The lensing and Einstein ring at the core of the galaxy cluster Abell 3827 are reproduced in the modified gravity theory (MOG). The estimated effective lensing mass $M_L=(1+\alpha )M_b=5.2\times {10}^{12}{M}_{\odot }$ within $R=18.3\mathrm{kpc}$ for a baryon mass $M_b=1.0\times {10}^{12}{M}_{\odot }$ within the same radius produces the observed Einstein ring angular radius ${\theta }_E=10^{\prime \prime }$. A detailed derivation of the total lensing mass is based on modeling of the cluster configuration of galaxies, intracluster light and x-ray emission. The MOG can fit the lensing and Einstein ring in Abell 3827 without dark matter as well as general relativity with dark matter.

We show that gapless modes in relativistic hydrodynamics could become topologically nontrivial by weakly breaking the conservation of energy momentum tensor in a specific way. This system has topological semimetal-like crossing nodes in the spectrum of hydrodynamic modes that require the protection of a special combination of translational and boost symmetries in two spatial directions. We confirm the nontrivial topology from the existence of an undetermined Berry phase. These energy momentum nonconservation terms could naturally be produced by an external gravitational field that comes from a reference frame change from the original inertial frame, i.e., by fictitious forces in a noninertial reference frame. This noninertial frame is the rest frame of an accelerating observer moving along a trajectory of a helix. This suggests that topologically trivial modes could become nontrivial by being observed in a special noninertial reference frame, and this fact could be verified in laboratories, in principle. Finally, we propose a holographic realization of this system.

Working within the very-low-acceleration limit of modified Newtonian dynamics (MOND)—the deep-MOND limit (DML)—I describe spherical, self-gravitating systems governed by a polytropic equation of state, $P=\mathcal{K}{\rho }^{\gamma }$ ($P$ is the pressure, and $\rho$ the density). As self-consistent structures, such idealized systems can serve as heuristic models for DML, astronomical systems, such as dwarf spheroidal galaxies, low-surface-density elliptical galaxies and star clusters, and diffuse galaxy groups. They can also serve as testing ground for various theoretical MOND inferences. In dimensionless form, the equation satisfied by the radial density profile $\zeta (y)$ is (for $\gamma \ne 1$) $[{\int }_0^y\zeta {\overline{y}}^{2}d\overline{y}{]}^{1/2}=-yd({\zeta }^{\gamma -1})/dy$. Or, ${\theta }^n(y)=y^{-2}[(y{\theta }^{\prime }{)}^2{]}^{\prime }$, where $\theta ={\zeta }^{\gamma -1}$, and $n\equiv (\gamma -1{)}^{-1}$. I discuss general properties of the solutions, contrasting them with those of their Newtonian analogues—the Lane–Emden polytropes. Due to the stronger MOND gravity, all DML polytropes have a finite mass, and for $n<\infty$ ($\gamma >1$) all have a finite radius (Lane–Emden spheres have a finite mass only for $n\le 5$). I use the DML polytropes to study DML scaling relations. For example, they satisfy a universal relation (for all $\mathcal{K}$ and $\gamma$) between the total mass, $M$, and the mass-average velocity dispersion $\sigma$: $MG{a}_0=(9/4){\sigma }^4$. However, the relation between $M$ and other measures of the velocity dispersion, such as the central, projected one, $\overline{\sigma }$, does depend on $n$ (but not $\mathcal{K}$), defining a “fundamental surface” in the $[M,\overline{\sigma },n]$ space. I also describe the generalization to anisotropic polytropes, which also all have a finite radius (for $\gamma >1$) and which all satisfy the above universal $M-\sigma$ relation. This more extended class of models exhibits the central-surface-densities relation: a tight relation between the baryonic and the dynamical central-surface-densities predicted by MOND.

Scalar-tensor theory predicts solutions to the gravitational field equations which describe compact objects in the presence of a nonminimally coupled scalar field to the Einstein tensor. These objects are black holes with scalar hair and wormholes supporting scalar phantom matter. The evolution of test fields in fixed asymptotically-flat backgrounds of exotic compact objects leads to the formation of echoes in the ringdown signal, which designate the existence of trapping regions close to the event horizon. Here, we consider minimally coupled test scalar fields propagating on compact object solutions of the Horndeski action, which possess an effective cosmological constant, leading to anti-de Sitter asymptotics, and show that echoes can form in the ringdown waveform due to the entrapment of test fields between the photon sphere and the effective asymptotic boundary. Although the presence of an event horizon leads to the usual echoes with decaying amplitude, signifying modal stability of the scalarized black hole considered, we find that test scalar fields propagating on a scalarized wormhole solution give rise to echoes of constant and equal amplitude to that of the initial ringdown, indicating the existence of normal modes. Finally, we find that, near extremality, the test field exhibits a concatenation of echoes; the primary ones are associated with the trapping region between the photon sphere and the effective anti–de Sitter boundary while the secondary ones are linked to the existence of a potential well at the throat of the wormhole.

Motivated by the models of geometry with discrete spaces as additional dimensions we investigate the stability of cosmological solutions in models with two metrics of the Friedmann-Lemaître-Robertson-Walker type. We propose an effective gravity action that couples the two metrics in a similar manner as in bimetric theory of gravity and analyze whether standard solutions with identical metrics are stable under small perturbations.

We explore the possibility that the annihilation of dark matter (DM) is boosted due to enhanced substructure in the presence of primordial black holes (PBHs) which constitute a subcomponent of DM. The PBHs can generate entropy fluctuations at the small scales which trigger early structure formation, and a large fraction of the whole DM can reside in these collapsed objects that formed at high redshift ($z\gtrsim 100$). Such early forming minihalos consequently possess higher densities than those in the conventional scenarios (without PBHs) and would be more resilient to tidal disruptions. Our scenarios of the annihilation boost due to DM substructures are of particular interest for light ($<1\mathrm{GeV}$) DM which has been less explored compared to heavier DM in the presence of the PBHs.

A promising idea to resolve the long standing Hubble tension is to postulate a new subdominant dark-energy-like component in the prerecombination Universe which is traditionally termed as the early dark energy (EDE). However, as shown in the Refs. [J. C. Hill et al., Early dark energy does not restore cosmological concordance, Phys. Rev. D 102, 043507 (2020), M. M. Ivanov et al.,Constraining early dark energy with large-scale structure, Phys. Rev. D 102, 103502 (2020).] the cosmic microwave background (CMB) and large-scale structure (LSS) data impose tight constraints on this proposal. Here, we revisit these strong bounds considering the Planck CMB temperature anisotropy data at large angular scales and the SPTPol polarization and lensing measurements. As advocated in [A. Chudaykin et al., Combined analysis of Planck and SPTPol data favors the early dark energy models, J. Cosmol. Astropart. Phys. 08 (2020) 013.] another paper, this combined data approach predicts the CMB lensing effect consistent with the $\mathrm{\Lambda }\mathrm{CDM}$ expectation and allows one to efficiently probe both large and small angular scales. Combining Planck and SPTPol CMB data with the full-shape BOSS likelihood and information from photometric LSS surveys in the EDE analysis we found for the Hubble constant $H_0=69.79\pm 0.99\mathrm{km}{\mathrm{s}}^{-1}{\mathrm{Mpc}}^{-1}$ and for the EDE fraction $f_{\mathrm{EDE}}<0.094(2\sigma )$. These bounds obtained without including a local distance ladder measurement of $H_0$ (SH0ES) alleviate the Hubble tension to a $2.5\sigma$ level. Including further the SH0ES data we obtain $H_0=71.81\pm 1.19\mathrm{km}{\mathrm{s}}^{-1}{\mathrm{Mpc}}^{-1}$ and $f_{\mathrm{EDE}}=0.088\pm 0.034$ in full accordance with SH0ES. We also found that a higher value of $H_0$ does not significantly deteriorate the fit to the LSS data. Overall, the EDE scenario is (though weakly) favored over $\mathrm{\Lambda }\mathrm{CDM}$ even after accounting for unconstrained directions in the cosmological parameter space. We conclude that the large-scale Planck temperature and SPTPol polarization measurements along with LSS data do not rule out the EDE model as a resolution of the Hubble tension. This paper underlines the importance of the CMB lensing effect for robust constraints on the EDE scenario.

It has been suggested that late-Universe dark matter decays can alleviate the tension between measurements of $H_0$ in the local Universe and its value inferred from cosmic microwave background fluctuations. It has been suggested that decaying dark matter can potentially account for this discrepancy as it reshuffles the energy density between matter and radiation and as a result allows dark energy to become dominant at earlier times. In this work, we show that the low multipole amplitude of the cosmic microwave background anisotropy power spectrum severely constrains the feasibility of late-time decays as a solution to the $H_0$ tension.

We present fully general-relativistic numerical evolutions of self-gravitating tori around spinning black holes with dimensionless spin $a/M=0.7$ parallel or antiparallel to the disk angular momentum. The initial disks are unstable to the hydrodynamic Papaloizou-Pringle instability which causes them to grow persistent orbiting matter clumps. The effect of black hole spin on the growth and saturation of the instability is assessed. We find that the instability behaves similarly to prior simulations with nonspinning black holes, with a shift in frequency due to spin-induced changes in disk orbital period. Copious gravitational waves are generated by these systems, and we analyze their detectability by current and future gravitational wave observatories for a large range of masses. We find that systems of $10M_{\odot }$—relevant for black hole–neutron star mergers—are detectable by Cosmic Explorer out to $\sim 300\mathrm{Mpc}$, while DECIGO (LISA) will be able to detect systems of $1000M_{\odot }$ (${10}^5{M}_{\odot }$)—relevant for disks forming in collapsing supermassive stars—out to cosmological redshift of $z\sim 5$ ($z\sim 1$). Computing the accretion rate of these systems we find that these systems may also be promising sources of coincident electromagnetic signals.

Using a density dependent quark mass (QMDD) model for strange quark matter, we investigate the effects of non-Newtonian gravity on the properties of strange stars and constrain the parameters of the QMDD model by employing the mass of PSR $\mathrm{J}0740+6620$ and the tidal deformability of GW170817. We find that for the QMDD model these mass and tidal deformability observations would rule out the existence of strange stars if non-Newtonian gravity effects are ignored. For the current quark masses of $m_{u0}=2.16\mathrm{MeV}$, $m_{d0}=4.67\mathrm{MeV}$, and $m_{s0}=93\mathrm{MeV}$, we find that a strange star can exist for values of the non-Newtonian gravity parameter $g^2/{\mu }^2$ in the range of $4.58{\mathrm{GeV}}^{-2}\le g^2/{\mu }^2\le 9.32{\mathrm{GeV}}^{-2}$, and that the parameters $D$ and $C$ of the QMDD model are restricted to $158.3\mathrm{MeV}\le D^{1/2}\le 181.2\mathrm{MeV}$ and $-0.65\le C\le -0.12$. It is found that the largest possible maximum mass of a strange star obtained with the QMDD model is $2.42M_{\odot }$ and that the secondary component of GW190814 with a mass of ${2.59}_{-0.09}^{+0.08}{M}_{\odot }$ could not be a static strange star. We also find that for the mass and radius of PSR $\mathrm{J}0030+0451$ given by Riley et al. through the analysis of observational data of NICER, there exists a very tiny allowed parameter space for which strange stars computed for the QMDD model agree with the observations of PSR $\mathrm{J}0740+6620$, GW170817 and PSR $\mathrm{J}0030+0451$ simultaneously. However, for the mass and radius given by Miller et al., no such parameter space exist.

We analyze the distributions of energy, the opening angle, and the invariant mass in muonic neutrino trident production processes, ${\nu }_{\mu }\to {\nu }_{\mu }\mu \overline{\mu }$, in a minimal gauged $U(1{)}_{L_{\mu }-L_{\tau }}$ model, in which the discrepancy of the anomalous magnetic moment of muon can be solved. It is known that the total cross section of neutrino trident production has parameter degeneracy in the new gauge boson mass and gauge coupling constant, and therefore other observables are needed to determine these parameters. From numerical analyses, we find that the muon energy and invariant mass distributions show the differences among the new physics parameter sets with which the total cross section has the same value, while the antimuon energy and opening angle distributions are not sensitive to the parameters.

The extent to which the dual meson condensates obtained in the Polyakov-loop enhanced linear sigma model can indicate deconfining transition is investigated by imposing the twisted boundary conditions. The influence of the improved unquenching effect, the dependence on the glue potential parametrization, and the role of the fermion vacuum contribution are focused on at the mean field level. At zero density, the rapid rise of the dual sigma condensate with $T$ is confirmed, which is more sensitive to the chiral transition than the increase of the Polyakov loop. For finite isospin chemical potential ${\mu }_I>m_{\pi }/2$, the dual sigma condensate shows abnormal thermal behavior which decreases with $T$ below the melting temperature $T_c^{I_3}$ of pion superfluidity. In contrast, the dual pion condensate always increases with $T$, with the maximum slope located at $T_c^{I_3}$ rather than $T_c^P$, as determined by the Polyakov loop. The dual vector meson condensate for ${\mu }_I>m_{\pi }/2$ is also more sensitive to the chiral restoration when considering the fermion vacuum contribution. The study suggests that the dual condensates calculated in this model are not appropriate indicators of deconfinement due to some limitations and uncertainty.

We present numerical solutions of several spacetimes of physical interest, including binary black hole mergers, in shift-symmetric Einstein-scalar-Gauss-Bonnet (ESGB) gravity, and describe our methods for solving the full equations of motion, without approximation, for general spacetimes. While we concentrate on the specific example of shift-symmetric ESGB, our methods, which make use of a recently proposed modification to the generalized harmonic formulation, should be generally applicable to all Horndeski theories of gravity (including general relativity). We demonstrate that these methods can stably follow the formation of scalar clouds about initially vacuum nonspinning and spinning black holes for values of the Gauss-Bonnet coupling approaching the maximum value above which the hyperbolicity of the theory breaks down in spherical symmetry. We study the collision of black holes with scalar hair, finding that the theory remains hyperbolic in the spacetime region exterior to the black hole horizons in a similar regime, which includes cases where the deviations from general relativity in the gravitational radiation is appreciable. Finally, we demonstrate that these methods can be used to follow the inspiral and merger of binary black holes in full ESGB gravity. This allows for making predictions for Horndeski theories of gravity in the strong-field and nonperturbative regime, which can confronted with gravitational wave observations, and compared to approximate treatments of modifications to general relativity.

Multimessenger astronomy is of great interest. The localization speed of gravitational wave sources is important for the success of electromagnetic follow-up. Although current gravitational wave source localization methods take up to a few seconds, even that is not sufficient for some electromagnetic bands. Therefore, one needs a more rapid localization method even if it is less accurate. Building upon an excess power method, we describe a new localization method for compact object collisions that produces posterior probability maps in only a few hundred milliseconds. Some accuracy is lost, with the searched sky areas being approximately 10 times larger. We imagine this new technique playing a role in a hierarchical scheme where fast early location estimates are iteratively improved upon as better analyses complete on longer timescales.

The ABCD method is one of the most widely used data-driven background estimation techniques in high energy physics. Cuts on two statistically independent classifiers separate signal and background into four regions, so that background in the signal region can be estimated simply using the other three control regions. Typically, the independent classifiers are chosen “by hand” to be intuitive and physically motivated variables. Here, we explore the possibility of automating the design of one or both of these classifiers using machine learning. We show how to use state-of-the-art decorrelation methods to construct powerful yet independent discriminators. Along the way, we uncover a previously unappreciated aspect of the ABCD method: its accuracy hinges on having low signal contamination in control regions not just overall, but relative to the signal fraction in the signal region. We demonstrate the method with three examples: a simple model consisting of three-dimensional Gaussians; boosted hadronic top jet tagging; and a recasted search for paired dijet resonances. In all cases, automating the ABCD method with machine learning significantly improves performance in terms of ABCD closure, background rejection, and signal contamination.

We consider a texture for the neutrino mass matrix characterized by one vanishing $2\times 2$ subtrace. We analyze phenomenologically and analytically all the six possible patterns, and show that all nonsingular ones are able to accommodate the experimental bounds, whereas singular patterns allow for only four inverted-hierarchy type textures. We then present some possible realizations of this texture, within seesaw scenarios, either directly or indirectly by relating it to zero textures.

An excess of low-energy electronic recoil events over known backgrounds was recently observed in the XENON1T detector, where 285 events are observed compared to an expected $232\pm 15$ events from the background-only fit to the data in the energy range 1–7 keV. This could be due to the beta decay of an unexpected tritium component, or possibly to new physics. One plausible new physics explanation for the excess is absorption of hidden photon dark matter relics with mass around 2.8 keV and kinetic mixing of about ${10}^{-15}$, which can also explain cooling excesses in horizontal-branch (HB) stars. Such small gauge boson masses and couplings can naturally arise from type-IIB low scale string theory. We provide a fit of the XENON1T excess in terms of a minimal low scale type-IIB string theory parameter space and present some benchmark points which provide a good fit to the data. It is also demonstrated how the required transformation properties of the massless spectrum are obtained in intersecting D-brane models.

We compute the nucleon axial and induced pseudoscalar form factors using three ensembles of gauge configurations, generated with dynamical light quarks with mass tuned to approximately their physical value. One of the ensembles also includes the strange and charm quarks with their mass close to physical. The latter ensemble has large statistics and finer lattice spacing and it is used to obtain final results, while the other two are used for assessing volume effects. The pseudoscalar form factor is also computed using these ensembles. We examine the momentum dependence of these form factors as well as relations based on pion pole dominance and the partially conserved axial-vector current hypothesis.

The dipion transitions $\mathrm{\Upsilon }(10860)\to {\pi }^{+}{\pi }^{-}\mathrm{\Upsilon }(nS)$ ($n=1$, 2, 3) are studied in the framework of a unitary and analytic coupled-channel formalism previously developed for analyzing experimental data on the bottomoniumlike states $Z_b(10610)$ and $Z_b(10650)$ [Phys. Rev. D 98, 074023 (2018)] and predicting the properties of their spin partners [Phys. Rev. D 99, 094013 (2019)]. In this work we use a relatively simple but realistic version of this approach, where the scattering and production amplitudes are constructed employing only short-ranged interactions between the open- and hidden-flavor channels consistent with the constraints from heavy quark spin symmetry, for an extended analysis of the experimental line shapes. In particular, the transitions from the $\mathrm{\Upsilon }(10860)$ to the final states $\pi \pi h_b(mP)$ ($m=1$, 2) and $\pi B^{(*)}{\overline{B}}^{*}$ already studied before, are now augmented by the $\mathrm{\Upsilon }(10860)\to {\pi }^{+}{\pi }^{-}\mathrm{\Upsilon }(nS)$ final states ($n=1$, 2, 3). This is achieved by employing dispersion theory to account for the final state interaction of the $\pi \pi$ subsystem including its coupling to the $K\overline{K}$ channel. Fits to the two-dimensional Dalitz plots for the ${\pi }^{+}{\pi }^{-}\mathrm{\Upsilon }$ final states were performed. Two real subtraction constants are adjusted to achieve the best description of the Dalitz plot for each $\mathrm{\Upsilon }(nS)$ ($n=1$, 2, 3) while all the parameters related to the properties of the $Z_b\mathrm{s}$ are kept fixed from the previous study. A good overall description of the data for all $\mathrm{\Upsilon }(10860)\to {\pi }^{+}{\pi }^{-}\mathrm{\Upsilon }(nS)$ channels achieved in this work provides additional strong support for the molecular interpretation of the $Z_b$ states.

We study the inclusive production of bottom-flavored hadrons from semileptonic decays of polarized top quarks at next-to-leading order in QCD using fragmentation functions recently determined from a global fit to $e^{+}{e}^{-}$ data. We provide the relevant differential decay widths at parton level in analytic form. These results fill an important gap in the theoretical interpretation of recent measurements of the top-quark polarization and the $t\overline{t}$ spin correlations using dilepton final states in proton-proton collisions at the CERN Large Hadron Collider. As an illustration, we study the distributions in the scaled bottom-hadron energy of the polarized-top-quark decay widths for different $W$-boson helicities.