A model of the dark sector where $O(\text{few}\mathrm{GeV})$ mass dark matter particles $\chi$ couple to a lighter dark force mediator $V$, $m_V\ll m_{\chi }$, is motivated by the recently discovered mismatch between simulated and observed shapes of galactic halos. Such models, in general, provide a challenge for direct detection efforts and collider searches. We show that for a large range of coupling constants and masses, the production and decay of the bound states of $\chi$, such as $0^{-+}$ and $1^{--}$ states, ${\eta }_D$ and ${\mathrm{\Upsilon }}_D$, is an important search channel. We show that $e^{+}{e}^{-}\to {\eta }_D+V$ or ${\mathrm{\Upsilon }}_D+\gamma$ production at $B$ factories for ${\alpha }_D>0.1$ is sufficiently strong to result in multiple pairs of charged leptons and pions via ${\eta }_D\to 2V\to 2(l^{+}{l}^{-})$ and ${\mathrm{\Upsilon }}_D\to 3V\to 3(l^{+}{l}^{-})$ $(l=e,\mu ,\pi )$. The absence of such final states in the existing searches performed at BABAR and Belle sets new constraints on the parameter space of the model. We also show that a search for multiple bremsstrahlung of dark force mediators, $e^{+}{e}^{-}\to \chi \overline{\chi }+nV$, resulting in missing energy and multiple leptons, will further improve the sensitivity to self-interacting dark matter.

We generalize the problem of strongly interacting neutron matter by adding a periodic external modulation. This allows us to study from first principles a neutron system that is extended and inhomogeneous, with connections to the physics of both neutron-star crusts and neutron-rich nuclei. We carry out fully nonperturbative microscopic quantum Monte Carlo calculations of the energy of neutron matter at different densities, as well as different strengths and periodicities of the external potential. In order to remove systematic errors, we examine finite-size effects and the impact of the wave function ansatz. We also make contact with energy-density functional theories of nuclei and disentangle isovector gradient contributions from bulk properties. Finally, we calculate the static density-density linear response function of neutron matter and compare it with the response of other physical systems.

We show that the Nambu-Goldstone formalism of the broken gauge symmetry in the presence of the $T=1$ pairing condensate offers a quantitative description of the binding-energy differences of open-shell superfluid nuclei. We conclude that the pairing-rotational moments of inertia are excellent pairing indicators, which are free from ambiguities attributed to odd-mass systems. We offer a new, unified interpretation of the binding-energy differences traditionally viewed in the shell model picture as signatures of the valence nucleon properties. We present the first systematic analysis of the off-diagonal pairing-rotational moments of inertia and demonstrate the mixing of the neutron and proton pairing-rotational modes in the ground states of even-even nuclei. Finally, we discuss the importance of mass measurements of neutron-rich nuclei for constraining the pairing energy density functional.

An experimental method is demonstrated that allows determination of the ratio between the electric ($E1$) and magnetic ($M1$) transition dipole moments in the $A-X$ band of OH, including their relative sign. Although the transition strengths differ by more than 3 orders of magnitude, the measured $M1$-to-$E1$ ratio agrees with the ratio of the ab initio calculated values to within 3%. The relative sign is found to be negative, also in agreement with theory.

Reaching exceptionally long times up to 500 ns in equilibrium and nonequilibrium molecular dynamics simulations studies, we have attained a fundamental molecular understanding of the correlation of ionomer clusters structure and multiscale dynamics, providing new insight into one critical, long-standing challenge in ionic polymer physics. The cluster structure in melts of sulfonated polystyrene with ${\mathrm{Na}}^{+}$ and ${\mathrm{Mg}}^{2+}$ counterions are resolved and correlated with the dynamics on multiple length and time scales extracted from measurements of the dynamic structure factor and shear rheology. We find that as the morphology of the ionic clusters changes from ladderlike for ${\mathrm{Na}}^{+}$ to disordered structures for ${\mathrm{Mg}}^{2+}$, the dynamic structure factor is affected on the length scale corresponding to the ionic clusters. Rheology studies show that the viscosity for ${\mathrm{Mg}}^{2+}$ melts is higher than for ${\mathrm{Na}}^{+}$ ones for all shear rates, which is well correlated with the larger ionic clusters’ size for the ${\mathrm{Mg}}^{2+}$ melts.

We present a method that uses dynamic decoupling of a multilevel quantum probe to distinguish small frequency shifts that depend on $m_j^2$, where $m_j^2$ is the angular momentum of level $|j⟩$ along the quantization axis, from large noisy shifts that are linear in $m_j$, such as those due to magnetic field noise. Using this method we measured the electric-quadrupole moment of the $4D_{5/2}$ level in ${}^{88}{\mathrm{Sr}}^{+}$ to be $2.973_{-0.033}^{+0.026}e{a}_0^2$. Our measurement improves the uncertainty of this value by an order of magnitude and thus helps mitigate an important systematic uncertainty in ${}^{88}{\mathrm{Sr}}^{+}$ based optical atomic clocks and verifies complicated many-body quantum calculations.

The relic neutrinos are expected to acquire a bulk relative velocity with respect to the dark matter at low redshifts, and neutrino wakes are expected to develop downstream of the dark matter halos. We propose a method of measuring the neutrino mass based on this mechanism. This neutrino wake will cause a dipole distortion of the galaxy-galaxy lensing pattern. This effect could be detected by combining upcoming lensing surveys with a low redshift galaxy survey or a 21 cm intensity mapping survey, which can map the neutrino flow field. The data obtained with LSST and Euclid should enable us to make a positive detection if the three neutrino masses are quasidegenerate with each neutrino mass of $\sim 0.1\mathrm{eV}$, and a future high precision 21 cm lensing survey would allow the normal hierarchy and inverted hierarchy cases to be distinguished, and even the right-handed Dirac neutrinos may be detectable.

Given conformal data on a flat Euclidean space, we use crosscap conformal bootstrap equations to numerically solve the Lee-Yang model as well as the critical Ising model on a three dimensional real projective space. We check the rapid convergence of our bootstrap program in two dimensions from the exact solutions available. Based on the comparison, we estimate that our systematic error on the numerically solved one-point functions of the critical Ising model on a three dimensional real projective space is less than 1%. Our method opens up a novel way to solve conformal field theories on nontrivial geometries.

We show that by adding a single new scalar particle to the standard model, a TeV-scale leptoquark with the quantum numbers of a right-handed down quark, one can explain in a natural way three of the most striking anomalies of particle physics: the violation of lepton universality in $\overline{B}\to \overline{K}{\ell }^{+}{\ell }^{-}$ decays, the enhanced $\overline{B}\to D^{(*)}\tau \overline{\nu }$ decay rates, and the anomalous magnetic moment of the muon. Constraints from other precision measurements in the flavor sector can be satisfied without fine-tuning. Our model predicts enhanced $\overline{B}\to {\overline{K}}^{(*)}\nu \overline{\nu }$ decay rates and a new-physics contribution to $B_s-{\overline{B}}_s$ mixing close to the current central fit value.

We propose a simple mechanism to suppress axion isocurvature fluctuations using hidden sector magnetic monopoles. This allows for the Peccei-Quinn scale to be of the order of the unification scale consistently with high scale inflation.

The dynamics of ultraslow electrons in the combined potential of an ionic core and a static electric field is discussed. With state-of-the-art detection it is possible to create such electrons through strong intense-field photoabsorption and to detect them via high-resolution time-of-flight spectroscopy despite their very low kinetic energy. The characteristic feature of their momentum spectrum, which emerges at the same position for different laser orientations, is derived and could be revealed experimentally with an energy resolution of the order of 1 meV.

We carry out a combined theoretical and experimental investigation on the population distributions in the ground and excited states of tunnel-ionized nitrogen molecules at various driver wavelengths in the near- and midinfrared range. Our results reveal that efficient couplings (i.e., population exchanges) between the ground ${\mathrm{N}}_2^{+}(X^2{\mathrm{\Sigma }}_g^{+})$ state and the excited ${\mathrm{N}}_2^{+}(A^2{\mathrm{\Pi }}_u)$ and ${\mathrm{N}}_2^{+}(B^2{\mathrm{\Sigma }}_u^{+})$ states occur in strong laser fields. The couplings result in a population inversion between the ${\mathrm{N}}_2^{+}(X^2{\mathrm{\Sigma }}_g^{+})$ and ${\mathrm{N}}_2^{+}(B^2{\mathrm{\Sigma }}_u^{+})$ states at wavelengths near 800 nm, which is verified by our experimental observation of the amplification of a seed at $\sim 391\mathrm{nm}$. The result provides insight into the mechanism of free-space nitrogen ion lasers generated in remote air with strong femtosecond laser pulses.

We explore the phase diagram of the dissipative Rabi-Hubbard model, as could be realized by a Raman-pumping scheme applied to a coupled cavity array. There exist various exotic attractors, including ferroelectric, antiferroelectric, and incommensurate fixed points, as well as regions of persistent oscillations. Many of these features can be understood analytically by truncating to the two lowest lying states of the Rabi model on each site. We also show that these features survive beyond mean field, using matrix product operator simulations.

We present infrared absorption studies of solid hydrogen deuteride to pressures as high as 340 GPa ($100\mathrm{GPa}=1\mathrm{Mbar}$) in a diamond anvil cell and temperatures in the range 5–295 K. Above 198 GPa the HD sample transforms to a mixture of HD, ${\mathrm{H}}_2$, and ${\mathrm{D}}_2$, interpreted as a process of dissociation and recombination. Three new phase lines are observed, two of which differ remarkably from those of the high-pressure homonuclear species, but none are metallic. The time-dependent spectral changes are analyzed to determine the molecular concentrations as a function of time; the nucleon exchange achieves steady state concentrations in $\sim 20\mathrm{h}$ at $\sim 200\mathrm{GPa}$.

We revisit the phenomenon of spinodals in the presence of quenched disorder and develop a complete theory for it. We focus on the spinodal of an Ising model in a quenched random field (RFIM), which has applications in many areas from materials to social science. By working at zero temperature in the quasistatically driven RFIM, thermal fluctuations are eliminated and one can give a rigorous content to the notion of spinodal. We show that the latter is due to the depinning and the subsequent expansion of rare droplets. We work out the associated critical behavior, which, in any finite dimension, is very different from the mean-field one: the characteristic length diverges exponentially and the thermodynamic quantities display very mild nonanalyticities much like in a Griffith phenomenon. From the recently established connection between the spinodal of the RFIM and glassy dynamics, our results also allow us to conclusively assess the physical content and the status of the dynamical transition predicted by the mean-field theory of glass-forming liquids.

We investigate the thermal and electronic collective fluctuations that contribute to the finite-temperature adsorption properties of flexible adsorbates on surfaces on the example of the molecular switch azobenzene ${\mathrm{C}}_{12}{\mathrm{H}}_{10}{\mathrm{N}}_2$ on the Ag(111) surface. Using first-principles molecular dynamics simulations, we obtain the free energy of adsorption that accurately accounts for entropic contributions, whereas the inclusion of many-body dispersion interactions accounts for the electronic correlations that govern the adsorbate binding. We find the adsorbate properties to be strongly entropy driven, as can be judged by a kinetic molecular desorption prefactor of ${10}^{24}{\mathrm{s}}^{-1}$ that largely exceeds previously reported estimates. We relate this effect to sizable fluctuations across structural and electronic observables. A comparison of our calculations to temperature-programed desorption measurements demonstrates that finite-temperature effects play a dominant role for flexible molecules in contact with polarizable surfaces, and that recently developed first-principles methods offer an optimal tool to reveal novel collective behavior in such complex systems.

The magnetization of a ferromagnet ($F$) driven out of equilibrium injects pure spin current into an adjacent conductor ($N$). Such $F|N$ bilayers have become basic building blocks in a wide variety of spin-based devices. We evaluate the shot noise of the spin current traversing the $F|N$ interface when $F$ is subjected to a coherent microwave drive. We find that the noise spectrum is frequency independent up to the drive frequency, and increases linearly with frequency thereafter. The low frequency noise indicates super-Poissonian spin transfer, which results from quasiparticles with effective spin ${\hslash }^{*}=\hslash (1+\delta )$. For typical ferromagnetic thin films, $\delta \sim 1$ is related to the dipolar interaction-mediated squeezing of $F$ eigenmodes.

Spin-wave technology (magnonics) has the potential to further reduce the size and energy consumption of information-processing devices. In the submicrometer regime (exchange spin waves), topological defects such as domain walls may constitute active elements to manipulate spin waves and perform logic operations. We predict that spin waves that pass through a domain wall in an ultrathin perpendicular-anisotropy film experience a phase shift that depends on the orientation of the domain wall (chirality). The effect, which is absent in bulk materials, originates from the interfacial Dzyaloshinskii-Moriya interaction and can be interpreted as a geometric phase. We demonstrate analytically and by means of micromagnetic simulations that the phase shift is strong enough to switch between constructive and destructive interference. The two chirality states of the domain wall may serve as a memory bit or spin-wave switch in magnonic devices.