We study tidal effects induced by a particle moving along a slightly eccentric equatorial orbit in a Schwarzschild spacetime within the gravitational self-force framework. We compute the first-order (conservative) corrections in the mass ratio to the eigenvalues of the electric-type and magnetic-type tidal tensors up to the second order in eccentricity and through the 9.5 post-Newtonian order. Previous results on circular orbits are thus generalized and recovered in a proper limit.

Topological insulators (TIs) exhibit a quantized magnetoelectric response when time-reversal symmetry is broken on its surface. This unusual electromagnetic (EM) response is a unique macroscopic manifestation of the quantum Hall effect on the TI surface and it is described by a quantized Chern-Simons theory. In this paper, we construct the Green’s function (GF) describing the EM response of two topological media separated by a cylindrical interface. This GF, in the appropriate limits, describes the magnetoelectric effect of both (i) a cylindrical TI surrounded by a dielectric fluid and (ii) a TI with a cylindrical dielectric-filled cavity. We calculate the EM fields produced by a line charge and a line current near the TI surface and we show that, in addition to the standard image electromagnetic sources, charge and current densities of magnetic monopoles will also appear. We discuss some experimental setups which could be used to test these magnetic monopole fields.

We study a gauged $CP(2)$ model with the Chern-Simons term, focusing our attention on those time-independent radially symmetric configurations with a nontopological profile. We proceed with the minimization of the effective energy in order to introduce the corresponding first-order framework, from which we define a legitimate self-dual scenario. We solve the resulting first-order equations numerically by means of the finite-difference scheme, from which we depict the nontopological solutions. We also identify a special kind of solution which can be partially described by an analytical treatment.

The focus of this article is on providing compact analytical expressions for the differential number of polarization-flipped signal photons constituting the signal of vacuum birefringence in the head-on collision of x-ray free electron (XFEL) and optical high-intensity laser pulses. Our results allow for unprecedented insights into the scaling of the effect with the waists and pulse durations of both laser beams, the Rayleigh range of the high-intensity beam, as well as transverse and longitudinal offsets. They account for the decay of the differential number of signal photons in the far field as a function of the azimuthal angle measured relative to the beam axis of the probe beam in the forward direction, typically neglected by conventional approximations. Moreover, they even allow us to extract an analytical expression for the angular divergence of the perpendicularly polarized signal photons. We expect our formulas to be very useful for the planning and optimization of experimental scenarios aiming at the detection of vacuum birefringence in XFEL/high-intensity laser setups, such as the one put forward at the Helmholtz International Beamline for Extreme Fields at the European XFEL.

The Sauter-Schwinger process of electron-positron pair creation from the vacuum, driven by a sequence of time-dependent electric-field pulses, is studied in the framework of the quantum-field theoretical approach. As demonstrated by our numerical results, the momentum distributions of produced pairs exhibit intra- and interpulse interference structures. We show that such structures can be observed beyond the regime of applicability of the Wentzel-Kramers-Brillouin theory, which was the focus of earlier investigations. Going beyond these developments, we perform the analysis of the time-evolution operator for an arbitrary eigenmode of the fermionic field. This shows that a perfect coherent enhancement of the interpulse peaks can never be reached. A nearly perfect coherence, on the other hand, is due to nonadiabatic transitions at avoided crossings of the phases defining the unitary time evolution. This analysis allows us to determine the conditions under which the nearly perfect coherence is lost.

We propose a generalized version of the tribimaximal (TBM) ansatz for lepton mixing, leading to a nonzero reactor angle ${\theta }_{13}$ and $CP$ violation. The latter is characterized by two $CP$ phases. The Dirac phase, affecting neutrino oscillations, is nearly maximal (${\delta }_{CP}\sim \pm \pi /2$), while the Majorana phase implies narrow allowed ranges for the neutrinoless double beta decay amplitude. The solar angle ${\theta }_{12}$ lies nearly at its TBM value, while the atmospheric angle ${\theta }_{23}$ has the TBM value for a maximal ${\delta }_{CP}$. Neutrino oscillation predictions can be tested in present and upcoming experiments.

If the LHC is able to produce dark matter particles, they would appear at the end of cascade decay chains, manifesting themselves as missing transverse energy. However, such “dark matter candidates” may themselves decay invisibly. We propose to test for this possibility by studying the effect of particle widths on the observable invariant mass distributions of the visible particles seen in the detector. We consider the simplest nontrivial case of a two-step two-body cascade decay and derive analytically the shapes of the invariant mass distributions, for generic values of the widths of the new particles. We demonstrate that the resulting distortion in the shape of the invariant mass distribution can be significant enough to measure the width of the dark matter “candidate,” ruling it out as the source of the cosmological dark matter.

We investigate the behavior of the pseudocritical temperature of $N_f=2+1$ QCD as a function of a static magnetic background field for different values of the pion mass, going up to $m_{\pi }\simeq 660\mathrm{MeV}$. The study is performed by lattice QCD simulations, adopting a stout staggered discretization of the theory on lattices with $N_t=6$ slices in the Euclidean temporal direction; for each value of the pion mass the temperature is changed moving along a line of constant physics. We find that the decrease of $T_c$ as a function of $B$, which is observed for physical quark masses, persists in the whole explored mass range, even if the relative variation of $T_c$ appears to be a decreasing function of $m_{\pi }$, approaching zero in the quenched limit. The location of $T_c$ is based on the renormalized quark condensate and its susceptibility; determinations based on the Polyakov loop lead to compatible results. On the contrary, inverse magnetic catalysis, i.e., the decrease of the quark condensate as a function of $B$ in some temperature range around $T_c$, is not observed when the pion mass is high enough. That supports the idea that inverse magnetic catalysis might be a secondary phenomenon, while the modifications induced by the magnetic background on the gauge field distribution and on the confining properties of the medium could play a primary role in the whole range of pion masses.

We revisit the calculation of multiple parton scattering of a heavy quark in nuclei within the framework of recently improved high-twist factorization formalism, in which gauge invariance is ensured by a delicate setup of the initial partons’ transverse momenta. We derive a new result for medium modified heavy quark fragmentation functions in deeply inelastic scattering. It is consistent with the previous calculation of light quark energy loss in the massless limit, but leads to a new correction term in the heavy quark case, which vanishes in the soft gluon radiation limit. We show numerically the significance of the new correction term in the calculation of heavy quark energy loss as compared to previous studies and with soft gluon radiation approximation.

In the manuscript, we concluded that Horowitz’s as well as Dirac’s and Ostrogradski’s formalisms fail to produce a viable quantum description of the modified Einstein-Gauss-Bonnet-dilatonic (MEGBD) action. However, later we note that such conclusion stems from an error in the solution to the classical field equations. Here, we rectify the error, along with all the expressions associated with it. In the process, we find that both Horowitz’s formalism (as well as Dirac’s and Ostrogradski’s formalisms) and modified Horowitz’s formalism produce a viable, although inequivalent, quantum description of the MEGBD action. Nevertheless, the main motivation of the manuscript, viz. “canonical formulation of higher-order theories of gravity following different prescriptions in some cases lead to equivalent and in some other cases inequivalent phase-space structures”, remains unaltered.

In the context of a five-dimensional theory with a scalar field nonminimally coupled to gravity, we look for solutions that describe novel black-string or maximally symmetric solutions in the bulk. The brane line element is found to describe a Schwarzschild–(anti)–de Sitter spacetime, and, here, we choose to study solutions with a positive four-dimensional cosmological constant. We consider two different forms of the coupling function of the scalar field to the bulk scalar curvature, a linear one and a quadratic one. In the linear case, we find solutions where the theory, close to our brane, mimics an ordinary gravitational theory with a minimally coupled scalar field giving rise to an exponentially decreasing warp factor in the absence of a negative bulk cosmological constant. The solution is characterized by the presence of a normal gravity regime around our brane and an antigravitating regime away from it. In the quadratic case, there is no normal-gravity regime at all; however, scalar field and energy-momentum tensor components are well defined and an exponentially decreasing warp factor emerges again. We demonstrate that, in the context of this theory, the emergence of a positive cosmological constant on our brane is always accompanied by an antigravitating regime in the five-dimensional bulk.

We derive an analytical expression for the growth rate of matter density perturbations on the phantom brane (which is the normal branch of the Dvali–Gabadadze–Porrati model). This model is characterized by a phantomlike effective equation of state for dark energy at the present epoch. It agrees very well with observations. We demonstrate that the traditional parametrization $f={\mathrm{\Omega }}_m^{\gamma }$ with a quasiconstant growth index $\gamma$ is not successful in this case. Based on a power series expansion at large redshifts, we propose a different parametrization for this model: $f={\mathrm{\Omega }}_m^{\gamma }{(1+\frac{b}{\ell H})}^{\beta }$, where $\beta$ and $b$ are constants. Our numerical simulations demonstrate that this new parametrization describes the growth rate with great accuracy—the maximum error being $\le 0.1\%$ for parameter values consistent with observations.

In this paper, we will study the complete equations of motion for a ghost-free quadratic-curvature infinite-derivative gravity. We will argue that within the scale of nonlocality, a Schwarzschild-type singular metric solution is not permissible. Therefore, the Schwarzschild-type vacuum solution which is a prediction in Einstein-Hilbert gravity may not persist within the region of nonlocality. We will also show that just quadratic-curvature gravity, without infinite derivatives, always allows Schwarzschild-type singular metric solution.

We consider string-inspired models in $D=10$ spacetime dimensions, which include couplings with 1- and 3-form fields as well as $R^4$ higher-curvature corrections to the gravitational action. For such models, we explicitly construct a family of black hole solutions with both electric and magnetic charges, and with different horizon topologies. The solutions exhibit some features similar to those of self-gravitating monopoles in Einstein-Yang-Mills theory, which we discuss. When higher-curvature corrections are switched off, our solutions reduce to charged $p$-brane solutions previously studied in the literature. Novel qualitative features appear due to the $R^4$ terms, though. Such is the case for the emergence of branch singularities for charged solutions that, nonetheless, can be shielded by the event horizon.

We analyze rigidly rotating Nambu-Goto strings in the Kerr spacetime, particularly focusing on the strings sticking in the horizon. From the regularity on the horizon, we find the condition for sticking in the horizon, which is consistent with the second law of black hole thermodynamics. Energy extraction through the sticking string from a Kerr black hole occurs. We obtain the maximum value of the luminosity of the energy extraction.

We study the effect of noncommutative spacetime geometry on one-loop corrections to the primordial curvature two-point function, arising from various forms of massless spectator matter fields interacting gravitationally with the inflaton. After deforming the algebra of functions on the inflationary background to a spatially noncommutative one, we find that this induces momentum-dependent corrections to one-loop terms which imply that the vacuum fluctuations of the energy-momentum tensor source that of the curvature fluctuation even for distances beyond horizon scales. The one-loop corrections break spatial isotropy by being functions of the noncommutative parameters lying in the transverse plane while reducing smoothly to the commutative limit. This furnishes an example of how UV/IR mixing manifests itself in the context of noncommutative field theories defined on inflationary backgrounds, and demonstrates how in principle, the primordial spectrum could carry a signature of nonlocality and anisotropy in the setting of noncommutative spacetime geometry.

Using a semianalytic code, we show how baryon physics in a $\mathrm{\Lambda }\mathrm{CDM}$ cosmology could solve the discrepancy between numerical predictions of dark matter haloes and observations, ranging from dwarf galaxies to clusters, without the need of nonstandard dark matter models as advocated, for example, by [Kaplinghat et al., Phys. Rev. Lett. 116, 041302, (2016)]. Combining well established results, we show, for the first time, how accounting for baryon physics, in particular dynamical friction mechanisms, leads to flat galaxy-cluster profiles and correlations in several of their properties, solves the so-called “diversity problem” and reproduces very well the challenging, extremely low-rising rotation curve of IC2574. We, therefore, suggest treating baryonic physics properly before introducing new exotic features, albeit legitimate, in the standard cosmological model.

The default assumption of early Universe cosmology is that the postinflationary Universe was radiation dominated until it was about 47,000 years old. Direct evidence for the radiation-dominated epoch extends back until nucleosynthesis, which began during the first second. However there are theoretical reasons to prefer a period of earlier matter domination, prior to nucleosynthesis, e.g., due to late decaying massive particles needed to explain baryogenesis. Axion cosmology is quantitatively affected by an early period of matter domination, with a different axion mass range preferred and greater inhomogeneity produced on small scales. In this work we show that such increased inhomogeneity can lead to the formation of axion miniclusters in axion parameter ranges that are different from those usually assumed. If the reheating temperature is below 58 MeV, axion miniclusters can form even if the axion field is present during inflation and has been previously homogenized. The upper bound on the typical initial axion minicluster mass is raised from ${10}^{-10}{M}_{\odot }$ to ${10}^{-7}{M}_{\odot }$, where $M_{\odot }$ is a solar mass. These results may have consequences for indirect detection of axion miniclusters, and could conceivably probe the thermal history of the Universe before nucleosynthesis.

We analyze the flow into inflation for generic “single-clock” systems, by combining an effective field theory approach with a dynamical-systems analysis. In this approach, we construct an expansion for the potential-like term in the effective action as a function of time, rather than specifying a particular functional dependence on a scalar field. We may then identify fixed points in the effective phase space for such systems, order by order, as various constraints are placed on the $M$th time derivative of the potential-like function. For relatively simple systems, we find significant probability for the background spacetime to flow into an inflationary state and for inflation to persist for at least 60 $e$-folds. Moreover, for systems that are compatible with single-scalar-field realizations, we find a single, universal functional form for the effective potential, $V(\varphi )$, which is similar to the well-studied potential for power-law inflation. We discuss the compatibility of such dynamical systems with observational constraints.