High Energy Physics (Phenomenology)
The Masses of Bosons and Usual Fermions on Supersymmetric $SU(3)_{C}\times SU(4)_{L}\times U(1)_{X}$ Model
M. C. Rodriguez
We will study in details the masses spectrum of
bosons and usual
fermions of the Minimal Supersymmetric $SU(3)_{C}\times SU(4)_{L}\times U(1)_{X}$ Model.
High Energy Physics (Phenomenology)
Fermion mass hierarchy and flavor signals from a $D_4$ dihedral symmetry within a 2HDM-Tx with four-zero textures
M. A. Arroyo-Ureña, E. Díaz, J. L. Díaz-Cruz et al. (+1 more)
We propose an extended Texturized Two-
Higgs Doublet Model (2HDM-Tx) where a discrete $D_4$
symmetry predicts a four-zero texture in the
fermion mass
matrices. In contrast to the standard ansatz where the underlying Yukawa
matrices are assumed to be structurally identical, we introduce a novel configuration of non-equivalent
matrices that complementarily generate a specific Hermitian four-zero mass structure. This framework naturally suppresses flavor-changing neutral currents and provides a structural rationale for the
fermion mass hierarchy, while in addition including a dark matter candidate. As a concrete phenomenological application, we show that the model simultaneously accommodates the persistent neutral resonance excesses at $95\text{ GeV}$ and $152\text{ GeV}$, satisfies current \text{LHC}
Higgs data, and is consistent with the stringent upper bounds from lepton flavor violation processes. These combined constraints severely restrict the parameter space of the scalar phenomenology. Finally, we study the prospects for the discovery of the lepton-flavor violating process $h \to \tau \mu$ at the High-Luminosity LHC.
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All authors M. A. Arroyo-Ureña, E. Díaz, J. L. Díaz-Cruz, H. Hernández-Arellano
High Energy Physics (Phenomenology) · Cross-listed from physics.ed-ph
AI in Particle Physics Education: Research Problems and Foundational Skills
M. Mikhasenko, M. Stahl, I. Segal et al. (+3 more)
Generative AI can produce perfect solutions to standard physics homework, weakening the connection between submitted work and knowledge a student can use independently. We report a redesign of the introductory nuclear and particle physics course at Ruhr University Bochum, in which AI was permitted and encouraged alongside traditional tools on unusually difficult, research-shaped assignments. We found that most students remained engaged with the assignments throughout the course and produced ambitious work, while the course did not reliably secure its foundational objective. We offer this mixed experience as a reference point for discussion.
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All authors M. Mikhasenko, M. Stahl, I. Segal, D. Parmar, A. Zimmer, A. Kazatsky
High Energy Physics (Phenomenology) · Cross-listed from nucl-th
Beyond Viscosity Matching: Microscopic Relaxation in Anisotropic Flow
Olga Soloveva
When a gas of scattering particles is disturbed, each angular harmonic of its velocity distribution decays at its own rate. Hydrodynamics, and with it the shear viscosity, depends on only one of these rates, the one for the quadrupole harmonic. A system that scatters only a few times before it stops interacting remembers all of them. This is the situation of small collision systems such as $p+p$, $p+$Pb and O$+$O, where kinetic models tuned to the same viscosity nevertheless predict different anisotropic flow. We show that this difference is not a model uncertainty but a measurement of the remaining rates: to first order in the number of collisions, ratios of flow responses equal ratios of relaxation rates, independently of the initial geometry. For the QCD collision kernel, where the rates also depend on momentum, we obtain the full spectrum of relaxation modes in closed form and show that dilute flow, viscosity, and late-time decay probe three different averages of it. A momentum-resolved kinetic solver confirms that the angular hierarchy is lost first at soft momenta and that the flow response settles at a value no single-rate model produces. The same structure governs two-dimensional electron and atomic Fermi gases.
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High Energy Physics (Phenomenology)
Agnostic search for a vector-like top partner at a lepton collider via the recoil mass technique
Higinio Valle, Cristina Oropeza Barrera and Oscar Ochoa-Valeriano
A study of the single production of a vector-like top partner $T$ at a $\sqrt{s}=3$ TeV $e^{+}e^{-}$
collider is presented, using a decay-mode and mass-agnostic event selection built around the recoil mass observable. The analysis relies on fully simulated samples processed through a common reconstruction and event selection chain. The baseline selection is validated without beam polarization or initial-state radiation (ISR). The impact of more realistic running conditions, including ISR together with an $e^{-}$ beam polarization of $-80\%$, is then evaluated and the discovery reach is mapped as a function of the top partner mass $m_{T}$ and coupling strength $\kappa_{T}$. In the baseline scan, the estimated statistical significance rises above $3\sigma$ for the lowest
benchmark masses once $\kappa_{T}$ exceeds approximately 0.3.
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High Energy Physics (Phenomenology)
Macroscopic dark matter constraints for extended mass functions
Zachary S. C. Picker, Andrew Buchanan, Melissa Diamond et al. (+1 more)
We compile and recompute a subset of the landscape of constraints for macroscopic dark matter (macros), explicitly including the dependence on the fraction of dark matter in macros $f_{\rm dm}$. This allows us to map these constraints to scenarios with extended mass functions for the macros, which is a generic outcome for many of the assembly processes relevant to macro formation. We compute a number of examples of constraints for extended mass functions, finding that in many cases, wider mass functions can be severely constrained by just the interactions of the tails of the distributions. Finally, we present the code and data required for computing these limits and generating these plots in a publicly accessible repository.
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All authors Zachary S. C. Picker, Andrew Buchanan, Melissa Diamond, Joseph Bramante
High Energy Physics (Phenomenology)
High-sensitivity Ultralight Dark Matter detector: Parametrically Amplified Casimir Devices
Muping Chen, Hideo Iizuka, Kyohei Mukaida et al. (+2 more)
We propose the use of sphere-and-plate Casimir force measurement setups to detect ultralight vector dark matter. We demonstrate that sub-picometer signals can be parametrically amplified to be detectable. We present a novel improvement that allows the continuous tuning of the natural frequency of the system, opening new research opportunities at the submicron scale. We show that the improved setup can determine the dark matter mass with high accuracy, significantly expand the detectable mass range, and achieve the best sensitivity to date in the $8\times10^{-14}\sim1\times10^{-12}{\rm~ eV}$ mass range.
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All authors Muping Chen, Hideo Iizuka, Kyohei Mukaida, Kazunori Nakayama, Burkhant Suerfu
High Energy Physics (Phenomenology)
Energy-energy correlators and color decoherence from a generating functional
Yacine Mehtar-Tani
Using jet calculus at leading-logarithmic accuracy, we develop a generating-functional approach to describe the hard-collinear sector of jets propagating through the
quark-gluon
plasma. This framework yields coupled
evolution equations for the jet nuclear modification factor and energy-energy correlators (EECs). We first construct the EEC
evolution in the fully incoherent regime, and then derive
evolution equations that account for the transition from the coherent to the incoherent limit in the large-$N_c$ limit. Furthermore, we show that combining the EEC with the jet nuclear modification factor provides complementary sensitivity to the overall jet suppression and to medium-induced modifications of the jet's internal structure. This framework therefore offers a way to constrain the magnitude and flavor dependence of jet energy loss, together with the medium resolution angle governing color decoherence.
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High Energy Physics (Phenomenology)
The Colors of Jet Quenching
Hannah Bossi, Maxence Larose and Yacine Mehtar-Tani
We combine inclusive jet nuclear modification factors with energy-energy correlators to perform a data-driven extraction of the
quark and gluon quenching factors and the medium resolution scale from the small-angle region. Taking coherent energy loss as a null hypothesis, we find jet quenching factors incompatible with Casimir scaling. Incorporating color decoherence through
antenna energy loss improves the description of the data and restores Casimir scaling, providing evidence that the
quark-gluon
plasma partially resolves the internal structure of jets in heavy-ion collisions.
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High Energy Physics (Phenomenology)
Minimal spontaneous baryogenesis from flavor
Martin A. Mojahed and Alfredo Stanzione
In its minimal realization, the Froggatt-Nielsen (FN) mechanism addresses the Standard Model (SM) flavor puzzle via the spontaneous breaking of a horizontal $U(1)_H$
symmetry. If $U(1)_H$ is global and broken before the end of inflation, it gives rise to a pseudo-Nambu-Goldstone
boson (
axion-like particle) with a homogeneous initial misalignment, whose subsequent coherent
evolution sources spontaneous $CPT$ violation in the SM sector. We show that in the presence of $B-L$-violating processes $-$ parametrized here model-independently via the dimension-five Weinberg operator responsible for light
neutrino masses $-$ the minimal FN setup can generate the baryon asymmetry of the Universe (BAU), linking the origin of flavor directly to the BAU and
neutrino masses. Solving a complete set of
evolution equations for SM asymmetries, we demonstrate that this mechanism can readily yield a baryon asymmetry comparable to the observed value, or even exceeding it by several orders of magnitude. Accounting for baryonic isocurvature and
entropy dilution from
axion decays, we find that the observed BAU is successfully reproduced for
axion oscillation temperatures above $10^{11}$ GeV and
axion decay constants ranging from $10^{13\cdots 14}$ GeV to above $10^{17}$ GeV. Finally, while we focus on a global $U(1)_H$
symmetry and
axion motion from standard misalignment, our framework is readily extendable to other global horizontal
symmetries and arbitrary
axion motion.
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High Energy Physics (Phenomenology) · Cross-listed from astro-ph.GA
Baryon-Accelerated Core Collapse in SIDM Halos and its Imprint on Galactic Disks
Zeineb Mezghanni, Elliot Y. Davies, Adriana Dropulic et al. (+3 more)
The gravitational coupling between dark matter (DM)
halos and the baryonic structures they host is one of the most powerful windows into the particle nature of DM. Self-interacting dark matter (SIDM) presents a minimal, well-motivated extension to the dark sector with dramatic consequences for the structure of
galaxies and their
halos. However, the impact of baryons on SIDM
halo evolution and the resulting galactic structure has been underexplored in Milky Way (MW)-size
galaxies. In this paper, we demonstrate that the inclusion of a baryonic component in a MW-size
galaxy causes accelerated core collapse to begin within the MW's lifetime for a cross section as low as $\sigma/m = 1 \, \rm{cm}^2/\rm{g}$. We present a suite of $N$-body simulations of cold dark matter and SIDM MW-size
galaxies with and without a baryonic component for cross sections $\sigma/m =[1.0, 2.5, 5.0]$ cm$^2$/g. We find numerically, and semi-analytically, that the presence of a stellar disk and bulge shortens the predicted core collapse timescales from the DM only simulations by a factor of $\sim 40$. Further, as the core collapse begins within the lifetime of the
galaxy, the subsequent density increase strengthens the mid-plane restoring force exerted on stellar disk orbits, leading the disk to
flare. This work quantifies both directions of the baryon–SIDM coupling: baryons accelerate core collapse in MW-sized
halos, and the resulting
halo evolution reshapes the disk through thinning and flaring. Both processes open new observational windows into DM.
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All authors Zeineb Mezghanni, Elliot Y. Davies, Adriana Dropulic, Gonzalo Herrera, Abdelaziz Hussein, Lina Necib
High Energy Physics (Phenomenology)
Displaced Signals from Long-lived Particles in Neutrinoless Double Beta Decay
Patrick D. Bolton, Noor-Inès Boudjema, Frank F. Deppisch et al. (+2 more)
Much of the literature on neutrinoless double beta ($0\nu\beta\beta$) decay with light new-physics mediators focuses on invisible missing energy. We investigate the scenario in which a massive Majoron-like particle $\phi$ is produced on-shell during $0\nu\beta\beta$ decay and subsequently decays into visible final states after travelling a macroscopic distance. Specifically, we analyze the displaced energy deposition from $\phi$ decays into a
photon pair ($\gamma\gamma$), a
photon and a dark
photon ($\gamma\gamma_D$) and an electron-positron pair ($e^+e^-$). We demonstrate that the displaced decays modify the expected visible energy spectra and provide novel, distinct experimental signatures at current and upcoming $0\nu\beta\beta$ experiments, with the promise of improving the sensitivity of the standard invisible Majoron searches in $0\nu\beta\beta$ decay by more than two orders of magnitude. The relevant effective couplings can naturally arise in well-motivated ultraviolet-complete scenarios that conventional $0\nu\beta\beta$ decay searches cannot probe.
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All authors Patrick D. Bolton, Noor-Inès Boudjema, Frank F. Deppisch, Chandan Hati, Chayan Majumdar
High Energy Physics (Phenomenology)
Chaos is Target-Blind in High-Energy QCD Evolution
Raktim Abir
Chaotic
evolution measures how rapidly nearby configurations separate, but the existence of such rapid
evolution does not by itself determine what physical information the
evolution actually carries. For fixed-coupling JIMWLK
evolution with fresh transverse-local, color-isotropic noise, we show that this distinction becomes exact - leading to a no go
theorem. At finite rapidity step and finite transverse regulator, the exact linearized update depends on the Wilson-line background only through local adjoint rotations of fresh color-isotropic noise. Once the past is conditioned upon, these rotations leave the complete local noise measure invariant, so the tangent process has the same probability law for any target ensemble evolved with the same regulated fixed-coupling dynamics, including dilute and saturated ensembles. After the exact global color-rotation mode is removed, the reduced tangent process found to have a positive leading Lyapunov exponent which indicate chaotic
evolution. Fixed-coupling JIMWLK therefor can be dynamically chaotic while its tangent-only statistics carry no information about the target ensemble. Spatially nonlocal noise however evades the argument because correlations between distinct sites leave relative Wilson lines in the conditional covariance.
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High Energy Physics (Phenomenology)
Inelastic from the Other Side: Xenon Excitation Signals in Light of the LZ High-Recoil Event
Guanhua Gu, Lingfeng Li, Shao-Song Tang et al. (+1 more)
The LUX-ZEPLIN (LZ) experiment recently reported a single event consistent with a nuclear recoil of $E_{\rm NR}\sim248\pm23\,(\mathrm{stat})\pm23\,(\mathrm{syst})$~keV in an extended-energy search. We study the accompanying inelastic-xenon channel, $\chi+\Xe\to\chi+\Xe^{*}$, which provides a complementary test of DM interpretations of such high-recoil events. Using the non-relativistic effective-field-theory (NREFT) framework with shell-model nuclear-transition inputs, we compute the inelastic-xenon rates for representative scenarios including inelastic dark matter and accelerated DM populations. We also simulate their S1–S2 responses, with detector modeling validated against public LZ data. The nuclear de-excitation adds an electromagnetic component shifting the signal toward the electronic-recoil band and, in some cases, toward clustered backgrounds from isotopes. We therefore construct a schematic, physics-motivated background model and perform a simplified statistical analysis. For many
benchmarks, the inelastic-xenon rate is $\mathcal{O}(0.1)$ of the elastic rate or below, suggesting that substantially larger exposures are required before this companion channel becomes observable. Our results illustrate the importance of isotope-induced background structures in the extended-energy region and extend the phenomenology of inelastic-xenon signatures to a wider range of DM scenarios.
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All authors Guanhua Gu, Lingfeng Li, Shao-Song Tang, Yongheng Xu
High Energy Physics (Phenomenology)
New measurements in leptonic kaon and pion decays: experimental and theoretical perspectives
Lukas Allwicher, Stefan Alexandru Ghinescu, Federico Mescia et al. (+2 more)
We study the future prospects for precision measurements of purely leptonic charged-current kaon and pion decays. Together with the ratio of leptonic widths $R_K^\nu=\Gamma(K\to e\nu)/\Gamma(K\to\mu\nu)$, we consider the single ratios $R_{K\pi}^{\ell=\mu,e} = \Gamma(K \to \ell\nu) / \Gamma(\pi \to \ell\nu)$, for which many experimental uncertainties cancel, as well as the double ratio $R_{K\pi}^e / R_{K\pi}^\mu$, which provides a particularly sensitive probe of new physics. This study is timely in light of two converging developments. On the experimental side, a new conceptual design for a dedicated setup based on a slow-extracted
proton beam and a multi-year data-taking program, is expected to achieve a precision at the few $10^{-4}$ level. On the theory side, recent
lattice-QCD calculations have reached a comparable level of accuracy. Finally, we assess the impact of these next-generation measurements on searches for physics beyond the Standard Model and show that they can provide constraints that are either competitive with or complementary to existing bounds.
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All authors Lukas Allwicher, Stefan Alexandru Ghinescu, Federico Mescia, Tommaso Spadaro, Lucine Tabatt
High Energy Physics (Phenomenology)
Exothermic Dark Matter at LZ
Carlos Henrique de Lima
We investigate whether the high-energy nuclear recoil reported by the LUX-ZEPLIN (LZ) experiment can be explained by exothermic dark matter. We realize this framework in a minimal inelastic dark
photon model and show that both freeze-out and low-reheating-temperature freeze-in cosmologies can reproduce the observed rate, with GeV-scale mediator masses and small kinetic mixing. We find that the LZ event can occur in a preferred parameter region with dark matter mass around $m_\chi \sim 30-200~\mathrm{GeV}$, and mass splitting $\delta \sim 0.5-1~\mathrm{MeV}$. The scenario is largely insensitive to
halo uncertainties and has robust predictions for different targets. In particular, argon and germanium detectors are expected to observe events at energies above the current xenon window.
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High Energy Physics (Phenomenology)
The axial-vector nucleon form factor in the meson dominance picture: the role triangle singularities from a dispersive view
Enrique Ruiz Arriola and Pablo Sanchez-Puertas
The nucleon axial form factor is analyzed in terms of a dispersion relation comprising chiral perturbation theory (ChPT) and perturbative QCD (pQCD) in the low- and high-momentum regimes respectively, which implies a set of superconvergence sum rules for the $A \to N \bar N$ spectral function. In the timelike region below the $N \bar N$ production threshold we include the $a_1$ and $a_1'$ resonances, with finite-width effects modeled through $\rho \pi$ and $\sigma \pi$ intermediate states. Above the $N \bar N$ threshold, we model an infinite tower of radially excited $1^{++}$ resonances with a non-integer power fall-off, eventually matching pQCD. In this setup, we find that both the ChPT and pQCD contributions are tiny. In turn, the dominant $\rho\pi$ triangle provides the leading deviations from axial
meson dominance. Our calculation is not a fit; it contains parameters with a priori uncertainties estimates. The axial radius is predicted to be $r_A^2 =(0.28-0.33)~\textrm{fm}^2 = ( 0.47-0.57~\textrm{fm})^2$ in agreement with recent
lattice QCD results but inconsistent with the MINER$\nu$A determination. A simple semiempirical formula is provided accounting for the main physical effects.
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High Energy Physics (Phenomenology) · Cross-listed from hep-lat
Accessing the Wess-Zumino-Witten term using Lattice QCD
Fernando Romero-López and Stephen R. Sharpe
The Wess-Zumino-Witten interaction in chiral perturbation theory is a manifestation of chiral anomalies. One of its consequences is the presence of a nonvanishing $K \overline K \to \pi^+ \pi^0 \pi^-$ amplitude. We derive the finite-volume formalism that allows one to access this, and related, amplitudes, using the spectra of two and three particles in finite volumes, spectra that can be calculated using
lattice QCD. Specifically, we present the formalism for the systems $K \overline K + 3 \pi$ with $I=0$ and $\pi K + \pi\pi K$ with $I=1/2$ and $3/2$. In addition, we determine the threshold expansions for the $2\leftrightarrow 3$ and $3\leftrightarrow 3$ K
matrices that enter the formalism, and calculate the leading order predictions from chiral perturbation theory for the coefficients that enter these expansions.
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High Energy Physics (Phenomenology)
Tracing Gluon Saturation through Hadronization at EIC
Weiyao Ke, Xu Liu, Yu Shi et al. (+2 more)
Gluon saturation provides a window into the nonlinear nature of the strong interaction in nuclear matter. One direct consequence of saturation is the $\boldsymbol{k}_T$ broadening in the final state.We investigate how hadronization reshapes conventional signatures of gluon saturation at EIC within a complete event-generator framework. To this end, we implement in eHIJING an initial-state-radiation
algorithm based on nonlinear small-$x$
evolution and complete the events with beam remnants, final-state radiation, and hadronization. In our simulations, the signal of parton-level nuclear $\boldsymbol{k}_T$ broadening is strongly diluted in both the nucleon energy correlator and leading-dihadron azimuthal decorrelation after hadronization. Global hadronic recoil, by contrast, remains sensitive to the underlying $\boldsymbol{k}_T$ broadening. We further demonstrate that
Bayesian unfolding of the global hadronic recoil provides access to the underlying hard-scattering $\boldsymbol{k}_T$ distribution. These results establish the global hadronic recoil as a promising saturation observable at the EIC.
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All authors Weiyao Ke, Xu Liu, Yu Shi, Xin-Nian Wang, Jian Zhou
High Energy Physics (Phenomenology)
Global Fixed Point Potentials in the Abelian Higgs Model with $N$ flavors
Gergely Fejős and Shunsuke Yabunaka
Existence of charged fixed points in the Abelian
Higgs model with $N$ flavors in $d$ dimensions is studied using the functional renormalization group. We numerically solve the coupled fixed point equations for the scale dependent charge and the non-perturbative effective potential for the scalar field. We show that the $\epsilon=4-d$ expansion, famously successful in theories with $O(N)$
symmetry, fails to produce reliable results when taking the $\epsilon \rightarrow 1$ limit. By determining global fixed point potentials, it is shown that the critical flavor number at which charged fixed points appear, modifies significantly compared to the perturbative treatment. In $d=3$, signs of a richer fixed point structure with presumably multicritical fixed points are also found. Discussions include subtleties of the gauge fixing and the corresponding modified Ward-Takahashi identities, including the possibility of a nonzero dimensionless
photon mass at the infrared fixed point.
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High Energy Physics (Phenomenology)
Di-hadron Fragmentation Functions beyond LO
Luca Polano, Alessandro Bacchetta and Marco Radici
In this talk, we discuss the extraction of Dihadron Fragmentation Functions (DiFFs) beyond leading order. In particular, we review the latest extraction by the MAP Collaboration of the Unpolarized Dihadron Fragmentation Functions (DiFFs) from a fit of the 2017 BELLE data for the inclusive $\pi^+\pi^-$ pair production within the same jet in $e^+e^-$ annihilations. This new extraction improves the perturbative QCD accuracy by including NNLO calculations, relies on Monte Carlo generators only for flavor decomposition, and complements the traditional physics-informed parametrization with a Neural Network extraction. We also discuss the setup for the extraction of the transversely polarized DiFFs, where we revisit the NLO calculation for $e^+e^-$ annihilation into a transversely polarized
quark-antiquark pair, obtaining a result different from the one reported in the literature.
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High Energy Physics (Phenomenology)
Higgs Boson Pair Production via Gluon Fusion: Higher-Order Corrections and Theoretical Uncertainties
Ajjath A H, Simone Alioli, Emanuele Bagnaschi et al. (+51 more)
In this contribution, the higher-order QCD and electroweak corrections to Standard Model
Higgs boson pair production via the gluon-fusion mechanism, $gg\to hh$, are summarized and the different sources of theoretical uncertainty are assessed. The discussion includes finite top
quark mass effects, matching to parton showers, approximate NNLO and N$^3$LO QCD corrections, NLO electroweak effects, and uncertainties associated with the top
quark mass scheme and perturbative scale choices. In addition, we provide an updated state-of-the-art recommendation for the inclusive gluon-fusion
Higgs boson pair production cross section and the corresponding
Higgs boson pair invariant-mass distribution.
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All authors Ajjath A H, Simone Alioli, Emanuele Bagnaschi, Arunima Bhattacharya, Huan-Yu Bi, Roberto Bonciani, Marco Bonetti, Francisco Campanario, Sauro Carlotti, Jamie Chang, Long-Bin Chen, Xuan Chen, Yuesheng Dai, Joshua Davies, Giuseppe Degrassi, Pier Paolo Giardino, Massimiliano Grazzini, Ramona Gröber, Gudrun Heinrich, Li-Hong Huang, Rui-Jun Huang, Sebastian Jaskiewicz, Stephen Jones, Stefan Kallweit, Matthias Kerner, Hai Tao Li, Shi-Yuan Li, Jonas M. Lindert, Yan-Qing Ma, Giulia Marinelli, Javier Mazzitelli, Margarete Mühlleitner, Davide Napoletano, Philipp Rendler, Jonathan Ronca, Johannes Schlenk, Kay Schönwald, Hua-Sheng Shao, Michael Spira, Thomas Stone, Daniel Stremmer, Robert Szafron, William J. Torres Bobadilla, Yannick Ulrich, Augustin Vestner, Marco Vitti, Jian Wang, Huai-Min Yu, Hantian Zhang, Fabio Monti, Arantxa Ruiz Martínez, Angela Taliercio, Andreas Papaefstathiou, Ludovic Scyboz
High Energy Physics (Phenomenology)
Flavor Tomography of Long-Lived Neutrino-Mass Mediators: Probing the Neutrino Mass Ordering at the HL-LHC
Renjie Wang
The
neutrino mass ordering remains unresolved because long-baseline oscillation measurements are entangled with the unknown CP phase $\delta_{CP}$; a
collider probe free of this degeneracy would provide a qualitatively different, complementary test. We show that when the long-lived charged particle producing a displaced-lepton signal at the High-Luminosity LHC is also the mediator responsible for Majorana
neutrino masses—the shared-coupling condition—the Casas–Ibarra parametrization determines the lepton flavor ratio $N_e/N_\mu$ of time-delayed leptons in terms of Pontecorvo–Maki–Nakagawa–Sakata (PMNS) mixing parameters alone. Within the resulting shared-coupling class of models the ratio is fixed by oscillation data, independent of all beyond-Standard-Model mass and coupling parameters up to calculable corrections bounded by charged-lepton-flavor-violation data, yielding $N_e/N_\mu = 0.140$ for the Normal and $2.11$ for the Inverted Hierarchy—a separation of more than an order of magnitude between the two predictions. This prediction holds identically across the Scotogenic model, the Type-III seesaw, the inverse and linear seesaw, and lepton-portal dark matter, and is stable against oscillation-parameter uncertainties and detector-efficiency variations, which cancel in the ratio. A single efficiency-corrected decision criterion identifies the hierarchy, and explicit signal-yield estimates combined with an exact Poisson test show that $\mathcal{O}(25)$ displaced-lepton events suffice for a $3\sigma$ discrimination with the timing infrastructure already under construction at CMS and ATLAS—so that a positive long-lived-particle signal would simultaneously resolve the mass ordering, with no dependence on $\delta_{CP}$.
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High Energy Physics (Phenomenology)
Exothermic and Endothermic Inelastic Dark Matter Interpretations at LZ: Sideband Constraints and Future Prospects
James B. Dent and Jayden L. Newstead
The LZ experiment has extended its nuclear-recoil search to 270 keV and reports a single nuclear-recoil-like event, LZ230616, at $\sim250$ keV, in a region with negligible expected background. We show that exothermic inelastic dark matter, in which the ambient dark state down-scatters and releases its mass splitting $|\delta|$ as recoil energy, can naturally produce a recoil peak at this energy while remaining consistent with the null result at lower energies. Our simple fit leaves the mass unconstrained, because a heavy candidate can hide its peak above the LZ region-of-interest. However, we show that the empty high-energy sideband, which LZ uses for background validation, disfavors broadly peaked spectra. For an exothermic explanation, the sharper peaks produced by lighter dark matter with larger mass splittings are therefore preferred. Realizing this scenario requires cosmologically stable states and a leptophobic mediator. Normalizing to the one observed event, we predict $\simeq4.5$ signal events in LZ's projected 1000 live-day exposure, and show that existing XENONnT and PandaX-4T data could already test the interpretation in an extended analysis window.
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