Kai Schmitz
A5054880808- Cosmology and Gravitation Theories
- Particle physics theoretical and experimental studies
- Pulsars and Gravitational Waves Research
- Dark Matter and Cosmic Phenomena
- Black Holes and Theoretical Physics
- Geophysics and Gravity Measurements
- Radio Astronomy Observations and Technology
- Neutrino Physics Research
- Computational Physics and Python Applications
- Astrophysics and Cosmic Phenomena
- Galaxies: Formation, Evolution, Phenomena
- Gamma-ray bursts and supernovae
- Solar and Space Plasma Dynamics
- Astronomy and Astrophysical Research
- Astrophysical Phenomena and Observations
- Geomagnetism and Paleomagnetism Studies
- Seismology and Earthquake Studies
- Geophysical and Geoelectrical Methods
- Superconducting and THz Device Technology
- Adaptive optics and wavefront sensing
- Stochastic processes and financial applications
- Quantum Electrodynamics and Casimir Effect
- Computer Graphics and Visualization Techniques
- CCD and CMOS Imaging Sensors
- Modeling and Simulation Systems
University of Münster
2023-2025
European Organization for Nuclear Research
2020-2023
Campbell Collaboration
2023
Istituto Nazionale di Fisica Nucleare, Sezione di Padova
2019
University of Padua
2019
Max Planck Institute for Nuclear Physics
2016-2018
The University of Tokyo
2013-2016
Kavli Institute for the Physics and Mathematics of the Universe
2013-2016
Deutsches Elektronen-Synchrotron DESY
2010-2013
Michigan State University
2010
Abstract We report multiple lines of evidence for a stochastic signal that is correlated among 67 pulsars from the 15 yr pulsar timing data set collected by North American Nanohertz Observatory Gravitational Waves. The correlations follow Hellings–Downs pattern expected gravitational-wave background. presence such background with power-law spectrum favored over model only independent noises Bayes factor in excess 10 14 , and this same an uncorrelated common factors 200–1000, depending on...
Abstract The 15 yr pulsar timing data set collected by the North American Nanohertz Observatory for Gravitational Waves (NANOGrav) shows positive evidence presence of a low-frequency gravitational-wave (GW) background. In this paper, we investigate potential cosmological interpretations signal, specifically cosmic inflation, scalar-induced GWs, first-order phase transitions, strings, and domain walls. We find that, with exception stable strings field theory origin, all these models can...
We searched for an isotropic stochastic gravitational wave background in the second data release of International Pulsar Timing Array, a global collaboration synthesizing decadal-length pulsar-timing campaigns North America, Europe, and Australia. In our reference search power law strain spectrum form $h_c = A(f/1\,\mathrm{yr}^{-1})^{\alpha}$, we found strong evidence spectrally-similar low-frequency process amplitude $A 3.8^{+6.3}_{-2.5}\times10^{-15}$ spectral index $\alpha -0.5 \pm 0.5$,...
Gravitational waves (GWs) from strong first-order phase transitions (SFOPTs) in the early Universe are a prime target for upcoming GW experiments. In this paper, I construct novel peak-integrated sensitivity curves (PISCs) these experiments, which faithfully represent their projected sensitivities to signal cosmological SFOPT by explicitly taking into account expected shape of signal. Designed be handy tool phenomenologists and model builders, PISCs allow quick systematic comparison...
The North American Nanohertz Observatory for Gravitational Waves (NANOGrav) has recently reported strong evidence a stochastic common-spectrum process affecting the pulsar timing residuals in its 12.5-year data set. We demonstrate that this admits an interpretation terms of gravitational-wave background emitted by cosmic-string network early Universe. study stable Nambu-Goto strings dependence their tension $G\mu$ and loop size $\alpha$ show entire viable parameter space will be probed array...
The NANOGrav 15-year data set shows evidence for the presence of a low-frequency gravitational-wave background (GWB). While many physical processes can source such gravitational waves, here we analyze signal as coming from population supermassive black hole (SMBH) binaries distributed throughout Universe. We show that astrophysically motivated models SMBH binary populations are able to reproduce both amplitude and shape observed spectrum. multiple model variations GWB spectrum at our current...
Abstract We present observations and timing analyses of 68 millisecond pulsars (MSPs) comprising the 15 yr data set North American Nanohertz Observatory for Gravitational Waves (NANOGrav). NANOGrav is a pulsar array (PTA) experiment that sensitive to low-frequency gravitational waves (GWs). This NANOGrav’s fifth public release, including both “narrowband” “wideband” time-of-arrival (TOA) measurements corresponding models. have added 21 MSPs extended our baselines by 3 yr, now spanning nearly...
We interpret the recent NANOGrav results in terms of a stochastic gravitational wave background from metastable cosmic strings. The observed amplitude signal can be translated into range for string tension and mass magnetic monopoles arising theories grand unification. In sizable part parameter space, this interpretation predicts large frequency band ground-based interferometers, which probed very near future. confront these with predictions successful inflation, leptogenesis dark matter...
Pulsar timing arrays (PTAs) are galactic-scale gravitational wave detectors. Each individual arm, composed of a millisecond pulsar, radio telescope, and kiloparsecs-long path, differs in its properties but, aggregate, can be used to extract low-frequency (GW) signals. We present noise sensitivity analysis accompany the NANOGrav 15-year data release associated papers, along with an in-depth introduction PTA models. As first step our analysis, we characterize each pulsar set three types white...
Abstract Evidence for a low-frequency stochastic gravitational-wave background has recently been reported based on analyses of pulsar timing array data. The most likely source such is population supermassive black hole binaries, the loudest which may be individually detected in these data sets. Here we present search individual binaries NANOGrav 15 yr set. We introduce several new techniques, enhance efficiency and modeling accuracy analysis. uncovered weak evidence two candidate signals,...
Abstract The North American Nanohertz Observatory for Gravitational Waves (NANOGrav) has reported evidence the presence of an isotropic nanohertz gravitational-wave background (GWB) in its 15 yr data set. However, if GWB is produced by a population inspiraling supermassive black hole binary (SMBHB) systems, then predicted to be anisotropic, depending on distribution these systems local Universe and statistical properties SMBHB population. In this work, we search anisotropy using multiple...
Abstract Many symmetry breaking patterns in grand unified theories (GUTs) give rise to cosmic strings that eventually decay when pairs of GUT monopoles spontaneously nucleate along the string cores. These are known as metastable and have intriguing implications for particle physics cosmology. In this article, we discuss current status strings, with a focus on possible embeddings connections inflation, neutrinos, gravitational waves (GWs). The GW signal emitted by network early universe...
Abstract The NANOGrav 15 yr data provide compelling evidence for a stochastic gravitational-wave (GW) background at nanohertz frequencies. simplest model-independent approach to characterizing the frequency spectrum of this signal consists simple power-law fit involving two parameters: an amplitude A and spectral index γ . In Letter, we consider next logical step beyond minimal model, allowing running (i.e., logarithmic dependence) index, <mml:math...
The spontaneous breaking of U(1)_B-L around the scale grand unification can simultaneously account for hybrid inflation, leptogenesis, and neutralino dark matter, thus resolving three major puzzles particle physics cosmology in a single predictive framework. B-L phase transition also results network cosmic strings. If strong electroweak interactions are unified an SO(10) gauge group, containing as subgroup, these strings metastable. In this case, they produce stochastic background...
We provide an easy method to obtain the kinetic energy fraction in gravitational waves, generated during a cosmological first-order phase transition, as function of only wall velocity and quantities that can be determined from particle physics model at nucleation temperature. This generalizes recent work achieved this goal for detonations. Here we present corresponding results deflagrations hybrids. Unlike detonations, sound speed symmetric also enters analysis. perform detailed comparison...
The scotogenic model proposed by Ernest Ma represents an attractive and minimal example for the generation of small Standard Model neutrino masses via radiative corrections in dark matter sector. In this paper, we demonstrate that, addition to matter, also allows explain baryon asymmetry Universe low-scale leptogenesis. First, consider case two right-handed neutrinos (RHNs) N_{1,2}, which provide analytical argument why it is impossible push RHN mass scale below M_1^min ~ 10^10 GeV,...
A metastable cosmic-string network is a generic consequence of many grand unified theories (GUTs) when combined with cosmic inflation. Metastable strings are not topologically stable, but decay on time scales due to pair production GUT monopoles. This leads consisting long superhorizon as well string loops and segments subhorizon scales. We compute for the first complete stochastic gravitational-wave background (SGWB) arising from all these constituents, including several technical...
Many models of physics beyond the Standard Model predict a strong first-order phase transition (SFOPT) in early Universe that leads to observable gravitational waves (GWs). In this paper, we propose novel method for presenting and comparing GW signals are predicted by different models. Our approach is based on observation signal has an approximately model-independent spectral shape. This allows us represent it solely terms finite number observables, is, set peak amplitudes frequencies. As...
We study the explosive production of gauge fields during axion inflation in a novel gradient expansion formalism that describes time evolution set bilinear electromagnetic functions position space. Based on this formalism, we are able to simultaneously account for two important effects have thus far been mostly treated isolation: (i) backreaction produced inflaton field and (ii) Schwinger pair charged particles strong gauge-field background. This allows us show suppression due effect can...
The NANOGrav 15-year data set shows evidence for the presence of a low-frequency gravitational-wave background (GWB). While many physical processes can source such gravitational waves, here we analyze signal as coming from population supermassive black hole (SMBH) binaries distributed throughout Universe. We show that astrophysically motivated models SMBH binary populations are able to reproduce both amplitude and shape observed spectrum. multiple model variations GWB spectrum at our current...
Wash-in leptogenesis is a powerful mechanism to generate the baryon asymmetry of Universe that treats right-handed-neutrino interactions on same footing as electroweak sphaleron processes: mere spectator processes acting background chemical potentials in Standard Model plasma. Successful wash-in requires this be CP-violating, which can achieved by violating any more than ten global charges are conserved at very high temperatures. In paper, we demonstrate primordial charge asymmetries...
Abstract Recently we found compelling evidence for a gravitational-wave background with Hellings and Downs (HD) correlations in our 15 yr data set. These describe gravitational waves as predicted by general relativity, which has two transverse polarization modes. However, more metric theories of gravity can have additional modes, produce different interpulsar correlations. In this work, search the NANOGrav set quadrupolar HD scalar-transverse (ST) We find that are best fit to no significant...
Abstract We present the results of a Bayesian search for gravitational wave (GW) memory in NANOGrav 12.5 yr data set. find no convincing evidence any signals this Bayes factor 2.8 favor model that includes signal and common spatially uncorrelated red noise (CURN) compared to including only CURN. However, further investigation shows disproportionate amount support comes from three dubious pulsars. Using more flexible red-noise these pulsars reduces 1.3. Having found compelling evidence, we go...
Pulsar timing arrays (PTAs) use an array of millisecond pulsars to search for gravitational waves in the nanohertz regime pulse time arrival data. This paper presents rigorous tests PTA methods, examining their consistency across relevant parameter space. We discuss updates 15-year isotropic gravitational-wave background analyses and corresponding code representations. Descriptions internal structure flagship algorithms enterprise ptmcmcsampler are given facilitate understanding likelihood...