We continue to study the optical properties of the solar gravitational lens (SGL). The aim is prospective applications of the SGL for imaging purposes. We investigate the solution of Maxwell’s equations for the electromagnetic (EM) field, obtained on the background of a static gravitational field of the Sun. We now treat the Sun as an extended body with a gravitational field that can be described using an infinite series of gravitational multipole moments. Studying the propagation of monochromatic EM waves in this extended solar gravitational field, we develop a wave-optical treatment of the SGL that allows us to study the caustics formed in an image plane in the SGL’s strong interference region. We investigate the EM field in several important regions, namely, (i) the area in the inner part of the caustic and close to the optical axis, (ii) the region outside the caustic, and (iii) the region in the immediate vicinity of the caustic, especially around its cusps and folds. We show that in the first two regions the physical behavior of the EM field may be understood using the method of stationary phase. However, in the immediate vicinity of the caustic, the method of stationary phase is inadequate, and a wave-optical treatment is necessary. Relying on the angular eikonal method, we develop a new approach to describe the EM field accurately in all regions, including the immediate vicinity of the caustics and especially near the cusps and folds. The method allows us to investigate the EM field in this important region, which is characterized by rapidly oscillating behavior. Our results are new and can be used to describe gravitational lensing by realistic astrophysical objects, such as stars, spiral, and elliptical galaxies.

The weak-field Schwarzschild and NUT solutions of general relativity are gravitoelectromagnetically dual to each other, except on the positive $z$-axis. The presence of nonlocality weakens this duality and violates it within a smeared region around the positive $z$-axis, whose typical transverse size is given by the scale of nonlocality. We restore an exact nonlocal gravitoelectromagnetic duality everywhere via a manifestly dual modification of the linearized nonlocal field equations. In the limit of vanishing nonlocality we recover the well-known results from weak-field general relativity. Nonlocality, as a possible ultraviolet completion of gravity, does not pose a fundamental impediment to duality structures at the linear level.

The motion of three bodies can be solved perturbatively when a tightly bound inner binary is orbited by a distant perturber, giving rise, for example, to the well-known Kozai-Lidov oscillations. We propose to study the relativistic hierarchical three-body orbits by adapting the effective field theory techniques used in the two-body problem. This allows us to conveniently treat the inner binary as an effective point particle, thus reducing the complexity of the three-body problem to a simpler spinning two-body motion. We present in detail the mapping between the inner binary osculating elements and the resulting spin of the effective point particle. Our study builds towards a derivation of three-body analytic waveforms.

Gravitational-wave (GW) data can be used to test general relativity in the highly nonlinear and strong field regime. Modified gravity theories such as Einstein-dilation-Gauss-Bonnet and dynamical Chern-Simons can be tested with the additional GW signals detected in the first half of the third observing run of Advanced LIGO/Virgo. Specifically, we analyze gravitational-wave data of GW190412 and GW190814 to place constraints on the parameters of these two theories. Our results indicate that dynamical Chern-Simons gravity remains unconstrained. For Einstein-dilation-Gauss-Bonnet gravity, we find $\sqrt{{\alpha }_{\mathrm{EdGB}}}\lesssim 0.40\mathrm{km}$ when considering GW190814 data, assuming it is a black hole binary. Such a constraint are improved by a factor of approximately 10 in comparison to that set by the first Gravitational-Wave Transient Catalog events.

Self-force methods can be applied in calculations of the scatter angle in two-body hyperbolic encounters, working order by order in the mass ratio (assumed small) but with no recourse to a weak-field approximation. This, in turn, can inform ongoing efforts to construct an accurate model of the general-relativistic binary dynamics via an effective-one-body description and other semianalytical approaches. Existing self-force methods are to a large extent specialized to bound, inspiral orbits. Here, we develop a technique for (numerical) self-force calculations that can efficiently tackle scatter orbits. The method is based on a time-domain reconstruction of the metric perturbation from a scalarlike Hertz potential that satisfies the Teukolsky equation, an idea pursued so far only for bound orbits. The crucial ingredient in this formulation is certain jump conditions that (each multipole mode of) the Hertz potential must satisfy along the orbit, in a $1+1$-dimensional multipole reduction of the problem. We obtain a closed-form expression for these jumps, for an arbitrary geodesic orbit in Schwarzschild spacetime, and present a full numerical implementation for a scatter orbit. In this paper, we focus on method development and go only as far as calculating the Hertz potential; a calculation of the self-force and its physical effects on the scatter orbit will be the subject of forthcoming work.

We generalize gravitational particle production in a radiation-dominated $CPT$-symmetric universe to nonstandard but also $CPT$-symmetric early-Universe cosmologies. We calculate the mass of a right-handed “sterile” neutrino needed for it to be the cosmological dark matter. Since generically sterile neutrinos mix with the standard model active neutrinos, we use state-of-the-art tools to compute the expected spectrum of gamma rays and high-energy active neutrinos from ultraheavy sterile neutrino dark matter decay. We demonstrate that the sterile neutrinos are never in thermal equilibrium in the early Universe. We show that very high-energy Cherenkov telescopes might detect a signal for sterile neutrino lifetimes up to around ${10}^{27}\mathrm{s}$, while a signal in high-energy neutrino telescopes such as IceCube could be detectable for lifetimes up to ${10}^{30}\mathrm{s}$, offering a better chance of detection across a vast landscape of possible masses.

We construct and study a simple noncommutative scheme (theta-deformation) for the effective loop quantum cosmology of the flat Friedmann-Lemaître-Robertson-Walker model in the presence of a homogeneous scalar field $\varphi$ with a potential $\mathcal{V}(\varphi )=\frac{1}{2}{m}^2{\varphi }^2$. We first conduct a simple analysis from the corresponding Hamilton equations of motion considering a generic term $\mathcal{V}(\varphi )$. It is observed that the characteristic big bounce of loop quantum cosmology is preserved under such noncommutative extension. When specializing to the quadratic case, numerical solutions to the corresponding Hamilton equations exhibiting an early inflationary epoch with a sufficiently large number of $e$-foldings are found. It is concluded that, in this noncommutative setup, solutions exist which are in the overall compatible with the early universe predicted by standard (effective) Loop Quantum Cosmology (i.e., a bouncing and inflationary early universe). The issue of the genericness of a sufficiently long inflationary period on the space of solutions in this noncommutative construct remains to be addressed.

We investigate the contribution of cosmic string loops to the cosmic microwave background (CMB) anisotropies. This is done by extending the unconnected segment model (USM) to include the contribution of the cosmic string loops created throughout the cosmological evolution of a cosmic string network to the stress-energy tensor. We then implement this extended USM in the publicly available CMBACT code and obtain the linear cold dark matter power spectrum and the CMB angular power spectra generated by cosmic string loops. We find that the shape of the angular power spectra generated by loops is, in general, similar to that of long strings. However, there is generally an enhancement of the anisotropies on small angular scales. Vector modes produced by loops dominate over those produced by long strings for large multipole moments $\ell$. The contribution of loops to the CMB anisotropies generated by cosmic string networks may reach a level of 10% for large loops but decreases as the size of loops decreases. This contribution may then be significant and, thus, this extension provides a more accurate prediction of the CMB anisotropies generated by cosmic string networks.

We show that energy should be dissipated or extracted in the current sheet (CS) of a split magnetosphere deviating from the Michel split monopole, with the CS heating up or cooling down; but the electromagnetic energy remains unchanged everywhere. Based on the decentered monopole solution generated by symmetry in flat spacetime, we construct two generalized split monopole configurations, in which the field lines intersect with the CS at arbitrary angles. One configuration resembles the outer geometry of the so-called “new pulsar magnetosphere model”, for which up to 47% of the spin down energy is transferred to the Joule heating process in the CS. In the other configuration, we observe that negative energy is dissipated in the CS, which is usually observed in magnetospheres on rotating black holes. This means that energy is extracted simultaneously from the central star and the CS to power the output Poynting flux at infinity. We interpret the extraction of energy from the CS as that thermal energy of charged particles in the CS is transferred to the ordered kinetic energy of these particles drifting in the force-free (FF) electromagnetic fields. Hence, the CS is like an “air conditioner” in the sky, which can heat up or cool down, depending on the configurations .

Axion particles are among the best candidates to explain dark matter and resolve the strong $CP$ problem in the Standard Model. If such a particle exists, the core of stars will produce them in large amounts. For the first time, we predict the axion spectra and their associated luminosities for several low-mass stars—one and two solar masses stars in the main sequence and post-main sequence stages of evolution. Equally, we also compute the x-ray excess emission resulting from the conversion of axions back to photons in the presence of a strong magnetic field in the envelope of these stars. Hence, a given star will have a unique axion spectrum and $L_a$ axion luminosity. And if such star has a strong magnetic field in its stellar envelope, it will also show a characteristic x-ray spectrum and $L_{a\gamma }$ x-ray luminosity. Such radiation will add up to the x-ray electromagnetic spectrum and $L_X$ luminosity of the star. The present study focuses on axion models with an axion-photon coupling constant, $5{10}^{-11}{\mathrm{GeV}}^{-1}$, a value just below the most recent upper limit of $6.6{10}^{-11}{\mathrm{GeV}}^{-1}$ found by CAST and IAXO helioscopes. The range of axion parameters discussed here spans many axion models’ parameter space, including the DFSZ and KSVZ models. We found that axions with a mass in the range ${10}^{-7}$ to ${10}^{-5}\mathrm{eV}$ and an axion-photon coupling constant of $5{10}^{-11}{\mathrm{GeV}}^{-1}$ produce an axion emission spectra with an averaged axion energy that varies from 1 to 5 KeV, and an $L_a$ ranging from ${10}^{-6}$ to $7{10}^{-3}{L}_{\odot }$. We also predict that $L_{a\gamma }$ varies from $5{10}^{-8}$ to ${10}^{-5}{L}_{\odot }$ for stars with an averaged magnetic field of $310^4\mathrm{G}$ in their atmospheres. Most of these $L_{a\gamma }$ predictions are larger than the $L_X$ observed in some stars. Therefore, such preliminary results show the potential of the next generation of stellar x-ray missions to constrain several classes of axion models.

We present a novel universal relation for binary neutron star mergers with long-lived neutron star remnants: inspired by recent work based on numerical relativity simulations, we propose a novel approach using perturbative calculations that allow us to relate the premerger neutron star binary tidal deformability to the effective compactness of the postmerger remnant. Our results allow for the prediction of the stellar parameters of a long-lived remnant neutron star from the study of gravitational waves emitted during the premerger phase.

We study the transverse single-spin asymmetry (TSSA) in $p^{\uparrow }p\to J/\psi X$ reaction, incorporating both transverse momentum and spin effects. To predict production cross section of prompt $J/\psi$, we use two different approaches, the color-singlet model and the improved color evaporation model, and show how the predicted results for TSSAs depend on the choice of hadronization model. For initial-state factorization, we also consider two options: the standard generalized parton model and the color gauge-invariant version of it. Estimates for the TSSAs in $p^{\uparrow }p\to J/\psi X$ process for the conditions of the future Spin Physics Detector Nuclotron-based Ion Collider fAcility (NICA) experiment are presented for the first time.

Accelerated charges emit electromagnetic radiation and the consequent energy-momentum loss alters their trajectory. This phenomenon is known as radiation reaction and the Landau-Lifshitz (LL) equation is the classical equation of motion of the electron, which takes into account radiation-reaction effects in the electron trajectory. By using the analytical solution of the LL equation in an arbitrary plane wave, we compute the analytical expression of the classical emission spectrum via nonlinear Thomson scattering including radiation-reaction effects. Both the angularly resolved and the angularly integrated spectra are reported, which are valid in an arbitrary plane wave. Also, we have obtained a phase-dependent expression of the electron dressed mass, which includes radiation-reaction effects. Finally, the corresponding spectra within the locally constant field approximation have been derived.

We study the potential of future parity-violating electron scattering (PVES) data to probe the parameter space of the Standard Model effective field theory. We contrast the constraints derived from Drell-Yan data taken at the Large Hadron Collider (LHC) with projections of the planned PVES experiments SoLID and P2. We show that the PVES data can complement the bounds set by the LHC data in the dimension-six operator space since it probes different combinations of operators than Drell-Yan. The lower characteristic energy of P2 and SoLID also helps disentangle effects of dimension-six and dimension-eight operators that are difficult to resolve with LHC Drell-Yan data alone.

We study the semileptonic decay of the $B_c(0^{-})$ to charmonia through the bottom-to-charm-quark electroweak current in the framework of basis light-front quantization. Explicitly, we calculate the weak transition form factors for processes of $B_c$ decaying into ${\eta }_c$ or $J/\psi$ based on the corresponding initial and final valence light-front wave functions both obtained from the basis light-front quantization. We also present the corresponding differential decay width and branching ratios, as well as the branching ratios for decays into the ${{\eta }_c}^{\prime }$ and the ${\psi }^{\prime }$. We observe unphysical frame dependence of the calculated form factors, which is attributed to only including the valence light-front wave functions. Based on the analysis of the current component, we propose a preferred set of frames to calculate these form factors.

We study the recent XENON1T excess in the context of solar scalar, specifically in the framework of Higgs portal and the relaxion model. We show that $m_{\varphi }=1.9\mathrm{keV}$ and $g_{\varphi e}=2.4\times {10}^{-14}$ can explain the observed excess in science run 1 (SR1) analysis in the 1–7 keV range. In the minimal scenarios we consider, the best-fit parameters are in tension with stellar cooling bounds. Despite this fact, the excess represents an example bringing attention to two interesting effects of general relevance. First, the scalar-Higgs mixing angle reproducing the excess, $\sin \theta \simeq {10}^{-8}$, is intriguingly close to the maximum value of mixing angle for the technical naturalness of the scalar mass. While finding a parameter value very close to its theoretical limit may naively seem an unlikely coincidence, we demonstrate that there exists a class of models which generically saturate the mixing naturalness bound. Secondly, we discuss a possibility that a large density of red giant stars may trigger a phase transition, resulting in a local scalar mass increase suppressing the stellar cooling. For the particular case of minimal relaxion scenarios, we find that such type of chameleon effects is automatically present but they can not ease the cooling bounds. They are however capable of triggering a catastrophic phase transition in the entire Universe. Following this observation we derive a new set of bounds on the relaxed relaxion parameter space. Finally, we present two nonminimal models that demonstrate how the cooling bounds can be relaxed as a result of high density effects.

In extensive air showers induced by ultrahigh-energy (UHE) cosmic rays, secondary photons are expected to be produced at energies far above those accessible by other means. It has been shown that the decay of such photons, as possible in certain theories allowing Lorentz violation, can lead to significant changes of the shower development. Based on observations of the average depth of the shower maximum $⟨X_{\max }⟩$, a stringent bound on Lorentz violation has been placed in a previous work. Here we include the shower-to-shower fluctuations $\sigma (X_{\max })$ as an additional observable. The combined comparison of $⟨X_{\max }⟩$ and $\sigma (X_{\max })$ to shower observations allows a much stricter test of the possible decay of UHE photons, improving the previous bound by a factor of 50.

We consider a scenario where light bino is the next-to-lightest supersymmetric particle (NLSP) and gravitino/axino is the lightest superysmmetric particle (LSP). For a bino mass less than or around hundred GeV, it can be pair produced at the future lepton colliders through $t-$channel slepton exchange, subsequently decaying into a gravitino/axino plus a photon. We study the prospects to look for such binos at the future colliders and find that a bino mass around 100 GeV can be probed at the $2\sigma$ ($5\sigma$) level for a slepton below 2 TeV (1.5 TeV) with a luminosity $5.6{\mathrm{ab}}^{-1}$. For a bino mass around 10 GeV, a slepton mass less than 4.5 TeV (3.5 TeV) can be probed at the $2\sigma$ ($5\sigma$) level, which is much beyond the reach of the LHC for direct slepton searches.

We investigate the metal-insulator transition of the ($1+1$)-dimensional Hubbard model in the path-integral formalism with the tensor renormalization group method. The critical chemical potential ${\mu }_{\mathrm{c}}$ and the critical exponent $\nu$ are determined from the $\mu$ dependence of the electron density in the thermodynamic limit. Our results for ${\mu }_{\mathrm{c}}$ and $\nu$ show consistency with an exact solution based on the Bethe ansatz. Our encouraging results indicate the applicability of the tensor renormalization group method to the analysis of higher-dimensional Hubbard models.

A simple exactly solvable model is proposed for describing the decays $\mathrm{\Upsilon }(4S)\to B^0{\overline{B}}^0$ and $\mathrm{\Upsilon }(4S)\to B^{+}{B}^{-}$. Our predictions agree with available experimental data. Using this model, we analyze the Coulomb effects in the spectra of these decays. It is shown that the frequently used assumption of factorization of Coulomb effects is not fulfilled. The Coulomb interaction leads to the difference in the positions and heights of the peaks corresponding to the charged and neutral modes. As a result, the ratio of probability of $\mathrm{\Upsilon }(4S)\to B^{+}{B}^{-}$ decay and $\mathrm{\Upsilon }(4S)\to B^0{\overline{B}}^0$ decay is a nontrivial function of energy.