=150~\text{ab}^{-1}$. We analyze three scenarios, $\mathbf{c}_R=0$, $\mathbf{c}_L=0$ and $\mathbf{c}_R=\mathbf{c}_L$, for both unpolarized and polarized beams with $(P_{e^-}, P_{e^+}) = (+80\%, -80\%)$, and derive projected lower limits on the effective coupling strengths. The polarized case provides higher sensitivity than the unpolarized case. Specifically, for the $\mathbf{c}_R=0$ scenario (probing the ALP-neutrino coupling $\text{Tr}(g_{aνν})/f_a$), the projected sensitivity in the polarized case reaches approximately $0.0105~\text{GeV}^{-1}$ for the ALP mass in the range $10$--$24$ GeV; for $\mathbf{c}_L=0$ (probing the ALP-charged lepton coupling $\text{Tr}(g_{a\ell\ell})/f_a$), it reaches $0.0174~\text{GeV}^{-1}$ in the $10$--$27$ GeV range; and for $\mathbf{c}_R=\mathbf{c}_L$ (probing the ALP-neutrino coupling $\text{Tr}(g_{aνν})/f_a$), it reaches $0.00394~\text{GeV}^{-1}$ in the $45$--$80$ GeV range. In these ALP mass ranges, our projected sensitivities are complementary to the projected sensitivities from other search channels at future colliders.

The SHiP/NA67 experiment aims to search for feebly interacting GeV-scale new particles and to perform all-flavour neutrino-physics measurements at the HI-ECN3 beam facility at the CERN SPS. The collaboration is currently optimising the experiment's initial configuration for the commissioning and first physics runs of 2032-2033. The detector subsystems comprise a few large-area instruments: for new-particle searches, highly sophisticated veto detectors, high timing-resolution detectors, a lightweight straw tracker system, and high-spatial-precision calorimeters; and, for neutrino reconstruction, small transverse-size, high-granularity calorimeters.

A confining dark sector modeled after quantum chromodynamics provides a well-motivated framework for strongly-interacting dark matter. We show that dark vector mesons in a confining dark sector can be resonantly produced in high-energy neutrino scattering on the cosmic neutrino background, generating a distinctive absorption feature in the cosmic neutrino energy spectrum. Unlike conventional attenuation effects, this feature directly reflects the mass spectrum of dark resonances and can therefore serve as a spectroscopic signature of a strongly-interacting dark sector. We find that a broad range of dark-sector parameter space is within the reach of future neutrino telescopes, including IceCube-Gen2 Radio. Our proposal thus turns the cosmic neutrino background into a target for discovering dark-sector resonances, while simultaneously providing a novel probe of dark sector interactions with neutrinos.

Microscopic black holes may form at the centers of neutron stars through the accumulation and collapse of dark matter. While Standard Model particles produced by Hawking evaporation are efficiently absorbed by the dense stellar medium, sufficiently weakly interacting and long-lived particles can escape and subsequently decay into high-energy neutrinos, photons, or charged particles, providing an indirect probe of Hawking radiation. We examine the joint energy--angular distribution of these secondary particles, incorporating mediator propagation, energy-dependent decay, and relativistic decay kinematics. For relativistic mediators, the normalized energy-integrated angular profile becomes approximately independent of the black hole temperature, with its characteristic extent controlled primarily by the combination $cτ_S/D$ of the mediator lifetime and source distance, as the boost enhancement of the decay length is compensated by relativistic beaming. We demonstrate the viability of this mechanism and illustrate its phenomenology with gravitationally coupled scalars, dark photons, dark-$Z$ bosons, and heavy neutral leptons. Comparing with monochromatic mediator production from dark matter annihilation, we find that the energy-integrated angular profiles can be nearly degenerate, while the energy spectra and energy-resolved angular distributions remain distinct. These complementary spectral and angular signatures provide targets for high-energy neutrino and gamma-ray searches.

The detection of high-energy astrophysical neutrinos has opened a new avenue for identifying cosmic particle accelerators. Blazars, active galactic nuclei (AGN) with relativistic jets oriented close to the observer's line of sight, are promising sites of hadronic interactions capable of producing PeV-scale neutrinos. We investigate the flat-spectrum radio quasar (FSRQ) PKS~0215+015 ($z \simeq 1.715$), positionally consistent with the \textit{IceCube-220225A} neutrino event of estimated energy $\sim$154~TeV. We combine \textit{Fermi}-LAT $γ$-ray data with Swift-XRT and Swift-UVOT observations to characterise the source around the neutrino epoch. PKS~0215+015 exhibited pronounced $γ$-ray, X-ray and optical activity in early 2022, consistent with a disturbance propagating along the jet. We construct broadband spectral energy distributions (SEDs) for the flaring interval and model them using leptonic and lepto-hadronic frameworks. The SED is well reproduced by a leptonic model comprising synchrotron, synchrotron self-Compton and external Compton emission, indicating that electron processes dominate. A co-accelerated proton population remains radiatively subdominant but requires a proton kinetic luminosity roughly two orders of magnitude above equipartition with the magnetic field. The predicted neutrino flux is well below that implied by a single \textit{IceCube-220225A}-like detection. Independent analysis of short-term $γ$-ray variability yields an emission-region size consistent with the SED fit, supporting the model's physical self-consistency. We discuss the temporal and energetic plausibility of the association between PKS~0215+015 and \textit{IceCube-220225A} and implications for future multimessenger studies of high-redshift FSRQs.

When multiple differential cross-section measurements are extracted from a common event sample, the same events contribute simultaneously to multiple distributions. This event-sharing structure imposes exact linear constraints among the bin counts, reducing the effective dimensionality of the measurement below the total number of bins. Since the covariance matrix obeys these inter-distribution constraints, it contains a rank deficiency. While limited numerical precision may inadvertently restore invertibility, the $χ^{2}$ contributions along constrained dimensions will be arbitrary, yielding unphysically inflated $χ^{2}$ values in global goodness-of-fit tests. We present the range-projected $χ^{2}$, a test statistic that restricts the goodness-of-fit test to the subspace carrying independent statistical information, yielding a $χ^{2}$ with $N_\text{bins} - N_\text{null}$ degrees of freedom, where $N_\text{null}$ is the number of independent constraints. We show that this rank deficiency is a predictable consequence of the event-sharing structure, and that $N_\text{null}$ decomposes into a structural contribution determined a priori from the binning geometry and a kinematic contribution that depends on the phase-space occupancy. The method is validated with an analytical toy model and a simulated neutrino--argon cross-section measurement including unfolding and multi-source systematic uncertainties.