The invisible axion is a hypothetical particle that arises from the Peccei-Quinn mechanism proposed to resolve the $CP$ problem in quantum chromodynamics, and is considered one of the most favored candidates for cold dark matter. Dish antennas can provide a useful scheme for sensitive searches for dark matter axions. The conversion power through axion-photon couplings is proportional to the surface area of the metal plate, rather than the volume of the available magnetic field. To maximize the effect, we propose an advanced concept of haloscope that involves an array of horn antennas to increase the axion-induced photons and a reflector to focus them onto a photo sensor. Compared with other proposed schemes, this configuration can significantly improve the experimental sensitivity, especially in the terahertz region.

The differential cross sections of elastic proton-proton $(pp)$ and proton-antiproton $(p\overline{p})$ scattering are studied in a holographic QCD model, considering the strong and Coulomb interaction in the Regge regime. Based on previous studies of strong interactions described in terms of Pomeron and Reggeon exchange, we add the contribution of Coulomb interaction described by photon exchange. We present the momentum transfer dependence of the contribution rates for each component, especially for the Coulomb-nuclear interference, which refers to the cross term between both interactions. For the adjustable parameters for the strong interaction, we can adopt the values determined in previous studies, and there are no extra adjustable parameters that need to be determined for the Coulomb interaction. It is presented that the resulting differential cross sections are consistent with the data for $pp$ and $p\overline{p}$ scattering.

To fully exploit the capabilities of next-generation gravitational wave detectors, we need to significantly improve the accuracy of our models of gravitational-wave-emitting systems. This paper focuses on one way of doing so: by taking black hole perturbation theory to second perturbative order. Such calculations are critical for the development of nonlinear ringdown models and of gravitational self-force models of extreme-mass-ratio inspirals. In the most astrophysically realistic case of a Kerr background, a second-order Teukolsky equation presents the most viable avenue for calculating second-order perturbations. Motivated by this, we analyze two second-order Teukolsky formalisms and advocate for the one that is well-behaved for gravitational self-force calculations and which meshes naturally with recent metric reconstruction methods due to Green, Hollands, and Zimmerman [CQG 37, 075001 (2020)] and others. Our main result is an expression for the nonlinear source term in the second-order field equation; we make this available, along with other useful tools, in an accompanying Mathematica notebook. Using our expression for the source, we also show that infrared divergences at second order can be evaded by adopting a Bondi-Sachs gauge.

Ultralight bosons are predicted in many extensions to the Standard Model and are popular dark matter candidates. The black hole superradiance mechanism allows for these particles to be probed using only their gravitational interaction. In this scenario, an ultralight boson cloud may form spontaneously around a spinning black hole and extract a non-negligible fraction of the black hole’s mass. These oscillating clouds produce quasi-monochromatic, long-duration gravitational waves that may be detectable by ground-based or space-based gravitational wave detectors. We discuss the capability of a new long-duration signal tracking method, based on a hidden Markov model, to detect gravitational wave signals generated by ultralight vector-boson clouds, including cases where the signal frequency evolution timescale is much shorter than that of a typical continuous wave signal. We quantify the detection horizon distances for vector-boson clouds with current- and next-generation ground-based detectors. We demonstrate that vector clouds hosted by black holes with mass $\gtrsim 60M_{\odot }$ and spin $\gtrsim 0.6$ are within the reach of current-generation detectors up to a luminosity distance of $\sim 1\mathrm{Gpc}$. This search method enables one to target vector-boson clouds around remnant black holes from compact binary mergers detected by gravitational-wave detectors. We discuss the impact of the sky localization of the merger events and demonstrate that a typical remnant black hole reasonably well-localized by the current generation detector network is accessible in a follow-up search.

Tensions between cosmological parameters (in particular the local expansion rate $H_0$ and the amplitude of matter clustering $S_8$) inferred from low-redshift data and data from the cosmic microwave background (CMB) and large-scale structure experiments have inspired many extensions to the standard cosmological model, $\mathrm{\Lambda }\mathrm{CDM}$. Models which simultaneously lessen both tensions are of particular interest. We consider one scenario with the potential for such a resolution, in which some fraction of the dark matter has converted into dark radiation since the release of the CMB. Such a scenario encompasses and generalizes the more standard “decaying dark matter” model, allowing additional flexibility in the rate and time at which the dark matter converts into dark radiation. In this paper, we constrain this scenario with a focus on exploring whether it can solve (or reduce) these tensions. We find that such a model is effectively ruled out by CMB data, in particular by the reduced peak-smearing due to CMB lensing on the power spectrum and the excess integrated Sachs-Wolfe signal caused by the additional dark energy density required to preserve flatness after dark matter conversion into dark radiation. Thus, such a model does not have the power to reduce these tensions without further modifications. This conclusion extends and generalizes related conclusions derived for the standard decaying dark matter model.

Solid states of strange-cluster matter called strangeon matter can form strangeon stars that are highly compact. We show that strangeon matter and strangeon stars can be recast into dimensionless forms by a simple reparametrization and rescaling, through which we manage to maximally reduce the number of degrees of freedom. With this dimensionless scheme, we find that strangeon stars are generally compact enough to feature a photon sphere that is essential to foster gravitational-wave (GW) echoes. Rescaling the dimension back, we illustrate its implications on the expanded dimensional parameter space, and calculate the characteristic GW echo frequencies associated with strangeon stars, showing that the minimum echo frequency is $\sim 8\mathrm{kHz}$ for empirical parameter space that satisfies the GW170817 constraint, and can reduce to $\mathcal{O}(100)$ Hertz at the extended limit.

Axion dark matter can be converted into photons in the magnetospheres of neutron stars leading to a spectral line centered on the Compton wavelength of the axion. Due to the rotation of the star and the plasma effects in the magnetosphere the signal is predicted to be periodic with significant time variation that persists across phase but is narrow in frequency—a unique smoking gun for axion dark matter. As a proof of principle and to develop the methodology, we carry out the first time domain search of the signal using data from PSR J2144-3933 taken as part of the MeerTIME project on MeerKAT telescope. We search for specific signal templates using a matched filter technique and discuss when a time-domain analysis (as is typically the case in pulsar observations) gives greater sensitivity to the axion coupling to photons in comparison to a simple time-averaged total flux study. We do not find any candidate signals and, hence, impose an upper limit on the axion-to-photon coupling of $g_{a\gamma \gamma }<5.5\times {10}^{-11}(D/0.165\mathrm{pc}){\mathrm{GeV}}^{-1}$ where $D$ is the pulsar distance, over the mass range $m_{\mathrm{a}}=3.9–4.7\mathrm{\mu }\mathrm{eV}$ using this data. This limit relies on PSR J2144-3933 not being an extremely aligned rotator, as strongly supported by simple arguments based on the observed pulse profile width. We discuss the possibilities of improving this limit using future observations with MeerKAT and also SKA1-mid and the possibility of using other objects. Finally, to evade modeling uncertainties in axion radio signals, we also carry out a generic “any periodic-signal search” in the data, finding no evidence for an axion signal.

Amorphous silicon (a-Si) is a promising material with a high refractive index that shows great potential in the development of low-thermal-noise, highly reflective coatings for gravitational-wave detectors due to its low mechanical loss. However, its high optical absorption has hindered its practical use. The primary objective of this paper is to investigate the effects of hydrogen incorporation into a-Si on its optical properties and mechanical loss with ion-beam sputtering (IBS) technology, which is widely used to produce coatings with low absorption and scattering loss. It is demonstrated that hydrogenation can effectively reduce the optical absorption of a-Si, with the concentration of hydrogen proving to be a crucial factor. Optimal annealing temperature can further enhance the coating quality, in which silicon atom rearrangement also contributes to the improvement. Overall, using the process combination can reduce the extinction coefficient of a-Si coatings by 16-fold at 1064 nm and 85-fold at 1550 nm, while simultaneously reducing mechanical loss by a factor of 12. The degree of mechanical loss reduction is closely related to the order present in the atomic structure of the silicon network. To our knowledge, this study represents the first comprehensive analysis of coating mechanical loss in hydrogenated a-Si deposited via IBS.

The locking of lasers to optical cavities is ubiquitously required in the field of precision interferometry such as Advanced LIGO to yield optimal sensitivity. Using higher-order Hermite-Gauss (HG) modes for the main interferometer beam has been a topic of recent study, due to their potential for reducing thermal noise of the test masses. It has been shown however that higher-order HG modes are more susceptible to coupling losses into optical cavities: for a generic ${\mathrm{HG}}_{n,n}$ mode, the misalignment and mode-mismatch-induced power losses scale as $2n+1$ and $n^2+n+1$ respectively with $n$ being the mode index. In this paper we calculate analytically for the first time the alignment and mode mismatch sensing signals for arbitrary higher-order HG modes with both the traditional sensing schemes (using Gouy phase telescopes and quadrant photodetectors) and the more recently proposed radio-frequency jitter-based sensing schemes (using only single-element photodiodes). We show that the sensing signals and also the signal-to-shot noise ratios for higher-order HG modes are larger than for the fundamental mode. In particular, for a generic ${\mathrm{HG}}_{n,n}$ mode, the alignment and mode mismatch sensing signals in the traditional sensing schemes scale approximately as $\sqrt{n}$ and $n$ respectively, whereas in the jitter-based sensing schemes they scale exactly as $2n+1$ and $n^2+n+1$, respectively, which exactly matches the decrease in their respective tolerances. This potentially mitigates the downside of higher-order HG modes for their suffering from excessive misalignment and mode-mismatch-induced power losses.

In hydrodynamics, for generic relaxations, the stress tensor and $U(1)$ charge current two-point functions are not time-reversal covariant. This remains true even if the Martin-Kadanoff procedure happens to yield Onsager reciprocal correlators. We consider linearized relativistic hydrodynamics on Minkowski space in the presence of energy, $U(1)$ charge, and momentum relaxation. We then show how one can find the minimal relaxed hydrodynamic framework that does yield two-point functions consistent with time-reversal covariance. We claim the same approach naturally applies to boost agnostic hydrodynamics and its limits (e.g., Carrollian, Galilean, and Lifshitz fluids).

The Dyson-Schwinger (DS) equations for a quantum field theory in $D$-dimensional space-time are an infinite sequence of coupled integro-differential equations that are satisfied exactly by the Green’s functions of the field theory. This sequence of equations is underdetermined because if the infinite sequence of DS equations is truncated to a finite sequence, there are always more Green’s functions than equations. An approach to this problem is to close the finite system by setting the highest Green’s function(s) to zero. One can examine the accuracy of this procedure in $D=0$ because in this special case the DS equations are just a sequence of coupled polynomial equations whose roots are the Green’s functions. For the closed system one can calculate the roots and compare them with the exact values of the Green’s functions. This procedure raises a general mathematical question: When do the roots of a sequence of polynomial approximants to a function converge to the exact roots of that function? Some roots of the polynomial approximants may (i) converge to the exact roots of the function, or (ii) approach the exact roots at first and then veer away, or (iii) converge to limiting values that are unequal to the exact roots. In this study five field-theory models in $D=0$ are examined, Hermitian ${\varphi }^4$ and ${\varphi }^6$ theories and non-Hermitian $i{\varphi }^3$, $-{\varphi }^4$, and $-i{\varphi }^5$ theories. In all cases the sequences of roots converge to limits that differ by a few percent from the exact answers. Sophisticated asymptotic techniques are devised that increase the accuracy to one part in ${10}^7$. Part of this work appears in abbreviated form in Phys. Rev. Lett. 130, 101602 (2023).

We study ${\overline{B}}_q\to {\mathbf{B}\overline{\mathbf{B}}}^{\prime }l\overline{\nu }$ and ${\overline{B}}_q\to {\mathbf{B}\overline{\mathbf{B}}}^{\prime }\nu \overline{\nu }$ decays with all low lying octet ($\mathcal{B}$) and decuplet ($\mathcal{D}$) baryons using a topological amplitude approach. In tree-induced ${\overline{B}}_q\to {\mathbf{B}\overline{\mathbf{B}}}^{\prime }l\overline{\nu }$ decay modes, we need two tree amplitudes and one annihilation amplitude in ${\overline{B}}_q\to \mathcal{B}{\overline{\mathcal{B}}}^{\prime }l\overline{\nu }$ decays, one tree amplitude in ${\overline{B}}_q\to \mathcal{B}\overline{\mathcal{D}}l\overline{\nu }$ decays, one tree amplitude in ${\overline{B}}_q\to \mathcal{D}\overline{\mathcal{B}}l\overline{\nu }$ decays and one tree amplitude and one annihilation amplitude in ${\overline{B}}_q\to \mathcal{D}{\overline{\mathcal{D}}}^{\prime }l\overline{\nu }$ decays. In loop induced ${\overline{B}}_q\to {\mathbf{B}\overline{\mathbf{B}}}^{\prime }\nu \overline{\nu }$ decay modes, similar numbers of penguin-box and penguin-box-annihilation amplitudes are needed. As the numbers of independent topological amplitudes are highly limited, there are plenty of relations on these semileptonic baryonic $B_q$ decay amplitudes. Furthermore, the loop topological amplitudes and tree topological amplitudes have simple relations, as their ratios are fixed by known Cabibbo-Kobayashi-Maskawa (CKM) factors and loop functions. It is observed that the $B^{-}\to p\overline{p}{\mu }^{-}\overline{\nu }$ differential rate exhibits threshold enhancement, which is expected to hold in all other semileptonic baryonic modes. The threshold enhancement effectively squeezes the phase space toward the threshold region and leads to very large SU(3) breaking effects in the decay rates. They are estimated using the measured $B^{-}\to p\overline{p}{\mu }^{-}\overline{\nu }$ differential rate and model calculations. From the model calculations, we find that branching ratios of nonannihilation ${\overline{B}}_q\to {\mathbf{B}\overline{\mathbf{B}}}^{\prime }l\overline{\nu }$ modes are of the orders of ${10}^{-9}–{10}^{-6}$, while branching ratios of nonpenguin-box-annihilation ${\overline{B}}_q\to {\mathbf{B}\overline{\mathbf{B}}}^{\prime }\nu \overline{\nu }$ modes are of the orders of ${10}^{-12}–{10}^{-8}$. Modes with relatively unsuppressed rates and good detectability are identified. These modes can be searched experimentally in near future and the rate estimations can be improved when more modes are discovered. Ratios of rates of some loop induced ${\overline{B}}_q\to {\mathbf{B}\overline{\mathbf{B}}}^{\prime }\nu \overline{\nu }$ decays and tree induced ${\overline{B}}_q\to {\mathbf{B}\overline{\mathbf{B}}}^{\prime }l\overline{\nu }$ decays are predicted and can be checked experimentally. They can be tests of the SM. Some implications on ${\overline{B}}_q\to \mathbf{B}{\overline{\mathbf{B}}}^{\prime }{l}^{+}{l}^{-}$ decays are also discussed.

We consider the possible production of a new MeV-scale fermion at the COHERENT experiment. The new fermion, belonging to a dark sector, can be produced through the up-scattering process of neutrinos off the nuclei and the electrons of the detector material, via the exchange of a light vector or scalar mediator. We perform a detailed statistical analysis of the combined COHERENT CsI and LAr datasets and obtain up-to-date constraints on the couplings and masses of the dark fermion and mediators. We finally briefly comment about the stability of the dark fermion.

Third-generation (3G) gravitational wave detectors, in particular Einstein Telescope (ET) and Cosmic Explorer (CE), will explore unprecedented cosmic volumes in search for compact binary mergers, providing us with tens of thousands of detections per year. In this study, we simulate and employ binary black holes detected by 3G interferometers as dark sirens, to extract and infer cosmological parameters by cross-matching gravitational wave data with electromagnetic information retrieved from a simulated galaxy catalog. Considering a standard $\mathrm{\Lambda }\mathrm{CDM}$ model, we apply a suitable Bayesian framework to obtain joint posterior distributions for the Hubble constant $H_0$ and the matter energy density parameter ${\mathrm{\Omega }}_m$ in different scenarios. Assuming a galaxy catalog complete up to $z=1$ and dark sirens detected with a network signal-to-noise ratio greater than 300, we show that a network made of ET and two CEs can constrain $H_0$ (${\mathrm{\Omega }}_m$) to a promising 0.8% (10.0%) at 90% confidence interval within one year of continuous observations. Additionally, we find that most of the information on $H_0$ is contained in local, single-host dark sirens, and that dark sirens at $z>1$ do not substantially improve these estimates. Our results imply that a subpercent measure of $H_0$ can confidently be attained by a network of 3G detectors, highlighting the need for characterizing all systematic effects to a higher accuracy.

Machine learning has become an effective tool for processing the extensive datasets produced by large physics experiments. Gravitational-wave detectors are now listening to the universe with quantum-enhanced sensitivity, accomplished with the injection of squeezed vacuum states. Squeezed state preparation and injection is operationally complicated, as well as highly sensitive to environmental fluctuations and variations in the interferometer state. Achieving and maintaining optimal squeezing levels is a challenging problem and will require development of new techniques to reach the lofty targets set by design goals for future observing runs and next-generation detectors. We use machine learning techniques to predict the squeezing level during the third observing run of the Laser Interferometer Gravitational-Wave Observatory (LIGO) based on auxiliary data streams, and offer interpretations of our models to identify and quantify salient sources of squeezing degradation. The development of these techniques lays the groundwork for future efforts to optimize squeezed state injection in gravitational-wave detectors, with the goal of enabling closed-loop control of the squeezer subsystem by an agent based on machine learning.

We initiate the study of Dyson equations of perturbative quantum field theory in anti–de Sitter (AdS) and their consequences for large-$N$ conformal field theory (CFT). We show that the dressed one-particle AdS propagator features wave function renormalization and operator mixing, giving rise to finite corrections to one-pion exchange data. We show how the resummation of $1/N$ effects in the CFT emerges from the dressing in AdS. When a boundary-to-bulk propagator is dressed by propagators whose sum of conformal dimensions is lower than the main dimension, it cannot map onto a CFT source; we relate this to an $\mathrm{AdS}/\mathrm{CFT}$ version of particle instability. We investigate the dressing of the two-particle propagator and obtain a conformal Bethe-Salpeter equation for the conformal partial wave of a “bound state” operator. We provide a self-contained calculation for the case of a ladder kernel. We show that a bound state with conformal dimension equal to the sum of its constituents plus a $1/N^2$-suppressed “binding energy” emerges. Resummation of the Dyson equations is essential for deriving these results.

Field-theoretic descriptions of Carrollian theories have largely remained classical so far. In this paper, we attempt to study the renormalization of Carrollian gauge field theories via path integral techniques. The case of Carrollian electrodynamics minimally coupled to a massive Carrollian scalar is considered. We report potential problems such as IR divergences and mass-shell singularity cropping up at the first order in the perturbation. Perhaps, the most important result that we report is how conventional arguments for gauge independence for mass and coupling are invalidated for a gauge theory in a Carrollian setting. As of now, the renormalization of Carrollian gauge field theories seems to suffer from unphysical ramifications. Possible cures to resolve these issues are suggested.

We propose that models with spacetime subsystem symmetry are connected to Lorentz invariant models via the Carrollian limit. In this way, a recently proposed model with spacetime subsystem symmetry was readily reproduced together with its conserved charges. We then couple this model to a dynamical Abelian gauge field and Carroll gravity. Our procedure can be applied in arbitrary dimensions and paves the way to construct new models with spacetime subsystem symmetry.

We generalize the idea of the quantized Hall current to count gapless edge states in topological materials, applying equally well to theories in different dimensions, with or without continuous symmetries in the bulk or chiral anomalies on the boundaries. This current is related to the index of the Euclidean fermion operator and can be calculated via one-loop Feynman diagrams. Quantization of the current is shown to be governed by topology in phase space, and the procedure can be applied to topological classes governed by either $\mathbb{Z}$ or ${\mathbb{Z}}_2$ invariants. We analyze several explicit examples of free fermions in relativistic field theories. We speculate that it may be possible to extend the technique to interacting theories as well, such as the interesting cases where interactions gap the edge states.

We study the process of gravitational collapse in pure Gauss-Bonnet gravity. In the homogeneous dust collapse, we show that the $D=7$ pure Gauss-Bonnet theory has gravitational dynamics indistinguishable from Einstein’s theory in $D=4$, meaning that collapsing particles feel the same potential as in the classical four-dimensional general relativistic case. In $D<7$ pure Gauss-Bonnet gravity becomes weaker, while in $D>7$ it becomes stronger, with respect to general relativity. In the inhomogeneous dust collapse we find the mass modes in the expansion of the energy density in any dimensions that lead to either naked singularities or black holes as final states of collapse.