We present fully nonperturbative quantum Monte Carlo calculations with nonlocal chiral effective field theory (EFT) interactions for the ground-state properties of neutron matter. The equation of state, the nucleon chemical potentials, and the momentum distribution in pure neutron matter up to one and a half times the nuclear saturation density are computed with a newly optimized chiral EFT interaction at next-to-next-to-leading order. This work opens the way to systematic order by order benchmarking of chiral EFT interactions and ab initio prediction of nuclear properties while respecting the symmetries of quantum chromodynamics.

Soliton mode locking is an essential technique for building compact mode-locked lasers with multigigahertz repetition rates. In this scheme, pulses behave like dissipative solitons due to the presence of gain, loss, frequency filtering, and nonlinear absorption in the cavity. The continuum waves that radiate from the perturbed soliton act back on the soliton, resulting in periodic changes in the electric field of the pulse. We find that, in the presence of gain filtering or two-photon absorption, this field modulation is converted to power modulation, which is observable from the radio-frequency spectrum of the laser’s output power. We investigate its physical origin in the context of soliton perturbation theory. For comparison, we also perform numerical simulations and experiments.

Dynamic wavelength conversion (DWC) is obtained by controlling copropagating slow-light signal and control pulse trajectories. Our method is based on the understanding that conventional resonator-based DWC can be generalized, and is linked to cross-phase modulation. Dispersion-engineered Si photonic crystal waveguides produce such slow-light pulses. Free carriers generated by two-photon absorption of the control pulse dynamically shift the signal wavelength. Matching the group velocities of the two pulses enhances the shift, elongating the interaction length. We demonstrate an extremely large wavelength shift in DWC (4.9 nm blueshift) for the signal wavelength. Although DWC is similar to the Doppler effect, we highlight their essential differences.

We demonstrate experimentally that a part-per-million addition of Sn solutes in Al-Mg-Si alloys can inhibit natural aging and enhance artificial aging. The mechanism controlling the aging is argued to be vacancy diffusion, with solutes trapping vacancies at low temperature and releasing them at elevated temperature, which is supported by a thermodynamic model and first-principles computations of Sn-vacancy binding. This “diffusion on demand” solves the long-standing problem of detrimental natural aging in Al-Mg-Si alloys, which is of great scientific and industrial importance. Moreover, the mechanism of controlled buffering and release of excess vacancies is generally applicable to modulate diffusion in other metallic systems.

It has long been under debate whether the electron transport performance of graphene could be enhanced by the possible occurrence of van Hove singularities in grain boundaries. Here, we provide direct experimental evidence to confirm the existence of van Hove singularity states close to the Fermi energy in certain ordered grain boundaries using scanning tunneling microscopy. The intrinsic atomic and electronic structures of two ordered grain boundaries, one with alternative pentagon and heptagon rings and the other with alternative pentagon pair and octagon rings, are determined. It is firmly verified that the carrier concentration and, thus, the conductance around ordered grain boundaries can be significantly enhanced by the van Hove singularity states. This finding strongly suggests that a graphene nanoribbon with a properly embedded ordered grain boundary can be a promising structure to improve the performance of graphene-based electronic devices.

We report the observation of multiple harmonic generation in electric dipole spin resonance in an InAs nanowire double quantum dot. The harmonics display a remarkable detuning dependence: near the interdot charge transition as many as eight harmonics are observed, while at large detunings we only observe the fundamental spin resonance condition. The detuning dependence indicates that the observed harmonics may be due to Landau-Zener transition dynamics at anticrossings in the energy level spectrum.

We study the impact of a projectile onto a bed of 3 mm grains immersed in an index-matched fluid. We vary the amount of prestrain on the sample, strengthening the force chains within the system. We find this affects only the prefactor of the linear depth-dependent term in the stopping force. We propose a simple model to account for the strain dependence of this term, owing to increased pressure in the pile. Interestingly, we find that the presence of the fluid does not affect the impact dynamics, suggesting that dynamic friction is not a factor. Using a laser sheet scanning technique to visualize internal grain motion, we measure the trajectory of each grain throughout an impact. Microscopically, our results indicate that weaker initial force chains result in more irreversible, plastic rearrangements, suggesting static friction between grains does play a substantial role in the energy dissipation.

We consider a quantum quench in a finite system of length $L$ described by a $1+1$-dimensional conformal field theory (CFT), of central charge $c$, from a state with finite energy density corresponding to an inverse temperature $\beta \ll L$. For times $t$ such that $\ell /2<t<(L-\ell )/2$ the reduced density matrix of a subsystem of length $\ell$ is exponentially close to a thermal density matrix. We compute exactly the overlap $\mathcal{F}$ of the state at time $t$ with the initial state and show that in general it is exponentially suppressed at large $L/\beta$. However, for minimal models with $c<1$ (more generally, rational CFTs), at times which are integer multiples of $L/2$ (for periodic boundary conditions, $L$ for open boundary conditions) there are (in general, partial) revivals at which $\mathcal{F}$ is $O(1)$, leading to an eventual complete revival with $\mathcal{F}=1$. There is also interesting structure at all rational values of $t/L$, related to properties of the CFT under modular transformations. At early times $t\ll (L\beta {)}^{1/2}$ there is a universal decay $\mathcal{F}\sim \exp (-(\pi c/3)L{t}^2/\beta ({\beta }^2+4t^2))$. The effect of an irrelevant nonintegrable perturbation of the CFT is to progressively broaden each revival at $t=nL/2$ by an amount $O(n^{1/2})$.

The velocity field of dark matter and galaxies reflects the continued action of gravity throughout cosmic history. We show that the low-order moments of the pairwise velocity distribution $v_{12}$ are a powerful diagnostic of the laws of gravity on cosmological scales. In particular, the projected line-of-sight galaxy pairwise velocity dispersion ${\sigma }_{12}(r)$ is very sensitive to the presence of modified gravity. Using a set of high-resolution $N$-body simulations, we compute the pairwise velocity distribution and its projected line-of-sight dispersion for a class of modified gravity theories: the chameleon $f(R)$ gravity and Galileon gravity (cubic and quartic). The velocities of dark matter halos with a wide range of masses would exhibit deviations from general relativity at the $(5–10)\sigma$ level. We examine strategies for detecting these deviations in galaxy redshift and peculiar velocity surveys. If detected, this signature would be a “smoking gun” for modified gravity.

Photoelectron angular distributions (PADs) obtained from ionization of potassium atoms using moderately intense femtosecond IR fields ($\sim {10}^{12}\mathrm{W}{\mathrm{cm}}^{-2}$) of various polarization states are shown to provide a route to “complete” photoionization experiments. Ionization occurs by a net three-photon absorption process, driven via the $4s\to 4p$ resonance at the one-photon level. A theoretical treatment incorporating the intrapulse electronic dynamics allows for a full set of ionization matrix elements to be extracted from 2D imaging data. 3D PADs generated from the extracted matrix elements are also compared to experimental, tomographically reconstructed, 3D photoelectron distributions, providing a sensitive test of their validity. Finally, application of the determined matrix elements to ionization via more complex, polarization-shaped, pulses is demonstrated, illustrating the utility of this methodology towards detailed understanding of complex ionization control schemes and suggesting the utility of such “multiplexed” intrapulse processes as powerful tools for measurement.

Typical Kondo insulators (KIs) can have a nontrivial ${\mathbb{Z}}_2$ topology because the energy gap opens at the Fermi energy ($E_F$) by a hybridization between odd- and even-parity bands. ${\mathrm{SmB}}_6$ deviates from such KI behavior, and it has been unclear how the insulating phase occurs. Here, we demonstrate that charge fluctuations are the origin of the topological insulating phase in ${\mathrm{SmB}}_6$. Our angle-resolved photoemission spectroscopy results reveal that with decreasing temperature the bottom of the $d\text{−}f$ hybridized band at the $\overline{X}$ point, which is predicted to have odd parity and is required for a topological phase, gradually shifts from below to above $E_F$. We conclude that ${\mathrm{SmB}}_6$ is a charge-fluctuating topological insulator.

We propose a real-space renormalization group method to explicitly decouple into independent components a many-body system that, as in the phenomenon of spin-charge separation, exhibits separation of degrees of freedom at low energies. Our approach produces a branching holographic description of such systems that opens the path to the efficient simulation of the most entangled phases of quantum matter, such as those whose ground state violates a boundary law for entanglement entropy. As in the coarse-graining transformation of Vidal [Phys. Rev. Lett. 99, 220405 (2007)], the key ingredient of this decoupling transformation is the concept of entanglement renormalization, or removal of short-range entanglement. We demonstrate the feasibility of the approach, both analytically and numerically, by decoupling in real space the ground state of a critical quantum spin chain into two. Generalized notions of renormalization group flow and of scale invariance are also put forward.

We analyze the collective dynamics of self-propelled particles in the large-density regime where passive particles undergo a kinetic arrest to an amorphous glassy state. We capture the competition between self-propulsion and crowding effects using a two-dimensional model of self-propelled hard disks, which we study using Monte Carlo simulations. Although the activity drives the system far from equilibrium, self-propelled particles undergo a kinetic arrest, which we characterize in detail and compare with its equilibrium counterpart. In particular, the critical density for dynamic arrest continuously shifts to larger densities with increasing activity, and the relaxation time is surprisingly well described by an algebraic divergence resulting from the emergence of highly collective dynamics. These results show that dense assemblies of active particles undergo a nonequilibrium glass transition that is profoundly affected by self-propulsion mechanisms.

Measuring a nonzero value for the cross section of any lepton number violating (LNV) process would put a strong lower limit on the washout factor for the effective lepton number density in the early Universe at times close to the electroweak phase transition and thus would lead to important constraints on any high-scale model for the generation of the observed baryon asymmetry based on LNV. In particular, for leptogenesis (LG) models with masses of the right-handed neutrinos heavier than the mass scale observed at the LHC, the implied large washout factors would lead to a violation of the out-of-equilibrium condition and exponentially suppress the net lepton number produced in such LG models. We thus demonstrate that the observation of LNV processes at the LHC results in the falsification of high-scale LG models. However, no conclusions about the viability of LG models can be drawn from the nonobservation of LNV processes.

As a model of the longitudinal structure in heavy ion collisions, we simulate gravitational shock wave collisions in anti–de Sitter space in which each shock is composed of multiple constituents. We find that all constituents act coherently, and their separation leaves no imprint on the resulting plasma, when this separation is $\lesssim 0.26/T_{\mathrm{hyd}}$, with $T_{\mathrm{hyd}}$ the temperature of the plasma at the time when hydrodynamics first becomes applicable. In particular, the center-of-mass of the plasma coincides with the center-of-mass of all the constituents participating in the collision, as opposed to the center-of-mass of the individual collisions. We discuss the implications for nucleus-nucleus and proton-nucleus collisions.

A massive, but light, Abelian $U(1)$ gauge boson is a well-motivated possible signature of physics beyond the standard model of particle physics. In this Letter, the search for the signal of such a $U(1)$ gauge boson in electron-positron pair production at the spectrometer setup of the A1 Collaboration at the Mainz Microtron is described. Exclusion limits in the mass range of $40\mathrm{MeV}/c^2$ to $300\mathrm{MeV}/c^2$, with a sensitivity in the squared mixing parameter of as little as ${\epsilon }^2=8\times 10^{-7}$ are presented. A large fraction of the parameter space has been excluded where the discrepancy of the measured anomalous magnetic moment of the muon with theory might be explained by an additional $U(1)$ gauge boson.

We reveal a set of novel decay topologies for the 125 GeV Higgs boson in supersymmetry which are initiated by its decay into a pair of neutralinos, and discuss their collider search strategies. This category of exotic Higgs decays is characterized by the collider signature: visible $\text{objects}+{\cancel{E}}_T$, with ${\cancel{E}}_T$ dominantly arising from escaping dark matter particles. Their benchmark arises naturally in the Peccei-Quinn symmetry limit of the minimal supersymmetric standard model singlet extensions, which is typified by the coexistence of three light particles: singletlike scalar $h_1$ and pseudoscalar $a_1$, and singlinolike neutralino ${\chi }_1$, all with masses of $\lesssim 10\mathrm{GeV}$, and the generic suppression of the exotic decays of the 125 GeV Higgs boson $h_2\to h_1{h}_1$, $a_1{a}_1$ and ${\chi }_1{\chi }_1$, however. As an illustration, we study the decay topology: $h_2\to {\chi }_1{\chi }_2$, where the binolike ${\chi }_2$ decays to $h_1{\chi }_1$ or $a_1{\chi }_1$, and $h_1/a_1\to f\overline{f}$, with $f\overline{f}={\mu }^{+}{\mu }^{-}$, $b\overline{b}$. In the dimuon case ($m_{h_1/a_1}\sim 1\mathrm{GeV}$), a statistical sensitivity of $S/\sqrt{B}>6\sigma$ can be achieved easily at the 8 TeV LHC, assuming $\sigma (pp\to W{h}_2)/\sigma (pp\to W{h}_{\text{SM}})\text{Br}(h_2\to {\mu }^{+}{\mu }^{-}{\chi }_1{\chi }_1)=0.1$. In the $b\overline{b}$ case ($m_{h_1/a_1}\sim 45\mathrm{GeV}$), $600{\mathrm{fb}}^{-1}$ data at the 14 TeV LHC can lead to a statistical sensitivity of $S/\sqrt{B}>5\sigma$, assuming $\sigma (pp\to Z{h}_2)/\sigma (pp\to Z{h}_{\text{SM}})\text{Br}(h_2\to b\overline{b}{\chi }_1{\chi }_1)=0.5$. These exotic decays open a new avenue for exploring new physics couplings with the 125 GeV Higgs boson at colliders.