arXiv subjects

J. Müller

Publications and source records attributed to J. Müller.

At least 19 recordsLinked to original sources

arXiv2026

Facing the phase: Gravity-mode offset and buoyancy glitches in red--giant branch stars

With the increasing precision of asteroseismic observations, it becomes possible to reliably measure oscillation properties of an increasing number of stars. Interpreting these measurements requires a good theoretical understanding of their link to fundamental stellar properties. In this study, we focus on the phase offset in gravity(g)-mode frequencies, which is imprinted in the asymptotic eigenfrequency pattern of mixed dipole modes observed in red--giant branch stars. We aim to unravel its physical origin and thus enable an informed interpretation of observations. Using stellar models, we empirically test the contribution of the g-mode offset $\varepsilon_\mathrm{g}$ (which is related to the wave reflection at cavity boundaries and commonly considered to be the dominant phase term) and glitches to the total observable phase. We find that, additionally to $\varepsilon_\mathrm{g}$, buoyancy glitches play an important role in the correct interpretation of the g--mode frequency phase. We further find that glitches in the evanescent zone also contribute to the phase, and we present a formalism to quantify this contribution. Finally, we propose a modification to the widely used formula for $\varepsilon_\mathrm{g}$. The g--mode frequency phase carries more information than previously considered. It has large analytic potential to study not only the reflection properties of the buoyancy cavity, but also the properties of glitches in the Brunt-V\"ais\"al\"a frequency.

astro-ph.SR↗

arXiv2025

Development & Characterization of Electrodes for large-scale Xenon Time Projection Chambers

Dual-phase liquid xenon time projection chambers are the core detector elements of many experiments that conduct searches for Dark Matter and rare events, as well as in neutrino and high-energy physics. As part of this detector technology, high-voltage electrodes are instrumental for the generation of observable signals and their physical interpretation. Thus, electrode design and manufacturing has to fulfill stringent requirements, and their production is associated with significant engineering challenges. In this work we describe the successful development of electrodes on the 1.5 m-scale, from their design and simulation to subsequent assembly and high-voltage testing in a gaseous argon environment. The produced electrodes were recently installed as an anode and a cathode during an upgrade to the XENONnT experiment.

physics.ins-det↗

arXiv2025

Probing a cosmogenic origin of astrophysical neutrinos and cosmic rays using gamma-ray observations of TXS 0506+056

In September 2017, a high-energy neutrino event detected by the IceCube Neutrino Observatory (IceCube-170922A) was associated, at the $3\sigma$ level, with a gamma-ray flare from the blazar TXS 0506+056. Cosmic rays that are accelerated in astrophysical sources can escape from their jets and interact with background radiation fields. Interactions with the extragalactic background light can produce pions and hence neutrinos, while interactions with the cosmic microwave background predominantly drive inverse Compton scattering, contributing to electromagnetic cascades in intergalactic space. The resulting secondary gamma-ray emission can be detected with high-energy gamma-ray telescopes. Here, we report on a new search for such cosmogenic cascade emission from the blazar TXS 0506+056, using a combined data set from the Fermi-Large Area Telescope and VERITAS. We compare the gamma-ray spectrum and neutrino observations with the predictions of cosmic-ray induced cascades in intergalactic space. The observed gamma-ray spectrum is modeled as a combination of the primary spectrum and the cascade spectrum. We apply a Monte Carlo simulation with a $\Delta\chi^2$-based likelihood analysis to jointly determine the best-fit parameters of a proton emission spectrum describing the data and derive constraints on the proton escape luminosity. Assuming a log-parabola primary photon spectrum, we find consistency with a proton injection spectral index of $\alpha_{p} \simeq 2.0$ and a cutoff energy of $E_{p,\text{max}} \simeq 1.3 \times 10^{16}$ eV, and constrain the isotropic proton escape luminosity to $1 \times 10^{44}$ erg s$^{-1}$ $\lesssim L_{p, esc} \lesssim 3 \times 10^{45}$ erg s$^{-1}$ at the 90 % confidence level.

astro-ph.HE↗

arXiv2025

Weak or strong: coupling of mixed oscillation modes on the red-giant branch

Context. The high precision of recent asteroseismic observations of red-giant stars has revealed the presence of mixed dipole modes in their oscillation spectra. These modes allow for a look inside the stars. Among the parameters used to characterize mixed modes is the coupling strength q, which is sensitive to the stellar structure in the evanescent zone near the bottom of the convective envelope. Aims. The aim of this work is to probe the validity of the weak and strong coupling approximations, commonly used to calculate q, during stellar evolution along the red-giant branch (RGB). Methods. To test the approximations empirically, we calculate q-values in both, the weak and strong limit for stellar models on the RGB and compare them to the coupling derived from the mixed mode frequency pattern obtained from numerical solutions to the oscillation equations. Results. We find good agreement with the strong coupling approximation on the early RGB, when the evanescent zone lies in the radiative layer right above the hydrogen-burning shell; and with the weak coupling approximation once the evanescent zone is situated in the convective envelope. This is consistent with earlier studies. Additionally, we find that it is viable to use the weak coupling approximation as an estimate for q in the intermediate regime, in the mass range considered in this work (1.00 Msun <= M <= 2.00 Msun). Conclusions. The width of the evanescent zone serves as a good measure for which approximation to use. The serendipitous alignment of the weak coupling approximation with the observable q in the regime where neither approximation is expected to be valid simplifies the asymptotic calculation of mixed mode properties.

astro-ph.SR↗

arXiv2024

Magnetic and electronic inhomogeneity in Sm$_{1-x}$Eu$_x$B$_6$

While SmB$_6$ attracts attention as a possible topological Kondo insulator, EuB$_6$ is known to host magnetic polarons that give rise to large magnetoresistive effects above its ferromagnetic order transition. Here we investigate single crystals of Sm$_{1-x}$Eu$_x$B$_6$ by magnetic and magnetotransport measurements to explore a possible interplay of these two intriguing phenomena, with focus on the Eu-rich substitutions. Sm$_{0.01}$Eu$_{0.99}$B$_6$ exhibits generally similar behavior as EuB$_6$. Interestingly, Sm$_{0.05}$Eu$_{0.95}$B$_6$ combines global antiferromagnetic order with local polaron formation. A pronounced hysteresis is found in the magnetoresistance of Sm$_{0.1}$Eu$_{0.9}$B$_6$ at low temperature ($T=$ 1.9 K) and applied magnetic fields between 2.3 $-$ 3.6 T. The latter is in agreement with a phenomenological model that predicts the stabilization of ferromagnetic polarons with increasing magnetic field within materials with global antiferromagnetic order.

cond-mat.str-el↗

arXiv2024

Thermodynamic evidence for polaron stabilization inside the antiferromagnetic order of Eu$_5$In$_2$Sb$_6$

Materials exhibiting electronic inhomogeneities at the nanometer scale have enormous potential for applications. Magnetic polarons are one such type of inhomogeneity which link the electronic, magnetic and lattice degrees of freedom in correlated matter and often give rise to colossal magnetoresistance. Here, we investigate single crystals of Eu$_5$In$_2$Sb$_6$ by thermal expansion and magnetostriction along different crystallographic directions. These data provide compelling evidence for the formation of magnetic polarons in Eu$_5$In$_2$Sb$_6$ well above the magnetic ordering temperature. More specifically, our results are consistent with anisotropic polarons with varying extent along the different crystallographic directions. A crossover revealed within the magnetically ordered phase can be associated with a surprising stabilization of ferromagnetic polarons within the global antiferromagnetic order upon decreasing temperature. These findings make Eu$_5$In$_2$Sb$_6$ a rare example of such coexisting and competing magnetic orders and, importantly, shed new light on colossal magnetoresistive behavior beyond manganites.

cond-mat.str-el↗

arXiv2024

Emission of Single and Few Electrons in XENON1T and Limits on Light Dark Matter

Delayed single- and few-electron emissions plague dual-phase time projection chambers, limiting their potential to search for light-mass dark matter. This paper examines the origins of these events in the XENON1T experiment. Characterization of the intensity of delayed electron backgrounds shows that the resulting emissions are correlated, in time and position, with high-energy events and can effectively be vetoed. In this work we extend previous S2-only analyses down to a single electron. From this analysis, after removing the correlated backgrounds, we observe rates < 30 events/(electron*kg*day) in the region of interest spanning 1 to 5 electrons. We derive 90% confidence upper limits for dark matter-electron scattering, first direct limits on the electric dipole, magnetic dipole, and anapole interactions, and bosonic dark matter models, where we exclude new parameter space for dark photons and solar dark photons.

hep-ex↗

arXiv2023

Nuclear density dependence of polarization transfer in quasi-elastic ${\rm A}(\vec{e},e' \vec{p})$ reactions

The ratio of the transverse and longitudinal component of polarization transfer to protons in the quasi-elastic $(\vec{e}, e^{\prime} \vec{p}\,)$ reaction, $P^{\prime}_x/P^{\prime}_z$, is sensitive to the proton's electromagnetic form factor ratio, $G_E/G_M$. To explore density-dependent in-medium modifications, a comparison of polarization transfer ratios involving protons from distinct nuclear shells, each with different local nuclear densities, has been proposed. In this study, we present such comparisons between four shells, $1s_{1/2}$, $1p_{3/2}$ in $^{12}\mathrm{C}$ and $1d_{3/2}$, $2s_{1/2}$ in $^{40}\mathrm{Ca}$. In an effort to account for other many-body effects that may differ between shells, we use a state-of-the-art relativistic distorted-wave impulse-approximation (RDWIA) calculation and present the double ratios, $(P^{\prime}_x/P^{\prime}_z)_{\rm Data}/(P^{\prime}_x/P^{\prime}_z)_{\rm RDWIA}$ as well as the super ratios, $\left[(P^{\prime}_x/P^{\prime}_z)_{\rm A}/(P^{\prime}_x/P^{\prime}_z)_{\rm B}\right]_{\rm Data}/\left[(P^{\prime}_x/P^{\prime}_z)_{\rm A}/(P^{\prime}_x/P^{\prime}_z)_{\rm B}\right]_{\rm RDWIA}$, for chosen shells A and B, as a function of effective local nuclear densities. We find that double ratios for individual shells show a dependence on the probed effective nuclear densities. Studying the ratios, we observed a systematic variation between pairs of higher- and lower-density shells.

nucl-ex↗

arXiv2023

Measurement of polarization transfer in the quasi-elastic $^{40}{\rm Ca}(\vec{e},e' \vec{p})$ process

Polarization transfer to a bound proton in polarized electron knock-out reactions, $\mathrm{A}(\vec{e},e^{\prime}\vec{p})$, is a powerful tool to look for in-medium modification of the bound proton. It requires comparison to calculations which consider the many-body effects accompanying the quasi-free process. We report here measured components $P_x^{\prime}$, $P_z^{\prime}$, and their ratio $P_x^{\prime}/P_z^{\prime}$, of polarization transfer to protons bound in $^{40}\mathrm{Ca}$, which is described well by the shell model and for which reliable calculations are available. While the calculations capture the essence of the data, our statistical precision allows us to observe deviations which cannot be explained by simple scaling, including by varying the proton electromagnetic form factor ratio $G_E/G_M$. We further explore the deviations of the ratio of the polarization transfer components from that of a free proton, $(P_x^{\prime}/P_z^{\prime})_{\rm A}/(P_x^{\prime}/P_z^{\prime})_{\rm H}$, and its dependence on the bound-proton virtuality.

nucl-ex↗

arXiv2023

Magnetic and electronic properties of Eu$_5$In$_2$Sb$_6$

The intermetallic compound Eu$_5$In$_2$Sb$_6$, an antiferromagnetic material with nonsymmorphic crystalline structure, is investigated by magnetic, electronic transport and specific heat measurements. Being a Zintl phase, insulating behavior is expected. Our thermodynamic and magnetotransport measurements along different crystallographic directions strongly indicate polaron formation well above the magnetic ordering temperatures. Pronounced anisotropies of the magnetic and transport properties even above the magnetic ordering temperature are observed despite the Eu$^{2+}$ configuration which testify to complex and competing magnetic interactions between these ions and give rise to intricate phase diagrams discussed in detail. Our results provide a comprehensive framework for further detailed study of this multifaceted compound with possible nontrivial topology.

cond-mat.mtrl-sci↗

arXiv2022

CARIOQA: Definition of a Quantum Pathfinder Mission

A strong potential gain for space applications is expected from the anticipated performances of inertial sensors based on cold atom interferometry (CAI) that measure the acceleration of freely falling independent atoms by manipulating them with laser light. In this context, CNES and its partners initiated a phase 0 study, called CARIOQA, in order to develop a Quantum Pathfinder Mission unlocking key features of atom interferometry for space and paving the way for future ambitious space missions utilizing this technology. As a cornerstone for the implementation of quantum sensors in space, the CARIOQA phase 0 aimed at defining the Quantum Pathfinder Mission's scenario and associated performance objectives. To comply with these objectives, the payload architecture has been designed to achieve long interrogation time and active rotation compensation on a BEC-based atom interferometer. A study of the satellite architecture, including all the subsystems, has been conducted. Several technical solutions for propulsion and attitude control have been investigated in order to guarantee optimal operating conditions (limitation of micro-vibrations, maximization of measurement time). A preliminary design of the satellite platform was performed.

physics.atom-ph↗

arXiv2022

An approximate likelihood for nuclear recoil searches with XENON1T data

The XENON collaboration has published stringent limits on specific dark matter -nucleon recoil spectra from dark matter recoiling on the liquid xenon detector target. In this paper, we present an approximate likelihood for the XENON1T 1 tonne-year nuclear recoil search applicable to any nuclear recoil spectrum. Alongside this paper, we publish data and code to compute upper limits using the method we present. The approximate likelihood is constructed in bins of reconstructed energy, profiled along the signal expectation in each bin. This approach can be used to compute an approximate likelihood and therefore most statistical results for any nuclear recoil spectrum. Computing approximate results with this method is approximately three orders of magnitude faster than the likelihood used in the original publications of XENON1T, where limits were set for specific families of recoil spectra. Using this same method, we include toy Monte Carlo simulation-derived binwise likelihoods for the upcoming XENONnT experiment that can similarly be used to assess the sensitivity to arbitrary nuclear recoil signatures in its eventual 20 tonne-year exposure.

hep-ex↗

arXiv2022

Polarization observables in double neutral pion photoproduction

Measurements of target asymmetries and double-polarization observables for the reaction $\gamma p\to p\pi^0\pi^0$ are reported. The data were taken with the CBELSA/TAPS experiment at the ELSA facility (Bonn University) using the Bonn frozen-spin butanol (C$_4$H$_9$OH) target, which provided transversely polarized protons. Linearly polarized photons were produced via bremsstrahlung off a diamond crystal. The data cover the photon energy range from $E_{\gamma}$=650 MeV to $E_{\gamma}$=2600 MeV and nearly the complete angular range. The results have been included in the BnGa partial wave analysis. Experimental results and the fit agree very well. Observed systematic differences in the branching ratios for decays of $N^*$ and $\Delta^*$ resonances are attributed to the internal structure of these excited nucleon states. Resonances which can be assigned to SU(6)$\times$O(3) two-oscillator configurations show larger branching ratios to intermediate states with non-zero intrinsic orbital angular momenta than resonances assigned to one-oscillator configurations.

nucl-ex↗

arXiv2022

Surface and electronic structure at atomic length scales of the non-symmorphic antiferromagnet Eu$_5$In$_2$Sb$_6$

We performed Scanning Tunneling Microscopy and Spectroscopy (STM/STS) measurements to investigate the Zintl phase Eu$_5$In$_2$Sb$_6$, a non-symmorphic antiferromagnet. The theoretical prediction of a non-trivial Fermi surface topology stabilized by the non-symmorphic symmetry motivated our research. On the cleaved (010) plane, we obtained striped patterns that can be correlated to the stacking of the [In$_2$Sb$_6$]$^{10-}$ double chains along the crystallographic $c$ axis. The attempted cleavage along the $a$ axis revealed a more complex pattern. We combined the STS measurement on non-reconstructed (010) and (081) surfaces with DFT calculations to further elucidate the electronic structure of Eu$_5$In$_2$Sb$_6$. From our investigations so far, direct experimental evidence of the predicted topological surface states remains elusive.

cond-mat.str-el↗

arXiv2022

Systematic treatment of hypernuclear data and application to the hypertriton

A database is under construction to provide a complete collection of published basic properties of hypernuclei such as Λ binding energies, lifetimes, or excitation energies. From these values, averages with related errors are computed in a systematic way. For each property, the overall experimental situation is depicted in form of an ideogram showing the combined probability density function of the measurements. The database is accessible via a dynamic website at https://hypernuclei.kph.uni-mainz.de with an user interface offering customizable visualizations, selections, or unit conversions. The capabilities of the database are demonstrated for the puzzling and disputed data situation of the hypertriton.

physics.data-an↗

arXiv2021

Observation of a structure in the M$_{pη}$ invariant mass distribution near 1700 MeV/$c^2$ in the $\mathbf{γp \rightarrow p π^0 η} $ reaction

The reaction $γp \rightarrow p π^0 η$ has been studied with the CBELSA/TAPS detector at the electron stretcher accelerator ELSA in Bonn for incident photon energies from threshold up to 3.1 GeV. This paper has been motivated by the recently claimed observation of a narrow structure in the M$_{Nη}$ invariant mass distribution at a mass of 1678 MeV/$c^2$. The existence of this structure cannot be confirmed in the present work. Instead, for E$_γ$ = 1400 - 1500 MeV and the cut M$_{pπ^0} \le 1190 $ MeV/$c^2$ a statistically significant structure in the M$_{pη}$ invariant mass distribution near 1700 MeV/$c^2$ is observed with a width of $Γ\approx 35$ MeV/$c^2$ while the mass resolution is $σ_{res}$ = 5 MeV/$c^2$. Increasing the incident photon energy from 1420 to 1540 MeV this structure shifts in mass from $\approx$ 1700MeV/c$^2$ to $\approx$ 1725 MeV/$c^2$; the width increases to about 50 MeV/$c^2$ and decreases thereafter. The cross section associated with this structure reaches a maximum of $\approx$ 100 nb around E$_γ \approx$ 1490 MeV (W $\approx $ 1920 MeV), which coincides with the $p a_0$ threshold. Three scenarios are discussed which might be the origin of this structure in the M$_{pη}$ invariant mass distribution. The most likely interpretation is that it is due to a triangular singularity in the $γp \rightarrow p a_0 \rightarrow p π^0 η$ reaction

nucl-ex↗

arXiv2021

The CN2HDM

We present the CP-violating Next-to-2-Higgs-Doublet Model (CN2HDM) which is based on the extension of the CP-violating 2-Higgs-Doublet-Model (C2HDM) by a complex singlet field that obeys a discrete $\mathbb{Z}_2$ symmetry. The model thus features not only CP violation required for successful electroweak baryogenesis but also a Dark Matter (DM) candidate. The model has an extended Higgs sector with four CP-mixing visible neutral Higgs bosons, a DM candidate and a pair of oppositely charged Higgs bosons. The possibility of singlet and CP-odd admixtures to the observed Higgs boson in addition to the large number of visible scalar particles leads to an interesting Higgs phenomenology. We find that the model can easily provide 100\% of the DM relic density and investigate interesting LHC and DM observables within the model. We provide all the tools necessary to study the CN2HDM in detail and point out future research directions for this interesting benchmark model that can address some of the most pressing open questions of the Standard Model.

hep-ph↗

arXiv2021

BSMPT v2 A Tool for the Electroweak Phase Transition and the Baryon Asymmetry of the Universe in Extended Higgs Sectors

We present the C++ code BSMPT v2 which is an extension of the previous code BSMPT for the calculation of the strength of the electroweak phase transition in extended Higgs sectors. The new version BSMPT v2 includes the features of BSMPT and extends the already implemented models (the 2-Higgs-Doublet model (2HDM) in its CP-conserving and CP-violating versions and the Next-to-2HDM) by the Complex Singlet Extension of the Standard Model (CxSM). The major upgrade is the implementation of the computation of the baryon asymmetry of the Universe (at present for the C2HDM) in two different approximation, called the FH and the VIA approach. Furthermore, the possibility of varying the renormalisation scale in the loop-corrected effective potential has been added. These changes and further smaller modifications are described in this manual. Additionally, a detailed explanation of the procedure for the implementation of new models is given, which has also changed with respect to the previous version.

hep-ph↗