The “QCD Kondo effect” stems from the color exchange interaction in QCD with non-Abelian property, and can be realized in a high-density quark matter containing heavy-quark impurities. We propose a novel type of the QCD Kondo effect induced by a strong magnetic field. In addition to the fact that the magnetic field does not affect the color degrees of freedom, two properties caused by the Landau quantization in a strong magnetic field are essential for the “magnetically induced QCD Kondo effect”; (1) dimensional reduction to $1+1$-dimensions, and (2) finiteness of the density of states for lowest energy quarks. We demonstrate that, in a strong magnetic field $B$, the scattering amplitude of a massless quark off a heavy quark impurity indeed shows a characteristic behavior of the Kondo effect. The resulting Kondo scale is estimated as ${\mathrm{\Lambda }}_{\mathrm{K}}\simeq \sqrt{e_{q}B}{\alpha }_s^{1/3}\exp \{-4\pi /N_c{\alpha }_s\log (4\pi /{\alpha }_s)\}$ where ${\alpha }_s$ and $N_c$ are the fine structure constant of strong interaction and the number of colors in QCD, and $e_q$ is the electric charge of light quarks.

Transition probability calculations of strong field particle processes in the Furry picture typically use fermion Volkov solutions. These solutions have a relatively complicated spinor due to the interaction of the electron spin with a strong external field, which in turn leads to unwieldy trace calculations. The simplification of these calculations would aid theoretical studies of strong field phenomena such as the predicted resonance behavior of higher order Furry picture processes. Here, Fierz transformations of Volkov spinors are developed and applied to a first-order and a second-order Furry picture process. Combined with symmetry properties, the techniques presented here are generally applicable and lead to considerable simplification of Furry picture analytic calculations.

We construct a set of nonrational conformal field theories that consist of deformations of Toda field theory for $sl(n)$. In addition to preserving conformal invariance, the theories may still exhibit a remnant infinite-dimensional affine symmetry. The case $n=3$ is used to illustrate this phenomenon, together with further deformations that yield enhanced Kac-Moody symmetry algebras. For generic $n$ we compute $N$-point correlation functions on the Riemann sphere and show that these can be expressed in terms of $sl(n)$ Toda field theory $((N-2)n+2)$-point correlation functions.

We compare numerical solutions to the full field equations to simplified approaches based on implementing three collective coordinates for kink-antikink interactions within the ${\phi }^4$ and ${\varphi }^6$ models in one time and one space dimensions. We particularly pursue the question whether the collective coordinate approximation substantiates the conjecture that vibrational modes are important for resonance structures to occur in kink-antikink scattering.

It was reported that Kerr-Newman black holes can support linear charged scalar fields in their exterior regions. These stationary massive charged scalar fields can form bound states, which are called stationary scalar clouds. In this paper, we show that Kerr-Sen black holes can also support stationary massive charged scalar clouds by matching the near- and far-region solutions of the radial part of the Klein-Gordon wave equation. We also review stationary scalar clouds within the background of static electrically charged black hole solutions in the low-energy limit of heterotic string field theory, namely, the Gibbons-Maeda-Garfinkle-Horowitz-Strominger black holes.

We revisit the mixed-derivative extension of Hořava gravity which was designed to address the naturalness problems of the standard theory in the presence of matter couplings. We consider the minimal theory with mixed-derivative terms that contain two spatial and two temporal derivatives. Including all terms compatible with the (modified) scaling rules and the foliation-preserving diffeomorphisms, we calculate the dispersion relations of propagating modes. We find that the theory contains four propagating degrees of freedom, as opposed to three in the standard Hořava gravity. The new degree of freedom is another scalar graviton, and it is unstable at low energies. Our result brings tension to the Lorentz-violation suppression mechanism that relies on separation of scales.

It was recently suggested that the merger of $\sim 30M_{\odot }$ primordial black holes (PBHs) may provide a significant number of events in gravitational-wave observatories over the next decade, if they make up an appreciable fraction of the dark matter. Here we show that measurement of the eccentricities of the inspiralling binary black holes can be used to distinguish these binaries from those produced by more traditional astrophysical mechanisms. These PBH binaries are formed on highly eccentric orbits and can then merge on time scales that in some cases are years or less, retaining some eccentricity in the last seconds before the merger. This is to be contrasted with massive-stellar-binary, globular-cluster, or other astrophysical origins for binary black holes (BBHs) in which the orbits have very effectively circularized by the time the BBH enters the observable LIGO window. Here we discuss the features of the gravitational-wave signals that indicate this eccentricity and forecast the sensitivity of LIGO and the Einstein Telescope to such effects. We show that if PBHs make up the dark matter, then roughly one event should have a detectable eccentricity given LIGO’s expected sensitivity and observing time of six years. The Einstein Telescope should see $O(10)$ such events after ten years.

We derive a theoretical model of mass and angular momentum scaling in type-II critical collapse with rotation. We focus on the case where the critical solution has precisely one, spherically symmetric, unstable mode. We demonstrate agreement with numerical results for critical collapse of a rotating radiation fluid, which falls into this case.

Topological solitons are relevant in several areas of physics. Recently, these configurations have been investigated in contexts as diverse as hydrodynamics, Bose-Einstein condensates, ferromagnetism, knotted light and non-Abelian gauge theories. In this paper we address the issue of wave propagation about a static Hopf soliton in the context of the Nicole model. Working within the geometrical optics limit, we show that several nontrivial lensing effects emerge due to nonlinear interactions as long as the theory remains hyperbolic. We conclude that similar effects are very likely to occur in effective field theories characterized by a topological invariant such as the Skyrme model of pions.

The two gravitomagnetic effects which influence bodies orbiting around a gravitational source are the geodetic effect and the Lense-Thirring effect. The former describes the precession angle of the axis of a spinning gyroscope while in orbit around a nonrotating gravitational source whereas the latter provides a correction for this angle in the case of a spinning source. In this paper we derive the relevant equations in quadratic gravity and relate them to their equivalents in general relativity. Starting with an investigation into Kepler’s third law in quadratic gravity with a scalar field, the effects of an axisymmetric and rotating gravitational source on an orbiting body in a circular, equatorial orbit are introduced.

We show that certain solutions to the linearized Einstein equation can—by the application of a particular type of linearized gauge transformation—be straightforwardly transformed into solutions of the exact Einstein equation. In cases with nontrivial matter content, the exact stress-energy tensor of the transformed metric has the same eigenvalues and eigenvectors as the linearized stress-energy tensor of the initial approximation. When our gauge exists, the tensorial structure of transformed metric perturbations identically eliminates all nonlinearities in Einstein’s equation. As examples, we derive the exact Kerr and gravitational plane wave metrics from standard harmonic-gauge approximations.

We revisit the issue of interpreting the results of large volume cosmological simulations in the context of large-scale general relativistic effects. We look for simple modifications to the nonlinear evolution of the gravitational potential $\psi$ that lead on large scales to the correct, fully relativistic description of density perturbations in the Newtonian gauge. We note that the relativistic constraint equation for $\psi$ can be cast as a diffusion equation, with a diffusion length scale determined by the expansion of the Universe. Exploiting the weak time evolution of $\psi$ in all regimes of interest, this equation can be further accurately approximated as a Helmholtz equation, with an effective relativistic “screening” scale $\ell$ related to the Hubble radius. We demonstrate that it is thus possible to carry out N-body simulations in the Newtonian gauge by replacing Poisson’s equation with this Helmholtz equation, involving a trivial change in the Green’s function kernel. Our results also motivate a simple, approximate (but very accurate) gauge transformation—${\delta }_{\mathrm{N}}(\mathbf{k})\approx {\delta }_{\mathrm{sim}}(\mathbf{k})\times (k^2+{\ell }^{-2})/k^2$—to convert the density field ${\delta }_{\mathrm{sim}}$ of standard collisionless $N$-body simulations (initialized in the comoving synchronous gauge) into the Newtonian gauge density ${\delta }_{\mathrm{N}}$ at arbitrary times. A similar conversion can also be written in terms of particle positions. Our results can be interpreted in terms of a Jeans stability criterion induced by the expansion of the Universe. The appearance of the screening scale $\ell$ in the evolution of $\psi$, in particular, leads to a natural resolution of the “Jeans swindle” in the presence of superhorizon modes.

Strong gravitational lensing provides a geometric probe of cosmology in a unique manner through distance ratios involving the source and lens. This is well-known for the time delay distance derived from measured delays between lightcurves of the images of variable sources such as quasars. Recently, double source plane lens systems involving two constant sources lensed by the same foreground lens have been proposed as another probe, involving a different ratio of distances measured from the image positions and fairly insensitive to the lens modeling. Here we demonstrate that these two different sets of strong lensing distance ratios have strong complementarity in cosmological leverage. Unlike other probes, the double source distance ratio is actually more sensitive to the dark energy equation of state parameters $w_0$ and $w_a$ than to the matter density ${\mathrm{\Omega }}_m$, for low redshift lenses. Adding double source distance ratio measurements can improve the dark energy figure of merit by 40% for a sample of fewer than 100 low redshift systems, or even better for the optimal redshift distribution we derive.

Configurational entropy has been revealed as a reliable method for constraining some parameters of a given model [Phys. Rev. D 92, 126005 (2015); Eur. Phys. J. C 76, 100 (2016)]. In this work, we calculate the configurational entropy in Gauss-Bonnet braneworld models. Our results restrict the range of acceptability of the Gauss-Bonnet scalar values. In this way, the information theoretical measure in Gauss-Bonnet scenarios opens a new window to probe situations where the additional parameters, responsible for the Gauss-Bonnet sector, are arbitrary.

We consider a time-dependent deformation of anti–de Sitter (AdS) space-time which contains a spacelike “singularity”—a spacelike region of high curvature. Making use of the AdS/CFT correspondence we can map the bulk dynamics onto the boundary. The boundary theory has a time dependent coupling constant which becomes small at times when the bulk space-time is highly curved. We investigate the propagation of small fluctuations of a test scalar field from early times before the bulk singularity to late times after the singularity. Under the assumption that the AdS/CFT correspondence extends to deformed AdS space-times, we can map the bulk evolution of the scalar field onto the evolution of the boundary gauge field. The time evolution of linearized fluctuations is well-defined in the boundary theory as long as the coupling remains finite, so that we can extend the boundary perturbations to late times after the singularity. Assuming that the spacetime in the future of the singularity has a weakly coupled region near the boundary, we reconstruct the bulk fluctuations after the singularity crossing making use of generic properties of boundary-to-bulk propagators. Finally, we extract the spectrum of the fluctuations at late times given some initial spectrum. We find that the spectral index is unchanged, but the amplitude increases due to the squeezing of the fluctuations during the course of the evolution. This investigation can teach us important lessons on how the spectrum of cosmological perturbations passes through a bounce which is singular from the bulk point of view but which is resolved using an ultraviolet complete theory of quantum gravity.

A model of the self-interacting charged massive spin-two field is constructed. We investigate several properties of the model and find that the trivial vacuum is only allowed due to the internal symmetry. This suggests that the Higgs mechanism might not be induced by the model of the massive spin-two field with the ghost-free potential.

The issue of Hermiticity of the Higgs boson interaction with fermions is addressed. A model for non-Hermitian Yukawa interaction is proposed and approximation of one fermion generation is considered. Symmetry properties of the corresponding $hf\overline{f}$ Lagrangian with respect to the discrete $\mathcal{P}$, $\mathcal{C}$, and $\mathcal{T}$ transformations are analyzed, and the modified Dirac equation for the free fermion is studied. Longitudinal polarization of the fermions in the decay $h\to f\overline{f}$, which arises due to non-Hermiticity of the $hf\overline{f}$ interaction, is discussed. It is suggested to study effects of this non-Hermiticity in the decay $h\to {\tau }^{-}{\tau }^{+}\to {\mu }^{-}{\overline{\nu }}_{\mu }{\nu }_{\tau }{\mu }^{+}{\nu }_{\mu }{\overline{\nu }}_{\tau }$, for which observables (asymmetries) are constructed which take nonzero values for a non-Hermitian $h{\tau }^{-}{\tau }^{+}$ interaction. These asymmetries are analyzed for various configurations of the muon energies.

We enumerate the conditions necessary for $CP$ violation to be manifest in $n-\overline{n}$ oscillations and build a simple model that can give rise to such effects. We discuss a possible connection between neutron oscillations and dark matter, provided the mass of the latter lies between $m_p-m_e$ and $m_p+m_e$. We apply our results to a possible baryogenesis scenario involving $CP$ violation in the oscillations of the ${\mathrm{\Xi }}^0$.

In this work, we consider a model-independent lepton-flavor-violating $Z^{\prime }$ gauge boson at TeV scale, which can be probed at the LHC in the near future. The lepton-flavor-changing neutral currents originated from nonuniversal couplings to charged leptons and nondiagonal charge lepton mass matrices. We assume that the left-handed charged-lepton mixing matrix equals the PMNS matrix and that there is no mixing in the neutrino sector to make this phenomenological $Z^{\prime }$ model more predictive. There are indeed some parameter regions where the $Z^{\prime }$ can generate a large enough $e^{\pm }{\mu }^{\mp }$ production cross section at the LHC, while at the same time satisfying various observables from lepton-flavor-violation and other constraints from the LHC.