We show that adjoint QCD features very strong Bose-Fermi cancellations in the large-$N$ limit, despite the fact that it is manifestly nonsupersymmetric. The difference between the bosonic and fermionic densities of states in large-$N$ adjoint QCD turns out to have a “two-dimensional” scaling $\sim \exp (\sqrt{\ell E})$ for large energies $E$ in finite spatial volume, where $\ell$ is a length scale associated with the curvature of the spatial manifold. In particular, all Hagedorn growth cancels, and so does the growth $\exp (V^{1/4}{E}^{3/4})$ expected in a standard local four-dimensional theory in spatial volume $V$. In these ways, large-$N$ adjoint QCD, a manifestly nonsupersymmetric theory, acts similarly to supersymmetric theories. We also show that at large-$N$ the vacuum energy of multiflavor adjoint QCD is non-negative and exponentially small compared to the UV cutoff with several natural regulators.

The LHCb Collaboration announced the observation of three narrow structures consistent with hidden-charm pentaquark states. They are candidates of hadronic molecules formed of a pair of a charmed baryon and an anticharmed meson. Among them, the $P_c(4457)$ mass is consistent with earlier predictions of a ${\mathrm{\Sigma }}_c{\overline{D}}^{*}$ molecule with $I=1/2$. We point out that if such a picture were true, one would have $\mathcal{B}(P_c(4457)\to J/\psi {\mathrm{\Delta }}^{+})/\mathcal{B}(P_c(4457)\to J/\psi p)$ at the level ranging from a few percent to about 30%. Such a large isospin breaking decay ratio is two to three orders of magnitude larger than that for normal hadron resonances. It is a unique feature of the ${\mathrm{\Sigma }}_c{\overline{D}}^{*}$ molecular model, and can be checked by LHCb.

We perform a search for light sterile neutrinos using the data from the T2K far detector at a baseline of 295 km, with an exposure of $14.7(7.6)\times {10}^{20}$ protons on target in neutrino (antineutrino) mode. A selection of neutral-current interaction samples is also used to enhance the sensitivity to sterile mixing. No evidence of sterile neutrino mixing in the $3+1$ model was found from a simultaneous fit to the charged-current muon, electron and neutral-current neutrino samples. We set the most stringent limit on the sterile oscillation amplitude ${\sin }^2{\theta }_{24}$ for the sterile neutrino mass splitting $\mathrm{\Delta }{m}_{41}^2<3\times {10}^{-3}{\mathrm{eV}}^2/c^4$.

We present a new method to expose the dead-cone effect at colliders using iterative declustering techniques. Iterative declustering allows one to unwind the jet clustering and to access the subjets or branches at different depths of the jet tree. Our method consists of declustering the heavy flavor-tagged jet using the Cambridge-Achen algorithm following the branch containing the heavy flavor at each step and registering the kinematics of the complementary untagged prong. The kinematics of the complementary untagged prong fill a Lund map representing the gluon radiation off the heavy-flavor quark at each step of the vacuum shower. Using Pythia8 Monte Carlo, we show that a simple cut on the Lund plane introduced by $\ln (k_{\mathrm{T}})>0$ suppresses hadronization effects and the angular separation between the jet prongs becomes very sensitive to flavor effects. A clear suppression for heavy-flavor jets relative to inclusive jets in the region of splitting angles delimited by the relation $\theta <m_Q/E$ is observed, where $m_Q$ is the mass of the heavy quark and $E$ is the energy of the radiator or splitting prong.

The gravitational wave memory effect is characterized by the permanent relative displacement of a pair of initially comoving test particles that is caused by the passage of a burst of gravitational waves. Recent research on this effect has clarified the physical origin and the interpretation of this gravitational phenomenon in terms of conserved charges at null infinity and “soft theorems.” In this paper, we describe a more general class of effects than the gravitational wave memory that are not necessarily associated with these charges and soft theorems, but that are, in principle, measurable. We shall refer to these effects as persistent gravitational wave observables. These observables vanish in nonradiative regions of a spacetime, and their effects “persist” after a region of spacetime which is radiating. We give three examples of such persistent observables, as well as general techniques to calculate them. These examples, for simplicity, restrict the class of nonradiative regions to those which are exactly flat. Our first example is a generalization of geodesic deviation that allows for arbitrary acceleration. The second example is a holonomy observable, which is defined in terms of a closed loop. It contains the usual “displacement” gravitational wave memory; three previously identified, though less well known memory effects (the proper time, velocity, and rotation memories); and additional new observables. Finally, the third example we give is an explicit procedure by which an observer could measure a persistent effect using a spinning test particle. We briefly discuss the ability of gravitational wave detectors (such as LIGO and Virgo) to measure these observables.

By introducing an auxiliary parameter, we find a new representation for Feynman integrals, which defines a Feynman integral by analytical continuation of a series containing only vacuum integrals. The new representation therefore conceptually translates the problem of computing Feynman integrals to the problem of performing analytical continuations. As an application of the new representation, we use it to construct a novel reduction method for multiloop Feynman integrals, which is expected to be more efficient than the known integration-by-parts reduction method. Using the new method, we successfully reduced all complicated two-loop integrals in the $gg\to HH$ process and $gg\to ggg$ process.

We forecast the constraints on the neutrino mass sum ($\mathrm{\Sigma }{m}_{\nu }$) from the one-point probability distribution function (PDF) and power spectrum of weak lensing measurements for an Large Synoptic Survey Telescope-like survey, using MassiveNuS simulations. The PDF provides access to non-Gaussian information beyond the power spectrum. It is particularly sensitive to nonlinear growth on small scales, where massive neutrinos also have the largest effect. We find that tomography helps improve the constraint on $\mathrm{\Sigma }{m}_{\nu }$ by 14% and 32% for the power spectrum and the PDF, respectively, compared to a single redshift bin. The PDF alone outperforms the power spectrum in constraining $\mathrm{\Sigma }{m}_{\nu }$. When the two statistics are combined, the constraint is further tightened by 35%, with respect to the power spectrum alone. We conclude that the weak lensing PDF is complementary to the power spectrum and has the potential to become a powerful tool for constraining neutrino mass. In this work, we do not include systematics such as baryon effects, intrinsic alignments, $\mathrm{photo}\text{−}z$ errors, and stress that they need to be carefully studied in future work.

The $B_c^{+}$ family of $(c\overline{b})$ mesons with beauty and charm is of special interest among heavy quarkonium systems. The $B_c^{+}$ mesons are intermediate between $(c\overline{c})$ and $(b\overline{b})$ states both in mass and size, so many features of the $(c\overline{b})$ spectrum can be inferred from what we know of the charmonium and bottomonium systems. The unequal quark masses mean that the dynamics may be richer than a simple interpolation would imply, in part because the charmed quark moves faster in $B_c$ than in the $J/\psi$. Close examination of the $B_c^{+}$ spectrum can test our understanding of the interactions between heavy quarks and antiquarks and may reveal where approximations break down. Whereas the $J/\psi$ and $\mathrm{\Upsilon }$ levels that lie below the flavor threshold are metastable with respect to strong decays, the $B_c$ ground state is absolutely stable against strong or electromagnetic decays. Its dominant weak decays arise from $\overline{b}\to \overline{c}{W}^{\star +}$, $c\to s{W}^{\star +}$, and $c\overline{b}\to W^{\star +}$ transitions, where $W^{\star }$ designates a virtual weak boson. Prominent examples of the first category are quarkonium transmutations such as $B_c^{+}\to J/\psi {\pi }^{+}$ and $B_c^{+}\to J/\psi {\ell }^{+}{\nu }_{\ell }$, where $J/\psi$ designates the $(c\overline{c})$ $1S$ level. The high data rates and extraordinarily capable detectors at the Large Hadron Collider give renewed impetus to the study of mesons with beauty and charm. Motivated by the recent experimental searches for the radially excited $B_c$ states, we update the expectations for the low-lying spectrum of the $B_c$ system. We make use of lattice QCD results, a novel treatment of spin splittings, and an improved quarkonium potential to obtain detailed predictions for masses and decays. We suggest promising modes in which to observe excited states at the LHC. The $3P$ and $3S$ states, which lie close to or just above the threshold for strong decays, may provide new insights into the mixing between quarkonium bound states and nearby two-body open-flavor channels. Searches in the $B^{(*)}{D}^{(*)}$ final states could well reveal narrow resonances in the $J^P=0^{-}$, $1^{-}$, and $2^{+}$ channels and possibly in the $J^P=0^{+}$ and $1^{+}$ channels at threshold. Looking further ahead, the prospect of very-high-luminosity $e^{+}{e}^{-}$ colliders capable of producing tera-$Z$ samples raises the possibility of investigating $B_c$ spectroscopy and rare decays in a controlled environment.

We consider the standard problem of observational astronomy, i.e., the observations of light emission from a distant region of spacetime in general relativity. The goal is to describe the changes between the measurements of the light performed by a sample of observers slightly displaced with respect to each other and moving with different 4-velocities and 4-accelerations. In our approach, all results of observations can be expressed as functions of the kinematic variables, describing the motions of the observers and the emitting bodies with respect to their local inertial frames, and four linear bilocal geodesic operators, describing the influence of the spacetime geometry on light propagation. The operators are functionals of the curvature tensor along the line of sight. The results are based on the assumption that the regions of emissions and observations are sufficiently small so that the spacetime curvature effects are negligible within each of them, although they are significant for the light propagation between them. The new formulation provides a uniform approach to optical phenomena in curved spacetimes and, as an application, we discuss the problem of a fully relativistic definition of the parallax and position drifts (or proper motions). We then use the results to construct combinations of observables which are completely insensitive to the motion of both the observer and the emitter. These combinations by construction probe the spacetime geometry between the observation and emission regions and in our formalism we may express them as functionals of the Riemann tensor along the line of sight. For short distances one of these combinations depends only on the matter content along the line of sight. This opens up the possibility to measure the matter content of a spacetime in a tomographylike manner irrespective of the motions of the emitter and the observer.

We present nuclear structure factors that describe the generalized spin-independent coupling of weakly interacting massive particles (WIMPs) to nuclei. Our results are based on state-of-the-art nuclear structure calculations using the large-scale nuclear shell model. Starting from quark- and gluon-level operators, we consider all possible coherently enhanced couplings of spin-$1/2$ and spin-0 WIMPs to one and two nucleons up to third order in chiral effective field theory. This includes a comprehensive discussion of the structure factors corresponding to the leading two-nucleon currents covering, for the first time, the contribution of spin-2 operators. We provide results for the most relevant nuclear targets considered in present and planned dark matter direct detection experiments: fluorine, silicon, argon, and germanium, complementing our previous work on xenon. All results are also publicly available in a Python notebook.

We study thermalization, hydrodynamization, and chemical equilibration in out-of-equilibrium quark-gluon plasma starting from various initial conditions using QCD effective kinetic theory, valid at weak coupling. In nonexpanding systems gauge bosons rapidly lose information of the initial state and achieve kinetic equilibrium among themselves, while fermions approach the equilibrium distribution only at a later time. In systems undergoing rapid longitudinal expansion, both gluons and quarks are kept away from equilibrium by the expansion, but the evolution is well described by fluid dynamics even before local thermal equilibrium is reached. For realistic couplings we determine the ordering between the separate hydrodynamization, chemical equilibration and thermalization time scales to be ${\tau }_{\text{hydro}}<{\tau }_{\mathrm{chem}}<{\tau }_{\text{therm}}$.

Following a semiclassical eikonal approach—justified at transplanckian energies order by order in the deflection angle ${\mathrm{\Theta }}_s\sim \frac{4G\sqrt{s}}{b}\equiv \frac{2R}{b}$—we investigate the infrared features of gravitational scattering and radiation in four space-time dimensions, and we illustrate the factorization and cancellation of the infinite Coulomb phase for scattering and the eikonal resummation for radiation. As a consequence, both the eikonal phase $2\delta (E,b)$ and the gravitational-wave (GW) spectrum $\frac{\mathrm{d}{E}^{\mathrm{GW}}}{\mathrm{d}\omega }$ are free from infrared problems in a frequency region extending from zero to (and possibly beyond) $\omega =1/R$. The infrared-singular behavior of 4-D gravity leaves a memory in the deep infrared region ($\omega R\ll \omega b<1$) of the spectrum. At $\mathcal{O}(\omega b)$ we confirm the presence of logarithmic enhancements of the form already pointed out by Sen and collaborators on the basis of nonleading corrections to soft-graviton theorems. These, however, do not contribute to the unpolarized and/or azimuthally averaged flux. At $\mathcal{O}({\omega }^2{b}^2)$ we find instead a positive logarithmically enhanced correction to the total flux implying an unexpected maximum of its spectrum at $\omega b\sim 0.5$. At higher orders we find subleading enhanced contributions as well, which can be resummed, and have the interpretation of a finite rescattering Coulomb phase of emitted gravitons.

We investigate whether inflation requires finely tuned initial conditions in order to explain the degree of flatness and homogeneity observed in the Universe. We achieve this by using the Eisenhart lift, which can be used to write any scalar field theory in a purely geometric manner. Using this formalism, we construct a manifold whose points represent all possible initial conditions for an inflationary theory. After equipping this manifold with a natural metric, we show that the total volume of this manifold is finite for a wide class of inflationary potentials. Hence, we identify a natural measure that enables us to distinguish between generic and finely tuned sets of initial conditions without the need for a regulator, in contrast to previous work in the literature. Using this measure, we find that the initial conditions that allow for sufficient inflation are indeed finely tuned. The degree of fine-tuning also depends crucially on the value of the cosmological constant at the time of inflation. Examining some concrete examples, we find that we require percent-level fine tuning if we allow the cosmological constant during inflation to be much larger than it is today. However, if we fix the cosmological constant to its presently observed value, the degree of fine tuning required is of order ${10}^{-54}$.

The radio detection of cosmic rays consists in the estimation of the properties of a primary cosmic ray by observing the electric field emitted by the extensive air shower (EAS) created when the primary cosmic ray enters the atmosphere. This technique is fully operative nowadays and presents a good degree of maturity. In addition, several projects intend to employ this technique for the detection of neutrinos. In order for the technique to be useful, accurate methods for computing the electric field created by a particle shower in the context of a particular experiment must exist. Although current ground-based radio experiments lie on the air-soil interface and some planned experiments on the South Pole envision antennas near the air-ice interface, most of the analytical approaches and Monte Carlo codes used for calculating the electric field either do not take into account the effect of the boundary or calculate the radiation fields only (direct, reflected and transmitted radiation fields). When the particle shower and the antenna are close to the boundary, compared to the observation wavelength, the far-field approximation breaks down, which is the case for the low-frequency EXTASIS experiment, for instance. We present in this work a new formula for calculating the exact field emitted by a particle track in two semi-infinite media separated by a planar boundary. We also explore the validity of the far-field approximation and make some predictions for EAS using a simple shower model.

Sub-GeV dark matter candidates are of increasing interest, because long-favored candidates such as GeV-scale weakly interacting massive particles have not been detected. For low-mass dark matter, model-independent constraints are weak or nonexistent. We show that for such candidates, because the number density is high, cosmic ray propagation can be affected by elastic scattering with dark matter. We call this type of search “reverse direct detection,” because dark matter is the target and standard model particles are the beam. Using a simple propagation model for galactic cosmic rays, we calculate how dark matter affects cosmic ray spectra at Earth, and set new limits on the dark matter-proton and dark matter-electron cross sections. For protons, our limit is competitive with cosmological constraints, but is independent. For electrons, our limit covers masses not yet probed, and improves on cosmological constraints by one to two orders of magnitude. We comment on how future work can significantly improve the sensitivity of cosmic-ray probes of dark matter interactions.

Marginally outer trapped surfaces (MOTSs, or marginal surfaces in short) are routinely used in numerical simulations of black-hole spacetimes. They are an invaluable tool for locating and characterizing black holes quasilocally in real time while the simulation is ongoing. It is often believed that a MOTS can behave unpredictably under time evolution; an existing MOTS can disappear, and a new one can appear without any apparent reason. In this paper we show that in fact the behavior of a MOTS is perfectly predictable and its behavior is dictated by a single real parameter, the stability parameter, which can be monitored during the course of a numerical simulation. We demonstrate the utility of the stability parameter to fully understand the variety of marginal surfaces that can be present in binary black-hole initial data. We also develop a new horizon finder capable of locating very highly distorted marginal surfaces and we show that even in these cases, the stability parameter perfectly predicts the existence and stability of marginal surfaces.

Far-from-equilibrium dynamics of $SU(2)$ gauge theory with Wilson fermions is studied in $1+1$ space-time dimensions using a real-time lattice approach. Lattice improved Hamiltonians are shown to be very efficient in simulating Schwinger pair creation and emergent phenomena such as plasma oscillations. As a consequence, significantly smaller lattices can be employed to approach continuum physics in the infinite-volume limit as compared to unimproved implementations. This allows us to compute also higher-order correlation functions including four fermion fields, which give unprecedented insights into the real-time dynamics of the fragmentation process of strings between fermions and antifermions.

We explore paleo-detectors as an approach to the direct detection of weakly interacting massive particle (WIMP) dark matter radically different from conventional detectors. Instead of instrumenting a (large) target mass in a laboratory in order to observe WIMP-induced nuclear recoils in real time, the approach is to examine ancient minerals for traces of WIMP-nucleus interactions recorded over timescales as large as 1 Gyr. Here, we discuss the paleo-detector proposal in detail, including background sources and possible target materials. In order to suppress backgrounds induced by radioactive contaminants such as uranium, we propose to use minerals found in marine evaporites or in ultrabasic rocks. We estimate the sensitivity of paleo-detectors to spin-independent and spin-dependent WIMP-nucleus interactions. The sensitivity to low-mass WIMPs with masses $m_{\chi }\lesssim 10\mathrm{GeV}$ extends to WIMP-nucleon cross sections many orders of magnitude smaller than current upper limits. For heavier WIMPs with masses $m_{\chi }\gtrsim 30\mathrm{GeV}$ cross sections a factor of a few to $\sim 100$ smaller than current upper limits can be probed by paleo-detectors.

We present a new initial data formulation to solve the full set of Einstein equations for spacetimes that contain a black hole under general conditions. The method can be used to construct complete initial data for spacetimes (the full metric) that contain a black hole. Contrary to most current studies the formulation requires minimal assumptions. For example, rather than imposing the form of the spatial conformal metric we impose 3 gauge conditions adapted to the coordinates describing the system under consideration. For stationary, axisymmetric spacetimes our method yields Kerr-Schild black holes in vacuum and rotating equilibrium neutron stars. We demonstrate the power of our new method by solving for the first time the whole system of Einstein equations for a nonaxisymmetric, self-gravitating torus in the presence of a black hole. The black hole has dimensionless spin $J_{\mathrm{bh}}/M_{\mathrm{bh}}^2=0.9918$, a rotation axis tilted at a 30° angle with respect to the angular momentum of the disk, and a mass of $\sim 1/5$ of the disk.

We study numerically the onset of chaos and thermalization in the Banks-Fischler-Shenker-Susskind (BFSS) matrix model with and without fermions, considering Lyapunov exponents, entanglement generation, and quasinormal ringing. We approximate the real-time dynamics in terms of the most general Gaussian density matrices with parameters which obey self-consistent equations of motion, thus extending the applicability of real-time simulations beyond the classical limit. Initial values of these Gaussian density matrices are optimized to be as close as possible to the thermal equilibrium state of the system. Thus attempting to bridge between the low-energy regime with a calculable holographic description and the classical regime at high energies, we find that quantum corrections to classical dynamics tend to decrease the Lyapunov exponents, which is essential for consistency with the Maldacena-Shenker-Stanford bound at low temperatures. The entanglement entropy is found to exhibit an expected “scrambling” behavior—rapid initial growth followed by saturation. At least at high temperatures the entanglement saturation time appears to be governed by classical Lyapunov exponents. Decay of quasinormal modes is found to be characterized by the shortest timescale of all. We also find that while the bosonic matrix model becomes nonchaotic in the low-temperature regime, for the full BFSS model with fermions the leading Lyapunov exponent, entanglement saturation time, and decay rate of quasinormal modes all remain finite and nonzero down to the lowest temperatures.