The type-II terminated $1T\text{−}{\mathrm{TaS}}_2$ surface of a three-dimensional $1T\text{−}{\mathrm{TaS}}_2$ bulk material realizes the effective spin-$1/2$ degree of freedom on each David star cluster with ${\mathcal{T}}^2=-1$ such that the time-reversal symmetry is realized anomalously, despite the fact that bulk three-dimensional $1T\text{−}{\mathrm{TaS}}_2$ material has an even number of electrons per unit cell with ${\mathcal{T}}^2=+1$. This surface is effectively viewed as a spin-$1/2$ triangular lattice magnet, except with a fully gapped topological bulk. We further propose this surface termination realizes a spinon Fermi surface spin liquid with the surface fractionalization but with a nonexotic three-dimensional bulk. We analyze possible experimental consequences, especially the surface spectroscopic measurements, of the type-II terminated surface spin liquid.

We perform experiments and computer simulations to study the effective interactions between like-charged colloidal tracers moving in a two-dimensional fluctuating background of colloidal crystal. By a counting method that properly accounts for the configurational degeneracy of tracer pairs, we extract the relative probability of finding a tracer pair in neighboring triangular cells formed by background particles. We find that this probability at the nearest neighbor cell is remarkably greater than those at cells with larger separations, implying an effective attraction between the tracers. This effective attraction weakens sharply as the background lattice constant increases. Furthermore, we clarify that the lattice-mediated effective attraction originates from the minimization of free energy increase from deformation of the crystalline background due to the presence of diffusing tracers.

We introduce a self-consistent tomography for arbitrary quantum nondemolition (QND) detectors. Based on this, we build a complete physical characterization of the detector, including the measurement processes and a quantification of the fidelity, ideality, and backaction of the measurement. This framework is a diagnostic tool for the dynamics of QND detectors, allowing us to identify errors, and to improve their calibration and design. We illustrate this on a realistic Jaynes-Cummings simulation of a superconducting qubit readout. We characterize nondispersive errors, quantify the backaction introduced by the readout cavity, and calibrate the optimal measurement point.

Heavy axionlike particles (ALPs) with masses up to a few 100 keV and coupled with photons can be efficiently produced in stellar plasmas. We present a new “ballistic” recipe that covers both the energy-loss and energy-transfer regimes, and we perform the first dedicated simulation of Globular Cluster stars including the ALP energy transfer. This argument allows us to constrain ALPs with $m_a\lesssim 0.4\mathrm{MeV}$ and $g_{a\gamma }\simeq {10}^{-5}{\mathrm{GeV}}^{-1}$, probing a section of the ALP parameter space informally known as the “cosmological triangle”. This region is particularly interesting since it has been excluded only using standard cosmological arguments that can be evaded in nonstandard scenarios.

We present a one-parameter family of large $N$ disordered models, with and without supersymmetry, in three spacetime dimensions. They interpolate from the critical large $N$ vector model dual to a classical higher spin theory toward a theory with a classical string dual. We analyze the spectrum and operator product expansion data of the theories. While the supersymmetric model is always well-behaved the nonsupersymmetric model is unitary only over a small parameter range. We offer some speculations on the origin of strings from the higher spins.

The diphoton channel at lepton colliders, $e^{+}{e}^{-}({\mu }^{+}{\mu }^{-})\to \gamma \gamma$, has a remarkable feature that the leading new physics contribution comes only from dimension-eight operators. This contribution is subject to a set of positivity bounds, derived from the fundamental principles of quantum field theory, such as unitarity, locality, analyticity and Lorentz invariance. These positivity bounds are thus applicable to the most direct observable: the diphoton cross section. This unique feature provides a clear, robust, and unambiguous test of these principles. We estimate the capability of various future lepton colliders in probing the dimension-eight operators and testing the positivity bounds in this channel. We show that positivity bounds can lift certain flat directions among the effective operators and significantly change the perspectives of a global analysis. We also discuss the positivity bounds of the $Z\gamma /ZZ$ processes which are related to the $\gamma \gamma$ ones, but are more complicated due to the massive $Z$ boson.

Single-mode operation is a desirable but elusive property for lasers operating at high pump powers. Typically, single-mode lasing is attainable close to threshold, but increasing the pump power gives rise to multiple lasing peaks due to inter-modal gain competition. We propose a laser with the opposite behavior: multimode lasing occurs at low output powers, but pumping beyond a certain value produces a single lasing mode, with all other candidate modes experiencing negative effective gain. This phenomenon arises in a lattice of coupled optical resonators with non-fine-tuned asymmetric couplings, and is caused by an interaction between nonlinear gain saturation and the non-Hermitian skin effect. The single-mode lasing is observed in both frequency domain and time domain simulations. It is robust against on-site disorder, and scales up to large lattice sizes. This finding might be useful for implementing high-power laser arrays.

A family of marginally rigid (isostatic) spring networks with fractal structure up to a controllable length was devised, and the viscoelastic spectra $G^{*}(\omega )$ calculated. Two nontrivial scaling regimes were observed, (i) $G^{\prime }\approx G^{\prime \prime }\propto {\omega }^{\mathrm{\Delta }}$ at low frequencies, consistent with $\mathrm{\Delta }=1/2$, and (ii) $G^{\prime }\propto G^{\prime \prime }\propto {\omega }^{{\mathrm{\Delta }}^{\prime }}$ for intermediate frequencies corresponding to fractal structure, consistent with a theoretical prediction ${\mathrm{\Delta }}^{\prime }=(\ln 3-\ln 2)/(\ln 3+\ln 2)$. The crossover between these two regimes occurred at lower frequencies for larger fractals in a manner suggesting diffusivelike dispersion. Solid gels generated by introducing internal stresses exhibited similar behavior above a low-frequency cutoff, indicating the relevance of these findings to real-world applications.

We establish bounds on quantum correlations in many-body systems. They reveal what sort of information about a quantum system can be simultaneously recorded in different parts of its environment. Specifically, independent agents who monitor environment fragments can eavesdrop only on amplified and redundantly disseminated—hence, effectively classical—information about the decoherence-resistant pointer observable. We also show that the emergence of classical objectivity is signaled by a distinctive scaling of the conditional mutual information, bypassing hard numerical optimizations. Our results validate the core idea of quantum Darwinism: objective classical reality does not need to be postulated and is not accidental, but rather a compelling emergent feature of quantum theory that otherwise—in the absence of decoherence and amplification—leads to “quantum weirdness.” In particular, a lack of consensus between agents that access environment fragments is bounded by the information deficit, a measure of the incompleteness of the information about the system.

A search for exclusive two-photon production via photon exchange in proton-proton collisions, $pp\to p\gamma \gamma p$ with intact protons, is presented. The data correspond to an integrated luminosity of $9.4{\mathrm{fb}}^{-1}$ collected in 2016 using the CMS and TOTEM detectors at a center-of-mass energy of 13 TeV at the LHC. Events are selected with a diphoton invariant mass above 350 GeV and with both protons intact in the final state, to reduce backgrounds from strong interactions. The events of interest are those where the invariant mass and rapidity calculated from the momentum losses of the forward-moving protons match the mass and rapidity of the central, two-photon system. No events are found that satisfy this condition. Interpreting this result in an effective dimension-8 extension of the standard model, the first limits are set on the two anomalous four-photon coupling parameters. If the other parameter is constrained to its standard model value, the limits at 95% confidence level are $|{\zeta }_1|<2.9\times {10}^{-13}{\mathrm{GeV}}^{-4}$ and $|{\zeta }_2|<6.0\times {10}^{-13}{\mathrm{GeV}}^{-4}$.

We point out that the Hermitian and anti-Hermitian components of the effective Hamiltonian for decaying neutrinos cannot be simultaneously diagonalized by unitary transformations for all matter densities. We develop a formalism for the two-flavor neutrino propagation through matter of uniform density, for neutrino decay to invisible states. Employing a resummation of the Zassenhaus expansion, we obtain compact analytic expressions for neutrino survival and conversion probabilities, to first and second order in the “mismatch parameter” $\overline{\gamma }$.

Charged-lepton flavor violation (CLFV) is a smoking-gun signature of physics beyond the standard model. The discovery of CLFV in upcoming experiments would indicate that CLFV processes must have been efficient in the early Universe at relatively low temperatures. In this Letter, we point out that such efficient CLFV interactions open up new ways of creating the baryon asymmetry of the Universe. First, we quote the two-loop corrections from charged-lepton Yukawa interactions to the chemical transport in the standard model plasma, which imply that nonzero lepton flavor asymmetries summing up to $B-L=0$ are enough to generate the baryon asymmetry. Then, we describe two scenarios of what we call leptoflavorgenesis, where efficient CLFV processes are responsible for the generation of primordial lepton flavor asymmetries that are subsequently converted to a baryon asymmetry by weak sphaleron processes. Here, the conversion factor from lepton flavor asymmetry to baryon asymmetry is suppressed by charged-lepton Yukawa couplings squared, which provides a natural explanation for the smallness of the observed baryon-to-photon ratio.

A narrow near-threshold proton-emitting resonance ($E_x=11.4\mathrm{MeV}$, $J^{\pi }=1/2^{+}$, and ${\mathrm{\Gamma }}_p=4.4\mathrm{keV}$) was directly observed in ${}^{11}\mathrm{B}$ via proton resonance scattering. This resonance was previously inferred in the $\beta$-delayed proton emission of the neutron halo nucleus ${}^{11}\mathrm{Be}$. The good agreement between both experimental results serves as a ground to confirm the existence of such exotic decay and the particular behavior of weakly bound nuclei coupled to the continuum. $R$-matrix analysis shows a sizable partial decay width for both, proton and $\alpha$ (${\mathrm{\Gamma }}_{\alpha }=11\mathrm{keV}$) emission channels.

A near-threshold proton resonance in ${}^{11}\mathrm{B}$ at $E_{\mathrm{ex}}=11.44\pm 0.04\mathrm{MeV}$ is observed via the reaction ${}^{10}\mathrm{Be}(d,n){}^{11}\mathrm{B}\to {}^{10}\mathrm{Be}+p$ in inverse kinematics, measured with a beam of the radioactive isotope ${}^{10}\mathrm{Be}$. The resonance energy at $E_{\mathrm{res}}=211(40)\mathrm{keV}$ is consistent with a proton signal observed by Ayyad et al. in the $\beta$-delayed proton decay of ${}^{11}\mathrm{Be}$. By comparison to a distorted wave Born approximation calculation, a 0.27(6) spectroscopic factor is extracted and a tentative ($\ell =0$) character is assigned for this resonance. The significant cross section in the proton-transfer $(d,n)$ reaction, as well as the observation of its proton-decay signal, point to the threshold-resonance character of this state. The position of this state, its structure, and strong coupling to the $s$-wave continuum represent an ideal case to study quantum near-threshold many-body dynamics of unstable states. The presence of this state is an important step toward understanding the excessively large beta-delayed proton-decay branch of ${}^{11}\mathrm{Be}$.