A search for the production of long-lived particles in proton-proton collisions at a center-of-mass energy of 13 TeV at the CERN LHC is presented. The search is based on data collected by the CMS experiment in 2016–2018, corresponding to a total integrated luminosity of $137{\mathrm{fb}}^{-1}$. This search is designed to be sensitive to long-lived particles with mean proper decay lengths between 0.1 and 1000 mm, whose decay products produce a final state with at least one displaced vertex and missing transverse momentum. A machine learning algorithm, which improves the background rejection power by more than an order of magnitude, is applied to improve the sensitivity. The observation is consistent with the standard model background prediction, and the results are used to constrain split supersymmetry (SUSY) and gauge-mediated SUSY breaking models with different gluino mean proper decay lengths and masses. This search is the first CMS search that shows sensitivity to hadronically decaying long-lived particles from signals with mass differences between the gluino and neutralino below 100 GeV. It sets the most stringent limits to date for split-SUSY models and gauge-mediated SUSY breaking models with gluino proper decay length less than 6 mm.

The energy-dependent cross section for $e^{+}{e}^{-}\to \eta \psi (2S)$ is measured at 18 center of mass energies from 4.288 to 4.951 GeV using the BESIII detector. Using the same data samples, we also perform the first search for the reaction $e^{+}{e}^{-}\to \eta \tilde{X}(3872)$, but no evidence is found for the $\tilde{X}(3872)$ in the ${\pi }^{+}{\pi }^{-}J/\psi$ mass distribution. At each of the 18 center of mass energies, upper limits at the 90% confidence level on the cross section for $e^{+}{e}^{-}\to \eta \psi (2S)$ and on the product of the $e^{+}{e}^{-}\to \eta \tilde{X}(3872)$ cross section with the branching fraction of $\tilde{X}(3872)\to {\pi }^{+}{\pi }^{-}J/\psi$ are reported.

We investigate the low-frequency spectral emission from a network of superconducting cosmic string loops in hopes of explaining the observed radio synchrotron background. After considering constraints from a variety of astrophysical and cosmological measurements, we identify a best-fit solution with string tension $G\mu \simeq 6.5\times {10}^{-12}$ and current $\mathcal{I}\simeq 2.5\times {10}^6\mathrm{GeV}$. This model yields a convincing fit to the data and may be testable in the near future by spectral distortion (TMS, BISOU) and 21 cm experiments (HERA, SKA, REACH). We also find that soft photon heating protects us against current constraints from global 21 cm experiments.

The universal eigenvalue distribution characterizing the Gram matrix of semiclassical ensembles of black hole microstates is recognized as the Marchenko-Pastur distribution, which plays a prominent role as the universal limit distribution in a large class of random matrix and vector models. It is proposed that this distribution also universally determines the energy spectral density of black holes, which allows one to construct a Krylov space for the time evolution of typical black hole states and calculate their state complexity. It is checked that the state complexity growth at late times saturates Lloyd’s bound. Some implications of the proposed spectral density for the generation of Hawking radiation and black hole evaporation are discussed.

We consider self-interacting scalar fields with a conformal coupling in the de Sitter background and study the quantum corrections from bubble loop diagrams. Incorporating the perturbative in-in formalism, we calculate the quantum corrections in the vacuum zero point energy and pressure of self-interacting fields with the potential $V\propto {\mathrm{\Phi }}^n$ for even values of $n$. We calculate the equation of state corresponding to these quantum corrections and examine the scaling of the divergent terms in the vacuum zero point energy and pressure associated to the dimensional regularization scheme. In particular, we show that for a quartic self-interacting scalar field the conformal invariance is respected at two-loop order at the conformal point.

We investigate the geometrical properties, spectral classification, geodesics, and causal structure of Bonnor’s spacetime [W. B. Bonnor, A rotating dust cloud in general relativity, J. Phys. A 10, 1673 (1977)], i.e., a stationary axisymmetric solution with a rotating dust as a source. This spacetime has a directional singularity at the origin of the coordinates (related to the diverging vorticity field of the fluid there), which is surrounded by a toroidal region where closed timelike curves (CTCs) are allowed, leading to chronology violations. We use the effective potential approach to provide a classification of the different kind of geodesic orbits on the symmetry plane as well as to study the helical-like motion around the symmetry axis on a cylinder with constant radius. In the former case we find that, as a general feature for positive values of the angular momentum, test particles released from a fixed space point and directed toward the singularity are repelled and scattered back as soon as they approach the CTC boundary, without reaching the central singularity. In contrast, for negative values of the angular momentum there exist conditions in the parameter space for which particles are allowed to enter the pathological region. Finally, as a more realistic mechanism, we study accelerated orbits undergoing friction forces due to the interaction with the background fluid, which may also act in order to prevent particles from approaching the CTC region.

Force-free electrodynamics is the theoretical paradigm used to describe electromagnetic fields in a region where the inertia of plasma is negligible compared to the strength of the electromagnetic field. While these fields are studied extensively around accreting black holes in an attempt to describe energy extraction, force-free fields also routinely appear in the study of cosmological magnetic fields. Despite this, there are no systematic studies of exact force-free fields in an expanding Universe. In this paper, we use geometric methods to find a wide variety of force-free solutions in a fixed Friedmann-Lemaître-Robertson-Walker metric background. The method we use can be directly generalized to any arbitrary electrically neutral spacetime, and hence provides a powerful tool to study force-free fields in general.

We investigate the possibility of improving the accuracy of the phenomenological waveform model, IMRPhenomD, by jointly optimizing all the calibration coefficients at once, given a set of numerical relativity (NR) waveforms. When IMRPhenomD was first calibrated to NR waveforms, different parts (i.e., the inspiral, merger, and ringdown) of the waveform were calibrated separately. Using ripple, a library of waveform models compatible with automatic differentiation, we can, for the first time, perform gradient-based optimization on all the waveform coefficients at the same time. This joint optimization process allows us to capture previously ignored correlations between separate parts of the waveform. We found that after recalibrating with a slightly restricted parameter subspace ($q\le 8$), despite the tail of the mismatch distribution remaining similar, the median mismatch between the model and NR waveforms decreases by 50%. We further explore how different regions of the source parameter space respond to the optimization procedure. We find that the degree of improvement correlates with the spins of the source. This work shows a promising avenue to help understand and treat systematic error in waveform models.

Fermion soliton stars are a consistent model of exotic compact objects which involve a nonlinear interaction between a real scalar field and fermions through a Yukawa term. This interaction results in an effective fermion mass that depends upon the vacuum structure in the scalar potential. In this work we investigate the tidal deformations of fermion soliton stars and compute the corresponding tidal Love numbers for different model parameters. Furthermore, we discuss the existence of approximate universal relations for the electric and magnetic tidal deformabilities of these stars, and compare them with other solutions of general relativity, such as neutron stars or boson stars. These relations for fermion soliton stars are less universal than for neutron stars, but they are sufficiently different from the ordinary neutron star case that a measurement of the electric and magnetic tidal Love numbers (as potentially achievable by next-generation gravitational wave detectors) can be used to disentangle these families of compact objects. Finally, we discuss the conditions for tidal disruption of fermion soliton stars in a binary system and estimate the detectability of the electromagnetic signal associated with such tidal disruption events.

We compute bounds from atomic spectroscopy on chameleon fields that couple to the photon. Chameleons are a wide class of scalar field models that generically lead to screened fifth forces and a host of novel phenomenologies, particularly when the photon coupling is included. We account for perturbations to the atomic energy levels from both the scalar field ‘fifth force’ and the scalar field’s correction to the electric field. We also account for the electromagnetic interaction’s contribution to the scalar charge of the proton, which enables a considerably wider class of models to be tested than without this effect. We find bounds that cover different areas of chameleon parameter space. A range of models spanning approximately one order of magnitude in chameleon coupling parameters (around $M,M_{\gamma }\approx {10}^{-16}{M}_{\mathrm{Pl}}$) are excluded for the first time. We also show that improvements to the theoretical uncertainty of hydrogen’s spectrum within the Standard Model would immediately rule out additional chameleon theory space by this analysis.

We construct a wide class of black hole solutions to the general theory of ghost-free multimetric gravity in arbitrary spacetime dimension, extending and generalizing the known results in four-dimensional dRGT massive gravity and bigravity. The solutions are split into three generic classes based on whether the metrics can be simultaneously diagonalized—one of which does not exist in dRGT massive gravity nor bigravity, and is only possible when one has more than two interacting metric fields. We also linearize the general multimetric theory to determine the dynamics of the massive spin-2 modes, including examples where this can be done analytically, and use the linear theory to discuss the stability of the four-dimensional multi-Schwarzschild and multi-Kerr solutions. We explain how the instabilities that plague these solutions in dRGT massive gravity and bigravity carry across to the general multimetric theory, touching upon ideas of dimensional deconstruction to make sense of the results.

We show that it is possible to directly measure the formation time of galaxies using a large-scale structure. In particular, we show that the large-scale distribution of galaxies is sensitive to whether galaxies form over a narrow period of time before their observed times, or are formed over a timescale on the order of the age of the Universe. Along the way, we derive simple recursion relations for the perturbative terms of the most general bias expansion for the galaxy density, thus fully extending the famous dark-matter recursion relations to generic tracers.

Pulsar timing array (PTA) collaborations recently reported evidence for the presence of a gravitational wave background (GWB) in their datasets. The main candidate that is expected to produce such a GWB is the population of supermassive black hole binaries. Some analyses showed that the recovered signal may exhibit time-dependent properties, i.e., nonstationarity. In this paper, we propose an approximated nonstationary Gaussian process model obtained from the perturbation of stationary processes. The presented method is applied to the second data release of the European Pulsar Timing Array to search for nonstationary features in the GWB. We analyzed the data in different time slices and showed that the inferred properties of the GWB evolve with time. We find no evidence for such nonstationary behavior and the Bayes factor in favor of the latter is ${\mathcal{B}}_S^{\mathrm{NS}}=1.5$. We argue that the evolution of the GWB properties most likely comes from the improvement of the observation cadence with time and better characterization of the noise of individual pulsars. Such nonstationary GWB could also be produced by the leakage of nonstationary features in the noise of individual pulsars or by the presence of an eccentric single source.

We use numerical relativity simulations of binary neutron star mergers to show that high density deconfinement phase transitions to quark matter can be probed using multimodal postmerger gravitational wave (GW) spectroscopy. Our simulations suggest that hadron-quark phase transitions may suppress the one-armed spiral instability in the remnant. This is manifested in an anticorrelation between the energy carried in the $\ell =2$, $m=1\mathrm{GW}$ mode and energy density gap which separates the two phases. Our work demonstrates a potential connection between features of the postmerger GW spectrum and microphysical features of the high-density equation of state.

In this paper, we have studied the realizations of the popular first trimaximal neutrino mixing and neutrino $\mu -\tau$ reflection symmetry (which are well motivated from the neutrino oscillation data and lead to interesting phenomenological consequences) in the most minimal seesaw model with a pseudo-Dirac pair of right-handed neutrinos and their consequences for leptogenesis. In order to realize the low-scale resonant leptogenesis scenario, we have considered two possible ways of generating the tiny mass splitting between the two right-handed neutrinos: one way is to modify their Majorana mass matrix to a form as shown in Eq. (25); the other way is to consider the renormalization-group corrections for their masses. For the $\mu -\tau$ reflection symmetry, in order for leptogenesis to work, we have further considered the flavor-dependent conversion efficiencies from the lepton asymmetry to the baryon asymmetry during the sphaleron processes and its breaking via the renormalization-group corrections.

In this paper, the reaction of electron-positron annihilation into ${\mathrm{\Lambda }}_c^{+}{\overline{\mathrm{\Lambda }}}_c^{-}$ is investigated. The ${\mathrm{\Lambda }}_c^{+}{\overline{\mathrm{\Lambda }}}_c^{-}$ scattering amplitudes are obtained by solving the Lippmann-Schwinger equation. The contact, annihilation, and two pseudoscalar-exchange potentials are taken into account in the spirit of the chiral effective field theory. The amplitudes of $e^{+}{e}^{-}\to {\mathrm{\Lambda }}_c^{+}{\overline{\mathrm{\Lambda }}}_c^{-}$ are constructed by the distorted wave Born approximation method, with the final state interactions of the ${\mathrm{\Lambda }}_c^{+}{\overline{\mathrm{\Lambda }}}_c^{-}$ rescattering implemented. By fitting to the experimental data, the unknown couplings are fixed, and high-quality solutions are obtained. With these amplitudes, the individual electromagnetic form factors in the timelike region, $G_E^{{\mathrm{\Lambda }}_c}$, $G_M^{{\mathrm{\Lambda }}_c}$, and their ratio, $G_E^{{\mathrm{\Lambda }}_c}/G_M^{{\mathrm{\Lambda }}_c}$, are extracted. Both modulus and phases are predicted. These individual electromagnetic form factors reveal new insights into the properties of the ${\mathrm{\Lambda }}_c$. The separated contributions of the Born term, contact, annihilation, as well as the two pseudoscalar-exchange potentials to the electromagnetic form factors are isolated. It is found that the Born term dominates the whole energy region. The contact term plays a crucial role in the enhancement near the threshold, and the annihilation term is essential in generating the fluctuation of the electromagnetic form factors.

The dynamics of heavy quarks within the hot QCD medium have been revisited, considering the influence of anomalous diffusion. This study has been conducted using the framework of the fractional Langevin equation involving the Caputo fractional derivative. We introduce a numerical scheme for the fractional Langevin equation and demonstrate that the mean-squared displacement of the particle exhibits anomalous diffusion, deviating from a linear relationship with time. Our analysis calculates various entities, such as mean-squared momentum, momentum spread, and the nuclear suppression factor $R_{AA}$. Notably, our findings indicate that superdiffusion strongly suppresses the $R_{AA}$ compared to normal diffusion in the hot QCD medium. The possible impacts on other parameters are also discussed.

The observation of the vector meson’s global spin alignment by the STAR Collaboration reveals that strong spin correlations may exist for quarks and antiquarks in relativistic heavy-ion collisions in the normal direction of the reaction plane. We propose a systematic method to describe such correlations in the quark matter. We classify them as local and long range quark spin correlations in the system. We show in particular that the effective quark spin correlations contain the genuine spin correlations originated directly from the dynamical process as well as those induced by averaging over other degrees of freedom. We also show that such correlations can be studied by measuring the vector meson’s spin density matrix and hyperon-hyperon and hyperon-anti-hyperon spin correlations. We present the relationships between these measurable quantities and spin correlations of quarks and antiquarks.

A search for pair production of scalar and vector leptoquarks (LQs) each decaying to a muon and a bottom quark is performed using proton-proton collision data collected at $\sqrt{s}=13\mathrm{TeV}$ with the CMS detector at the CERN LHC, corresponding to an integrated luminosity of $138{\mathrm{fb}}^{-1}$. No excess above standard model expectation is observed. Scalar (vector) LQs with masses less than 1810 (2120) GeV are excluded at 95% confidence level, assuming a 100% branching fraction of the LQ decaying to a muon and a bottom quark. These limits represent the most stringent to date.