We consider a low redshift ($z<0.7$) cosmological data set comprising megamasers, cosmic chronometers, type Ia supernovae and baryon acoustic oscillations, which we bin according to their redshift. For each bin, we read the value of $H_0$ by fitting directly to the flat $\mathrm{\Lambda }\mathrm{CDM}$ model. Doing so, we find that $H_0$ descends with redshift, allowing one to fit a line with a nonzero slope of statistical significance $2.1\sigma$. Our analysis rests on the use of cosmic chronometers to break a degeneracy in baryon acoustic oscillations data and it will be imperative to revisit this feature as data improves. Nevertheless, our results provide the first independent indication of the descending trend reported by the H0LiCOW Collaboration. If substantiated going forward, early Universe solutions to the Hubble tension will struggle explaining this trend.

Extreme mass ratio inspirals (EMRIs), i.e., binary systems comprised by a compact stellar-mass object orbiting a massive black hole, are expected to be among the primary gravitational wave (GW) sources for the forthcoming LISA mission. The astrophysical processes leading to the formation of such systems still remain poorly understood, resulting into large uncertainties in the predicted cosmic rate of these sources, spanning at least three orders of magnitude. As LISA can individually resolve mostly EMRIs up to $z\gtrsim 1$, the ensemble of signals below its detection threshold will add up incoherently forming an unresolved confusion noise, which can be formally described as a stochastic background. We perform an extensive study of this background by considering a collection of astrophysically motivated EMRI formation scenarios, spanning current uncertainties. We find that, for most astrophysical models, this signal is easily detectable by LISA, with signal to noise ratios of several hundreds. In fiducial EMRI models—predicting hundreds of EMRI detections during mission operations—the background level is comparable to the LISA noise, affecting the performance of the instrument around 3 mHz. In extreme cases, this background can even “erase” the whole LISA sensitivity bucket in the 2–10 mHz frequency range. This points to the need of a better understanding of EMRIs’ astrophysics for a full assessment of the LISA mission potential.

Vacuum and thermal properties of pseudoscalar and vector charm mesons are analyzed within a self-consistent many-body approach, employing a chiral effective field theory that incorporates heavy-quark spin symmetry. Upon unitarization of the vacuum interaction amplitudes for the scattering of charm mesons off light mesons in a fully coupled-channel basis, new dynamically generated states are searched. The imaginary-time formalism is employed to extend the calculation to finite temperatures up to $T=150\mathrm{MeV}$. Medium-modified spectral shapes of the $D$, $D^{*}$, $D_s$, and $D_s^{*}$ mesons are provided. The temperature dependence of the masses and decay widths of the nonstrange $D_0^{*}(2300)$ and $D_1^{*}(2430)$ mesons, both showing a double-pole structure in the complex-energy plane, is also reported, as well as that of the $D_{s0}^{*}(2317)$ and $D_{s1}^{*}(2460)$ resonances and other states not yet identified experimentally. Being the first calculation incorporating open-charm vector mesons at finite temperature in a self-consistent fashion, it brings up the opportunity to discuss the medium effects on the open-charm sector under the perspective of chiral and heavy-quark spin symmetries.

We present a calculation of Higgsino and gaugino pair production at the LHC at next-to-next-to-leading logarithmic (NNLL) accuracy, matched to approximate next-to-next-to-leading order (aNNLO) QCD corrections. We briefly review the formalism for the resummation of large threshold logarithms and highlight the analytical results required at $\mathrm{aNNLO}+\mathrm{NNLO}$ accuracy. Our numerical results are found to depend on the mass and nature of the produced charginos and neutralinos. The differential and total cross sections for light Higgsinos, which like sleptons are produced mostly at small $x$ and in the $s$-channel, are found to be again moderately increased with respect to our previous results. The differential and total cross sections for gauginos are, however, not increased any more due to the fact that gauginos, like squarks, are now constrained by ATLAS and CMS to be heavier than about 1 TeV, so that also $t$- and $u$-channels play an important role. The valence quarks probed at large $x$ then also induce substantially different cross sections for positively and negatively charged gauginos. The Higgsino and gaugino cross sections are both further stabilized at $\mathrm{aNNLO}+\mathrm{NNLL}$ with respect to the variation of renormalization and factorization scales. We also now take mixing in the squark sector into account and study the dependence of the total cross sections on the squark and gluino masses as well as the trilinear coupling controlling the mixing in particular in the sbottom sector.

Quantum computers have the potential to explore the vast Hilbert space of entangled states that play an important role in the behavior of strongly interacting matter. This opportunity has motivated reconsidering the Hamiltonian formulation of gauge theories, with a suitable truncation scheme to render the Hilbert space finite-dimensional. Conventional formulations lead to a Hilbert space largely spanned by unphysical states; given the current inability to perform large scale quantum computations, we examine here how one might restrict wave function evolution entirely or mostly to the physical subspace. We consider such constructions for the simplest of these theories containing dynamical gauge bosons—U(1) lattice gauge theory without matter in $d=2$, 3 spatial dimensions—and find that electric-magnetic duality naturally plays an important role. We conclude that this approach is likely to significantly reduce computational overhead in $d=2$ by a reduction of variables and by allowing one to regulate magnetic fluctuations instead of electric. The former advantage does not exist in $d=3$, but the latter might be important for asymptotically-free gauge theories.

Hadron masses are subject to few MeV corrections arising from QED interactions, almost entirely arising from the electric charge of the valence quarks. The QED effects include both self-energy contributions and interactions between the valence quarks/antiquarks. By combining results from different signs of the valence quark electric charge we are able to isolate the interaction term which is dominated by the Coulomb piece, $⟨{\alpha }_{\mathrm{QED}}{e}_{q_1}{e}_{{\overline{q}}_2}/r⟩$, in the nonrelativistic limit. We study this for $D_s$, ${\eta }_c$ and $J/\psi$ mesons, working in lattice QCD plus quenched QED. We use gluon field configurations that include up, down, strange and charm quarks in the sea at multiple values of the lattice spacing. Our results, including also values for mesons with quarks heavier than charm, can be used to improve phenomenological models for the QED contributions. The QED interaction term carries information about meson structure; we derive effective sizes $⟨1/r_{\mathrm{eff}}{⟩}^{-1}$ for ${\eta }_c$, $J/\psi$ and $D_s$ of 0.206(8) fm, 0.321(14) fm and 0.307(31) fm respectively.

We study the lepton-jet correlation in deep inelastic scattering. We perform one-loop calculations for the spin averaged and transverse spin-dependent differential cross sections depending on the total transverse momentum of the final state lepton and the jet. The transverse momentum dependent factorization formalism is applied to describe the relevant observables. To show the physics reach of this process, we perform a phenomenological study for HERA kinematics and comment on an ongoing analysis of experimental data. In addition, we highlight the potential of this process to constrain small-$x$ dynamics.

We report on new measurements of inclusive $J/\psi$ polarization at midrapidity in $p+p$ collisions at $\sqrt{s}=200\mathrm{GeV}$ by the STAR experiment at the Relativistic Heavy Ion Collider. The polarization parameters, ${\lambda }_{\theta }$, ${\lambda }_{\varphi }$, and ${\lambda }_{\theta \varphi }$, are measured as a function of transverse momentum ($p_{\mathrm{T}}$) in both the helicity and Collins-Soper (CS) reference frames within $p_{\mathrm{T}}<10\mathrm{GeV}/c$. Except for ${\lambda }_{\theta }$ in the CS frame at the highest measured $p_{\mathrm{T}}$, all three polarization parameters are consistent with 0 in both reference frames without any strong $p_{\mathrm{T}}$ dependence. Several model calculations are compared with data, and the one using the Color Glass Condensate effective field theory coupled with nonrelativistic QCD gives the best overall description of the experimental results, even though other models cannot be ruled out due to experimental uncertainties.

We show that the ${\mathrm{AdS}}_5\times L^{a,b,c}$ solution in type IIB theory is nonintegrable. To do so, we consider a string embedding and study its fluctuations which do not admit Liouville integrable solutions. We, also, perform a numerical analysis to study the time evolution of the string and compute the largest Lyapunov exponent. This analysis indicates that the string motion is chaotic. Finally, we consider the pointlike limit of the string that corresponds to Bogomol’nyi-Prasad-Sommerfied mesons of the quiver theory.

In this work, we use a specific parametrization of the hypergeometric approximants [the one by Mera et al. in Phys. Rev. Let. 115, 143001 (2015)] to approximate the seven-loop critical exponent $\nu$ for the $O(2)$-symmetric ${\varphi }^4$ model. Our prediction gives the result $\nu =0.6711(7)$ which is compatible with the value $\nu =0.6709(1)$ from the famous experiment carried on the space shuttle Columbia. On the other hand, our result is also compatible with recent precise theoretical predictions that are excluding the experimental result. These theoretical results include nonperturbative renormalization group calculations [$\nu =0.6716(6)$], the most precise result from Monte Carlo simulations [$\nu =0.67169(7)$] as well as the recent conformal bootstrap calculations [$\nu =0.67175(10)$]. Although our result is compatible with experiment, the plot of the renormalization group result versus the number of loops suggests that higher orders are expected to add significantly to the accuracy and precision of the $\nu$ exponent in a way that may favor the theoretical predictions.

The analysis of the validity of Birkhoff’s theorem about the uniqueness of the spherically symmetric solution of the gravitational field equations is extended to the framework of the Poincaré gauge gravity theory. The class of models with the most general Lagrangians of the Yang-Mills type constructed from all possible quadratic invariants of the curvature and the torsion is considered, including both parity-even and parity-odd sectors. We find the families of models in which the weak and strong versions of the generalized Birkhoff theorem are valid, by making use of the double duality technique.

We study self-gravitating stars in the bootstrapped Newtonian picture for polytropic equations of state. We consider stars that span a wide range of compactness values. Both matter density and pressure are sources of the gravitational potential. Numerical solutions show that the density profiles can be well approximated by Gaussian functions. Later we assume Gaussian density profiles to investigate the interplay between the compactness of the source, the width of the Gaussian density profile and the polytropic index. We also dedicate a section to comparing the pressure and density profiles of the bootstrapped Newtonian stars to the corresponding general relativistic solutions. We also point out that no Buchdahl limit is found, which means that the pressure can in principle support a star of arbitrarily large compactness. In fact, we find solutions representing polytropic stars with compactness above the Buchdhal limit.

We introduce the use of autoregressive normalizing flows for rapid likelihood-free inference of binary black hole system parameters from gravitational-wave data with deep neural networks. A normalizing flow is an invertible mapping on a sample space that can be used to induce a transformation from a simple probability distribution to a more complex one: if the simple distribution can be rapidly sampled and its density evaluated, then so can the complex distribution. Our first application to gravitational waves uses an autoregressive flow, conditioned on detector strain data, to map a multivariate standard normal distribution into the posterior distribution over system parameters. We train the model on artificial strain data using a model for the gravitational-wave signal that includes inspiral, merger and ringdown and draw waveforms from a five-parameter $(m_1,m_2,{\varphi }_0,t_c,d_L)$ prior and stationary Gaussian noise realizations with a fixed power spectral density. This gives performance comparable to current best deep-learning approaches to gravitational-wave parameter estimation. We then build a more powerful latent variable model by incorporating autoregressive flows within the variational autoencoder framework. This model has performance comparable to Markov chain Monte Carlo and, in particular, successfully models the multimodal ${\varphi }_0$ posterior. Finally, we train the autoregressive latent variable model on an expanded parameter space, including also aligned spins $({\chi }_{1z},{\chi }_{2z})$ and binary inclination ${\theta }_{JN}$, and show that all parameters and degeneracies and most uncertainties are well-recovered. In all cases, sampling is extremely fast, requiring less than two seconds to draw ${10}^4$ posterior samples.

We present a novel derivation of Einstein equations from the balance between Clausius entropy crossing the boundary of a local causal diamond and entanglement entropy associated with its horizon. Comparing this derivation with the entanglement equilibrium approach developed by Jacobson, we are able to argue for the equivalence of matter entanglement and Clausius entropy in the semiclassical regime. We also provide a direct comparison of both entropies for conformal matter, showing their equivalence without appealing to gravitational dynamics. Furthermore, we determine that gravitational dynamics implied by thermodynamics of spacetime, in fact, corresponds to unimodular gravity rather than general relativity.

We study the spectrum of quasinormal mode frequencies for a Proca field on a rotating black hole spacetime. First, we review how the introduction of field mass modifies the spectrum in the scalar-field case, leading to evanescent modes and to quasiresonance. Next, we examine the three physical polarizations of the Proca field and their relation to the electromagnetic field modes in the massless limit. Exploiting a separation of variables, we obtain a five-term recurrence relation from an appropriate ansatz for the radial function. Gaussian elimination and the modified Lentz algorithm are applied, and the quasinormal frequencies are computed from the roots of a continued fraction. We validate our method by calculating quasibound state frequencies, which are complementary to quasinormal modes, and which can be calculated using the same method. We present a selection of results for the low-lying overtones of all three polarizations, across a range of black hole spins and field masses.

We derive an electrically charged static black hole spacetime of the Einstein-Euler-Heisenberg theory, in terms of the Plebański dual variables. This solution is a nonlinear electromagnetic generalization of the Reissner-Nordström solution, and it is characterized by the mass $M$, the electric charge $Q$ of the black hole, and the Euler-Heisenberg nonlinear constant, which includes the fine structure constant $\alpha$. We study all possible equatorial trajectories of test particles. Moreover, the orbits of photons are analyzed by means of the effective Plebański pseudometric related to the geometrical metric and to the electromagnetic energy-momentum tensor. The shape of the shadow of the black hole is also presented and discussed.

We investigate the radiative stability of Horndeski scalar-tensor theories with luminally propagating gravitational waves (as extensively discussed in the wake of GW170817) and show that in general there is a tension between obtaining observable deviations from general relativity (GR) in cosmology and the requirement of radiative stability. Using this as a constraint, we discuss the subsets of theories that are capable of evading this conclusion and yielding observable, radiatively stable departures from GR. We find several classes of theories that can do so, recovering known cases and identifying several additional radiatively stable cases. Finally we also extract the cosmological signatures of two particularly well-motivated radiatively stable classes of theories: shift-symmetric theories and theories with a conformal coupling between the scalar and gravity. We find that cosmological parameter constraints on dark energy and modified gravity parameters for both of these two classes, which we explicitly compute using data from the Planck, SDSS/BOSS and 6dF surveys, are significantly tightened with respect to generic Horndeski theories.

We introduce a cosmological model in the framework of generalized massive gravity. This theory is an extension of nonlinear massive gravity with a broken translation symmetry in the Stückelberg space. In a recent work, we showed the existence of cosmological solutions stable against linear perturbations. In the present paper, we build up on the previous result and study the evolution of the background solutions and the linear perturbations. At the background level, we find that the mass terms act like a fluid with time dependent equation of state $w<-1$ at late times. At linear order, we derive the Poisson’s equation. We find that the scalar graviton mode invokes anisotropic stress, which brings a modification with respect to Lambda Cold Dark Matter (LCDM) in the effective Newton’s constant and the growth rate of matter perturbations. Moreover, we study the propagation of gravitational waves and find that the tensor modes acquire a time dependent mass.

Future space-based laser interferometry experiments such as LISA are expected to detect $\mathcal{O}(100–1000)$ stellar-mass compact objects falling into massive black holes in the centers of galaxies, the so-called extreme-mass-ratio inspirals (EMRIs). If dark matter forms a “spike” due to the growth of the massive black hole, it will induce a gravitational drag on the inspiralling object, changing the EMRI orbit and gravitational-wave signal. We show that detection of even a single dark matter spike from an EMRI will severely constrain several popular dark matter candidates, such as ultralight bosons, keV fermions, MeV–TeV self-annihilating dark matter, and sub-solar mass primordial black holes, as these candidates would flatten the spikes through various mechanisms. Future space gravitational wave experiments could thus have a significant impact on the particle identification of dark matter.

The production of ${}^3\mathrm{H}$, ${}^7\mathrm{Be}$, and ${}^{22}\mathrm{Na}$ by interactions of cosmic-ray particles with silicon can produce radioactive backgrounds in detectors used to search for rare events. Through controlled irradiation of silicon CCDs and wafers with a neutron beam that mimics the cosmic-ray neutron spectrum, followed by direct counting, we determined that the production rate from cosmic-ray neutrons at sea level is $(112\pm 24)\mathrm{atoms}/(\mathrm{kg}\mathrm{day})$ for ${}^3\mathrm{H}$, $(8.1\pm 1.9)\mathrm{atoms}/(\mathrm{kg}\mathrm{day})$ for ${}^7\mathrm{Be}$, and $(43.0\pm 7.2)\mathrm{atoms}/(\mathrm{kg}\mathrm{day})$ for ${}^{22}\mathrm{Na}$. Complementing these results with the current best estimates of activation cross sections for cosmic-ray particles other than neutrons, we obtain a total sea-level cosmic-ray production rate of $(124\pm 25)\mathrm{atoms}/(\mathrm{kg}\mathrm{day})$ for ${}^3\mathrm{H}$, $(9.4\pm 2.0)\mathrm{atoms}/(\mathrm{kg}\mathrm{day})$ for ${}^7\mathrm{Be}$, and $(49.6\pm 7.4)\mathrm{atoms}/(\mathrm{kg}\mathrm{day})$ for ${}^{22}\mathrm{Na}$. These measurements will help constrain background estimates and determine the maximum time that silicon-based detectors can remain unshielded during detector fabrication before cosmogenic backgrounds impact the sensitivity of next-generation rare-event searches.