arXiv subjects

Dominik Köhler

Publications and source records attributed to Dominik Köhler.

8 recordsLinked to original sources

arXiv2026

The Single Photon Signature of a Light Long-lived Neutralino at Remote Detectors at the LHC

We investigate the phenomenology of light long-lived neutralinos in R-parity violating supersymmetric models, focusing on the proposed remote detectors $\texttt{ANUBIS}$, $\texttt{CODEX-b}$, $\texttt{FACET}$, $\texttt{FASER}$, $\texttt{FASER2}$, $\texttt{MAPP}$, $\texttt{MAPP2}$, and $\texttt{MATHUSLA}$ at the LHC. We assume the production of the neutralinos at the ATLAS or CMS interaction points via rare scalar meson decays induced by R-parity violating couplings. We study six supersymmetric R-parity violating benchmark scenarios in which the dominant neutralino decay is $\tildeχ^0_1 \rightarrow γ+ ν$. For each scenario, we determine the projected search sensitivity at the above listed detectors. Extending previous work focused primarily on $\texttt{FASER}$ and $\texttt{FASER2}$, we improve the simulation by taking into account the extended flight path of the parent meson. We find that $\texttt{ANUBIS}$ provides the best sensitivity to our benchmark scenarios and $\texttt{FASER}$ the least among the considered experiments, while of course $\texttt{FASER}$ has already taken data.

hep-ph↗

arXiv2025

Flow-Attentional Graph Neural Networks

Graph Neural Networks (GNNs) have become essential for learning from graph-structured data. However, existing GNNs do not consider the conservation law inherent in graphs associated with a flow of physical resources, such as electrical current in power grids or traffic in transportation networks, which can lead to reduced model performance. To address this, we propose flow attention, which adapts existing graph attention mechanisms to satisfy Kirchhoff$\text{'}$s first law. Furthermore, we discuss how this modification influences the expressivity and identify sets of non-isomorphic graphs that can be discriminated by flow attention but not by standard attention. Through extensive experiments on two flow graph datasets (electronic circuits and power grids) we demonstrate that flow attention enhances the performance of attention-based GNNs on both graph-level classification and regression tasks.

cs.LG↗

arXiv2024

Utilizing Description Logics for Global Explanations of Heterogeneous Graph Neural Networks

Graph Neural Networks (GNNs) are effective for node classification in graph-structured data, but they lack explainability, especially at the global level. Current research mainly utilizes subgraphs of the input as local explanations or generates new graphs as global explanations. However, these graph-based methods are limited in their ability to explain classes with multiple sufficient explanations. To provide more expressive explanations, we propose utilizing class expressions (CEs) from the field of description logic (DL). Our approach explains heterogeneous graphs with different types of nodes using CEs in the EL description logic. To identify the best explanation among multiple candidate explanations, we employ and compare two different scoring functions: (1) For a given CE, we construct multiple graphs, have the GNN make a prediction for each graph, and aggregate the predicted scores. (2) We score the CE in terms of fidelity, i.e., we compare the predictions of the GNN to the predictions by the CE on a separate validation set. Instead of subgraph-based explanations, we offer CE-based explanations.

cs.AI↗

arXiv2024

A Novel Proton Decay Signature at DUNE, JUNO, and Hyper-K

Proton decay, although unobserved so far, is a natural expectation when attempting to explain the baryon asymmetry of the universe. $p\to K^+\barν$ or $p\to K^+\tildeχ_1^0$, with $\tildeχ_1^0$ a light exotic neutral particle, represent possible decay channels achievable in models of physics beyond the Standard Model, such as the MSSM with trilinear R-parity-violating terms, or the Standard Model extended by a heavy neutral lepton. Among the decay products of these modes, the neutral fermions would typically appear as missing energy in collider searches. The present study considers how such decay modes could be differentiated in experimental settings, as the exotic $\tildeχ_1^0$ may further decay if it is not protected by a symmetry (such as R-parity in the MSSM). We assess the detection prospects of the proposed experiments DUNE, JUNO and Hyper-K in this context.

hep-ph↗

arXiv2023

Recasting Bounds on Long-lived Heavy Neutral Leptons in Terms of a Light Supersymmetric R-parity Violating Neutralino

In R-parity-violating (RPV) supersymmetric models, light neutralinos with masses from the GeV-scale down to even zero are still allowed by all laboratory constraints. They are further consistent with dark matter observations, as they decay via RPV couplings. These RPV couplings are in general constrained to be small. Hence, such light neutralinos, if produced, e.g., at a beam-dump or collider experiment, appear as displaced vertices or missing energy at the detector level. The same signatures have been extensively searched for at various experiments in the theoretical context of sterile neutrinos which mix with active neutrinos. In this work, we recast the sensitivity of both past and present experiments to sterile neutrinos to obtain new bounds on RPV couplings associated with a light neutralino. We find experiments such as T2K, BEBC, FASER, DUNE, and MoEDAL-MAPP can improve the current bounds on RPV couplings by up to $3-4$ orders of magnitude in several benchmark scenarios.

hep-ph↗

arXiv2023

The ABC of RPV: Classification of R-Parity Violating Signatures at the LHC for Small Couplings

We perform a classification of all potential supersymmetric $R$-parity violating signatures at the LHC to address the question: are existing bounds on supersymmetric models robust, or are there still signatures not covered by existing searches, allowing LHC-scale supersymmetry to be hiding? We analyze all possible scenarios with one dominant RPV trilinear coupling at a time, allowing for arbitrary LSPs and mass spectra. We consider direct production of the LSP, as well as production via gauge-cascades, and find 6 different experimental signatures for the $LL\bar E$-case, 6 for the $LQ\bar D$-case, and 5 for the $\bar U\bar D\bar D$-case; together these provide complete coverage of the RPV-MSSM landscape. This set of signatures is confronted with the existing searches by \texttt{ATLAS} and \texttt{CMS}. We find all signatures have been covered at the LHC, although not at the sensitivity level needed to probe the direct production of all LSP types. For the case of a dominant $LL\bar E$-operator, we use \texttt{CheckMATE} to quantify the current lower bounds on the supersymmetric masses and find the limits to be comparable to or better than the $R$-parity conserving case. Our treatment can be easily extended to scenarios with more than one non-zero RPV coupling.

hep-ph↗

arXiv2023

Searching for a Single Photon from Lightest Neutralino Decays in R-parity-violating Supersymmetry at FASER

In this work, we propose a search for a single photon at \texttt{FASER} and \texttt{FASER2}, produced from decays of bino-like, sub-GeV lightest neutralinos in the theoretical framework of the R-parity-violating (RPV) Minimal Supersymmetric Standard Model (MSSM). We consider a list of representative benchmark scenarios with one or two non-vanishing RPV couplings. The photon has an energy $\mathcal{O}\left(0.1\right)-\mathcal{O}\left(1\right)$ TeV. We find a sensitivity reach for RPV couplings beyond the current bounds by orders of magnitude at \texttt{FASER} and \texttt{FASER2}.

hep-ph↗

arXiv2022

A $ν$ Approach to Analyzing Neutrino Data in the $\mathbf{R}$-Parity-Violating MSSM

The $R$-parity-violating Minimal Supersymmetric Standard Model (RPV-MSSM) can naturally accommodate massive neutrinos as required by the oscillation data. However, studying the phenomenology is complicated due to the large number of undetermined parameters involved. Thus, studies are usually restricted to specific submodels. In this work, we develop an approach that allows us to be less restrictive. Working in (almost) the completely general RPV-MSSM setting, we analyze the structure of the neutrino mass matrix, and identify -- for the case of two massive neutrinos -- only four minimal classes of structures that can solve the neutrino data; we call these Minimal Oscillation Models (MOMs). We study the general features of each MOM class, and present numerical fits to the oscillation data. Our approach allows us to study all RPV models satisfying the neutrino data in a unified manner, as long as they satisfy the MOM criteria. Through several examples, we show that this indeed holds for many interesting scenarios.

hep-ph↗