Recent measurements from the CMB and from high-redshift galaxy observations have placed rough constraints on the midpoint and duration of the epoch of reionization. Detailed measurements of the ionization history remain elusive, although two proposed probes show great promise for this purpose: the 21 cm global signal and the kinetic Sunyaev-Zel’dovich (kSZ) effect. We formally confirm the common assumption that these two probes are highly complementary, with the kSZ being more sensitive to extended ionization histories and the global signal to rapidly evolving ones. We do so by performing a Karhunen-Loève (KL) transformation, which casts the data in a basis designed to emphasize the information content of each probe. We find that reconstructing the ionization history using both probes gives significantly more precise results than individual constraints, although carefully chosen, physically motivated priors play a crucial part in obtaining a bias-free reconstruction. Additionally, in the KL basis, measurements from one probe can be used to detect the presence of residual systematics in the other, providing a safeguard against systematics that would go undetected when data from each probe is analyzed in isolation. Once detected, the modes contaminated by systematics can be discarded from the data analysis to avoid biases in reconstruction.

We improve the calculations of the elastic motion induced by dark matter hitting the surface of the mirror inside an interferometer used for gravitational-wave detection. We focus on the discovery potential of such a dark matter signal in the third-generation European gravitational-wave detector, the Einstein Telescope. By taking the thickness of the mirror into account, more than one resonance is predicted in the sensitive regime of the high-frequency interferometer. When the mass of dark matter is heavier than a few PeV or is highly boosted, the signal-to-noise ratio could exceed one, and the Einstein Telescope should be able to detect this dark matter signal.

We examine how subleading results in the operator and loop expansion for $\sigma (\mathcal{G}\mathcal{G}\to h)$ in the Standard Model effective field theory (SMEFT) inform theoretical error estimates when studying this production channel in global SMEFT studies. We also discuss the relationship between geometric SMEFT results and the $\kappa$ formalism.

Stimulated decays of axion dark matter, triggered by a source in the sky, could produce a photon flux along the continuation of the line of sight, pointing backward to the source. The strength of this so-called axion “echo” signal depends on the entire history of the source and could still be strong from sources that are dim today but had a large flux density in the past, such as supernova remnants (SNRs). This echo signal turns out to be most observable in the radio band. We study the sensitivity of radio telescopes such as the Square Kilometer Array (SKA) to echo signals generated by SNRs that have already been observed, and show that SKA could reach axion-photon couplings of order $g_{a\gamma \gamma }\sim \mathcal{O}({10}^{-11}){\mathrm{GeV}}^{-1}$ for axion masses $m_a\lesssim {10}^{-5}\mathrm{eV}$. In addition, we show projections of the detection reach for signals coming from old SNRs and from newly born supernovae that could be detected in the future. Intriguingly, an observable echo signal could come from old “ghost” SNRs which were very bright in the past but are now so dim that they have not been observed.

We propose an extension of the Standard Model (SM) with a $U_{A^{\prime }}(1)$ gauge-invariant dark sector connected to the SM via a new portal—the Stueckelberg portal, arising in the framework of dark photon $A^{\prime }$ mass generation via the Stueckelberg mechanism. This portal opens through the effective $\dim =5$ operators constructed from the covariant term of the auxiliary Stueckelberg scalar field $\sigma$ providing flavor nondiagonal renormalizable couplings of both $\sigma$ and $A^{\prime }$ to the SM fermions $\psi$. The Stueckelberg scalar plays a role of Goldstone boson in the generation of mass of the dark photon. Contrary to the conventional kinetic mixing portal, in our scenario, flavor diagonal $A^{\prime }-\psi$ couplings are not proportional to the fermion charges and are, in general, flavor nondiagonal. These features drastically change the phenomenology of dark photon $A^{\prime }$ relaxing or avoiding some previously established experimental constraints. We focus on the phenomenology of the described scenario of the Stueckelberg portal in the lepton sector and analyze the contribution of the dark sector fields $A^{\prime }$ to the anomalous magnetic moment of muon $(g-2{)}_{\mu }$, lepton flavor–violating decays $l_i\to l_k\gamma$, and $\mu -e$ conversion in nuclei. We obtain limits on the model parameters from the existing data on the corresponding observables.

Axions and other pseudoscalar fields comprise an interesting class of ultralight dark matter candidates, that may independently play a role in solving the strong $CP$ problem. In the presence of $CP$-violating sources, these pseudoscalar fields can develop a coherent nonderivative coupling to nucleons, ${\overline{g}}_{aNN}$, thus mediating ‘mass-mass’ and ‘mass-spin’ forces in matter that can be probed experimentally. We revisit the nonperturbative generation of these $CP$-odd axion forces, and refine estimates of ${\overline{g}}_{aNN}$ generated by the electric dipole moments and color electric dipole moments of quarks. We also revisit the Standard Model contribution to $CP$-odd axion couplings generated by the phase of the Cabibbo-Kobayashi-Maskawa quark mixing matrix.

A class of fermionic quantum field theories with interactions is shown to be equivalent to probabilistic cellular automata, namely cellular automata with a probability distribution for the initial states. Probabilistic cellular automata on a one-dimensional lattice are equivalent to two-dimensional quantum field theories for fermions. They can be viewed as generalized Ising models on a square lattice and therefore as classical statistical systems. As quantum field theories they are quantum systems. Thus quantum mechanics emerges from classical statistics. As an explicit example for an interacting fermionic quantum field theory we describe a type of discretized Thirring model as a cellular automaton. The updating rule of the automaton is encoded in the step evolution operator that can be expressed in terms of fermionic annihilation and creation operators. The complex structure of quantum mechanics is associated to particle-hole transformations. The naive continuum limit exhibits Lorentz symmetry. We exploit the equivalence to quantum field theory in order to show how quantum concepts as wave functions, density matrix, noncommuting operators for observables and similarity transformations are convenient and useful concepts for the description of probabilistic cellular automata.

Proton decay is a major prediction of grand-unified theories (GUT) and its observation would indicate baryon number violation that is required for baryogenesis. Many decades of searching for proton decay have constrained its rate and ruled out some of the simplest GUT models. Apart from the baryon number-violating interactions, this rate also depends on transition amplitudes between the protons and mesons or leptons produced in the decay, which are matrix elements of three-quark operators. We report the nonperturbative calculation of these matrix elements for the most studied two-body decay channels into a meson and antilepton done on a lattice with physical light and strange quark masses and lattice spacings $a\approx 0.14\mathrm{fm}$ and 0.20 fm. We perform nonperturbative renormalization and excited state analysis to control associated systematic effects. Our results largely agree with previous lattice calculations done with heavier quark masses and thus remove ambiguity in ruling out some simple GUT theories due to quark mass dependence of hadron structure.

In this paper we consider inhomogeneous solutions of two-dimensional linear sigma model in the large $N$ limit. These solutions are similar to the ones found recently in the two-dimensional $C{P}^N$ sigma model. The solution exists only for some range of coupling constant. We calculate the energy of the solutions as a function of the model parameters and show that it is negative. We analyze the zero modes of the soliton and argue that they can be interpreted as rotational excitations. The case of the nonlinear model at finite temperature is also discussed. The free energy of the inhomogeneous solution is shown to change sign at some critical temperature indicating possible phase transition.

In our previous work [Phys. Rev. D 103, 064044 (2021)] we calculated the overlap reduction function for the tensor polarization without employing the short wavelength approximation, this was done by obtaining a power series of nested sums which is valid for all gravitational wave frequencies and pulsar distances. In this work we generalize the power-series expansion method to vector and scalar polarizations. We have compared our expression for the breathing and vector modes with previous literature. We present for the first time analytic expressions for the overlap reduction function of the longitudinal mode for all angles between the pulsar pairs.

Which is the best metric for the space of collider events? Motivated by the success of the energy mover’s distance in characterizing collider events, we explore the larger space of unbalanced optimal transport distances, of which the energy mover’s distance is a particular case. Geometric and computational considerations favor an unbalanced optimal transport distance known as the Hellinger-Kantorovich distance, which possesses a Riemannian structure that lends itself to efficient linearization. We develop the particle linearized unbalanced optimal transport framework for collider events based on the linearized Hellinger-Kantorovich distance and demonstrate its efficacy in boosted jet tagging. This provides a flexible and computationally efficient optimal transport framework ideally suited for collider physics applications.

Flavor violating axion couplings can be in action before recombination, and they can fill the early Universe with an additional radiation component. Working within a model-independent framework, we consider an effective field theory for the axion field and quantify axion production. Current cosmological data exclude already a fraction of the available parameter space, and the bounds will improve significantly with future CMB-S4 surveys. Remarkably, we find that future cosmological bounds will be comparable or even stronger than the ones obtained in our terrestrial laboratories.

We show that the final-state interaction explains the nontrivial near-threshold energy dependence of the cross section of the process $e^{+}{e}^{-}\to {\mathrm{\Lambda }}_c{\overline{\mathrm{\Lambda }}}_c$ observed by the Belle and BESIII collaborations. This energy dependence is the result of the mixture of $S$-wave and $D$-wave components of the ${\mathrm{\Lambda }}_c{\overline{\mathrm{\Lambda }}}_c$ wave function due to a tensor interaction. The Coulomb potential is important only in the narrow energy region about a few MeV above the threshold of the process. It is shown that the widely used assumption that the impact of the Coulomb interaction on the cross sections of hadron production is reduced to the Sommerfeld-Gamow-Sakharov factor is not correct.

Quantum evolution of a scalar field’s modes propagating on quantum spacetime of a collapsing homogeneous dust ball is written effectively as an evolution of the same quantum modes on a (semiclassical) dressed geometry. When the backreaction of the field is discarded, the classical spacetime singularity is resolved due to quantum gravity effects and is replaced by a quantum bounce on the dressed collapse background. In the presence of backreaction, the emergent (interior) dressed geometry becomes mode dependent, and the energy density associated with the backreaction of each mode scales as a radiation fluid. Semiclassical dynamics of this so-called rainbow dressed background is analyzed. It turns out that the backreaction effects speed up the occurrence of the bounce in comparison to the case where only a dust fluid is present. By matching the interior and exterior regions at the boundary of dust, a mode-dependent black hole geometry emerges as the exterior spacetime. Properties of such a rainbow black hole are discussed. That mode dependence causes, in particular, a chromatic aberration in the gravitational lensing process of which maximal magnitude is estimated via calculation of the so-called Einstein angle.

We study the structure of scattering amplitudes of the Kaluza-Klein (KK) gravitons and of the gravitational KK Goldstone bosons in the compactified 5d general relativity (GR). We analyze the geometric “Higgs” mechanism for mass generation of KK gravitons under compactification with a general $R_{\xi }$ gauge-fixing and prove that the massive KK graviton propagator is free from the van Dam-Veltman and Zakharov discontinuity. With these, we newly formulate a gravitational equivalence theorem (GRET) to connect the longitudinal KK graviton amplitudes to the corresponding KK Goldstone amplitudes, which is a manifestation of the geometric Higgs mechanism at $S$-matrix level. We directly compute the gravitational KK Goldstone amplitudes at tree level and show that they equal the corresponding longitudinal KK graviton amplitudes in the high-energy limit. We further use the double-copy method with color-kinematics duality to reconstruct the KK longitudinal graviton (Goldstone) amplitudes from the KK longitudinal gauge boson (Goldstone) amplitudes in the compactified 5d Yang-Mills (YM) gauge theory, under the high-energy expansion. From these, we reconstruct the GRET of the KK longitudinal graviton (Goldstone) amplitudes in the 5d GR theory from the KK longitudinal gauge boson (Goldstone) amplitudes in the 5d YM theory. Using either the GRET or the double-copy reconstruction, we provide a theoretical mechanism showing that the sum of all the energy power terms up to $\mathcal{O}(E^{10})$ in the high-energy scattering amplitudes of four longitudinal KK gravitons must cancel down to $\mathcal{O}(E^2)$ as enforced by matching the energy dependence of the corresponding KK Goldstone amplitudes or by matching that of the double-copy amplitudes from the KK YM theory. With the double-copy approach, we establish a new correspondence between the two energy-cancellations in the four-particle longitudinal KK scattering amplitudes: $E^4\to E^0$ in the 5d KK YM theory and $E^{10}\to E^2$ in the 5d KK GR theory. We further analyze the structure of the residual term in the GRET and uncover a new energy-cancellation mechanism therein.

We analyze the emergence of classical inflationary universes in a kinetic-dominated stage using a suitable class of solutions of the Wheeler-DeWitt equation with a constant potential. These solutions are eigenfunctions of the inflaton momentum operator that are strongly peaked on classical solutions exhibiting either or both a kinetic-dominated period and an inflation period. Our analysis is based on semiclassical WKB solutions of the Wheeler-DeWitt equation interpreted in the sense of Borel (to perform a correct connection between classically allowed regions) and on the relationship of these solutions to the solutions of the classical model. For large values of the scale factor the WKB Vilenkin tunneling wave function and the Hartle-Hawking no-boundary wave functions are recovered as particular instances of our class of wave functions.

We argue that if the Newtonian gravitational field of a body can mediate entanglement with another body, then it should also be possible for the body producing the Newtonian field to entangle directly with on-shell gravitons. Our arguments are made by revisiting a gedankenexperiment previously analyzed by Belenchia et al., which showed that a quantum superposition of a massive body requires both quantized gravitational radiation and local vacuum fluctuations of the spacetime metric in order to avoid contradictions with complementarity and causality. We provide a precise and rigorous description of the entanglement and decoherence effects occurring in this gedankenexperiment, thereby significantly improving upon the back-of-the-envelope estimates given by Belenchia et al. and also showing that their conclusions are valid in much more general circumstances. As a by-product of our analysis, we show that under the protocols of the gedankenexperiment, there is no clear distinction between entanglement mediated by the Newtonian gravitational field of a body and entanglement mediated by on-shell gravitons emitted by the body. This suggests that Newtonian entanglement implies the existence of graviton entanglement and supports the view that the experimental discovery of Newtonian entanglement may be viewed as implying the existence of the graviton.

Rotating axisymmetric objects amplify incoming waves by superradiant scattering. When enclosed in a cavity, the repeated interaction of a confined field with the object may trigger superradiant instabilities. Rotating binaries are ubiquitous in physics, and play a fundamental role in astrophysics and in everyday life instruments. Such binaries may be prone to superradiant phenomena as well, but their inherent complexity makes it challenging to study how exactly such instabilities can be triggered. Here, we study a binary of two absorbing objects (mimicking black hole binaries, blades of a helicopter, etc.) revolving around a common center, and show that superradiant instabilities do occur, on expected timescales and frequency range. Our results provide the first demonstration that superradiance also occurs for highly asymmetric systems, and may have a wealth of applications in fluid dynamics and astrophysics. Extrapolating to astrophysical black holes, our findings indicate that compact binaries may be used as interesting particle detectors, depositing a fraction of their energy into putative new fundamental ultralight degrees of freedom.

Quasinormal modes of scalar, electromagnetic, and gravitational fields in the extreme Schwarzschild–de Sitter background are known to be expressed in analytic form as eigenvalues of the Pöschl-Teller wavelike equation. We show that perturbations of fermionic fields (given by Dirac and Rarita-Schwinger equations) do not lead to the Pöschl-Teller effective potential. Nevertheless, using the Frobenius method we find quasinormal modes analytically in this case as well. We write down the analytical formula for quasinormal frequencies of the near-extreme Schwarzschild–de Sitter black holes, which is valid for both bosonic and fermionic fields. We further extend the analysis to the case of charged rotating black holes and find a general analytical formula for quasinormal modes of the fields of various spin for the near extreme Kerr-Newman–de Sitter spacetime.

The proposed third-generation gravitational-wave detectors Einstein Telescope will have a triangular design that consists of three colocated interferometers. Summing the strain outputs from the three interferometers will cancel any gravitational-wave signal and the resultant signal-free stream is known as null stream. The null stream is in a fixed subspace of the observation space of Einstein telescope where no gravitational-wave signal can exist. In this paper, we establish the decomposition of the observation space of Einstein Telescope into the signal space that contains all possible gravitational-wave signals and the null space that contains the null stream. We show that the results of Bayesian parameter estimation and model selection using the strain data in the signal space are identical to that using the full set of strain data. This implies that one could use a fraction of the strain data to extract all information of the source, which reduces the memory usage and speeds up the likelihood evaluation. We also discuss the existence of a fixed null space in Einstein Telescope allows the unbiased estimation of the noise properties in the signal-free subspace.