Scattering interactions between dark matter and Standard Model states mediated by pseudoscalars are generically challenging to uncover at direct detection experiments due to rates suppressed by powers of the local dark matter velocity ${v}_{\mathrm{DM}}\ensuremath{\sim}{10}^{\ensuremath{-}3}c$. However, they may be observed in the dark matter-induced heating of neutron stars, whose steep gravitational potentials prevent such suppression by accelerating infalling particles to semirelativistic speeds. We investigate this phenomenon in the context of two specific, self-consistent scenarios for pseudoscalars coupled to dark matter, and compare the sensitivity of neutron star heating to bounds from direct searches for the mediators and dark matter. The first ``lighter'' scenario consists of sub-10 GeV mass dark matter mediated by an axionlike particle, while the second ``heavier'' scenario has dark matter above 10 GeV mediated by a dark pseudoscalar that mixes with a pseudoscalar from a two-Higgs doublet (the so-called $2\mathrm{HDM}+a$ model). In both frameworks, we show that imminent measurements of neutron stars will be able to test pseudoscalar-mediated dark matter beyond the reach of direct dark matter searches as well as bounds on the mediators from flavor observables, beam dump experiments, and high-energy colliders.
We present fully general relativistic simulations of the quasicircular inspiral and merger of charged, nonspinning, binary black holes with charge-to-mass ratio lambda <= 0.3. We discuss the key features that enabled long term and stable evolutions of these binaries. We also present a formalism for computing the angular momentum carried away by electromagnetic waves, and the electromagnetic contribution to black-hole horizon properties. We implement our formalism and present the results for the first time in numerical-relativity simulations. In addition, we compare our full nonlinear solutions with existing approximate models for the inspiral and ringdown phases. We show that Newtonian models based on the quadrupole approximation have errors of 20%-400% in key gauge-invariant quantities. On the other hand, for the systems considered, we find that estimates of the remnant black hole spin based on the motion of test particles in Kerr-Newman spacetimes agree with our nonlinear calculations to within a few percent. Finally, we discuss the prospects for detecting black hole charge by future gravitational-wave detectors using either the inspiral-merger-ringdown signal or the ringdown signal alone.
This paper extends prior work establishing an operationalized framework of mathematical sense making (MSM) in physics. The framework differentiates between the object being understood (either physical or mathematical) and various tools (physical or mathematical) used to mediate the sense-making process. This results in four modes of MSM that can be coordinated and linked in various ways. Here, the framework is applied to novel modalities of student written work (both short answer and multiple choice). In detailed studies of student reasoning about the photoelectric effect, we associate these MSM modes with particular multiple choice answers, and substantiate this association by linking both the MSM modes and multiple choice answers with finer-grained reasoning elements that students use in solving a specific problem. Through the multiple associations between MSM mode, distributions of reasoning elements, and multiplechoice answers, we confirm the applicability of this framework to analyzing these sparser modalities of student work and its utility for analyzing larger-scale (N > 100) datasets. The association between individual reasoning elements and both MSM modes and MC answers suggest that it is possible to cue particular modes of student reasoning and answer selection. Such findings suggest potential for this framework to be applicable to the analysis and design of curriculum.
Attosecond probing of core-level electronic transitions in molecules provides a sensitive tool for real-time observation of chemical dynamics. Here, we employ ultrafast extreme-ultraviolet (XUV) transient-absorption spectroscopy to investigate the excited state electronic and nuclear dynamics in a prototype molecule, I-2. A few-femtosecond visible pump pulse is employed to excite the I-2 molecule and an attosecond XUV pulse is used to probe the dynamics through iodine-4d core-to-valence transitions. A highly extended vibrational wave packet (v' = 10-50, v(max)' = 25) is prepared by one-photon absorption in the valence excited B ( 3)Pi(0+u) state of I-2 and its motion is directly mapped due to the strong shift of the XUV core-level transition with internuclear separation. Through the imaging of this vibrational motion, we directly reconstruct the transition energy between the valence and the core-excited states as a function of internuclear distance. Besides single-photon dynamics, distinct direct dissociation pathways arising from two-photon pump absorption are also revealed.
Binary neutron star mergers probe the dense-matter equation of state (EoS) across a wide range of densities and temperatures, from the cold conditions of the inspiral to the high-temperature matter of the massive neutron star remnant. In this paper, we explore the sensitivity of neutron star mergers to uncertainties in the finite-temperature part of the EoS with a series of merger simulations performed in full general relativity. We expand on our previous work to explore the interplay between the thermal prescription and the stiffness of the zero-temperature EoS, which determines the compactness of the initial neutron stars. Using a phenomenological model of the particle effective mass, M^*, to calculate the finite-temperature part of the EoS, we perform merger simulations for a range of thermal prescriptions, together with two cold EoSs that predict either compact or large-radius initial neutron stars. We report on how the choice of M^*-parameters influences the thermal properties of the post-merger remnant, and how this varies for stars with different initial stellar compactness. We characterize the post-merger gravitational wave signals, and find differences in the peak frequencies of up to 190 Hz depending on the choice of M^*-parameters. Finally, we find that the total dynamical ejecta is in general only weakly sensitive to the thermal prescription, but that a particular combination of M^*-parameters, together with a soft cold EoS, can lead to significant enhancements in the ejecta.
We show that under current experimental bounds of the decays ${e}_{a}\ensuremath{\rightarrow}{e}_{b}\ensuremath{\gamma}$, the recent experimental data of the muon anomalous magnetic dipole moment $(g\ensuremath{-}2{)}_{\ensuremath{\mu}}$ can be explained in the framework of the $3\ensuremath{-}3\ensuremath{-}1$ model with right-handed neutrinos. In addition, all of these branching ratios can reach closely the recent experimental upper bounds.
We report measurements of the parity-conserving beam-normal single-spin elastic scattering asymmetries $B_n$ on $^{12}$C and $^{27}$Al, obtained with an electron beam polarized transverse to its momentum direction. These measurements add an additional kinematic point to a series of previous measurements of $B_n$ on $^{12}$C and provide a first measurement on $^{27}$Al. The experiment utilized the Qweak apparatus at Jefferson Lab with a beam energy of 1.158 GeV. The average lab scattering angle for both targets was 7.7 degrees, and the average $Q^2$ for both targets was 0.02437 GeV$^2$ (Q=0.1561 GeV). The asymmetries are $B_n$ = -10.68 $\pm$ 0.90 stat) $\pm$ 0.57 (syst) ppm for $^{12}$C and $B_n$ = -12.16 $\pm$ 0.58 (stat) $\pm$ 0.62 (syst) ppm for $^{27}$Al. The results are consistent with theoretical predictions, and are compared to existing data. When scaled by Z/A, the Q-dependence of all the far-forward angle (theta < 10 degrees) data from $^{1}$H to $^{27}$Al can be described by the same slope out to $Q \approx 0.35$ GeV. Larger-angle data from other experiments in the same Q range are consistent with a slope about twice as steep.
From the amplitude analysis of the $D^+_s \to \pi^+ \pi^0 \eta$ decay, the BESIII Collaboration firstly observed the $D^+_s \to a_0(980)^+\pi^0$ and $D^+_s \to a_0(980)^0\pi^+$ decay modes, which are expected to occur through the pure $W$-annihilation processes. The measured branching fraction $\mathcal{B}[D_{s}^{+}\to a_{0}(980)^{+(0)}\pi^{0(+)},a_{0}(980)^{+(0)}\to \pi^{+(0)}\eta]$ is, however, found to be larger than those of known $W$-annihilation decays by one order of magnitude. This apparent contradiction can be reconciled if the two decays are induced by internal $W$-conversion or external $W$-emission mechanisms instead of $W$-annihilation mechanism. In this work, we propose that the $D^+_s$ decay proceeds via both the external and internal $W$-emission instead of $W$-annihilation mechanisms. In such a scenario, we perform a study of the $D^+_s \to \pi^+\pi^0\eta$ decay by taking into account the contributions from the tree diagram $D^+_s \to \rho^+ \eta \to \pi^+ \pi^0 \eta$ and the intermediate $\rho^+ \eta$ and $K^*\bar{K}/K\bar{K}^*$ triangle diagrams. The intermediate $a_0(980)$ state can be dynamically generated from the final state interactions of coupled $K \bar{K}$ and $\pi \eta$ channels, and it is shown that the experimental data can be described fairly well, which supports the interpretation of $a_0(980)$ as a molecular state.
We study the contributions of the kaon pair originating from the resonance $\rho(770)$ for the three-body decays $B \to D K\bar{K}$ by employing the perturbative QCD approach. According to the predictions in this work, the contributions from the intermediate state $\rho(770)^0 $ are relative small for the three-body decays such as $B^0 \to \bar{D}^0 K^+ K^-$, $B_s^0 \to \bar{D}^0 K^+ K^-$ and $B^+ \to D_s^+ K^+K^-$, while a percent at about $20\%$ of the total three-body branching fraction for $B^+ \to \bar{D}^0 K^+ \bar{K}^0$ could possibly come from the subprocess $\rho(770)^+\to K^+ \bar{K}^0$. We also estimate the branching fractions for $\rho(770)^\pm$ decay into kaon pair to be about one percent and that for the neutral $\rho(770)$ into $K^+K^-$ or $K^0\bar{K}^0$ to be about $0.5\%$, which will be tested by the future experiments.
We propose a simple model in which dark matter particle exchanges mediate a new quantum force between muons and nucleons, resolving the proton charge radius puzzle. At the same time, the discrepancy between the measured anomalous magnetic moment of the muon and the Standard Model prediction can be accommodated, and thermal relic abundance of the dark matter candidate is consistent with observations. The dark matter particle mass is in the MeV range. We show that the model is consistent with a variety of experimental and observational constraints.
Chiral condensed matter systems, such as liquid crystals and magnets, exhibit a host of spatially localized topological structures that emerge from the medium's tendency to twist and its competition with confinement and field coupling effects. We show that the strength of perpendicular surface boundary conditions can be used to control the structure and topology of solitonic and other localized field configurations. By combining numerical modeling and three-dimensional imaging of the director field, we reveal structural stability diagrams and intertransformation of twisted walls and fingers, torons, and skyrmions and their crystalline organizations upon changing boundary conditions. Our findings provide a recipe for controllably realizing skyrmions, torons, and hybrid solitonic structures possessing features of both of them, which will aid in fundamental explorations and technological uses of such topological solitons. Moreover, we discuss how other material parameters can be used to determine soliton stability and how similar principles can be systematically applied to other liquid crystal solitons and solitons in other material systems.
Introductory physics students who actively sought out information from multiple peers were less likely to solve well structured problems compared to those who did not seek help; for ill-structured problems, this effect depended on the features of the learning environment.
We present an investigation into the interdisciplinary role of physics in a physics-for-non-physicists course at Pomona College. This work is guided by prior research into introductory physics for life-science (IPLS) courses, but attends to significant differences in the scope and context of this course. We interviewed enrolled students, physics professors, and professors from non-physics disciplines to explore the function of this course and the role of physics in the education of non-physics-science students. Interviews were audio recorded and transcribed, then analyzed to identify emergent themes. These themes outline the authentic physics, including content knowledge and other, broader learning objectives, that play an important and distinct role in the science education of enrolled students. Stakeholders generally align in their emphasis of interdisciplinary relevance with some divergence in the specific articulation of that idea. The differences can be understood through the stakeholders' distinct areas of expertise, with non-physics professors expressing value through relevance to their discipline and physics professors focusing on essential aspects of physics.
We report on the impact of magnetoelastic coupling on the magnetocaloric properties of LaFe$_{11.4}$Si$_{1.6}$H$_{1.6}$ in terms of the vibrational density of states, which we determined with $^{57}$Fe nuclear resonant inelastic X-ray scattering measurements and with density-functional-theory based first-principles calculations in the ferromagnetic low-temperature and paramagnetic high-temperature phase. In experiments and calculations, we observe pronounced differences in the shape of the Fe-partial VDOS between non-hydrogenated and hydrogenated samples. This shows that hydrogen does not only shift the temperature of the first-order phase transition, but also affects the elastic response of the Fe-subsystem significantly. In turn, the anomalous redshift of the Fe VDOS, observed by going to the low-volume PM phase, survives hydrogenation. As a consequence, the change in the Fe specific vibrational entropy $\Delta S_\mathrm{lat}$ across the phase transition has the same sign as the magnetic and electronic contribution. DFT calculations show that the same mechanism, which is a consequence of the itinerant electron metamagnetism associated with the Fe subsystem, is effective in both the hydrogenated and he hydrogen-free compounds. Although reduced by 50 % as compared to the hydrogen-free system, the measured change $\Delta S_\mathrm{lat}$ of 3.2\pm1.9 J/kgK across the FM to PM transition contributes with 35 % significantly and cooperatively to the total isothermal entropy change $\Delta S_\mathrm{iso}$. Hydrogenation is observed to induce an overall blueshift of the Fe-VDOS with respect to the H-free compound; this effect, together with the enhanced Debye temperature observed, is a fingerprint of the hardening of the Fe sublattice by hydrogen incorporation. In addition, the mean Debye velocity of sound of LaFe$_{11.4}$Si$_{1.6}$H$_{1.6}$ was determined from the NRIXS and the DFT data.
Realizing axion insulator state with a uniform magnetization considerably facilitates experimental explorations of the intriguing topological magnetoelectric effect, a hallmark of three-dimensional (3D) topological insulators (TIs). Through density functional theory calculations and four-band model studies, we find that magnetic ions Cr3+ in monolayer CrI3 and Mn2+ in septuple-layer MnBi2Se4 have opposite exchange couplings to the topological surface states of 3D TI Bi2Se3. As an exciting result of such opposite exchange couplings, axion insulator state is realized by a uniform magnetization in CrI3/Bi2Se3/MnBi2Se4 heterostructure. Our work opens up opportunities for exploring topological magnetoelectric effect realized by the uniform magnetization induced axion insulator state in heterostructures of 3D TIs and two-dimensional van der Waals ferromagnetic insulators.
We conjecture that ${Z}_{c}^{\ensuremath{-}}(4100)$ found by the LHCb group from a Dalitz plot analysis of ${B}^{0}\ensuremath{\rightarrow}{\ensuremath{\eta}}_{c}{K}^{+}{\ensuremath{\pi}}^{\ensuremath{-}}$ decay is the charge conjugate of ${Z}_{1}^{+}(4050)$ observed in ${\ensuremath{\chi}}_{c1}{\ensuremath{\pi}}^{+}$ distribution from the Belle collaboration. Some interesting conclusions are inferred from this assumption. The ${Z}_{2}^{+}(4250)$ would be assigned to be a ${J}^{P}={1}^{+}$ or ${1}^{\ensuremath{-}}$ state because of its absence in ${\ensuremath{\eta}}_{c}{\ensuremath{\pi}}^{\ensuremath{-}}$ invariant mass distribution, while ${Z}_{1}^{+}(4050)/{Z}_{c}^{\ensuremath{-}}(4100)$ could be a ${0}^{+}$ or ${1}^{\ensuremath{-}}$ state but ${2}^{+}$ is unfavored because it would be coupled to ${\ensuremath{\eta}}_{c}\ensuremath{\pi}$ in $D$-wave. The null observation of ${Z}_{1}{Z}_{2}$, ${Z}_{1}{Z}_{1}$, and ${Z}_{2}{Z}_{2}$ production in ${e}^{+}{e}^{\ensuremath{-}}$ annihilation and $\mathrm{\ensuremath{\Upsilon}}(1S,2S)$ decay by the Belle collaboration would further allocate the spin parity combination of ${Z}_{1}^{+}(4050)/{Z}_{c}^{\ensuremath{-}}(4100)$ and ${Z}_{2}^{+}(4250)$. Our deductions can be used to exclude a set of proposed models and could be further tested by future experiment, e.g., in $\ensuremath{\gamma}\ensuremath{\gamma}$ collisions.
We carry out phase field simulations to study properties of the comblike step patterns induced by an adatom source. When an adatom source advances right in front of a step, step wandering is caused by the asymmetry of the surface diffusion field and small protrusions are formed. If the velocity of the source V_{p} is smaller than a critical value V_{p}^{c}, the protrusions follow the adatom source with coarsening of the step pattern, and a regular comblike pattern with finger-like protrusions is formed. With a sufficiently small V_{p}, the gap of the supersaturation is large at the adatom source. Since the period of protrusions, Λ, decreases with increasing V_{p}, the coarsening of step pattern is irrelevant for the protrusions to catch up with the adatom source. Near V_{p}^{c}, the gap of the supersaturation at the adatom source is small. Taking account of the increase in Λ with increasing V_{p}, the coarsening of the step pattern is essential for the protrusions to follow the adatom source.
Energy levels, lifetimes, and wave function compositions have been computed for all atomic states of the 4p(6) and 4p(5)4d configurations using the multiconfiguration Dirac-Hartree-Fock method. Calculations were done by parity and the configuration state function expansions were obtained by allowing single and double substitutions from the the 4p(6) and 4p(5)4d single references with orbitals in an orbital set that was extended to n = 7 and all possible angular symmetries. Lifetimes are computed from E1, E2, and M1 transitions between these levels. Energy levels and transition energies (or wavelengths) are compared with other theory and experiment, when available. Transition data for the 4p(6) (1)S0 - 4p(5) 4d J = 1 transitions are investigated in detail with respect to convergence of transition energies and the length and velocity forms of the line strengths. By classifying the upper states by J, parity (pi), and position, the compositions of the states with the same three quantum number change smoothly as a function of the nuclear charge Z and transition energies and transition matrix elements can be approximated by polynomial expressions in Z. A zero in the transition matrix element for the S-1(0) - P-3(1)o transition leads to a long lifetime at Z approximate to 58.
In this study, we present evidence that subsurface carbon nanoparticles in Bi₂Sr₂CaCu₂O8+δ can be manipulated with nanometer precision using a scanning tunneling microscope. High resolution images indicate that most of the carbon particles remain subsurface after transport observable as a local increase in height as the particle pushes up on the surface. Tunneling spectra in the vicinity of these protrusions exhibit semiconducting characteristics with a band gap of approximately 1.8 eV, indicating that the incorporation of carbon locally alters the electronic properties near the surface.
