We study quantum effects induced by a pointlike object that imposes Dirichlet boundary conditions along its worldline, on a real scalar field $\phi$ in 1, 2, and 3 spatial dimensions. The boundary conditions result from the strong coupling limit of a term quadratic in the field and localized on the particle’s trajectory. We discuss the renormalization issues that appear and evaluate the effective action. Special attention is paid to the case of two spatial dimensions where the coupling constant is adimensional.

In this work, starting from a spherically symmetric scale-dependent black hole, a rotating solution is obtained by following the Newman–Janis algorithm without complexification. Besides studying the horizon, the static conditions and causality issues of the rotating solution, we get and discuss the shape of its shadow.

We analyze the properties of the gravitational wave signal emitted after the merger of a binary neutron star system when the remnant survives for more than a 80 ms (and up to 140 ms). We employ four different piecewise polytropic equations of state supplemented by an ideal fluid thermal component. We find that the postmerger phase can be subdivided into three phases: an early postmerger phase (where the quadrupole mode and a few subdominant features are active), the intermediate postmerger phase (where only the quadrupole mode is active) and the late postmerger phase (where convective instabilities trigger inertial modes). The inertial modes have frequencies somewhat smaller than the quadrupole modes. In one model, we find an interesting association of a corotation of the quadrupole mode in parts of the star with a revival of its amplitude. The gravitational wave emission of inertial modes in the late postmerger phase is concentrated in a narrow frequency region and is potentially detectable by the planned third-generation detectors. This allows for the possibility of probing not only the cold part of the equation of state, but also its dependence on finite temperature. In view of these results, it will be important to investigate the impact of various type of viscosities on the potential excitation of inertial modes in binary neutron star merger remnants.

In this work we focus on the situation where a significant amount of matter could be located close to the event horizon of the central black hole and how it affects the gravitational lensing signal. We consider a simple toy model where matter is concentrated in the rather small region between the inner photon sphere associated with the mass of central black hole and outer photon sphere associated with the total mass outside. If no photon sphere is present inside the matter distribution, then effective potential displays an interesting trend with maxima at inner and outer photon sphere, with peak at inner photon sphere higher than that at outer photon sphere. In such a case we get three distinct set of infinitely many relativistic images and Einstein rings that occur due to the light rays that approach the black hole from distant source and get reflected back just outside the outer photon sphere, due to light rays that enter the outer photon sphere slightly above the outer peak and get reflected off the potential barrier inside the matter distribution and due to the light rays that get reflected just outside the inner photon sphere. This kind of pattern of images is quite unprecedented. We show that since relativistic images are highly demagnified, only three images are prominently visible from the point of observations in the presence of matter as opposed to only one prominent image in case of single isolated black hole and also compute the time delay between them. This provides a smoking gun signature of presence of matter lump around black hole. We further argue that if the mass of the black hole inferred from the observation of size of its shadow is less than the mass inferred from the motion of objects around it, it signals the presence of matter in the vicinity of black hole.

We perform a post-Newtonian (PN) solar system analysis for Palatini $f(R)$ theories considering finite volume nonspherical planets and with emphasis to $f(R)$ functions that are analytical about $R=0$. First we consider the Will-Nordtvedt parametrized post-Newtonian (PPN) formalism, from which the metric is shown to depend, in general, on terms not covered by the standard PPN potentials. Hence, a full analysis of the PN equations of motion is performed. From the latter we conclude that, apart from redefinitions on the internal energy and the pressure, which cannot be constrained by solar system tests, the center-of-mass orbits are the same as in general relativity. We discuss further the physics of these redefinitions and use an argument to extend our analytical $f(R)$ results towards some nonanalytical functions.

The dual configuration of the original one is proposed for the orbit design of Taiji spacecrafts. In terms of these two configurations of Taiji, an algorithm is devised to expand the unperturbed Keplerian orbits of spacecrafts to infinite order of $e$, the orbital eccentricity, in the heliocentric coordinate system. Further, based on the algorithm, all the kinematic indicators of Taiji triangles, say three arm-lengths and their corresponding rates of change, and three vertex angles, in both configurations are also be expanded to infinite order of $e$, and it is proved that both configurations of Taiji possess the same symmetry: At every order, three components of every kinematic indicator of the Taiji triangle are identical to each other up to a phase shift of $2\pi /3$, which is independent on the tilt angle of the Taiji plane relative to the ecliptic plane. Finally, the above algorithm is slightly modified, and according to it, by adjusting the tilt angle around $\pi /3$ to any order of $e$, the orbits of Taiji spacecrafts in each configuration can be optimized.

The distribution of matter fluctuations in our universe is key for understanding the nature of dark matter and the physics of the early cosmos. Different observables have been able to map this distribution at large scales, corresponding to wave numbers $k\lesssim 10{\mathrm{Mpc}}^{-1}$, but smaller scales remain much less constrained. In this work we study the sensitivity of upcoming measurements of the 21-cm line of neutral hydrogen to the small-scale matter power spectrum. The 21-cm line is a promising tracer of early stellar formation, which took place in small haloes (with masses $M\sim {10}^6–{10}^8{M}_{\odot }$), formed out of matter overdensities with wave numbers as large as $k\approx 100{\mathrm{Mpc}}^{-1}$. Here we forecast how well both the 21-cm global signal, and its fluctuations, could probe the matter power spectrum during cosmic dawn ($z=12–25$). In both cases we find that the long-wavelength modes (with $k\lesssim 40{\mathrm{Mpc}}^{-1}$) are highly degenerate with astrophysical parameters, whereas the modes with $k=(40–80){\mathrm{Mpc}}^{-1}$ are more readily observable. This is further illustrated in terms of the principal components of the matter power spectrum, which peak at $k\sim 50{\mathrm{Mpc}}^{-1}$ both for a typical experiment measuring the 21-cm global signal and its fluctuations. We find that, imposing broad priors on astrophysical parameters, a global-signal experiment can measure the amplitude of the matter power spectrum integrated over $k=(40–80){\mathrm{Mpc}}^{-1}$ with a precision of tens of percent. A fluctuation experiment, on the other hand, can constrain the power spectrum to a similar accuracy over both the $k=(40–60){\mathrm{Mpc}}^{-1}$ and $(60–80){\mathrm{Mpc}}^{-1}$ ranges even without astrophysical priors. The constraints outlined in this work would be able to test the behavior of dark matter at the smallest scales yet measured, for instance probing warm-dark matter masses up to $m_{\mathrm{WDM}}=8\mathrm{keV}$ for the global signal and 14 keV for the 21-cm fluctuations. This could shed light on the nature of dark matter beyond the reach of other cosmic probes.

The recent detections of the neutrino event IceCube-170922A, 13 muon-neutrino events observed in 2014–2015 and the IceCube-141209A by IceCube observatory from the Blazars TXS $0506+056$, PKS $0502+049$/TXS $0506+056$, and GB6 J1040+0617 respectively, all of which were in the state of enhanced gamma-ray emission, indicate that cosmic rays are accelerated in the blazar jets. The photomeson ($p\gamma$) interaction cannot explain the IceCube observations of 13 neutrino events. However, the nondetection of broadline emission in the optical spectra of the IceCube blazars questions the hadronuclear ($pp$) interaction interpretation, in which a relativistic jet interacts with a high density cloud. In this work, we investigate the proton blazar model in which the nonrelativistic protons that come into existence under the charge neutrality condition of the blazar jet can offer sufficient target matter for $pp$ interactions with shock-accelerated protons, to describe the observed high-energy gamma rays and neutrino signals from said blazars. Our findings suggest that the model can consistently explain the observed electromagnetic spectrum in combination with the appropriate number of neutrino events from the corresponding blazars.

The interplanetary counterpart of coronal mass ejections (ICMEs) and the interaction regions of slow-fast solar wind (CIRs) have both been known as potential drivers of Forbush decrease (FD). However, reported studies often take an independent approach for investigating FD caused by ICMEs and CIRs, since both the structures show different signature in in-situ observations. In this paper, we explore the common origin of the FD profile caused by these two large scale structures, within the framework of a diffusion-convection model. As a case study, we present one event of each type, in both of which, the solar wind is the most prominent driver. Possible extensions of this model could incorporate other parameters such as magnetic field strength, turbulence, etc which influence the observed FD features. This attempt could help to resolve the complex problem of the diversity in observed FD profiles.

We study the structure of scalar, vector, and tensor currents for on shell massive particles of any spin. When considering higher values for the spin of the particle, the number of form factors (FFs) involved in the decomposition of the matrix elements associated with these local currents increases. We identify all the fundamental structures that give rise to the independent FFs, systematically for any spin value. These structures can be conveniently organized using an expansion in covariant multipoles, built solely from the Lorentz generators. This approach allows one to uniquely identify the terms which are universal and those that arise because of spin. We derive counting rules which relate the number of FFs to the total spin $j$ of the state, showing explicitly that these rules match all the well-known cases up to spin 2.

In this work, we investigate the connection and compatibility between $\nu n\to \overline{\nu }\overline{n}$ reactions and $n\text{−}\overline{n}$ oscillations based on the $SU(3{)}_c\times SU(2{)}_L\times U(1)$ symmetry model with additional Higgs triplets. We explore the possibility that the scattering process $\nu n\to \overline{\nu }\overline{n}$ produced by low-energy solar neutrinos gives rise to an unavoidable background in the measurements of $n\text{−}\overline{n}$ oscillations. We focus on two different scenarios, depending on whether the ($B-L$) symmetry could be broken. We analyze the interplay of the various constraints on the two processes and their observable consequences. In the scenario where both ($B+L$) and ($B-L$) could be broken, we point out that if all the requirements, mainly arising from the type-II seesaw mechanism, are satisfied, the parameter space would be severely constrained. In this case, although the masses of the Higgs triplet bosons could be within the reach of a direct detection at the LHC or future high-energy experiments, the predicted $n\text{−}\overline{n}$ oscillation times would be completely beyond the detectable regions of the present experiments. In both scenarios, the present experiments are unable to distinguish a $\nu n\to \overline{\nu }\overline{n}$ reaction event from an $n\text{−}\overline{n}$ oscillation event within the accessible energy range. Nevertheless, if any of the two processes is detected, there could be signal associated with new physics beyond the Standard Model.

We study natural supersymmetric scenarios with light right-handed neutrino superfields, and consider the possibility of having either a neutrino or a sneutrino as a dark matter candidate. For the former, we evaluate the possibility of having SUSY corrections on the ${\nu }_4\to {\nu }_{\ell }\gamma$ decay rate, such that the NuStar bounds are relaxed. We find that corrections are too small. For sneutrino dark matter, we consider thermal and nonthermal production, taking into account freeze-out, freeze-in, and super-weakly interacting massive particles mechanisms. For the nonthermal case, we find that the ${\tilde{\nu }}_R$ can reproduce the observed relic density by adjusting the R-sneutrino mass and Yukawa couplings. For the thermal case, we find the need to extend the model in order to enhance sneutrino annihilations, which we exemplify in a model with an extended gauge symmetry.

We present a study of singlet-doublet vectorlike leptonic dark matter (DM) in the framework of the two-Higgs-doublet model (2HDM), where the dark sector is comprised of one doublet and one singlet vectorlike fermion (VLF). The DM, that arises as an admixture of the neutral components of the VLFs, is stabilized by an imposed discrete symmetry ${\mathcal{Z}}_2^{\prime }$. We test the viability of the DM candidate in the light of observations from Planck and recent limits on spin-independent direct detection experiments and search for its possible collider signals. In addition, we also look for the stochastic gravitational wave (GW) signatures resulting from strong first-order phase transition due to the presence of the second Higgs doublet. The model thus offers a viable parameter space for a stable DM candidate that can be probed from direct search, collider, and GW experiments.

We discuss the phase structure of QCD for $N_f=2$ and $N_f=2+1$ dynamical quark flavors at finite temperature and baryon chemical potential. It emerges dynamically from the underlying fundamental interactions between quarks and gluons in our work. To this end, starting from the perturbative high-energy regime, we systematically integrate out quantum fluctuations toward low energies by using the functional renormalization group. By dynamically hadronizing the dominant interaction channels responsible for the formation of light mesons and quark condensates, we are able to extract the phase diagram for ${\mu }_B/T\lesssim 6$. We find a critical endpoint at $(T_{\mathrm{CEP}},{\mu }_{B_{\mathrm{CEP}}})=(107,635)\mathrm{MeV}$. The curvature of the phase boundary at small chemical potential is $\kappa =0.0142(2)$, computed from the renormalized light chiral condensate ${\mathrm{\Delta }}_{l,R}$. Furthermore, we find indications for an inhomogeneous regime in the vicinity and above the chiral transition for ${\mu }_B\gtrsim 417\mathrm{MeV}$. Where applicable, our results are in very good agreement with the most recent lattice results. We also compare to results from other functional methods and phenomenological freeze-out data. This indicates that a consistent picture of the phase structure at finite baryon chemical potential is beginning to emerge. The systematic uncertainty of our results grows large in the density regime around the critical endpoint and we discuss necessary improvements of our current approximation toward a quantitatively precise determination of QCD phase diagram.

We employ the quark part of the symmetric energy-momentum tensor current to calculate the transition gravitational form factors of the $N(1535)\to N$ by means of the light-cone QCD sum rule formalism. In numerical analysis, we use two different sets of the shape parameters in the distribution amplitudes of the $N(1535)$ baryon and the general form of the nucleon’s interpolating current. It is seen that the momentum squared dependence of the gravitational form factors can be well described by the p-pole fit function. The results obtained by using two sets of parameters are found to be quite different from each other, and the $N(1535)\to N$ transition gravitational form factors depend highly on the shape parameters of the distribution amplitudes of the $N(1535)$ state that parametrize the relative orbital angular momentum of the constituent quarks.

Using an $e^{+}{e}^{-}$ annihilation data sample corresponding to an integrated luminosity of $2.93{\mathrm{fb}}^{-1}$ collected at the center-of-mass energy of 3.773 GeV with the BESIII detector, we measure the absolute branching fractions of $D^{+}\to \eta \eta {\pi }^{+}$, $D^{+}\to \eta {\pi }^{+}{\pi }^0$, and $D^0\to \eta {\pi }^{+}{\pi }^{-}$ to be $(2.96\pm 0.24\pm 0.10)\times {10}^{-3}$, $(2.23\pm 0.15\pm 0.10)\times {10}^{-3}$, and $(1.20\pm 0.07\pm 0.04)\times {10}^{-3}$, respectively, where the first uncertainties are statistical and the second ones are systematic. The $D^{+}\to \eta \eta {\pi }^{+}$ decay is observed for the first time, and the branching fractions of $D^{+(0)}\to \eta {\pi }^{+}{\pi }^{0(-)}$ are measured with much improved precision. In addition we test for $CP$ asymmetries in the separated charge-conjugate branching fractions; no evidence of $CP$ violation is found.

Motivated by the recent research of black holes with NUT charge, we investigate the validity of the weak cosmic censorship conjecture for the Kerr-Taub-NUT black hole with a test massive scalar field and a test particle, respectively. For the scalar field scattering gedanken experiment, we consider an infinitesimal time interval process. The result shows that both extremal and near-extremal Kerr-Taub-NUT black holes cannot be overspun. For the test particle thought experiment, the study suggests that the extremal Kerr-Taub-NUT black hole cannot be overspun; while the near-extremal Kerr-Taub-NUT black hole can be overspun. By comparing the two methods, the results indicate the time interval for particles crossing the black hole horizon might be important for consideration of the weak cosmic censorship conjecture.

As a first step in the computation of the orbital phase evolution of spinless compact binaries including tidal effects up to the next-to-next-to-leading (NNL) order, we obtain the equations of motion of those systems and the associated conserved integrals in harmonic coordinates. The internal structure and finite size effects of the compact objects are described by means of an effective Fokker-type action. Our results, complete to the NNL order, correspond to the second-post-Newtonian (2PN) approximation beyond the leading tidal effect itself, already occurring at the 5PN order. They are parametrized by three polarizability (or deformability) coefficients describing the mass-quadrupolar, mass-octupolar, and current-quadrupolar deformations of the objects through tidal interactions. Up to the next-to-leading (NL) order, we recover previous results in the literature; up to the NNL order for quasicircular orbits, we confirm the known tidal effects in the (PN reexpansion of the) effective-one-body (EOB) Hamiltonian. In a future work, we shall derive the tidal contributions to the gravitational-wave flux up to the NNL order, which is the second step required to find the orbital phase evolution.

We have done a study of the $B^{-}\to K^{-}{\pi }^{0}X(3872)$ reaction by means of a triangle mechanism via the chain of reactions: $B^{-}\to K^{-}{D}^{*0}{\overline{D}}^{*0}$; $D^{*0}\to {\pi }^0{D}^0$; $D^0{\overline{D}}^{*0}\to X(3872)$. We show that this mechanism generates a triangle singularity in the ${\pi }^{0}X(3872)$ invariant mass for a very narrow window of the $X(3872)$ mass, around the present measured values, and show that the peak positions and the shape of the mass distributions are sensitive to the $X(3872)$ mass, such that a measurement of the reaction can serve to improve on the present values of this mass. In particular, we point out that the $X(3872)$ mass relative to the $D^0{\overline{D}}^{*0}$ threshold may be extracted from the asymmetry of the ${\pi }^{0}X$ line shape.