Comet NEOWISE

The electron-positron stage of the Future Circular Collider, FCC-ee, is a frontier factory for Higgs, top, electroweak, and flavour physics. It is designed to operate in a 100 km circular tunnel built at CERN, and will serve as the first step towards ≥100 TeV proton-proton collisions. In addition to an essential and unique Higgs program, it offers powerful opportunities to discover direct or indirect evidence of physics beyond the Standard Model. Direct searches for long-lived particles at FCC-ee could be particularly fertile in the high-luminosity Z run, where 5 × 10¹² Z bosons are anticipated to be produced for the configuration with two interaction points. The high statistics of Higgs bosons, W bosons and top quarks in very clean experimental conditions could offer additional opportunities at other collision energies. Three physics cases producing long-lived signatures at FCC-ee are highlighted and studied in this paper: heavy neutral leptons (HNLs), axion-like particles (ALPs), and exotic decays of the Higgs boson. These searches motivate out-of-the-box optimization of experimental conditions and analysis techniques, which could lead to improvements in other physics searches.

The directional characteristics of human speech have many applications in speech acoustics, audio, telecommunications, room acoustical design, and other areas. However, professionals in these fields require carefully conducted, high-resolution, spherical speech directivity measurements taken under distinct circumstances to gain additional insights for their work. Because head orientation and human-body diffraction influence speech radiation, this work explores such effects under various controlled conditions through the changing directivity patterns of a head and torso simulator. The results show that head orientation and body diffraction at low frequencies impact directivities only slightly. However, the effects are more substantial at higher frequencies, particularly above 1 kHz.

Silicon (Si) is one of the most abundant elements on Earth, and it is the most widely used semiconductor. Despite extensive study, some properties of Si, such as its behaviour under dynamic compression, remain elusive. A detailed understanding of Si deformation is crucial for various fields, ranging from planetary science to materials design. Simulations suggest that in Si the shear stress generated during shock compression is released via a high-pressure phase transition, challenging the classical picture of relaxation via defect-mediated plasticity. However, direct evidence supporting either deformation mechanism remains elusive. Here, we use sub-picosecond, highly-monochromatic x-ray diffraction to study (100)-oriented single-crystal Si under laser-driven shock compression. We provide the first unambiguous, time-resolved picture of Si deformation at ultra-high strain rates, demonstrating the predicted shear release via phase transition. Our results resolve the longstanding controversy on silicon deformation and provide direct proof of strain rate-dependent deformation mechanisms in a non-metallic system.

Because the noise source mechanisms and radiation properties associated with high-thrust, tactical jet engines are not fully understood, analysis of full-scale measurements can shed significant insight on such characteristics. One method for examining spectral data is to compare them to empirical models for jet noise spectra. This paper compares measured near-field spectra from a T-7A-installed GE F404-103 engine with analytical similarity spectra for fine-scale mixing noise, large-scale mixing noise, and broadband shock-associated noise. This initial similarity spectra analysis enables the determination of spatial trends in overall level and peak frequency and the relative importance of each type of noise radiation as a function of location. This approach can be used to gain insights on spatial and frequency trends of noise source mechanisms for different engine conditions and for rapid comparisons to other aircraft and jets of other scales and conditions.

Multisource statistically-optimized near-field acoustical holography and hybrid beamforming are two inverse techniques that have been successfully used to reproduce sound fields from limited measurements of military aircraft. These methods solve the inverse problem through different means but arrive at the same conclusion. In this paper, the performance of each method is compared to the same baseline measurement. It is found that while both perform well at mid-range frequencies, holography excels at lower frequencies and beamforming at higher frequencies. The spatial Nyquist frequency imposes a soft limit on the accuracy of field reconstructions and limits the usable frequency range.

Multiwavelength variability studies of active galactic nuclei (AGN) can be used to probe their inner regions which are not directly resolvable. Dust reverberation mapping (DRM) estimates the size of the dust emitting region by measuring the delays between the infrared (IR) response to variability in the optical light curves. We measure DRM lags of Zw229-015 between optical ground-based and Kepler light curves and concurrent IR Spitzer 3.6 and 4.5 μm light curves from 2010–2015, finding an overall mean rest-frame lag of 18.3 ± 4.5 days. Each combination of optical and IR light curve returns lags that are consistent with each other within 1σ, which implies that the different wavelengths are dominated by the same hot dust emission. The lags measured for Zw229-015 are found to be consistently smaller than predictions using the lag-luminosity relationship. Also, the overall IR response to the optical emission actually depends on the geometry and structure of the dust emitting region as well, so we use Markov chain Monte Carlo (MCMC) modelling to simulate the dust distribution to further estimate these structural and geometrical properties. We find that a large increase in flux between the 2011–2012 observation seasons, which is more dramatic in the IR light curve, is not well simulated by a single dust component. When excluding this increase in flux, the modelling consistently suggests that the dust is distributed in an extended flat disk, and finds a mean inclination angle of 49 degrees.