arXiv subjects

Gudrid Moortgat-Pick

Publications and source records attributed to Gudrid Moortgat-Pick.

At least 19 recordsLinked to original sources

arXiv2026

Optimizing Superconducting Microwave Cavities for Gravitational Wave Sensing

Superconducting microwave cavities loaded with radio frequency fields are a powerful tool to search for weak forces or electromagnetic perturbations due to new physics. One source of such signals can be high-frequency gravitational waves emitted from cosmological or unknown astrophysical events. However, large sensitivity improvements are still necessary to reach the parameter space motivated by theoretical models. In this work, we present a formalism to guide the design of such detectors across a broad range of frequencies and signal forms. By incorporating the interdependencies of all relevant parameters and the back-action of the electromagnetic fields on the cavity structure, we describe how figures of merit can be derived for a broad class of relevant experimental setups. Using a two-dimensional model, we demonstrate this formalism and present examples for optimized cavity geometries. We find that the choice of geometry alone can increase the signal-to-noise power ratio by an order of magnitude compared to an existing prototype of the same size. We also show that different physics goals lead to different optimal cavities, thus proving the need to consider such figures of merit at an early stage when designing a new detector.

gr-qc↗

arXiv2026

Covariant eigenmode overlap formalism for gravitational wave signals in electromagnetic cavities

We develop a coordinate invariant formalism which describes the mechanical and electromagnetic interaction of gravitational waves (GWs) with a wide class of resonant detectors. We solve the GW-modified equations of electrodynamics and elasticity with dynamic boundary conditions using an eigenmode expansion. Furthermore, we take damping effects and electromagnetic back-action on mechanical systems covariantly into account. The resulting coupling coefficients are particularly useful for high-frequency gravitational wave experiments using microwave cavities and allow a straightforward numerical implementation for arbitrary detector geometries.

gr-qc↗

arXiv2026

Cryogenic RF characterization of the MAGO cavity for high-frequency gravitational-wave detection

Superconducting radio-frequency (SRF) cavities are promising resonant sensors for gravitational-wave detection in the kHz-MHz frequency range. We report the cryogenic RF characterization of a prototype superconducting niobium cavity with an unconventional geometry designed for narrow electromagnetic mode separation. Following an adapted surface preparation procedure, cryogenic tests were performed at Fermilab and DESY at temperatures down to 2\,K. Mechanical tuning at room temperature achieved a mode splitting of approximately 11\,kHz at cryogenic temperature. High electromagnetic quality factors consistent with previous prototype cavities were measured. The measurements further revealed phase transfer characteristics relevant for stable low-level RF control as well as indications of mode coupling potentially caused by one-point multipacting. In addition, first cryogenic measurements of the mechanical eigenmodes yielded mechanical quality factors significantly below commonly assumed theoretical values. These results demonstrate the successful application of established SRF preparation and characterization techniques to a non-standard resonator geometry and provide important experimental input for the development of future SRF-based gravitational-wave detectors.

physics.ins-det↗

arXiv2026

Search for Dark Matter in 2HDMS at LHC and future Lepton Colliders

We investigate the phenomenological prospects of the Two Higgs Doublet and Complex Singlet Scalar Extension (2HDMS) in the context of dark matter (DM) and Higgs phenomenology. The 2HDMS provides an enlarged Higgs sector along with a DM candidate. In this work, we perform an exhaustive scan to find representative benchmarks which are consistent with all theoretical and experimental constraints. We choose benchmarks with light, intermediate and massive DM masses and in some cases, also accommodate the 95 GeV excess in $b\bar{b}$ and $γγ$ channels observed at the Large Electron-Positron Collider (LEP) and Large Hadron Collider (LHC). We focus on the relevant signatures at the LHC and at proposed future lepton colliders including electron-positron and muon colliders. Using a cut and count analysis, we show that while the High Luminosity LHC (HL-LHC) may give a hint of new physics, future lepton colliders prove to be efficient discovery probes for the 2HDMS.

hep-ph↗

arXiv2026

BSM Searches at a Photon Collider with Energy $E_{γγ}< 12$ GeV

The possibility of a photon collider extension to the beam dump of the $17.5$ GeV European XFEL has already been discussed before as the first high energy collider of its sort. It would not only be the first proof of concept and test of a photon collider but would also be a collider without competition in the region of $E_{γγ}=5-12$ GeV for photon-photon collision. In this range, $b\bar{b}$ and $c\bar{c}$ resonances, tetraquarks and mesonic molecules can be observed. Furthermore, some BSM processes can also be reached in this range. In this paper we want to discuss the possibility of observing ALPs in the process of light-by-light scattering at such a collider. We will use a simplified description of the Compton backscattering process to get a first look at cross sections for the Standard Model light-by-light scattering and the extension including ALPs. Furthermore, we extend this to the full beam dynamics included prediction, discuss all effects that are important when working with a photon collider and show that the photon collider with energy $E_{γγ}<12$ GeV would offer an extended physics reach compared to current limits.

hep-ph↗

arXiv2026

CP-violation and its implications in a complex singlet extension of 2HDM

We investigate CP-violation in the complex singlet extension of the general Two Higgs Doublet Model (2HDM) with Yukawa alignment condition. We first explore the possibility of explicit CP-violation in the extended scalar sector while the 125 GeV Higgs remains exactly Standard Model (SM)-like. We identify an additional source of CP violation in the complex singlet extension compared to the 2HDM, which allows this model a substantially greater freedom in satisfying the stringent EDM constraints. We also incorporate dark matter in this model and investigate the impacts of constraints from the dark sector on the model parameter space and its interplay with CP-violation phases. We further explore the possibility of detecting such a scenario at future collider experiments via CP-violating trilinear couplings among the non-standard scalars. Finally, we also deviate from the exact alignment limit and investigate the CP-properties of the observed Higgs boson in the context of our model. We demonstrate the strong model-dependent nature of the detection prospects of the CP-phase of the Higgs boson at future experiments, exploring both fermion couplings as well as the trilinear self-coupling of the Higgs boson.

hep-ph↗

arXiv2025

Laboratory Frame Representation for General High-Frequency Gravitational Waveforms

Next-generation gravitational wave (GW) experiments will explore higher frequency ranges, where GW wavelengths approach the size of the detector itself. In this regime, GWs may be detected not just through the well-known mechanical deformation by tidal forces but also via induced effective currents in electromagnetic background fields. However, the calculation of this signal requires the GW metric in laboratory coordinates of the detector, and an accurate transformation to all orders into this frame is necessary. In this work, we derive a closed-form expression for the metric transformation of general chirp-like waveforms expressed in terms of the transverse-traceless GW metric, its integral, and its derivative. For more complex signals, where analytical integration is impractical, we provide an efficient approximation based on Taylor expansions of the retarded time to coalescence. Finally, we demonstrate how these results can be applied to calculate the signal response of a large class of detectors. Our approach provides essential tools for designing and interpreting high-frequency GW experiments that search for compact object mergers at MHz to GHz frequencies beyond the long-wavelength limit.

gr-qc↗

arXiv2025

Probing the Higgs potential at a Photon Collider

A $γγ$ collider, either in conjunction with an $e^+e^-$ linear collider or as a stand-alone facility, offers a very attractive Higgs physics programme at relatively low centre-of-mass (c.m.) energies. While the Higgs boson that has been discovered at the LHC can be studied in detail in resonant production at 125~GeV, a c.m.\ energy as low as 280~GeV can probe the Higgs potential via the Higgs pair production process providing access to the trilinear Higgs-boson self-coupling. High polarisation of the photon beams (produced via Compton back-scattering) can be achieved and adjusted by flipping the polarisation of the incident laser. The prospects for exploring the Higgs pair production process at a $γγ$ collider are assessed by comparing different running scenarios utilising different types of the incident laser. The possibility to use photon polarisations for disentangling different kinds of contributions to the Higgs pair production process is emphasised.

hep-ph↗

arXiv2025

Vacuum Instability and False Vacuum Decay Induced by Domain Walls in the N2HDM

The Next-to-Two-Higgs-Doublet model (N2HDM) has a rich vacuum structure where multiple electroweak (EW) breaking minima, as well as CP and electric-charge breaking minima, can coexist. These minima can be deeper than the electroweak vacuum $v_{ew} \approx 246\text{ GeV}$ of our universe, making our vacuum metastable. In such a case, one needs to calculate the tunneling rate from the EW vacuum to the deeper minimum. If the lifetime of the EW vacuum is longer than the universe's age, our vacuum is deemed long-lived, and the parameter point is, in principle, allowed. If the decay rate is smaller than the universe's age, then our vacuum is unstable and the parameter point is ruled out. However, domain walls (DW) in the N2HDM can substantially alter this picture. We show in this work that inside the DW, the barrier between our electroweak minimum and the deeper minimum can disappear, leading the scalar fields to classically roll over to the deeper minimum that nucleates inside the DW and then expands outside of it everywhere in the universe. We show that such behavior can happen to parameter points where the lifetime of our minimum is even several orders of magnitude larger than the age of the universe. Such parameter points with a metastable EW minimum are ruled out.

hep-ph↗

arXiv2025

First characterisation of the MAGO cavity, a superconducting RF detector for kHz-MHz gravitational waves

Heterodyne detection using microwave cavities is a promising method for detecting high-frequency gravitational waves or ultralight axion dark matter. In this work, we report on studies conducted on a spherical 2-cell cavity developed by the MAGO collaboration for high-frequency gravitational waves detection. Although fabricated around 20 years ago, the cavity had not been used since. Due to deviations from the nominal geometry, we conducted a mechanical survey and performed room-temperature plastic tuning. Measurements and simulations of the mechanical resonances and electromagnetic properties were carried out, as these are critical for estimating the cavity's gravitational wave coupling potential. Based on these results, we plan further studies in a cryogenic environment. The cavity characterisation does not only provide valuable experience for a planned physics run but also informs the future development of improved cavity designs.

gr-qc↗

arXiv2025

A High-Flux Electron Detector System to Measure Non-linear Compton Scattering at LUXE

Recently, advancements in high-intensity laser technology have enabled the exploration of non-perturbative Quantum Electrodynamics (QED) in strong-field regimes. Notable aspects include non-linear Compton scattering and Breit-Wheeler pair production, observable when colliding high-intensity laser pulses and relativistic electron beams. The LUXE experiment at DESY and the E-320 experiment at SLAC aim to study these phenomena by measuring the created high-flux Compton electrons and photons. We propose a novel detector system featuring a segmented gas-filled Cherenkov detector with a scintillator screen and camera setup, designed to efficiently detect high-flux Compton electrons. Preliminary results from E-320 measurement campaigns demonstrate methods for reconstructing electron energy spectra, aiming to reveal crucial features of non-perturbative QED.

physics.ins-det↗

arXiv2025

Phenomenology of the dark matter sector in the 2HDM extended with complex scalar singlet

The two-Higgs-doublet model augmented with a complex scalar singlet (2HDMS) is a well-motivated candidate for Beyond Standard Model (BSM) Physics. We investigate the dark matter phenomenology of the 2HDMS with the complex scalar singlet as the dark matter candidate. We perform a study of the parameter space allowed by existing theoretical and experimental constraints from dark matter, flavour physics and collider searches. Further, we discuss a few benchmark scenarios to test the discovery potential for the 2HDMS at the HL-LHC and at future high-energy $e^+e^-$ colliders.

hep-ph↗

arXiv2024

Searches for BSM physics at a gamma-gamma collider with Energy < $12$ GeV based on European XFEL

The possibility of a Photon-Photon collider extension to the Beam dump of the $17.5$ GeV European XFEL has been discussed before as the first high energy collider of its sort. It would not just be to study the concept of photon colliders but would also be a collider without competition in the region of $5 - 12$ GeV for photon-photon collision. In this range, $b\overline{b}$ and $c\overline{c}$ resonances, tetraquarks as well as mesonic molecules can be observed. Furthermore, some BSM processes can also be reached in this range. In this paper we want to discuss the possibility of observing ALPs at such a collider. We will use a simplified description of the compton backscattering process to get a first look at cross sections and extend this to the full beam dynamics included prediction.

hep-ph↗

arXiv2024

Physics case for an $e^+e^-$ collider at 500 GeV and above

Some highlights of the physics case for running an $e^+e^-$ collider at 500 GeV and above are discussed with a particular emphasis on the experimental access to the Higgs potential via di-Higgs and (at sufficiently high energy) triple Higgs production. The information obtainable from Higgs pair production at about 500 GeV is compared with the prospects for the HL-LHC and with the indirect information that can be obtained from a Higgs factory running at lower energies.

hep-ph↗

arXiv2024

Electroweak Symmetry Restoration in Extended Higgs Sectors via Domain Walls

Domain walls are a type of topological defects that can arise in the early universe after the spontaneous breaking of a discrete symmetry. This occurs in several beyond Standard Model theories with an extended Higgs sector such as the Next-to-Two-Higgs-Doublet model (N2HDM). In this talk, I will discuss the domain wall solution related to the singlet scalar of the N2HDM and demonstrate the possibility of electroweak symmetry restoration (EWSR) in the vicinity of the domain wall. Such symmetry restoration can have profound implications on the early universe cosmology as the sphaleron rate inside the domain wall would, in principle, be unsuppressed compared with the rate outside the wall.

hep-ph↗

arXiv2024

Dark Matter Phenomenology in 2HDMS in light of the 95 GeV excess

The Two Higgs Doublet model extended with a complex scalar singlet (2HDMS) is a well-motivated Beyond Standard Model candidate addressing several open problems of nature. In this work, we focus on the dark matter (DM) phenomenology of the complex scalar singlet where the real part of the complex scalar obtains a vacuum expectation value. The model is characterized by an enlarged Higgs spectrum comprising six physical Higgs bosons and a pseudoscalar DM candidate. We address the impact of accommodating the 95 GeV excess on the 2HDMS parameter space and DM observables after including all theoretical and experimental constraints. Finally, we look into the prospects of this scenario at HL-LHC and future lepton colliders for a representative benchmark.

hep-ph↗

arXiv2024

Vacuum (in)stability in 2HDMS vs N2HDM

In this work, we examine the criteria for vacuum stability in two models with extended scalar sectors namely, the N2HDM and the 2HDMS and make a detailed comparison between the two. For the purpose of demonstration, we choose a scenario which can accommodate the recently observed 95 GeV excess in both models. We further explore the impact of the measurement of the Yukawa couplings, the gauge boson couplings and most importantly the trilinear self-couplings of the scalars, in distinguishing the vacuum structure in both models. We further investigate the constraints from vacuum stability on the 2HDMS scenario that accommodates a viable dark matter candidate and compare it with the N2HDM case.

hep-ph↗

arXiv2024

Electroweak Symmetry Restoration in the N2HDM via Domain Walls

Domain walls are a type of topological defects that can arise in the early universe after the spontaneous breaking of a discrete symmetry. They can form in several beyond the Standard Model theories with an extended Higgs sector such as the Next to-Two-Higgs-Doublet model (N2HDM). In this work, we discuss the domain wall solution related to the singlet scalar of the N2HDM and demonstrate the possibility of restoring the electroweak symmetry inside and in the vicinity of the domain wall. Such symmetry restoration can have profound implications on early universe cosmology as the weak sphaleron rate inside the domain wall would, in principle, be unsuppressed compared to the rate outside the wall. We also discuss the possibility of generating CP-violating vacua localized in the vicinity of the domain wall. Our work is a first step towards the realization of electroweak baryogenesis mediated by domain walls in the N2HDM.

hep-ph↗