Double white dwarfs (DWDs) in the Laser Interferometer Space Antenna (LISA) band are major Galactic gravitational-wave sources, yet the standard isolated-binary picture is incomplete: a substantial fraction of tight DWD progenitors may reside in hierarchical triples. Triple evolution can therefore alter both the production rate and the parameter distributions of LISA DWDs. Using the multiple stellar evolution (MSE) code, we study how the adiabatic mass-loss model (Ge model) and the SCATTER formalism for triple common-envelope evolution affect triple-channel LISA DWD formation. Our main model (model 1) evolves ${10}^5$ triples adopting both ingredients. Three additional triple control models, each with ${10}^4$ triples, vary the mass-transfer stability criterion to the original MSE polytropic model, remove the SCATTER formalism, or adopt low metallicity ($Z=0.001$). We also evolve ${10}^6$ isolated binaries with the same binary-evolution framework to provide a binary-channel reference. Systems classified as dynamically unstable under the polytropic model can instead undergo stable Roche-lobe overflow under the Ge model. This sustained mass transfer modifies the donor envelope, reduces its binding energy, and helps the subsequent common-envelope phase form a close DWD rather than a merger. The Ge model increases the triple-channel LISA DWD yield by about 60% relative to the polytropic model, whereas the SCATTER formalism changes the integrated yield by only about 3%. After residence-time weighting, triples contribute about $1.3\times {10}^7$ LISA-band DWDs, including $1.4\times {10}^4$ individually resolvable systems. In the combined triple-plus-binary normalization, the binary channel contributes $3.1\times {10}^6$ LISA-band DWDs and $4.7\times {10}^3$ individually resolvable systems. These values are the binary share of the combined population, not the binary-only Galactic estimate. The main triple model has a flatter, higher-$q$ mass-ratio distribution than the polytropic-model triple populations, is dominated by He-CO and He-He binaries, and produces rare eccentric systems only when a tertiary star remains bound.

We investigate core composition $g_1$ modes of cold, nonrotating neutron stars containing antikaon condensates, hyperons, and $\mathrm{\Delta }(1232)$ baryons. To our knowledge, this is the first fully general-relativistic calculation of the continuous-composition core $g_1$-mode frequency and gravitational-wave damping time for stars with a $K^{-}$ condensate. Using the BigApple equation of state (EOS), we compute frequencies and damping times in full general relativity (GR) and evaluate frozen-composition tidal overlaps from full-GR eigenfunctions within a leading-order hybrid resonance prescription. A species-resolved Ledoux decomposition, cross-checked through mode-frequency sensitivities, identifies the driving channels. We compare frozen composition with a fast-$K$ limit for $n\leftrightarrow p+K^{-}$ and a strong-equilibrium limit for the $\mathrm{\Delta }$ quartet. Fast-$K$ equilibration retains 36%–44% of the peak local value of $c_s^2-c_e^2$. At the physical maxima or EOS-validity end points, the frequencies retain 65.7%–73.4% of their frozen values and the gravitational-wave damping times increase by factors of 14.3–31.9, while the kaon-associated mode remains above the nucleonic band. Strong $\mathrm{\Delta }$ equilibration removes most of the direct $\mathrm{\Delta }$-induced enhancement, returning the $N\mathrm{\Delta }$ mode toward the nucleonic band, whereas the high-frequency $NY\mathrm{\Delta }$ branch survives because of the frozen $\mathrm{\Lambda }$ gradient. Eigenfunction tracking confirms a continuous $g_1$ branch, and DD-ME2 reproduces this hierarchy. For circular, equal-mass binary neutron-star inspirals, the frozen-composition phase-shift estimates satisfy $|\mathrm{\Delta }{\mathrm{\Phi }}_{g_1}|\le 1.410\times {10}^{-3}\mathrm{rad}$, a factor of 21 below the 0.03-rad favorable-event benchmark reported for the Einstein Telescope. An exotic species therefore produces a distinct composition mode only if its composition gradient, or a coupled slowly equilibrating gradient, survives over the oscillation period.

Ultralight dark matter can induce weak oscillating magneticlike signals and can therefore be searched for with precision magnetometry. Levitated ferromagnets provide a sensitive platform for such searches, but a single ferromagnet is limited in total polarized spin and readout performance. We investigate a levitated ferromagnet lattice as a scalable detector architecture for ultralight dark matter. We develop a theoretical description of the collective lattice response in the fully trapped regime, incorporating dipole-dipole interactions, finite-size effects, and boundary-induced mode mixing. We further analyze the collective noise budget and show that interaction effects mainly produce a narrow blind zone through thermal-noise amplification, while away from this region, the lattice preserves favorable collective noise scaling. We then derive projected sensitivities to axion-electron, dark-photon, and axion-photon couplings for a reference theoretical benchmark. Under the benchmark assumptions, the lattice improves the projected reach in all three channels relative to a single-ferromagnet detector. The axion-photon channel receives an additional coherent enhancement at the level of an order-of-magnitude estimate, whose coefficient depends on the electromagnetic geometry of the lattice and shield.

We consider the possibility of dark matter in a warped extra-dimensional theory in the presence of a linear dilaton background, with a gapped continuum spectrum, in a brane-world cosmological scenario. Firstly, triggered by self-energy radiative corrections, we study the existence of an isolated resonance of massive gravitons, and its realization as a long-lived feebly interacting dark matter candidate, produced by the freeze-in mechanism. This massive graviton is proved to satisfy all theoretical and experimental constraints, in the sub-MeV mass range. We further consider the close relationship between the existence of this component of dark matter and the presence of an inflaton localized on the brane, with a mass around ${10}^{11}\mathrm{GeV}$ and a sub-TeV reheating temperature, in a brane inflationary scenario that allows one to reproduce the most recent cosmological observables. Secondly, the gapped continuum of gravitons, a particular five-dimensional realization of the physics of unparticles, is identified as a holographic fluid which can play the role of holographic dark matter. The production of the holographic fluid goes by an ultraviolet freeze-in mechanism, with an abundance mainly depending on the reheating temperature. Depending on the values of the mass gap and the reheating temperature, one or both components of dark matter can be present.

We perform a systematic study of two-meson form factors of the scalar, vector, and antisymmetric tensor types within the framework of the $U(3)$ resonance chiral theory. The complete perturbative form factors in both the strangeness-conserving and strangeness-changing channels are calculated by incorporating one-loop light-flavor pseudoscalar meson contributions and tree-level resonance exchanges. With these newly calculated chiral results, we construct the corresponding unitarized form factors by incorporating meson-meson final-state interactions. The parameter values obtained in previous meson-meson scattering studies are then exploited to predict the corresponding form factors. Different types of form factors are found to exhibit rather distinct resonance structures across channels.

We develop a fully quantized theory of nonlinear Compton scattering driven by a single-mode quantum field. Exact quantum-Volkov states retain pump depletion, backaction, and final-state correlations through displaced or squeezed-displaced Fock-state ladders. A finite Fock-state pump produces discrete photon-transfer edges and a terminal spectral cutoff. In the bright, weakly depleted regime, the exact theory reduces to a Wigner-function weighted-average of scattering probabilities evaluated at fixed complex field amplitudes, with ordinary and generalized Bessel functions describing the harmonic structure for circular and linear polarization, respectively. For squeezed coherent light, the squeezing angle controls the high-energy emission through photon-number fluctuations.

Scalar fields are ubiquitous in theories of high-energy physics. In the context of cosmic inflation, this suggests the existence of spectator fields, which provide a subdominant source of energy density. We show that spectator fields boost the inflationary production of primordial black holes, with single-field ultraslow roll evolution supplanted by a phase of evolution along the spectator direction, and primordial perturbations amplified by the resulting multifield dynamics. This generic mechanism is largely free from the severe fine-tuning that afflicts single-field inflationary PBH models.

A central lesson of gravity is that local observables are ill-defined. Coordinates themselves are a redundancy of description, so any particular point in spacetime is only meaningful once defined relationally by clocks, rulers, or asymptotic data. Despite extensive formal work on this subject, explicit calculations of the resulting gravitationally-dressed observables are more scarce. In this paper we perturbatively compute dressed matrix elements of local operators in electrodynamics and general relativity, including both potential and radiative photons and gravitons. Our expressions indicate that dressing is not ornamental: it universally induces kinematic singularities that can substantively reshape observables. We further show how dressing is mathematically equivalent to gauge fixing, as demonstrated by a dynamical temporal gauge in which the gauge-fixing vector is itself a geodesic fluid.

We analyse the role of approximate axionic shift symmetries in gravity-decoupling limits arising in type II Calabi-Yau compactifications. Associated with each shift symmetry there is an axionic string whose tension constrains the gradient of the Kähler potential, as expected in regimes where gravity becomes weakly coupled. The gradients of these tensions define vector fields on moduli space, analogous to those associated with Bogomol’nyi-Prasad-Sommerfield particle masses. Together, they characterize the evolution of different effective field theory sectors along asymptotic limits, encoding both their coupling to gravity and their kinetic mixing. By deriving upper bounds on the inner products of these vector fields, we show that they split into mutually orthogonal subsets, one of which decouples from gravity. Finally, we relate the Laplacian of certain axionic string tensions to a divergent moduli space curvature.

In this work, we provide evidence for a duality between 4-dimensional Calabi-Yau compactifications of the heterotic string, in which the base manifolds are linked by a conifold transition. In recent work, a geometric proposal was put forward for how 5-branes and gauge bundles are carried across such transitions. It was observed that compactifications connected in this way lead to 4-dimensional effective theories with the same massless spectrum. Here we provide much stronger evidence that these heterotic conifold transitions do indeed lead to dual theories. We construct a duality map between the field spaces of the two compactifications and use it to demonstrate the agreement of large numbers of holomorphic functions appearing in the definition of the effective theories. In an example, we show that 147,440 independent superpotential Yukawa couplings agree across the duality as holomorphic functions of the moduli. In certain special cases, the putative duality studied here reduces to the target space duality of (0,2) gauged linear sigma models.

Divergent series arising in the computation of Casimir energies admit two seemingly different treatments: a physically motivated regularization and subtraction procedure, and formal analytic continuation methods that assign finite values directly to divergent expressions. The agreement between these approaches for the Casimir energy between parallel plates is well known, but its origin is often left implicit. In this work, we provide a unified framework that makes this equivalence transparent. Building on Tao’s theory of smoothed sums, we show that the introduction of a smooth cutoff leads to an asymptotic expansion whose finite, regulator-independent part is universally determined by the analytic continuation of the associated Dirichlet series. This identification follows from a Mellin-transform representation, in which divergences and finite contributions are encoded in the pole structure of the integrand. We extend this approach to a class of series relevant to Casimir problems. In this setting, we show that logarithmic divergences arise from pole coincidences, and we obtain a natural decomposition of the result into universal and cutoff-dependent terms, mirroring the structure of renormalization in quantum field theory.

While the search for dark matter remains a central focus of modern astrophysics and high-energy physics, neutron stars could provide natural laboratories in which the interaction between dark matter and baryonic matter can be studied. In this work, we model dark matter as an ultralight bosonic field, which can accrete onto the neutron star and form a composite object bound through gravity. Using long-term, numerical relativity simulations in spherical symmetry, we extract and analyze the frequency spectra of the radial oscillation modes of fermion-boson stars. Our simulations reveal that the fermionic and bosonic components synchronize through gravitational coupling regardless of the equation of state, enriching their oscillation spectrum. This synchronization leads to new multistate scalar configurations and reshapes the hierarchy of the neutron-star radial modes. We further propose a procedure to compute the values of the new dominant modes as a function of the bosonic mass and discuss how the synchronization mechanism extends beyond spherical symmetry together with its implications for neutron-star physics and gravitational-wave astronomy.

How is the production of primordial black holes (PBHs) in single-field models of inflation impacted by the presence of additional scalar fields? We consider the effect of a spectator field—a free scalar field with sub-Hubble mass and no direct coupling to the inflaton and which makes a subdominant contribution to the total energy density—in the context of single-field models of inflation featuring a transient phase of ultraslow-roll evolution. Despite the modest title, a spectator field can have a dramatic impact: the slow-roll evolution of the spectator prevents the combined inflaton-and-spectator system from entering into ultraslow-roll, which naively might be expected to preclude the production of PBHs. However, we demonstrate that the growth of perturbations is maintained or enhanced by the spectator, through the rich interplay of curvature and isocurvature perturbations. We show in a model-independent way that the single-field phase of ultraslow-roll is replaced by two turns in field space encompassing a phase of tachyonic instability for the isocurvature perturbations and a transfer of power from isocurvature to curvature modes. Furthermore, we highlight a degeneracy between the fine-tuning of the feature in the inflaton potential and the parameters of the spectator, leading to an overall resilience of model predictions to parameter variations. This makes it easier for the underlying PBH model to accommodate both high-precision cosmic microwave background constraints and production of PBHs in the asteroid-mass range.

Axion stars, which are self-gravitating Bose-Einstein condensates of QCD axions or axionlike particles, are compelling dark-matter candidates whose stability controls their cosmological and astrophysical impact. We develop a unified framework for axion-star stability that combines a nonrelativistic Schrödinger-Poisson description with catastrophe theory. Starting from the Einstein-Klein-Gordon theory with a periodic axion potential, we derive the effective equations of motion and conserved quantities for axion stars and construct a one-parameter family of starlike solutions. Using a Gaussian variational ansatz, we obtain an analytic one-dimensional energy functional $E(R;N)$ and show that the appearance and disappearance of axion-star equilibria as a function of particle number $N$ is governed by Arnold $A_2$, $A_3$, and $A_4$ catastrophes. Including sextic self-interactions generates two distinct stable branches (dilute and dense axion stars) separated by an unstable branch. We further show how the catastrophe criteria extend beyond the sextic truncation to the full cosine and QCD-corrected axion potentials, for which the fold conditions are evaluated from the full variational energy. We distinguish explicitly between collective-coordinate stability within the ansatz and full radial perturbative stability, and we state the domain of validity of the nonrelativistic approximation. Our results provide a compact classification of axion-star phases and identify model-dependent critical masses directly linked to collapse, bosenovalike emission, and black-hole formation.

This work introduces the causal bootstrap, a framework for bounding smeared spectral observables from finite nonperturbative Euclidean data. The method optimizes over the convex set of positive spectral densities compatible with the data to compute rigorous upper and lower bounds on the target observable. Statistical uncertainties, including correlations, are incorporated through compatibility regions using the covariance matrix. The bounds are equivalent, via Lagrange duality, to certified bounds on the target smearing kernel. For polynomial, rational, and piecewise rational kernels, the resulting dual problems can be reduced to finite-dimensional semidefinite programs using techniques familiar, e.g., in the numerical conformal bootstrap. The present formulation clarifies the relation to moment problems, Nevanlinna-Pick interpolation, and linear kernel-reconstruction methods. Numerical examples demonstrate the method.

We consider how the recent CMS measurements of the masses and quantum numbers of $X(6600)$, $X(6900)$ and $X(7100)$ can help to reveal the internal structure of these apparent $cc\overline{c}\overline{c}$ tetraquarks. The measured $J^{PC}=2^{++}$ quantum numbers of $X(6600)$ are consistent with our previous prediction, and imply the inevitable existence of a lighter $0^{++}$ partner $X(6400)$ which also decays to $J/\psi J/\psi$. There are strong indications for this scalar partner in the recent CMS data fits, which include a Breit-Wigner peak with mass around 6400 MeV. We provide predictions for the masses and decay properties of the scalar and other partner states, which are key experimental tests to discriminate between quark and diquark models. Dedicated experimental scrutiny of this mass region is therefore required, to establish an S-wave multiplet of $cc\overline{c}\overline{c}$ states (the first of its kind for tetraquarks), leading to a breakthrough in exotic hadron research and our understanding of heavy quark exotics.

In order to meet the high-precision measurement of the current baryon spectroscopy, for the first time, we rigorously analyze the spin-dependent interactions and the fine structure of the negative-parity singly heavy baryons in the relativized quark model, which was previously unfeasible in the three-quark system. This gains access to the exploration of the strong interactions dominated by the nonperturbative QCD, and reveals how the various forms of strong interactions in a baryon compete with each other, affect the evolution of the energy levels, cause the energy level splitting, and contribute to the mixing effect responsible for the formation of the fine structures. It is shown that the rigorous calculation can nicely reproduce the data; the averaged deviation between the calculated and experimental energy levels is less than 5 MeV for the negative-parity singly heavy baryons. This confirms the reliability of the calculation and also helps make reasonable assignments for the observed negative-parity baryons. The large amount of data obtained by the rigorous calculations contains a wealth of interaction information and is helpful for both of the theoretical and experimental studies. The key to the rigorous calculation in this work is the proposal of a new method, namely the two-step Gaussian expansion method. This new method not only overcomes the long-standing unresolved problem in the relativized quark model, but also provides an effective approach for the high-precision calculation of other few-body systems such as the compact tetraquarks and pentaquarks, especially for the treatment of spin-orbit interactions and tensor interactions which actually appear ubiquitously in all of quantum many-body systems.

Experimental measurements of $J/\psi$ and $\psi (2S)$ decays to octet baryon pairs reveal a negative-$\mathrm{\Sigma }\overline{\mathrm{\Sigma }}$ puzzle in the angular distributions, ${\alpha }_{\mathrm{\Sigma }}^{J/\psi }<0$, whereas the other measured $J/\psi$ octet channels and the corresponding $\psi (2S)$ channels have positive angular parameters. We show that an $\mathrm{SU}(3{)}_F$-exact singlet description is strongly disfavored in a ${\chi }^2$ fit, giving ${\chi }^2\simeq {10}^5$. By contrast, a reduced scenario in which a common final-state interaction mixes the $\mathrm{S}$- and $\mathrm{D}$-wave amplitudes gives ${\chi }^2=4.21$ for the 22 isospin-reduced inputs and two nominal degrees of freedom. We find that the negative-$\mathrm{\Sigma }\overline{\mathrm{\Sigma }}$ puzzle can be reproduced with direct-production $\mathrm{SU}(3{)}_F$ breaking at the 40% level. This is larger than the conventional quark-mass expectation of about 30%, but numerically smaller than the order-one channel variation suggested by the experimental data. The sizable observable effect is amplified by $\mathrm{SU}(3{)}_F$-breaking rescattering paths involving S–D mixing. These paths feed the much larger D-wave source into the final $\mathrm{SU}(3{)}_F$-breaking S-wave amplitude. The largest remaining pull comes from the $\psi (2S)\to N\overline{N}$ angular input, motivating a renewed experimental check of $\psi (2S)\to n\overline{n}$.

The coherent elastic scattering of neutrinos on nuclei, also known as $\mathrm{CE}\nu \mathrm{NS}$, has been studied for several years by the COHERENT program of experiments using neutrinos from stopped-pion decays produced at the Oak Ridge Spallation Neutron Source (SNS). We propose a new approach for $\mathrm{CE}\nu \mathrm{NS}$ measurements at the SNS that aims to complement the COHERENT experiments in two main ways: by reconstructing the angular distribution of $\mathrm{CE}\nu \mathrm{NS}$ -induced recoils, and by measuring $\mathrm{CE}\nu \mathrm{NS}$ on much lighter target nuclei such as helium, carbon, and fluorine. The proposed detector would employ a gaseous time-projection chamber with a highly segmented charge readout to enable the spatial reconstruction of $\sim 10–500\mathrm{keV}$ ionization tracks created by $\mathrm{CE}\nu \mathrm{NS}$ -induced recoils. This would enable the simultaneous measurement of the $\mathrm{CE}\nu \mathrm{NS}$ recoil energy and scattering angle, thereby allowing event-by-event reconstruction of the neutrino energy. We estimate that a $60:40$ He:${\mathrm{CF}}_4$ gas mixture at atmospheric pressure offers a good trade-off between total target mass and good directionality and could deliver a detection of the angular distribution of $\mathrm{CE}\nu \mathrm{NS}$, even under pessimistic background conditions. We project the sensitivity of 1 and $10{\mathrm{m}}^3$-scale detectors in the context of several physics cases, including: the measurement of the Standard Model $\mathrm{CE}\nu \mathrm{NS}$ cross section, reconstruction of the flavor-dependent neutrino fluxes, observing the neutrino-induced Migdal effect, constraints on beyond-Standard-Model neutrino interactions, and probing 10-eV-scale sterile neutrinos.

Quantum operations that are perfectly admissible in nonrelativistic quantum theory can enable signaling between spacelike separated regions when naively imported into quantum field theory (QFT). Prominent examples of such “impossible measurements” include certain unitary kicks and projective measurements. It is generally accepted that only those quantum operations whose physical implementation arises from a fully relativistically covariant interaction, between the quantum field and a suitable probe, should be regarded as admissible. While this idea has been realized at the level of abstract algebraic QFT, or via particular measurement models, there is still no general set of operational criteria characterizing which measurements are physically implementable. In this work we adopt the local $S$-matrix formalism to describe local operations, and make use of a hierarchy of factorization conditions that exclude both superluminal signaling and retrocausality, thereby providing such a criterion. Realizing the local $S$-matrices through explicit interactions between smeared field operators and a pointer degree of freedom, we further derive local causality conditions for the induced Kraus operators, which guarantee the absence of signaling in “impossible measurement” scenarios. Finally, we show that the accuracy with which local field observables can be measured is fundamentally limited by the retarded propagator of the field, which plays an essential role in the factorization identity we prove for the field Kraus operators.