arXiv subjects

Julian Günther

Publications and source records attributed to Julian Günther.

5 recordsLinked to original sources

arXiv2026

Squeezing Enhancement in Lossy Multi-Path Atom Interferometers

This paper explores the sensitivity gains afforded by spin-squeezed states in atom interferometry, in particular using Bragg diffraction. We introduce a generalised input-output formalism that accurately describes realistic, non-unitary interferometers, including losses due to velocity selectivity and scattering into undesired momentum states. This formalism is applied to evaluate the performance of one-axis twisted spin-squeezed states in improving phase sensitivity. Our results show that by carefully optimising the parameters of the Bragg beam splitters and controlling the degree of squeezing, it is possible to improve the sensitivity of the interferometer by several dB with respect to the standard quantum limit despite realistic levels of losses in light pulse operations. However, the analysis also highlights the challenges associated with achieving these improvements in practice, most notably the impact of finite temperature on the benefits of entanglement. The results suggest ways of optimising interferometric setups to exploit quantum entanglement under realistic conditions, thereby contributing to advances in precision metrology with atom interferometers.

quant-ph↗

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

Heavy neutral leptons and top quarks in effective field theory

We study the phenomenology of heavy neutral leptons (HNLs) at the LHC in effective field theory, concentrating on $d=6$ operators with top quarks. Depending on the operator choice and HNL mass, the HNLs will be produced either from proton-proton collisions in association with a single top, or via non-standard decays of top quarks. For long-lived HNLs we estimate the sensitivity reach of different detectors to various operators with top quarks and the HNLs for the high-luminosity phase of the LHC. For certain operators, ATLAS and some far detectors (MATHUSLA and ANUBIS) will be able to probe the associated new-physics scale as large as 12 TeV and 4.5 TeV, respectively, covering complementary HNL-mass ranges.

hep-ph↗

arXiv2024

A C++ program for estimating detector sensitivities to long-lived particles: Displaced Decay Counter

A series of far-detector programs have been proposed for operation at various interaction points of the Large Hadron Collider during the upcoming runs. Investigating the potential and complementarity of these experiments for new-physics searches goes through the estimation of their sensitivity to specific long-lived particle models. Here, we present an integrated numerical tool written in the C++ language and called Displaced Decay Counter, which we have created to this end and which can be used in association with MadGraph5, Pythia8, or any other state-of-the-art Monte-Carlo collider simulation tool. Several far-detector models have been implemented within the program, accounting for the geometry and integrated luminosity of projected detectors. Additional or more accurate designs can be easily constructed through a dedicated interface. The functionality of this tool is exemplified through the discussion of three benchmark scenarios, which we consider for the validation of the implemented detector models.

hep-ph↗

arXiv2024

Heavy neutral leptons from kaons in effective field theory

In the framework of the low-energy effective theory containing in addition to the Standard Model fields heavy neutral leptons (HNLs), we compute the decay rates of neutral and charged kaons into HNLs. We consider both lepton-number-conserving and lepton-number-violating four-fermion operators, taking into account also the contribution of active-heavy neutrino mixing. Assuming that the produced HNLs are long-lived, we perform simulations and calculate the sensitivities of future long-lived-particle (LLP) detectors at the high-luminosity LHC as well as the near detector of the Deep Underground Neutrino Experiment (DUNE-ND) to the considered scenario. When applicable, we also recast the existing bounds on the minimal mixing case obtained by NA62, T2K, and PS191. Our findings show that while the future LHC LLP detectors can probe currently allowed parameter space only in certain benchmark scenarios, DUNE-ND should be sensitive to parameter space beyond the current bounds in almost all the benchmark scenarios and for some of the effective operators considered it can even probe new-physics scales in excess of 3000 TeV.

hep-ph↗