We study the validity of Bekenstein’s entropy bound for a charged black hole in the context of nonlinear electrodynamics. Bekenstein’s inequalities are commonly understood as universal relations between the entropy, the charge, the momentum and the energy of a physical system but independent of its dynamics. In particular, we consider the Born-Infeld electrodynamics coupled to gravity as described by general relativity. Following the steps that lead to these inequalities, we study the absorption of a charged test particle by the black hole and verify that the entropy bound is violated. We find a modified upper bound for the entropy that depends on the maximum field parameter of the Born-Infeld theory.

We numerically investigate reheating after quadratic inflation with up to 65 fields, focusing on the production of non-Gaussianity. We consider several sets of initial conditions, masses, and decay rates. As expected, we find that the reheating phase can have a significant effect on the non-Gaussian signal, but that for this number of fields a detectable level of non-Gaussianity requires the initial conditions, mass range, and decay rates to be ordered in a particular way. We speculate on whether this might change in the N-flation limit.

Cosmological bounces occur in many gravity theories. We define singularity scattering maps relating large scale geometries before and after the bounce (assuming no BKL oscillations) and encoding microscopic details of the theory. By classifying all suitably local maps we uncover three universal laws: scaling of Kasner exponents, canonical transformation of matter, and directional metric scaling. These are indeed obeyed by Bianchi I bounces in string theory, loop quantum cosmology, and modified matter models; our classification then determines how inhomogeneities and anisotropies traverse bounces and precisely extract model-dependent degrees of freedom.

Associating the formation sites of haloes with the maxima of the smoothed linear density field, we present nonperturbative predictions for the Lagrangian and evolved halo correlation functions that are valid at all separations. In Lagrangian space, we find significant deviations from the perturbative bias calculation at small scales, in particular, a pronounced exclusion region where $\xi =-1$ for maxima of unequal height. Our predictions are in good agreement with the Lagrangian clustering of dark matter proto-haloes reconstructed from $N$-body simulations. Our predictions for the mean infall and velocity dispersion of haloes, which differ from the local bias expansion, show a similar level of agreement with simulations. Finally, we displace the initial density peaks according to the Zeldovich approximation in order to predict the late-time clustering of dark matter haloes. While we are able to reproduce the early evolution of this conserved set of tracers, our approximation fails at the collapse epoch ($z=0$) on nonlinear scales $r\lesssim 10h^{-1}\mathrm{Mpc}$, emphasizing the need for a nonperturbative treatment of the halo displacement field.

Quantum cosmological models are commonly described by means of semiclassical approximations in which a smooth evolution of the expectation values of elementary geometry operators replaces the classical and singular dynamics. The advantage of such descriptions is that they are relatively simple and display the classical behavior for large universes. However, they may smooth out an important inner structure and to include it a more detailed treatment is needed. The purpose of the present work is to investigate quantum uncertainty in the basic background variables and its influence on primordial gravitational waves. To this end we quantize a model of the Friedmann-Lemaitre-Robertson-Walker universe filled with a linear barotropic cosmological fluid and with gravitational waves. We carefully derive the dynamical equations for the perturbations in quantum spacetime. The quantization yields an equation of motion for the Fourier modes of gravitational radiation, which is a quantum extension to the usual parametric oscillator equation for gravitational waves propagating in an expanding universe. The two quantum effects from the cosmological background that enter the enhanced equation of motion are (i) a repulsive potential resolving the big bang singularity and replacing it with a big bounce and (ii) uncertainties in the numerical values for the background spacetime dynamical variables. First we study the former effect and its consequences for the primordial amplitude spectrum and carefully discuss the relation between the bounce scale and the physical predictions of the model. Next we investigate the latter effect, in particular, the extent to which it may affect the primordial amplitude of gravitational waves. Making use of the WKB approximation, we find an analytical formula for the amplitude spectrum as a function of the quantum dispersion of the background spacetime.

We study the cosmology of the dark sector consisting of (ultra)light scalars. Since the scalar mass is radiatively unstable, a special explanation is required to make the mass much smaller than the UV scale. There are two well-known mechanisms for the origin of scalar mass. The scalar can be identified as a pseudo-Goldstone boson, whose shift symmetry is explicitly broken by nonperturbative corrections, like the axion. Alternatively, it can be identified as a composite particle like the glueball, whose mass is limited by the confinement scale of the theory because no scalar degree of freedom exists at high scales. In both cases, the scalar can be naturally light, but interaction behavior is quite different. The lighter the axion (glueball), the weaker (stronger) its interaction. As the simplest nontrivial example, we consider the dark axion whose shift symmetry is anomalously broken by the hidden non-Abelian gauge symmetry. After the confinement of the gauge group, the dark axion and the dark glueball get masses and both form multicomponent dark matter. We carefully consider the effects of energy flow from the dark gluons to the dark axions and derive the full equations of motion for the background and the perturbed variables. The effect of the dark axion–dark gluon coupling on the evolution of the entropy and the isocurvature perturbations is also clarified. Finally, we discuss the gravothermal collapse of the glueball subcomponent dark matter after the halos form, in order to explore the potential to contribute to the formation of seeds for the supermassive black holes observed at high redshifts. With the simplified assumptions, the glueball subcomponent dark matter with the mass of 0.01–0.1 MeV and the axion main dark matter component with the decay constant $f_a=\mathcal{O}({10}^{15}–{10}^{16})\mathrm{GeV}$ and the mass of $\mathcal{O}({10}^{-14}–{10}^{-18})\mathrm{eV}$ can provide a hint on the origin of the supermassive black holes at high redshifts.

We propose a new approach to constant-roll warm inflation as a generalization of constant-roll inflation. Based on the $\beta$-function formalism, it is shown that constant-roll warm inflation models with a natural end fall into universality classes defined by three different types of $\beta$ functions, under the assumption that radiation energy density is quasistable. Given that warm inflation is completely specified by the $\beta$ function and dissipation coefficient ratio, we investigate whether or not the inflation can physically be realized for enough number of e-foldings at the background level for some combinations of the $\beta$ functions and nontrivial dissipation coefficient ratios.

We use a modified version of the peak patch excursion set formalism to compute the mass and size distribution of QCD axion miniclusters from a fully non-Gaussian initial density field obtained from numerical simulations of axion string decay. We find strong agreement with $N$-body simulations at significantly lower computational cost. We employ a spherical collapse model, and provide fitting functions for the modified barrier in the radiation era. The halo mass function at $z=629$ has a power-law distribution $M^{-0.6}$ for masses within the range ${10}^{-15}\lesssim M\lesssim {10}^{-10}{M}_{\odot }$, with all masses scaling as $(m_a/50\mu \mathrm{eV}{)}^{-0.5}$. We construct merger trees to estimate the collapse redshift and concentration mass relation, $C(M)$, which is well described using analytical results from the initial power spectrum and linear growth. Using the calibrated analytic results to extrapolate to $z=0$, our method predicts a mean concentration $C\sim \mathcal{O}(\mathrm{few})\times {10}^4$. The low computational cost of our method makes future investigation of the statistics of rare, dense miniclusters easy to achieve.

A stochastic gravitational wave background (SGWB), created by the superposition of signals from unresolved astrophysical sources, may be detected in the next few years. Several theoretical predictions are being made about the possible nature of anisotropies in the background. Estimating the variation of intensity across the sky can, therefore, play a key role in improving our understanding of astrophysical models. Sky maps have been produced for all the data-taking runs of the advanced ground-based interferometric detectors. While these maps are being produced in pixel and spherical harmonic (SpH) bases, to probe, respectively, localized and diffuse astrophysical and cosmological sources, with algorithms that employ cross-correlation as the common strategy, the underlying algebra and numerical implementation remain different. As a consequence, there was a need for producing sky maps in both bases in those analyses. We show that these manifestly redundant methods could indeed be unified to a single analysis that can probe very different scales and demonstrate it by applying them on real data. We first develop the algebra to show that the results in two different bases are easily transformable. We then incorporate both the schemes in the now-standard analysis pipeline for anisotropic SGWB, pystoch. This will enable SGWB anisotropy searches in SpH basis also to take full advantage of integrated healpix tools and makes it computationally feasible to perform the search in every frequency bin. We, however, follow a different approach for direct estimation of the SpH moments. We show that the results obtained from these different methods match very well; the differences are less than 0.1% for the SpH moments and less than 0.01% for the Fisher information matrices. Thus, we conclude that a single sky map will be sufficient to describe the anisotropies in a stochastic background. The multiple capabilities of pystoch will be useful for estimating and constraining various measures that characterize an anisotropic background.

On May 21, 2019 the Advanced LIGO and Advanced Virgo detectors observed a gravitational-wave transient GW190521, the heaviest binary black-hole merger detected to date with remnant mass of $142M_{\odot }$ that was published recently. This observation is the first strong evidence for the existence of intermediate-mass black holes. The significance of this observation was determined by the coherent waveburst (cWB) search algorithm, which identified GW190521 with minimal assumptions of its source model. In this paper, we show the performance of cWB for the detection of the binary black-hole mergers without use of the signal templates, describe the details of the GW190521 detection, and establish the consistency of the model-agnostic reconstruction of GW190521 by cWB with the theoretical waveform model of a binary black hole.

We apply the exponential operator method to derive the propagator for a fermion immersed within a rigidly rotating environment with cylindrical geometry. Given that the rotation axis provides a preferred direction, Lorentz symmetry is lost and the general solution is not translationally invariant in the radial coordinate. However, under the approximation that the fermion is completely dragged by the vortical motion, valid for large angular velocities, translation invariance is recovered. The propagator can then be written in momentum space. The result is suited to be used applying ordinary Feynman rules for perturbative calculations in momentum space.

The longstanding muon $g-2$ anomaly may indicate the existence of new particles that couple to muons, which could either be light $(\lesssim \mathrm{GeV})$ and weakly coupled, or heavy $(\gg 100\mathrm{GeV})$ with large couplings. If light new states are responsible, upcoming intensity frontier experiments will discover further evidence of new physics. However, if heavy particles are responsible, many candidates are beyond the reach of existing colliders. We show that, if the $(g-2{)}_{\mu }$ anomaly is confirmed and no explanation is found at low-energy experiments, a high-energy muon collider program is guaranteed to make fundamental discoveries about our Universe. New physics scenarios that account for the anomaly can be classified as either “singlet” or “electroweak” (EW) models, involving only EW singlets or new EW-charged states respectively. We argue that a TeV-scale future muon collider will discover all possible singlet model solutions to the anomaly. If this does not yield a discovery, the next step would be a $\mathcal{O}(10\mathrm{TeV})$ muon collider. Such a machine would either discover new particles associated with high-scale EW model solutions to the anomaly, or empirically prove that nature is fine-tuned, both of which would have profound consequences for fundamental physics.

Evolution of spin polarization in the Gubser-expanding conformal perfect-fluid hydrodynamic background is studied. The analysis of the conformal transformation properties of the conservation laws is extended to the case of the angular momentum conservation. The explicit forms of equations of motion for spin components are derived and analyzed, and some special solutions are found.

Jet tagging techniques that make use of deep learning show great potential for improving physics analyses at colliders. One such method is the energy flow network (EFN)—a recently introduced neural network architecture that represents jets as permutation-invariant sets of particle momenta while maintaining infrared and collinear safety. We develop a variant of the EFN architecture based on the deep sets formalism, incorporating permutation-equivariant layers. We derive conditions under which infrared and collinear safety can be maintained, and study the performance of these networks on the canonical example of $W$-boson tagging. We find that equivariant EFNs have similar performance to particle flow networks, which are superior to standard EFNs. Due to convergence and generalization issues, the same improvement was not observed when extending particle flow networks with equivariant layers. Finally, we study how equivariant networks sculpt the jet mass and provide some initial results on decorrelation using planing.

The Born cross sections for the process $e^{+}{e}^{-}\to {\eta }^{\prime }{\pi }^{+}{\pi }^{-}$ at different center-of-mass energies between 2.00 and 3.08 GeV are reported with improved precision from an analysis of data samples collected with the BESIII detector operating at the BEPCII storage ring. An obvious structure is observed in the Born cross section line shape. Fit as a Breit-Wigner resonance, it has a statistical significance of $6.3\sigma$ and a mass and width of $M=(2111\pm 43\pm 25)\mathrm{MeV}/c^2$ and $\mathrm{\Gamma }=(135\pm 34\pm 30)\mathrm{MeV}$, where the uncertainties are statistical and systematic, respectively. These measured resonance parameters agree with the measurements of BABAR in $e^{+}{e}^{-}\to {\eta }^{\prime }{\pi }^{+}{\pi }^{-}$ and BESIII in $e^{+}{e}^{-}\to \omega {\pi }^0$ within two standard deviations.

We refine an earlier introduced 5-dimensional gravity solution capable of holographically capturing several qualitative aspects of (lattice) QCD in a strong magnetic background such as the anisotropic behavior of the string tension, inverse catalysis at the level of the deconfinement transition or sensitivity of the entanglement entropy to the latter. Here, we consistently modify our solution of the considered Einstein-Maxwell-dilaton system to not only overcome an unphysical flattening at large distances in the quark-antiquark potential plaguing earlier work, but also to encapsulate inverse catalysis for the chiral transition in the probe approximation. This brings our dynamical holographic QCD model yet again closer to a stage at which it can be used to predict magnetic QCD quantities not directly computable via lattice techniques.

We describe numerical and analytical investigations of causal sets sprinkled into spacetime manifolds. The first part of the paper is a numerical study of finite causal sets sprinkled into Alexandrov subsets of Minkowski spacetime of dimensions $1+1$, $1+2$ and $1+3$. In particular we consider the rank 2 past of sprinkled causet events, which is the set of events that are two links to the past. Assigning one of the rank 2 past events as “preferred past” for each event yields a “preferred past structure,” which was recently proposed as the basis for a causal set d’Alembertian. We test six criteria for selecting rank 2 past subsets. One criterion performs particularly well at uniquely selecting—with very high probability—a preferred past satisfying desirable properties. The second part of the paper concerns (infinite) sprinkled causal sets for general spacetime manifolds. After reviewing the construction of the sprinkling process with the Poisson measure, we consider various specific applications. Among other things, we compute the probability of obtaining a sprinkled causal set of a given isomorphism class by combinatorial means, using a correspondence between causal sets in Alexandrov subsets of $1+1$ dimensional Minkowski spacetime and 2D-orders. These methods are also used to compute the expected size of the past infinity as a proportion of the total size of a sprinkled causal set.

Using the holographic idea, we study the entanglement of purification in a field theory with a critical point in an intermediate and low temperature regime. This theory includes temperature $T$ as well as chemical potential $\mu$. In the intermediate regime, due to chemical potential, we observe that new terms proportional to temperature square appear in the final result of entanglement of purification or equivalently, apart from $T^0$ and $T^4$ terms in the case of $\mu =0$, it contains the terms proportional to $T^2$. Our results also indicate that the entanglement of purification, i.e., the correlation between subsystems, can decrease or increase depending on the value of $\frac{\mu }{T}$ when the other parameters are kept fixed. However, in the low temperature limit, the correlation always decreases, compared to the $\mu =0$ case, independent of the value of $\frac{\mu }{T}$ when the other parameters do not alter. The existence of a critical point in the theory changes the behavior of entanglement of purification in such a way that the entanglement of purification experiences a maximum or minimum. Moreover, near the critical point, we analytically show that the critical exponent is equal to 0.5 in both regimes and also the term proportional to $T^2$ changes sign and becomes negative in the intermediate regime.

We recast the soft $S$ matrices on the celestial sphere as correlation functions of certain two-dimensional models of topological defects. In pointing out the double-copy structure between the soft photon and soft graviton cases, we arrive at a putative classical double copy between the corresponding topological models and a rederivation of gauge invariance and the equivalence principle as Ward identities of the two-dimensional theories.