In the next decade, cosmological surveys will have the statistical power to detect the absolute neutrino mass scale. $N$-body simulations of large-scale structure formation play a central role in interpreting data from such surveys. Yet these simulations are Newtonian in nature. We provide a quantitative study of the limitations to treating neutrinos, implemented as $N$-body particles, in $N$-body codes, focusing on the error introduced by neglecting special relativistic effects. Special relativistic effects are potentially important due to the large thermal velocities of neutrino particles in the simulation box. We derive a self-consistent theory of linear perturbations in Newtonian and nonrelativistic neutrinos and use this to demonstrate that $N$-body simulations overestimate the neutrino free-streaming scale, and cause errors in the matter power spectrum that depend on the initial redshift of the simulations. For $z_i\lesssim 100$, and neutrino masses within the currently allowed range, this error is $\lesssim 0.5\%$, though represents an up to $\sim 10\%$ correction to the shape of the neutrino-induced suppression to the cold dark matter power spectrum. We argue that the simulations accurately model nonlinear clustering of neutrinos so that the error is confined to linear scales.

We propose a novel possibility to detect a very distinctive signal with more than four muons originating from pair-produced vector-like leptons decaying to a muon-philic $Z^{\prime }$ boson. These new particles are good candidates to explain the anomalies in the muon anomalous magnetic moment and the $b\to s\ell \ell$ processes. The doublet (singlet) vector-like leptons lighter than 1.3 (1.0) TeV are excluded by the latest data at the LHC if $\mathrm{BR}(E\to Z^{\prime }\mu )=1$. We also show that the excess in the signal region with more than five leptons can be explained by this scenario if the vector-like lepton is a weak singlet, with mass about 400 GeV and $\mathrm{BR}(E\to Z^{\prime }\mu )=0.25$. The future prospects at the HL-LHC are discussed.

We present mapff1.0, a determination of unpolarized charged-pion fragmentation functions (FFs) from a set of single-inclusive $e^{+}{e}^{-}$ annihilation and lepton-nucleon semi-inclusive deep-inelastic-scattering (SIDIS) data. FFs are parametrized in terms of a neural network and fitted to data exploiting the knowledge of the analytic derivative of the neural network itself with respect to its free parameters. Uncertainties on the FFs are determined by means of the Monte Carlo sampling method properly accounting for all sources of experimental uncertainties, including that of parton distribution functions. Theoretical predictions for the relevant observables, as well as evolution effects, are computed to next-to-leading order accuracy in perturbative QCD. We exploit the flavor sensitivity of the SIDIS measurements delivered by the HERMES and COMPASS experiments to determine a minimally biased set of seven independent FF combinations. Moreover, we discuss the quality of the fit to the SIDIS data with low virtuality $Q^2$ showing that, as expected, low-$Q^2$ SIDIS measurements are generally harder to describe within a next-to-leading-order-accurate perturbative framework.

The existence of feebly interacting massive particles (FIMPs) could have significant implications on the effective number of relativistic species $N_{\mathrm{eff}}$ in the early Universe. In this work, we investigate in detail how short-lived FIMPs that can decay into neutrinos affect $N_{\mathrm{eff}}$ and highlight the relevant effects that govern its evolution. We show that even if unstable FIMPs inject most of their energy into neutrinos, they may still decrease $N_{\mathrm{eff}}$, and identify neutrino spectral distortions as the driving power behind this effect. As a case study, we consider heavy neutral leptons (HNLs) and indicate which regions of their parameter space increase or decrease $N_{\mathrm{eff}}$. Moreover, we derive bounds on the HNL lifetime from the cosmic microwave background and comment on the possible role that HNLs could play in alleviating the Hubble tension.

A finite-temperature extension of the effective holographic models for QCD (EHQCD), proposed in Ref. [Ballon-Bayona et al., Phys. Rev. D 97, 046001 (2018).], is investigated in the present work. EHQCD models are characterized by two parameters, the conformal dimension of the relevant operator that deforms the conformal field theory and the associated coupling. We find that black hole solutions appear at temperatures higher than some temperature $T_{\min }$ and can be categorized into two classes: large and small black holes. A large black hole is thermally stable and it is therefore interpreted as the gravity dual of a nonconformal plasma. A small black hole, on the other hand, is thermally unstable. We show that thermodynamic quantities such as the entropy density $s$, specific heat $C_V$, and speed of sound $c_s$ are sensitive to the model parameters. We investigate perturbations of the black hole solutions and calculate the viscosity coefficients of the corresponding dual nonconformal plasma. For the shear viscosity, we confirm that the ratio $\eta /s$ is given by the universal result $1/4\pi$. For the bulk viscosity, the ratio $\zeta /s$ varies with the temperature, displaying a rapid growth close to $T_{\min }$, and it is sensitive to the model parameters. We compare our results for the thermodynamic quantities with the lattice $SU(N_C)$ results and find that they are compatible as long as the coupling is fixed appropriately as a function of the conformal dimension. We also compare our results for the viscosity coefficients against the JETSCAPE Collaboration results that are obtained from the analysis of experimental data on heavy ion collisions.

Relying on the method of spinorial geometry, purely bosonic supersymmetric solutions in $N=2$, five-dimensional supergravity theories coupled to vector multiplets in all space-time signatures are found. Explicit examples of some new solutions are presented.

The Bañados-Teitelboim-Zanelli (BTZ) black hole belongs to a family of locally three-dimensional anti-de Sitter (${\mathrm{AdS}}_3$) spacetimes labeled by their mass $M$ and angular momentum $J$. The case $M\ell \ge |J|$, where $\ell$ is the anti-de Sitter radius, provides the black hole. Extending the metric to other values of $M$ and $J$ leads to geometries with the same asymptotic behavior and global symmetries but containing a naked singularity at the origin. The case $M\ell \le -|J|$ corresponds to spinning conical singularities that are reasonably well understood. Here, we examine the remaining case, which is $-|J|<M\ell <|J|$. These naked singularities are mathematically acceptable solutions describing classical spacetimes. They are obtained by identifications of the covering pseudosphere in ${\mathbb{R}}^{2,2}$ and are free of closed timelike curves. Here, we study the causal structure and geodesics around these overspinning geometries. We present a review of the geodesics for the entire BTZ family. The geodesic equations are completely integrated, and the solutions are expressed in terms of elementary functions. Special attention is given to the determination of circular geodesics, where new results are found. According to the radial bounds, eight types of noncircular geodesics appear in the BTZ spacetimes. For the case of overspinning naked singularity, null, and spacelike geodesics can reach infinity passing by a point nearest to the singularity, others extend from the central singularity to infinity, and others still have a radial upper bound and terminate at the singularity. As expected for an anti-de Sitter spacetime, timelike geodesics cannot reach infinity; they either loop around the singularity or fall into it. The spatial projections of the geodesics (orbits) exhibit self-intersections, whose number is determined for null and spacelike geodesics, and it is found a special class of timelike geodesics whose spatial projections are closed.

We consider $k$-essence, a scalar-tensor theory with first-order derivative self-interactions that can screen local scales from scalar fifth forces, while allowing for sizeable deviations from general relativity on cosmological scales. We construct fully nonlinear static stellar solutions that show the presence of this screening mechanism, and we use them as initial data for simulations of stellar oscillations and gravitational collapse in spherical symmetry. We find that for $k$-essence theories of relevance for cosmology, the screening mechanism works in the case of stellar oscillation and suppresses the monopole scalar emission to undetectable levels. In collapsing stars, we find that the Cauchy problem, although locally well posed, can lead to diverging characteristic speeds for the scalar field. By introducing a “fixing equation” in the spirit of J. Cayuso et al. [Phys. Rev. D 96, 084043 (2017)], inspired in turn by dissipative relativistic hydrodynamics, we manage to evolve collapsing neutron stars past the divergence of the characteristic speeds. We show that, in these systems, the screening mechanism is less efficient than for oscillating and static stars, because the collapsing star must shed away all of its scalar hair before forming a black hole. For $k$-essence theories of relevance for cosmology, the characteristic frequency of the resulting scalar monopole signal is too low for terrestrial detectors, but we conjecture that space-borne interferometers such as the Laser Interferometer Space Antenna might detect it if a supernova explodes in the Galaxy.

We investigate a Lorentz invariant action that is quadratic in two rank-2 symmetric tensor fields in Minkowski spacetime. We apply a scalar-vector-tensor decomposition to two tensor fields by virtue of three-dimensional rotation invariance of Minkowski spacetime and classify theories with 7 degrees of freedom based on the Hamiltonian analysis. We find two new theories, which cannot be mapped from the linearized Hassan-Rosen bigravity. In these theories, the new mass interactions can be allowed thanks to the transverse diffeomorphism invariance of action.

We review the fundamentals and highlight the differences between some commonly used definitions for the PPN gamma parameter ($\gamma$) and the gravitational slip ($\eta$). Here we stress the usefulness of a gammalike parameter used by Berry and Gair (${\gamma }_{\mathrm{\Sigma }}$) that parametrizes the bending of light and the Shapiro time delay in situations in which the standard $\gamma$ cannot be promptly used. First we apply our considerations to two well-known cases, but for which some conflicting results can be found: massive Brans-Dicke gravity and $f(R)$ gravity (both the metric and the Palatini versions). Although the slip parameter is always well defined, it has in general no direct relation to either light deflection or the Shapiro time delay, hence care should be taken on imposing the PPN $\gamma$ bounds on the slip. We stress that, for any system with a well-posed Newtonian limit, Palatini $f(R)$ theories always have $\gamma =1$; while metric $f(R)$ theories can only have two values: either 1 or $1/2$. The extension toward Horndeski gravity shows no qualitative surprises, and ${\gamma }_{\mathrm{\Sigma }}$ is a constant in this context (only assuming that the Horndeski potentials can be approximated by analytical functions). This implies that a precise study on the bending of light for different impact parameters can in principle be used to rule out the complete Horndeski action as an action for gravity. Also, we comment on the consequences for $\gamma$ inferences at external galaxies.

We present a novel cosmological scenario that describes both inflation and dark matter. A concrete realization of our scenario is given based on a well-established particle physics model, where an axionlike field drives inflation until a potential barrier, which keeps a waterfall field at the origin, disappears to trigger a waterfall transition. Such a barrier makes the inflaton potential much flatter, improving significantly the naturalness and viability of the otherwise problematic setup adopted previously. The observed spectrum of the cosmic microwave background indicates that the inflationary Hubble scale, which is allowed to span a wide range, uniquely fixes the inflaton mass and decay constant. This raises an intriguing possibility of probing inflation via experimental searches for axionlike particles. Further, our model involves dark matter candidates including the inflaton itself. Also, for a complex waterfall field, we can determine cosmologically the Peccei-Quinn scale associated with the strong $CP$ problem.

We test a Yukawa correction to the Newtonian potential, making use of our own Galaxy—the Milky Way—as a test bed. We include as free parameter the Yukawa strength and range and the dark matter profile parameters, and compare several morphologies for the bulge, gas, and disk components, using Bayesian model selection criteria. We employ up-to-date datasets for both the visible (baryonic) component of the Milky Way, and for the tracers of the gravitational potential (the rotation curve). We find that the data are consistent with the Newtonian potential, and constrain the Yukawa coupling $\beta$ to be negative and $\lambda$ to range along the curve $\lambda =a|\beta {|}^c$ with $a=(0.77\pm 0.06)\mathrm{kpc}$ and $c=-0.503_{-0.019}^{+0.016}$.

Recent gravitational-wave observations have begun to constrain the internal physics of neutron stars. However, current detection searches for neutron star systems assume that potential neutron stars are low-mass black holes, ignoring any affect on the gravitational-wave signal due to the internal neutron star physics. We wish to create a template bank of binary neutron star waveforms including the effect of tidal deformability. However, we find that the Fisher matrix, which is commonly used to approximate match calculations when placing template banks, is unsuitable to predict the match between two binary neutron star waveforms. We find that the Fisher matrix can predict errors on the mismatch that are larger than 100% when attempting to identify waveforms with a match of 0.97. We explore the regime in which the Fisher matrix cannot be trusted and examine why it breaks down. We demonstrate that including higher-order terms in the Taylor series expansion of the match can reliably compute matches for these examples, but that it is prohibitively computationally expensive to do so. Finally, we demonstrate that stochastic placement can still be used to construct a template bank of tidally deformed neutron star waveforms.

We present bajes, a parallel and lightweight framework for Bayesian inference of multimessenger transients. bajes is a python modular package with minimal dependencies on external libraries adaptable to the majority of the Bayesian models and to various sampling methods. We describe the general workflow and the parameter estimation pipeline for compact-binary-coalescence gravitational-wave transients. The latter is validated against injections of binary black hole and binary neutron star waveforms, including confidence interval tests that demonstrate the inference is well calibrated. Binary neutron star postmerger injections are also studied using a network of five detectors made of LIGO, Virgo, KAGRA, and Einstein Telescope. Postmerger signals will be detectable for sources at $\lesssim 80\mathrm{Mpc}$, with Einstein Telescope contributing over 90% of the total signal-to-noise ratio. As a full scale application, we reanalyze the gravitational-wave transients catalog-1 black hole transients using the effective-one-body teobresums approximant and reproduce selected results with other approximants. bajes inferences are consistent with previous results; the direct comparison of bajes and bilby analyses of GW150914 shows a maximum Jensen-Shannon divergence of $5.2\times {10}^{-4}$. GW170817 is reanalyzed using taylorf2 with 5.5PN point mass and 7.5PN tides, teobresumspa, and imrphenompv2_nrtidal with different cutoff frequencies of 1024 and 2048 Hz. We find that the former choice minimizes systematics on the reduced tidal parameter, while a larger amount of tidal information is gained with the latter choice. bajes can perform these analyses in about 1 day using 128 CPUs.

We present a Monte Carlo approach to soft-gluon resummation at subleading color which can be used to improve existing parton shower algorithms. At the single-emission level, soft-collinear enhancements of the splitting functions are explicitly linked to quadratic Casimir operators, while wide angle single-soft enhancements are connected to nontrivial color correlators. We focus on a numerically stable implementation of color matrix element corrections to all orders and approximate the virtual corrections by requiring unitarity at the single-emission level. We provide a proof-of-concept implementation to compute nonglobal event shapes at lepton colliders.

We propose a new jet algorithm for deep-inelastic scattering (DIS) that accounts for the target-current asymmetry in the Breit frame. The Centauro algorithm is longitudinally invariant and can cluster jets with near-to Born kinematics, which enables novel studies of transverse-momentum-dependent observables. Furthermore, we show that spherically-invariant algorithms in the Breit frame give access to low-energy jets from current fragmentation. We perform a calculation of the energy spectrum of Centauro jets at next-to-leading logarithmic accuracy and compare to pythia simulations. We furthermore propose novel studies in unpolarized, polarized, and nuclear DIS at the future Electron-Ion Collider.

The quarkonium production mechanism in high-multiplicity small collision systems has recently been pursued in the color-glass-condensate (CGC) effective theory combined with the nonrelativistic QCD (NRQCD) factorization, allowing us to study initial state interactions. Quarkonium polarization, potentially measured in future experiments, would help elucidate the quarkonium production mechanism at high multiplicities. In this paper, we provide predictions on $J/\psi$ polarization parameters in high-multiplicity proton-proton ($pp$) and proton-nucleus ($pA$) collisions within the $\mathrm{CGC}+\mathrm{NRQCD}$ framework. Theoretical predictions are given for $J/\psi$ rapidity $2.5<y_{J/\psi }<4$, charged-particle multiplicity pseudorapidity $|{\eta }_{\mathrm{ch}}|<1$, and energies $\sqrt{S}=13\mathrm{TeV}$ for $pp$ collisions and $\sqrt{S}=8.16\mathrm{TeV}$ for $pA$ collisions. Considering two leptonic frame choices (the Collins-Soper and helicity frames) we find a weak polarization of $J/\psi$ that additionally decreases with growing event activities. No significant system size dependence between $pp$ and $pA$ collisions is obtained—this could be a new constraint to initial state interactions in small collision systems.

We apply the renormalization group optimized perturbation theory (RGOPT) to evaluate the quark contribution to the QCD pressure at finite temperatures and baryonic densities, at next-to-leading order (NLO). Our results are compared to NLO and state-of-the-art higher orders of standard perturbative QCD (pQCD) and hard thermal loop perturbation theory (HTLpt). The RGOPT provides an all order resummed pressure in a well-defined approximation, exhibiting a drastically better remnant renormalization scale dependence than pQCD, thanks to built-in renormalization group invariance consistency. At NLO, upon simply adding to the RGOPT-resummed quark contributions the purely perturbative NLO glue contribution, our results show a remarkable agreement with ab initio lattice simulation data for temperatures $0.25\lesssim T\lesssim 1\mathrm{GeV}$, with a remnant scale dependence drastically reduced as compared to HTLpt.

The technique of weak value amplification, proposed by Aharonov et al. in 1988, has been applied for various fields of physics for the purpose of precision measurement, which is made possible by exploiting the freedom of “postselection” specifying actively the final state in the physical process. Here we report the feasibility of utilizing the technique of weak value amplification in high-energy particle physics, especially in measuring the $CP$-violating parameters in $B$ meson decays, where the effective lifetime of the decay mode is expected to be prolonged statistically due to the postselection. Our analysis shows that, when adopted in the Belle II experiment at the SuperKEKB collider, the effective lifetime may be prolonged up to 2.6 times, and that the measurement precision of the $CP$-violating parameters will also be improved by its effect.

We present a novel procedure to construct Yang-Mills Berends-Giele currents from the Bern-Kosower formalism for one-loop gluon amplitudes. The obtained currents naturally obey color-kinematics duality. As a feedback to the Bern-Kosower formalism we outline how the multiparticle fields can be used to significantly streamline the pinch procedure for the reducible one-loop amplitudes.