A diffuse flux of astrophysical neutrinos above 100 TeV has been observed at the IceCube Neutrino Observatory. Here we extend this analysis to probe the astrophysical flux down to 35 TeV and analyze its flavor composition by classifying events as showers or tracks. Taking advantage of lower atmospheric backgrounds for showerlike events, we obtain a shower-biased sample containing 129 showers and 8 tracks collected in three years from 2010 to 2013. We demonstrate consistency with the $(f_e:f_{\mu }:f_{\tau }{)}_{\oplus }\approx (1:1:1{)}_{\oplus }$ flavor ratio at Earth commonly expected from the averaged oscillations of neutrinos produced by pion decay in distant astrophysical sources. Limits are placed on nonstandard flavor compositions that cannot be produced by averaged neutrino oscillations but could arise in exotic physics scenarios. A maximally tracklike composition of $(0:1:0{)}_{\oplus }$ is excluded at $3.3\sigma$, and a purely showerlike composition of $(1:0:0{)}_{\oplus }$ is excluded at $2.3\sigma$.

We present a study of angle-resolved quantum oscillations of electric and thermoelectric transport coefficients in semimetallic ${\mathrm{WTe}}_2$, which has the particularity of displaying a large ${\mathrm{B}}^2$ magnetoresistance. The Fermi surface consists of two pairs of electronlike and holelike pockets of equal volumes in a “Russian doll” structure. The carrier density, Fermi energy, mobility, and the mean-free path of the system are quantified. An additional frequency is observed above a threshold field and attributed to the magnetic breakdown across two orbits. In contrast to all other dilute metals, the Nernst signal remains linear in the magnetic field even in the high-field (${\omega }_c\tau \gg 1$) regime. Surprisingly, none of the pockets extend across the $c$ axis of the first Brillouin zone, making the system a three-dimensional metal with moderate anisotropy in Fermi velocity, yet a large anisotropy in the mean-free path.

Deformations of cell sheets are ubiquitous in early animal development, often arising from a complex and poorly understood interplay of cell shape changes, division, and migration. Here, we explore perhaps the simplest example of cell sheet folding: the “inversion” process of the algal genus Volvox, during which spherical embryos turn themselves inside out through a process hypothesized to arise from cell shape changes alone. We use light sheet microscopy to obtain the first three-dimensional visualizations of inversion in vivo, and develop the first theory of this process, in which cell shape changes appear as local variations of intrinsic curvature, contraction and stretching of an elastic shell. Our results support a scenario in which these active processes function in a defined spatiotemporal manner to enable inversion.

We present measurements of radio emission from cosmic ray air showers that took place during thunderstorms. The intensity and polarization patterns of these air showers are radically different from those measured during fair-weather conditions. With the use of a simple two-layer model for the atmospheric electric field, these patterns can be well reproduced by state-of-the-art simulation codes. This in turn provides a novel way to study atmospheric electric fields.

We show that memory, in the form of underdamped angular dynamics, is a crucial ingredient for the collective properties of self-propelled particles. Using Vicsek-style models with an Ornstein-Uhlenbeck process acting on angular velocity, we uncover a rich variety of collective phases not observed in usual overdamped systems, including vortex lattices and active foams. In a model with strictly nematic interactions the smectic arrangement of Vicsek waves giving rise to global polar order is observed. We also provide a calculation of the effective interaction between vortices in the case where a telegraphic noise process is at play, explaining thus the emergence and structure of the vortex lattices observed here and in motility assay experiments.

Parametric instabilities have long been studied as a potentially limiting effect in high-power interferometric gravitational wave detectors. Until now, however, these instabilities have never been observed in a kilometer-scale interferometer. In this Letter, we describe the first observation of parametric instability in a gravitational wave detector, and the means by which it has been removed as a barrier to progress.

Standard game theory cannot describe microbial interactions mediated by diffusible molecules. Nevertheless, we show that one can still model microbial dynamics using game theory with parameters renormalized by diffusion. Contrary to expectations, greater sharing of metabolites reduces the strength of cooperation and leads to species extinction via a nonequilibrium phase transition. We report analytic results for the critical diffusivity and the length scale of species intermixing. Species producing slower public good is favored by selection when fitness saturates with nutrient concentration.

The generation and detection of a decade-spanning terahertz (THz) frequency comb is reported using two Ti:sapphire femtosecond laser oscillators and asynchronous optical sampling THz time-domain spectroscopy. The comb extends from 0.15 to 2.4 THz, with a tooth spacing of 80 MHz, a linewidth of 3.7 kHz, and a fractional precision of $1.8\times {10}^{-9}$. With time-domain detection of the comb, we measure three transitions of water vapor at 10 mTorr between 1–2 THz with an average Doppler-limited fractional accuracy of $6.1\times {10}^{-8}$. Significant improvements in bandwidth, resolution, and sensitivity are possible with existing technologies.

It has been understood since 1897 that accelerating charges must emit electromagnetic radiation. Although first derived in 1904, cyclotron radiation from a single electron orbiting in a magnetic field has never been observed directly. We demonstrate single-electron detection in a novel radio-frequency spectrometer. The relativistic shift in the cyclotron frequency permits a precise electron energy measurement. Precise beta electron spectroscopy from gaseous radiation sources is a key technique in modern efforts to measure the neutrino mass via the tritium decay end point, and this work demonstrates a fundamentally new approach to precision beta spectroscopy for future neutrino mass experiments.

Recently it has been discovered that positronium (Ps), after forming in metal-organic framework (MOF) crystals, is emitted into vacuum with a high efficiency and low energy that can only be explained by its propagating as delocalized Bloch states. We show that the Ps atoms are emitted from MOFs in a series of narrow energy peaks consistent with Ps at Bloch-state energy minima being emitted adiabatically into the vacuum. This implies that the Ps emission energy spectra can be directly compared with calculations to obtain detailed information about the Ps band structure in the MOF crystal. The narrow energy width of the lowest energy Ps peak from one MOF sample (2-Methylimidazole zinc salt ZIF-8) suggests it originates from a polaronic Ps surface state. Other peaks can be assigned to Ps with an effective mass of about twice that of bare Ps. Given the immense catalog of available MOF crystals, it should be possible to tune the Ps properties to make vastly improved sources with high production efficiency and a narrow energy spread, for use in fundamental physics experiments.

We show that the disorder scaling of the low-temperature optical absorption linewidth of tubular molecular assemblies sharply contrasts with that known for one-dimensional aggregates. The difference can be explained by an anomalous localization of excitons, which arises from the combination of long-range intermolecular interactions and the tube’s higher-dimensional geometry. As a result, the exciton density of states near the band bottom drops to zero, leading to a strong suppression of exciton localization. Our results explain the strong linear dichroism and weak exciton-exciton scattering in tubular $J$ aggregates observed in experiments and suggest that for nanoscale wirelike applications a tubular shape is to be preferred over a truly one-dimensional chain.

We investigate a new form of collective dynamics displayed by Thiovulum majus, one of the fastest-swimming bacteria known. Cells spontaneously organize on a surface into a visually striking two-dimensional hexagonal lattice of rotating cells. As each constituent cell rotates its flagella, it creates a tornadolike flow that pulls neighboring cells towards and around it. As cells rotate against their neighbors, they exert forces on one another, causing the crystal to rotate and cells to reorganize. We show how these dynamics arise from hydrodynamic and steric interactions between cells. We derive the equations of motion for a crystal, show that this model explains several aspects of the observed dynamics, and discuss the stability of these active crystals.

A dispersive medium becomes entangled with zero-point fluctuations in the vacuum. We consider an arbitrary array of material bodies weakly interacting with a quantum field and compute the quantum mutual information between them. It is shown that the mutual information in $D$ dimensions can be mapped to classical thermodynamic entropy in $D+1$ dimensions. As a specific example, we compute the mutual information both analytically and numerically for a range of separation distances between two bodies in $D=2$ dimensions and find a logarithmic correction to the area law at short separations. A key advantage of our method is that it allows the strong subadditivity property to be easily verified.

The Reynolds number provides a characterization of the transition to turbulent flow, with wide application in classical fluid dynamics. Identifying such a parameter in superfluid systems is challenging due to their fundamentally inviscid nature. Performing a systematic study of superfluid cylinder wakes in two dimensions, we observe dynamical similarity of the frequency of vortex shedding by a cylindrical obstacle. The universality of the turbulent wake dynamics is revealed by expressing shedding frequencies in terms of an appropriately defined superfluid Reynolds number, ${\mathrm{Re}}_s$, that accounts for the breakdown of superfluid flow through quantum vortex shedding. For large obstacles, the dimensionless shedding frequency exhibits a universal form that is well-fitted by a classical empirical relation. In this regime the transition to turbulence occurs at ${\mathrm{Re}}_s\approx 0.7$, irrespective of obstacle width.

We use first-principles calculations to study structural, vibrational, and superconducting properties of ${\mathrm{H}}_2\mathrm{S}$ at pressures $P\ge 200\mathrm{GPa}$. The inclusion of zero-point energy leads to two different possible dissociations of ${\mathrm{H}}_2\mathrm{S}$, namely $3{\mathrm{H}}_2\mathrm{S}\to 2{\mathrm{H}}_3\mathrm{S}+\mathrm{S}$ and $5{\mathrm{H}}_2\mathrm{S}\to 3{\mathrm{H}}_3\mathrm{S}+{\mathrm{HS}}_2$, where both ${\mathrm{H}}_3\mathrm{S}$ and ${\mathrm{HS}}_2$ are metallic. For ${\mathrm{H}}_3\mathrm{S}$, we perform nonperturbative calculations of anharmonic effects within the self-consistent harmonic approximation and show that the harmonic approximation strongly overestimates the electron-phonon interaction ($\lambda \approx 2.64$ at 200 GPa) and $T_c$. Anharmonicity hardens H─S bond-stretching modes and softens H─S bond-bending modes. As a result, the electron-phonon coupling is suppressed by 30% ($\lambda \approx 1.84$ at 200 GPa). Moreover, while at the harmonic level $T_c$ decreases with increasing pressure, the inclusion of anharmonicity leads to a $T_c$ that is almost independent of pressure. High-pressure hydrogen sulfide is a strongly anharmonic superconductor.

We report, for the first time, about an intermediate band solar cell implemented with InAs/AlGaAs quantum dots whose photoresponse expands from 250 to $\sim 6000\mathrm{nm}$. To our knowledge, this is the broadest quantum efficiency reported to date for a solar cell and demonstrates that the intermediate band solar cell is capable of producing photocurrent when illuminated with photons whose energy equals the energy of the lowest band gap. We show experimental evidence indicating that this result is in agreement with the theory of the intermediate band solar cell, according to which the generation recombination between the intermediate band and the valence band makes this photocurrent detectable.

According to the no-hair theorem, static black holes are described by a Schwarzschild spacetime provided there are no other sources of the gravitational field. This requirement, however, is in astrophysical realistic scenarios often violated, e.g., if the black hole is part of a binary system or if it is surrounded by an accretion disk. In these cases, the black hole is distorted due to tidal forces. Nonetheless, the subsequent formulation of the no-hair theorem holds: The contribution of the distorted black hole to the multipole moments that describe the gravitational field close to infinity and, thus, all sources is that of a Schwarzschild black hole. It still has no hair. This implies that there is no multipole moment induced in the black hole and that its second Love numbers, which measure some aspects of the distortion, vanish as was already shown in approximations to general relativity. But here we prove this property for astrophysical relevant black holes in full general relativity.

Combined constraints from the CDF and D0 Collaborations on models of the Higgs boson with exotic spin $J$ and parity $P$ are presented and compared with results obtained assuming the standard model value $J^P=0^{+}$. Both collaborations analyzed approximately $10{\mathrm{fb}}^{-1}$ of proton-antiproton collisions with a center-of-mass energy of 1.96 TeV collected at the Fermilab Tevatron. Two models predicting exotic Higgs bosons with $J^P=0^{-}$ and $J^P=2^{+}$ are tested. The kinematic properties of exotic Higgs boson production in association with a vector boson differ from those predicted for the standard model Higgs boson. Upper limits at the 95% credibility level on the production rates of the exotic Higgs bosons, expressed as fractions of the standard model Higgs boson production rate, are set at 0.36 for both the $J^P=0^{-}$ hypothesis and the $J^P=2^{+}$ hypothesis. If the production rate times the branching ratio to a bottom-antibottom pair is the same as that predicted for the standard model Higgs boson, then the exotic bosons are excluded with significances of 5.0 standard deviations and 4.9 standard deviations for the $J^P=0^{-}$ and $J^P=2^{+}$ hypotheses, respectively.

Extreme ultraviolet frequency combs are a versatile tool with applications including precision measurement, strong-field physics, and solid-state physics. Here we report on an application of extreme ultraviolet frequency combs and their driving lasers for studying strong-field effects in molecular systems. We perform field-free molecular alignment and high-order harmonic generation with aligned molecules in a gas jet at a repetition rate of 154 MHz using a high-powered optical frequency comb inside a femtosecond enhancement cavity. The cavity-enhanced system provides a means to reach suitable intensities to study field-free molecular alignment and enhance the observable effects of the molecule-field interaction. We observe modulations of the driving field, arising from the nature of impulsive stimulated Raman scattering responsible for coherent molecular rotations. We foresee the impact of this work on the study of molecule-based strong-field physics, with improved precision and a more fundamental understanding of the interaction effects on both the field and molecules.

We provide strong evidence that, up to 99.999% of extremality, Kerr-Newman black holes (KNBHs) are linear mode stable within Einstein-Maxwell theory. We derive and solve, numerically, a coupled system of two partial differential equations for two gauge invariant fields that describe the most general linear perturbations of a KNBH. We determine the quasinormal mode (QNM) spectrum of the KNBH as a function of its three parameters and find no unstable modes. In addition, we find that the lowest radial overtone QNMs that are connected continuously to the gravitational $\ell =m=2$ Schwarzschild QNM dominate the spectrum for all values of the parameter space ($m$ is the azimuthal number of the wave function and $\ell$ measures the number of nodes along the polar direction). Furthermore, the (lowest radial overtone) QNMs with $\ell =m$ approach $\mathrm{Re}\omega =m{\mathrm{\Omega }}_H^{\text{ext}}$ and $\mathrm{Im}\omega =0$ at extremality; this is a universal property for any field of arbitrary spin $|s|\le 2$ propagating on a KNBH background ($\omega$ is the wave frequency and ${\mathrm{\Omega }}_H^{\text{ext}}$ the black hole angular velocity at extremality). We compare our results with available perturbative results in the small charge or small rotation regimes and find good agreement.